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Abstract\nKEY POINTSDevonian successions in the Calliope and Yarrol provinces of the northern New England Orogen in central to northern Queensland have a lithological assemblage and depositional environments indicative of a close association with a subduction-related volcanic arc. These rocks have been interpreted as related to island arc and backarc settings based on geochemical characteristics of magmatic rocks. We present new detrital zircon ages from the Devonian to lower Carboniferous successions of the Calliope and Yarrol province successions. Most samples have no or relatively few zircon grains extracted except for samples of quartz-rich sandstone in the Middle Devonian Erebus beds of Hunter Island, located 160 km north-northwest of Rockhampton and another sample in the Rockhampton district. The samples with abundant zircon, and some with less common zircon, have prominent peaks of mid Cambrian to Ordovician ages and are consistent with derivation from the northern Thomson Orogen where igneous rocks of this age are documented in the Charters Towers Province. These data indicate a connection between the Devonian arc-flank deposits of the northern New England Orogen and the Thomson Orogen, which had previously been well established for Carboniferous deep-marine sandstones of the subduction complex (e.g. Shoalwater Formation). These results favour an east-facing continental margin arc setting in the Devonian contra to intra-oceanic island arc settings previously proposed. Detrital zircon age spectra from sampled early Carboniferous units of northern New England Orogen association indicate a pulse of felsic magmatism of that age.Devonian quartz-rich sandstones from the northern New England Orogen have abundant detrital zircon ages of mid Cambrian to Ordovician indicating a provenance connection with the Charters Towers Province of the northern Thomson Orogen.These results confirm a provenance linkage to Gondwana and imply that the Devonian tectonic setting was a continental margin arc and associated forearc basinal infill.Geochemical comparisons suggesting an island arc setting have overly influenced previous tectonic interpretations. [ABSTRACT FROM AUTHOR]

Timing is a key data for understanding the origin of faulting. The Balcones fault system (BFS) extends ~600 km along the northern margin of the Gulf of Mexico oil basin and controls springs that supply the major cities in Texas, but its origin is unclear. We provide its first direct timing by applying U–Pb geochronology on seven calcite‐mineralized fault surfaces. We have found that this extensional fault system formed during the Palaeocene‐middle Eocene time (from 61.3 ± 2.7 to 45.4 ± 2.1 Ma), which is much earlier than previous estimates. We show that the formation of the BFS coincides with the largest clastic influx in the northern Gulf of Mexico basin that resulted from Laramide uplift and erosion. This timing and the location of the BFS along the Ouachita suture, support our interpretation of this fault system formed as the result of lithospheric flexure related to Paleogene sedimentary loading. [ABSTRACT FROM AUTHOR]

The Troiseck-Floning and Rosskogel nappes are part of the Austroalpine Unit in the eastern part of the Eastern Alps. The nappes are in tectonic contact and comprise Permian to Mesozoic lower greenschist facies metamorphic metasediments, but only the Troiseck-Floning Nappe consists of a pre-Permian crystalline basement (Troiseck Complex) as well. LA-ICP-MS U–Pb zircon ages, Rb–Sr biotite ages and geochemical data unravel the geological evolution of these tectonic units from Neoproterozoic to Mesozoic times. Detrital U–Pb zircon analyses from siliciclastic metasediments of the Troiseck Complex indicate a late Ediacaran to early Cambrian deposition age of the volcanoclastic sequence. The age distribution correlates with a position along the northeastern Gondwana margin. A late Cambrian crystallization age (502.4 ± 6.8 Ma) of granitic intrusions together with evidence for Late Cambrian/Ordovician magmatism and metamorphism indicate a position at an active plate margin. Polyphase overprinting during the Variscan orogeny is recorded by Late Devonian/early Carboniferous pegmatite dikes (~ 353 Ma) that formed after an early Variscan event, while Pennsylvanian ages of overgrowth rims and inherited grains (~ 320 Ma) are evidence for late Variscan metamorphism. Rhyolitic to andesitic volcanic rocks from the Troiseck-Floning and Rosskogel nappes (271–264 Ma) concomitant with intrusions of porphyric granitoids now transformed to augen gneiss (271 Ma) yield evidence for Permian rift-related magmatism that is widely reported from the Eastern Alps and Western Carpathians. Rb–Sr biotite ages (75–74 Ma) indicate Late Cretaceous cooling below c. 300 °C. This relates to Late Cretaceous exhumation of the Troiseck-Floning Nappe following an Eo-Alpine metamorphic overprint at lower greenschist-facies metamorphic conditions. Based on the similar lithostratigraphy, analogous geological evolution and structure, the Troiseck-Floning Nappe represents the lateral extension of the Seckau Nappe. The new dataset also allows for correlations with other basement complexes that occur in the Western Carpathians. [ABSTRACT FROM AUTHOR]

Bones and teeth are often the only fossil remains of vertebrates that are preserved over geological time in sedimentary rocks. They render valuable archives for geochemical proxies which are commonly used for paleo-reconstructions. However, the fossilization mechanisms of bone are not yet well understood. Crucial processes are the transformation of bioapatite into and the replacement of collagen by thermodynamically more stable apatite phases, such as fluorapatite. In the present study, aqueous alteration experiments on cortical bone samples were performed under simulated early diagenetic conditions in order to investigate whether and how an external phosphate (PO 4) source affects post mortem bone mineralization. Additionally, abiotic oxygen isotope exchange mechanisms between bioapatite and aqueous solutions were assessed by using either 18O-enriched water or PO 4 as a tracer. The presence of an external sedimentary 18O-labeled PO 4 source led to a rapid formation of new fluorapatite crystallites at the sample's margin that was highly enriched in 18O. Meanwhile, in the interior of the samples carbonate-poor hydroxylapatite formed through a dissolution-precipitation process without incorporating significant amounts of the 18O tracer. These two processes appear to act independently from each other. In samples exposed to 18O-labeled aqueous solutions lacking a PO 4 source, no newly grown apatite crystallites were found, however in the interior of these samples, nano-crystalline carbonate-poor or -free hydroxylapatite precipitated. A comparatively low but uniform 18O-enrichment was measured from the sample's margin towards its interior, which is assumed to have resulted from the adsorption of H 2 18O onto crystallite surface sites and collagen. Overall, our results suggest that a fast incorporation of 18O-doped PO 4 from the sediment source accelerated bone mineralization and consequently changed the oxygen isotope composition of the PO 4 group in the bone mineral phase more rapidly and to a greater extent than in a diagenetic setting lacking additional external PO 4. Dissolved PO 4 from the taphonomic setting thus seems to be an important factor fostering bone fossilization and preservation as well as oxygen isotope alteration. [ABSTRACT FROM AUTHOR]

Garnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information. This study systematically investigates the geochemistry and geochronology of garnet and zircon in the Dafang Au‐Pb‐Zn‐Ag deposit, which represents prominent gold mineralization in southern Hunan, China. Garnet samples with distinct zoning patterns and compositional variations were identified using various analytical techniques, including Backscattered Electron (BSE) imaging, Cathodoluminescence (CL) response, textural characterization, and analysis of rare‐earth elements (REE), major contents, and trace element compositions. The garnet was dated U‐Pb dating, which yielded a lower intercept age of 161.06 ± 1.93 Ma. This age is older than the underlying granodiorite porphyry, which has a concordia age of 155.13 ± 0.95 Ma determined by zircon U‐Pb dating. These results suggest that the gold mineralization may be related to the concealed granite. Two groups of garnet changed from depleted Al garnet to enriched Al garnet, and the rare earth element (REE) patterns of these groups were converted from light REE (LREE)‐enriched and heavy REE (HREE)‐depleted with positive europium (Eu) anomalies to medium REE (MREE)‐enriched from core to rim zoning. The different REE patterns of garnet in various zones may be attributed to changes in the fluid environment and late superposition alteration. The development of distal skarn in the southern Hunan could be a significant indicator for identifying gold mineralization. [ABSTRACT FROM AUTHOR]

The magma sources, origins and precise forming ages of the miarolite from Qishan and Kuiqi intrusions are still uncertain. New results reveal that, miarolites from the Qishan and Kuiqi intrusions yield crystallization ages of ∼101 and ∼98 Ma, and they have a high formation temperature (∼910°C) and low oxygen fugacity value, indicating crystallization condition at low pressure in the upper crust with temperature of 678°C. The Qishan and Kuiqi miarolites are characterized by enrichment in SiO2 and high‐K alkali, depletion in Ca and Mg, and belong to the high‐K weak peraluminous rock series. The samples are enriched in HFSEs (i.e., Ta, Zr and Hf) and LILEs (i.e., Ba, P and Sr), depleted in Ba and Sr with the negative anomaly of Eu. In the primitive mantle normalized trace element spider diagram, the samples show a right‐inclined 'seagull‐type' pattern, combined the ratios of (La/Yb)N, 10000 × Al/Ga, Rb/Nb and Nb/Ta etc., they were proved to be alkaline A‐type granite. Combined the characterize of the trace elements, they were derived from clay‐rich source accompanied pelite melting, and subjected to K‐feldspar crystallization fractional. The values of εHf(t) and tDM2 are distributed in the range of –2.8 to 3.3 with ∼1.2 Ga, and –6.0 to 4.0 with ∼1.2 Ga, revealing that they were generated from the Mesoproterozoic Cathaysia basement rocks. The comprehensive research reveals the Kuiqi and Qishan intrusions derived from crust‐mantle mixing and partial melting of the crust, respectively, resulting from lithospheric extension generated by the Paleo‐Pacific Plate subducted into the European–Asian Plate. [ABSTRACT FROM AUTHOR]

The paper presents new isotopic U–Pb data (LA-ICP-MS method) of zircon from the main types of intrusive rocks at the Kuru-Tegerek gold-copper-molybdenum skarn deposit situated in the Chatkal segment of the Middle Tien Shan. This and other gold, copper, tungsten and molybdenum deposits are parts of the extended Late Paleozoic metallogenic belt of Tien Shan. The concordant isotopic U–Pb values obtained for zircon autocrysts from the rocks of sequential intrusive phases span over the interval from approximately 323 to 311 Ma. This interval comprises the crystallization of gabbro-diorite (from 323.5 ± 2.5 Ma to 323.2 ± 6.8 Ma) and tonalite (from 321.4 ± 3.8 Ma to 311 ± 3.8 Ma). The age dates obtained for these zircon autocrysts correspond to the emplacement of these moderate-potassic intrusions in the Late Carboniferous and are almost coincident with the isotopic dates previously known for the high-potassic intrusions of the porphyry Cu–Au–Mo deposits of the Almalyk mineralized cluster (Kurama segment of the Middle Tien Shan), which were also emplaced in the Late Carboniferous (about 330–310 Ma). This corresponds to the subduction tectonic regime occurred in this region in relation to the steep-dipping (in the Kurama segment) or flat (in the Chatkal segment) subduction of a tectonic plate toward the north, under the structures of the Kazakhstan–North Tien Shan continental massif and accreted segments of the Middle Tien Shan. The intrusive rocks studied at the Kuru-Tegerek deposit contain also zircon xenocrysts (including these in the core of complex crystals) with the isotopic U–Pb age of some 1.9–2.1 Ga. These dates are in agreement with the age of metamorphic rocks in the Tarim craton basement and indicate the presence of the ancient continental crust in this segment of the Middle Tien Shan. [ABSTRACT FROM AUTHOR]

At temperatures above about 600 °C, alkali feldspar forms a continuous solid solution between the Na and K end members. Towards lower temperatures a miscibility gap opens, and alkali feldspar of intermediate composition exsolves, forming an intergrowth of relatively more Na-rich and K-rich lamellae. During exsolution, the crystal structure usually remains coherent across the lamellar interfaces, a feature that may be preserved over geological times. Due to the compositional dependence of the lattice parameters, coherent intergrowth requires that the lamellae are elastically strained. The associated elastic strain energy counteracts exsolution, and the solvus delimiting the misciblity gap for coherent intergrowth lies below the solvus for strain free phase equilibria. To determine the coherent solvus, homogeneous gem quality alkali feldspar of intermediate composition was annealed at conditions falling into the two-phase region of the phase diagram. Thereby a coherent intergrowth of approximately 10–20 nanometers wide lamellae was produced. Lamellar compositions were determined with atom probe tomography defining points on the coherent solvus. In parallel, the coherent solvus was calculated using a thermodynamic mixing model calibrated on the same alkali feldspar as used for the exsolution experiments and accounting for the elastic strain energy associated with coherent lamellar intergrwoth. The experimentally determined and the calculated coherent solvus are in excellent agreement indicating that phase equilibria in coherent lamellar intergrowth of alkali feldspar are adequately described, providing a sound basis for the interpretation of phase relations in coherently exsolved alkali feldspar. [ABSTRACT FROM AUTHOR]

Epidote group minerals, including allanite, clinozoisite and epidote are common in a range of metamorphic, igneous and hydrothermal systems, and are stable across a wide range of pressure–temperature (P–T) conditions. These minerals can incorporate substantial amounts of rare earth elements (REEs) during their crystallisation, making them potential candidates for Lu–Hf geochronology to provide age constraints on various geological processes. Here we report on a first exploration into the feasibility of in situ Lu–Hf geochronology for epidote group minerals from various geological settings and compare the results with age constraints from other geochronometers. Magmatic allanite samples from pegmatites and monzogranites in the Greenland anorthosite complex, Coompana Province and Qingling Orogen provided dates consistent with magmatic events spanning from c. 2660 to 1171 Ma. In the Qingling pegmatites, a younger phase of hydrothermal allanite was dated at c. 215 Ma, consistent with the timing of regional REE mineralisation. Allanite from the Yambah Shear Zone, Strangways Metamorphic Complex, yielded Lu–Hf age of c. 430 Ma. It predates the garnet and apatite growth at c. 380 Ma, suggesting the Lu–Hf system can be preserved in allanite during prograde amphibolite-facies metamorphism. Additionally, Lu–Hf dates for hydrothermal clinozoisite and epidote are consistent with the timing of hydrothermal alteration and mineralisation in a range of settings, demonstrating the utility of the technique for mineral exploration. Despite the current lack of matrix-matched reference materials, the successful application of laser ablation Lu–Hf geochronology to epidote group minerals offers valuable geochronological insights into various geological processes that can be difficult to access through other geochronometers. [ABSTRACT FROM AUTHOR]

We use U–Pb dating of allanite and REE-rich epidote in three polymetamorphosed units from the Eastern Alps to constrain the timing of prograde metamorphism. All three units (Ennstal, Wölz and Rappold Complex) record several metamorphic cycles (Variscan, Permian and Eoalpine) and presently define an Eoalpine (Cretaceous) metamorphic field gradient from lower greenschist to amphibolite facies. For U–Pb data, a method is introduced to test the magnitude of 230Th disequilibrium and potentially approximate the Th/U ratio of the reservoir out of which allanite and REE-rich epidote grew. We also show that the modelled stability of epidote-group minerals in the REE-free MnNCKFMASH and MnNCKFMASHTO systems and REE-bearing systems is nearly identical. By combining the stability fields of (clino-)zoisite and epidote modelled in REE-free systems with known geothermal gradients for the region, REE-rich epidote growth is constrained to 200–450 °C and 0.2–0.8 GPa during prograde metamorphism. In the Rappold Complex, allanite cores yield a Variscan age of ca. 327 Ma. In the Ennstal and Wölz Complex, allanite growth during the Permian event occurred at ca. 279–286 Ma. Importantly, recrystallized allanite laths and REE-rich epidote overgrowths in samples from all three units yield prograde Eoalpine ages of ca. 100 Ma, even though these units subsequently reached different peak conditions, most likely at different times. This suggests that all units were buried roughly at the same time during the onset of Eoalpine continental subduction. This interpretation leaves room for the model proposing that diachronous peak metamorphic conditions reported for the field gradient may be related to the inertia of thermal equilibration rather than tectonic processes. [ABSTRACT FROM AUTHOR]

As a tectonic window into the Lesser Himachal Himalaya, India, a group of metasediments and gneissic rocks, known as the Jutogh Group and Wangtu Gneissic Complex (WGC), occurs near the Jhakri thrust to the west and Wangtu to the east. In the Jutogh Group, chlorite-mica schist, garnet-staurolite schist and sillimanite-schist develop successively. The formation of chemically zoned garnet, which destabilized low-temperature assemblages, is predicted to be at 550–650 °C and 0.8–0.9 GPa by phase equilibria modelling. The retrograde segment consists of exhumation and cooling, yielding a tight clockwise P–T path. Moreover, textural observations and in-situ U-Th-Pb chemical dating indicate that metasedimentary rocks contain Cambrian monazites. These monazites have ages that cluster around 500 Ma. The ƐNd[1.8Ga] of Jutogh rocks ranges from − 1.0 to -8.1, with depleted mantle-model ages between 3.07 and 2.25 Ga. The garnet core and its leachates yield an Sm-Nd isochron age of 472 Ma. Another Sm-Nd isochron age of 454 Ma is obtained from biotite, garnet rim, and garnet rim leachate. According to phase equilibrium modelling, Sm-Nd dating, and monazite geochronology, the Jutogh Group experienced metamorphism along the northeast margin of Gondwana during the Cambro-Ordovician accretion. [ABSTRACT FROM AUTHOR]

The Tirodi Gneissic Complex (TGC) represents the basement sequence of the Central Indian Tectonic Zone (CITZ), underlying the Proterozoic supracrustal sequences of the Sausar and Betul Groups of rocks. Lithologically, the TGC constitutes a combination of pink and grey granitic gneiss assemblages, characterised by biotite-rich, hornblende-biotite-rich, and muscovite-biotite-rich granite gneiss. Compositionally, the TGC granitoids represent tonalite-trondhjemite-granodiorite to granite, and have calc-alkaline lineage with metaluminous to peraluminous characteristics. Geochemically, they dominantly belong to A2-type granitoids. Chondrite normalised REE ratios of La/Sm, La/Yb, La/Gd, and Gd/Yb indicate diverse LREE/HREE enrichment. Multi-element patterns for the TGC granitoids are characterised by light rare earth elements (LREE) and large ion lithophile elements (LILE) enrichment and depletion of high field strength elements (HFSE: Nb, P, and Ti) and strong positive Pb and Th anomalies. The observed negative anomalies for HFSE are attributed to diverse crustal/lithospheric sources, with some influence from K-feldspar, plagioclase and Ti-oxide fractionation. Sm–Nd data presents initial 143Nd/144Nd (t = 1.7 Ga) ratios (0.509898 to 0.510508), and εNd (t = 1.7 Ga) is (+ 0.58 to -10.59), with TDM model ages ranging from 2.11 to 2.95 Ga. Such a wide range of εNd (t = 1.7 Ga), indicates heterogeneous crustal/lithosphere sources, which have probably experienced longer crustal residence times. Zircon U–Pb ages for individual TGC samples are 1506 ± 11 Ma (TG-01), 1534 ± 26 Ma (MU-5), 1675 ± 9 Ma (BT-4), 1724 ± 11 Ma (BT-3), 1730 ± 13 Ma (BT-4), and 1960 ± 2 Ga (Ms-2), respectively. These ages have probably recorded the key periods of the Columbia supercontinent's assembly, growth, and breakup. Geochemical and geochronological results suggest that the TGC granitoids have a crustal/lithospheric origin and are formed by partial melting of felsic sources in dominantly VAG (volcanic arc granite) and, to some extents, WPG (within-plate granite) settings. [ABSTRACT FROM AUTHOR]

Comprehensive U-Pb detrital zircon geochronology of Ediacaran sandstones from Oman indicates that they originated from Neoproterozoic basement with a peak magmatic age of ca. 850-780 Ma (Tonian), with lesser Paleoproterozoic and Ediacaran sources and renewed magmatic input starting at ca. 550 Ma. Comparison with detrital zircons from the Arabian-Nubian and NW Indian Shields supports an eastern Gondwana affinity for the Ediacaran succession of Oman. Tonian basement sediment sources are present in Oman. Sources for older Paleoproterozoic zircons (ca. 2500 and 1800 Ma) are not found in Oman but are known from the cratonic Indian Shield. The signal of the main magmatic events of the juvenile Arabian-Nubian Shield, peaking at ca. 640-620 Ma, is rare or absent in the Ediacaran rock succession of Oman. However, deformed Ediacaran clastic units with an Arabian-Nubian Shield affinity occur in western Oman. Influx of latest Ediacaran-early Cambrian zircons (550-525 Ma) is interpreted as due to final Cambrian Angudan/Malagasy orogeny-related magmatism. These results, together with new ages for volcano-sedimentary terranes in the subsurface of SW Oman and seismic observations, support the interpretation that the Ediacaran succession of Oman was deposited along the western, passive margin of the Greater Indian Shield, on the eastern (east and west in this paper refer to present-day coordinates) side of the Mozambique Ocean. Oman then collided with the Arabian-Nubian Shield in the early Cambrian, when the Angudan/Malagasy orogeny led to final consolidation of Gondwana. Our data support the inference that the youngest and final suture between the Indian and Arabian Shields lies in the subsurface of Oman along the early Cambrian western deformation front. [ABSTRACT FROM AUTHOR]

U-Pb zircon geochronology and isotopic records have played an influential role in our understanding of convergent margin dynamics. Orogenic cyclicity models link tectonic regimes with magmatic isotopic signatures in advancing orogens, relating compressional regimes with evolved signatures and extension with juvenile signatures; however, such frameworks may not apply for retreating orogens, which commonly produce substantial crustal heterogeneities during backarc rifting and ocean spreading. We explore the Mesozoic to Cenozoic Patagonian Andes tectonic evolution, combining U-Pb zircon ages, bulk rock eNd, and new detrital zircon eHf from the retroarc basin to understand the associated magmatic arc evolution during retreat and advance of the margin. Our results reveal a protracted phase of isotopically juvenile magmatism between 150 and 80 Ma, which began during backarc extension and persisted long after the margin switched to a contractional regime. We propose that the prolonged juvenile isotopic trend started mainly due to trenchward migration of the arc during backarc extension (150-120 Ma) and persisted due to partial melting of underthrusted juvenile attenuated and oceanic crust during backarc basin closure (120-80 Ma). This interpretation implies that tectonic stress alone does not predict isotopic trends, and factors like assimilation or the composition of underthrusted crust are important controls on magmatic isotopic composition, especially in retreating and transitional orogens. [ABSTRACT FROM AUTHOR]

The Laird Lake property, southwest Red Lake greenstone belt, straddles the contact between the Balmer (2.99–2.96 Ga) and the Confederation (2.74–2.73 Ga) assemblages. The property is 10 km along strike from the Madsen and Starrat–Olsen Au mines that are hosted near the contact. The Balmer assemblage consists of fine-grained, aphyric, locally pillowed mafic volcanic rocks, ultramafic intrusive and volcanic rocks with flow breccia textures hosting local spinifex-bearing clasts, and banded-iron formations. In contrast, the Confederation assemblage comprises porphyritic mafic volcanic rocks intercalated with intermediate to felsic volcanic rocks that include crystal lapilli tuffs, crystal tuffs, and tuffs. The Balmer assemblage is composed of tholeiitic mafic volcanic rocks with minor Al-undepleted komatiites, whereas the Confederation assemblage is calc–alkalic. Neodymium isotopes, in conjunction with trace element geochemistry, suggests that parts of the Balmer assemblage were weakly contaminated by an older intermediate basement. Both arc and back-arc volcanism occurs in the Confederation assemblage, with the arc rocks showing a stronger crustal component than the back-arc rocks. A maximum U–Pb age of 2741 ± 19 Ma for a crystal tuff and an age of 2737.68 ± 0.79 Ma for a diorite are consistent with a Confederation assemblage affinity for the intermediate calc–alkaline rocks south of the Au-bearing horizon. The Balmer assemblage represents an oceanic plateau formed by plume magmatism on the margins of the North Caribou Terrane, whereas the Confederation assemblage at Laird Lake formed in an oceanic arc setting where both arc and back-arc volcanism occurred simultaneously. [ABSTRACT FROM AUTHOR]

The 3D microstructure and compositional zoning of garnet populations in micaschists from the Kolvik and Bekkarfjord nappes indicate the quasi‐equilibration of their major components across the rock matrices during interface‐controlled, size‐independent garnet growth. There is microstructural evidence for foliation‐parallel, small‐scale resorption of garnet rims in the Kolvik Nappe, influencing the metamorphic peak conditions obtained from thermodynamic modelling. The local chemical compositions of rims less affected by resorption indicate a peak temperature of ~630°C, which is ~40°C higher than the temperature obtained from resorbed rims of the largest garnet crystal. Using a diffusion geospeedometry approach that considers the geometry of the compositional zoning of the garnet population, as well as the higher, more realistic peak temperature, a duration of 1 to 4.9 Myr is obtained for garnet growth in the Kolvik Nappe. This is approximately 1 order of magnitude faster than duration estimates obtained when using the apparent, lower temperature estimated from the resorbed garnet rims. Concomitantly to garnet growth in the Kolvik Nappe, garnet overgrowths formed in the Bekkarfjord Nappe for circa 2.5 Myr at metamorphic peak temperatures of ~560°C. The garnet growth durations obtained here are comparable with the uncertainty on the Lu–Hf garnet–whole rock isochron ages of 419.9 ± 2.4 Ma and 423.0 ± 1.9 Ma, previously obtained for these rocks. These results provide new insight into the timescales of repeated Barrovian‐type metamorphic events experienced by the lower nappes of the Kalak Nappe Complex during the Caledonian Orogeny in Arctic Norway. This study emphasizes the importance of microstructural and chemical characterization of garnet populations in assessing metamorphic crystallization mechanisms and the extent of equilibration of garnet‐forming components during prograde metamorphism. Moreover, our results provide means for reducing the uncertainty on metamorphic durations obtained via diffusion geospeedometry and, so, contributing to our understanding of geological timescales and processes. [ABSTRACT FROM AUTHOR]

The paper reports data on the age and composition of poorly studied Cretaceous clastic rocks of the Lower Amur River area, which are part of the Zhuravlevka–Amur terrane and are attributed to the Berriasian–Valanginian Komsomolsk series. U/Pb dating of detrital zircons yielded reliable dates of 99 and 90 Ma for the Gorin and Pioneer formations, respectively. Thus, a sedimentary complex with a Late Cretaceous sedimentation age was identified for the first time in the Sikhote-Alin orogenic belt based on detrital zircon geochronology. In composition and detrital zircon age distribution pattern, the studied rocks are more similar to sediments of the upper, Hauterivian–Albian part of the Zhuravlevka–Amur terrane section rather than to those of the lower, Berriasian–Valanginian part. In rocks of the Pioneer Formation, the youngest zircon population with an age of about 90 Ma makes up more than 40% of all dated grains. The main source of detrital material of this age was probably proximal andesites hosting the Mnogovershinnoe deposit and granitoids of the Nizhneamurskii Complex. The source of detritus for sediments of the ∼99 Ma Gorin Formation was probably felsic rocks from the Albian–Cenomanian igneous province of Pacific Asia. The discrepancy between the Late Cretaceous age obtained by us and the paleontologically established Berriasian–Valanginian stratigraphic age of the formations requires additional research. New data on the Late Cretaceous age of the Zhuravlevka–Amur sediments of strike-slip marginal-continental basin requires revision of the geologic evolution of the terrane and the entire Sikhote-Alin orogenic belt. [ABSTRACT FROM AUTHOR]

This work presents an integrated structural, kinematic, and petrochronological study of the Monte Grighini dome within the Variscan hinterland–foreland transition zone of Sardinia (Italy). The area is characterised by dextral transpressive deformation partitioned into low- and high-strain zones (Monte Grighini shear zone, MGSZ). Geothermobarometry of one sample of sillimanite-bearing mylonitic metapelite indicates that the Monte Grighini shear zone developed under high-temperature (~ 625 °C) and low-pressure (~ 0.4–0.6 GPa) conditions. In situ U–(Th)–Pb monazite geochronology reveals that the deformation in the shear zone initiated at ca. 315 Ma. Although previous studies have interpreted the Monte Grighini shear zone to have formed in a transtensional regime, our structural and kinematic results integrated with constraints on the relative timing of deformation indicate that it shows similarities with other dextral ductile transpressive shear zones in the Southern European Variscan belt (i.e., the East Variscan Shear Zone, EVSZ). However, dextral transpression in the Monte Grighini shear zone started later than in other portions of the EVSZ within the framework of the Southern European Variscan Belt due to the progressive migration and rejuvenation of deformation from the core to the external sectors of the belt. [ABSTRACT FROM AUTHOR]

The Kirazlı deposit is located at the center of the Biga Peninsula metallogenic province, in a geological setting characterized by an extensional tectonic environment. A NNW-SSE trending high-sulfidation (HS) orebody with a total reserve of 33.86 Mt @ 0.69 g/t Au and 9.42 g/t Ag lies beneath the Kirazlı Main zone. A porphyry Cu orebody hosted by Eocene intrusive and volcanic rocks has been intersected by drilling within its vicinity. The HS epithermal deposit is hosted by a partly silicified and brecciated Oligocene volcanic and volcaniclastic sequence consisting mainly of basaltic andesite lava flow and lithic/crystal tuff. Lithogeochemistry and zircon U-Pb radiometric ages allow us to distinguish three distinct high-K calc-alkaline magmatic events at ca. 41, 38, and 32 Ma, sourced by metasomatized mantle melts, which have interacted with the crust during their ascent. Porphyry Cu mineralization took place at 36.7 ± 0.4 Ma (muscovite 40Ar/39Ar age) with subsequent re-opening and base metal deposition. Crosscutting quartz-pyrite-molybdenite veins were emplaced at 33.6 ± 0.2 Ma (molybdenite Re-Os age), and followed by the HS epithermal Au-Ag event at ca. 31 Ma, based on a previous study. Our radiometric data indicate that the Kirazlı deposit has recorded a long-lasting Cenozoic magmatic and metallogenic evolution during about 10 Myr. Our study demonstrates that successive, independent, and overprinting, but genetically unrelated, HS epithermal precious metal, hydrothermal Mo, base metal, and porphyry Cu systems have been active at the same location during protracted extensional tectonics of the Biga Peninsula. [ABSTRACT FROM AUTHOR]

The age and depositional environments of Middle Jurassic terrigenous rocks crowning the Mesozoic section on the northeastern flank of the Nagondzha terrane within the Ulakhan-Sis Ridge are discussed. Based on our finds of retrocerams and the analysis of biostratigraphic data of predecessors, the Bajocian–Middle Bathonian age of these rocks is accepted. Three lithologically different sequences are identified in the section. Sandstones from the lower unit belong to feldspathic litharenites; from the upper sequences, to litharenites dominated by extrabasinal carbonate clastics (calclithites). The analysis of structural-textural features, mineralogical-petrographic composition, and distribution of trace elements in litharenites suggests that all these sequences were deposited in the shelf part of paleobasin associated with an active volcanic island arc, which presumably existed since the Early Jurassic on the Omulevka Craton terrane until the termination of the Kolyma–Omolon superterrane formation. [ABSTRACT FROM AUTHOR]

The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes. [ABSTRACT FROM AUTHOR]

Re‐Os isotope‐dilution geochronology has been widely used to date the timing of molybdenite, pyrite and chalcopyrite formation across a variety of geological settings. However, in situ methods have been impeded by the isobaric interference of 187Re on 187Os. In situ Re‐Os geochronology using LA‐ICP‐MS/MS has been shown to be a useful technique to chemically separate Os from Re, as Os reacts with CH4 to create higher‐mass reaction products, which can then be measured with minimised interference of 187Re. However, application of the method requires matrix‐matched primary reference materials, e.g., age‐homogenous molybdenite amenable to laser ablation. Here, we characterise and present two new molybdenite mineral reference materials for in situ Re‐Os geochronology by LA‐ICP‐MS/MS, verified by ID‐TIMS Re‐Os measurements. We also present case studies from molybdenite samples with varying Re mass fractions and Re‐Os age mapping. The method provides accurate and precise age data, with excellent precision for high Re samples. The benefits of the LA‐ICP‐MS/MS approach include: (1) simple sample preparation, (2) rapid data acquisition, (3) targeting of specific textural domains including growth zones and (4) the ability to simultaneously collect trace elements used to link the timing and conditions of ore‐formation. [ABSTRACT FROM AUTHOR]

Simple Summary: Understanding how traits evolve across different life stages is crucial for species with complex life cycles. We investigated how tadpole morphology relates to adult shape in Neoaustrarana frogs, finding that larval and adult shapes show low correlation. Our study, encompassing 83 species across four families, highlights the importance of considering ontogenetic stages in evolutionary research. We observed distinct patterns among families, with larval morphospace exhibiting higher phylogenetic structure than adult morphospace. Our results support the Adaptive Decoupling Hypothesis as a mechanism driving phenotypic diversity, shedding light on the early evolution of Neoaustrarana frogs and emphasizing the need for further research in this area. Phenotypic traits can evolve independently at different stages of ontogeny, optimizing adaptation to distinct ecological contexts and increasing morphological diversity in species with complex life cycles. Given the relative independence resulting from the profound changes induced by metamorphosis, niche occupation and resource utilization in tadpoles may prompt evolutionary responses that do not necessarily affect the adults. Consequently, diversity patterns observed in the larval shape may not necessarily correspond to those found in the adult shape for the same species, a premise that can be tested through the Adaptive Decoupling Hypothesis (ADH). Herein, we investigate the ADH for larval and adult shape differentiation in Neoaustrarana frogs. Neoaustrarana frogs, particularly within the Cycloramphidae family, exhibit remarkable diversity in tadpole morphology, making them an ideal model for studying adaptive decoupling. By analyzing 83 representative species across four families (Alsodidae, Batrachylidae, Cycloramphidae, and Hylodidae), we generate a morphological dataset for both larval and adult forms. We found a low correlation between larval and adult shapes, species with a highly distinct larval shape having relatively similar shape when adults. Larval morphological disparity is not a good predictor for adult morphological disparity within the group, with distinct patterns observed among families. Differences between families are notable in other aspects as well, such as the role of allometric components influencing shape and morphospace occupancy. The larval shape has higher phylogenetic structure than the adult. Evolutionary convergence emerges as a mechanism of diversification for both larval and adult shapes in the early evolution of neoaustraranans, with shape disparity of tadpoles reaching stable levels since the Oligocene. The widest occupation in morphospace involves families associated with dynamically changing environments over geological time. Our findings support the ADH driving phenotypic diversity in Neoaustrarana, underscoring the importance of considering ontogenetic stages in evolutionary studies. [ABSTRACT FROM AUTHOR]

Iron oxide-copper-gold (IOCG) deposits are a vital source of copper and critical elements for emerging clean technologies. Andean-type IOCG deposits form in continental arcs undergoing extension, and they have a temporal relationship with magmatism although they do not exhibit a close spatial relation with the causative intrusions. The processes required to form IOCG deposits and their potential connections to iron oxide–apatite (IOA)-type mineralization remain poorly constrained, as well as the characteristics of magmatism linked to both deposit types. Here we combine zircon U–Pb geochronology with zircon trace element geochemistry of intrusive rocks associated with the Candelaria deposit, one of the world's largest IOCG deposits, to unravel distinctive signatures diagnostic of magmatic fertility. Our results reveal a marked transition in the geochemistry of intrusions in the Candelaria district, characterized by changes in the redox state, water content and temperature of magmas over time. The oldest magmatic stage (~ 128–125 Ma), prior to the formation of the Candelaria deposit, was characterized by zircon Eu/Eu* ratios of 0.20–0.42, and redox conditions of ΔFMQ − 0.4 to + 1.0. The earliest magmatic stage related to the formation of Fe-rich mineralization at Candelaria (118–115 Ma) exhibits low zircon Eu/Eu* ratios (0.09–0.18), low oxygen fugacity values (ΔFMQ ~− 1.8 to + 0.2) and relatively high crystallization temperatures. In contrast, the youngest stage at ~ 111–108 Ma shows higher zircon Eu/Eu* (~ 0.37–0.69), higher oxygen fugacity values (ΔFMQ ~ + 0.4 to + 1.3) and a decrease in crystallization temperatures, conditions that are favorable for the transport and precipitation of sulfur and chalcophile elements. We conclude that Candelaria was formed through two distinct ore-forming stages: the first associated with a reduced, high temperature, water-poor magma developed under a low tectonic stress, followed by a more oxidized, water-rich, and low temperature magmatic event related to a compressional regime. The first event led to Fe-rich and S-poor IOA-type mineralization, while the second event with geochemical signatures similar to those of porphyry copper systems, generated the Cu- and S-rich mineralization. This late stage overprinted preexisting IOA mineralization resulting in the formation of the giant Candelaria IOCG deposit. [ABSTRACT FROM AUTHOR]

Smøla island, situated within the mid-Norwegian passive margin, contains crystalline-basement-hosted intricate fracture and fault arrays formed during a polyphase brittle tectonic evolution. Its detailed study may strengthen correlation attempts between the well-exposed onshore domain and the inaccessible offshore domain, further the understanding of the passive margin evolution, and provide useful constraints on petrophysical properties of fractured basement blocks. A combination of geophysical and remote sensing lineament analysis, field mapping, high-resolution drill hole logging, 3D modelling, petrographic and microstructural studies, and fault gouge K–Ar geochronology made it possible to define five deformation episodes (D1 to D5). These episodes occurred between the post-Caledonian evolution of the regional-scale Møre–Trøndelag Fault Complex (MTFC) and the Late Cretaceous and younger crustal extension preceding the final stages of Greenland–Norway break-up. Each reconstructed deformation stage is associated with different structural features, fault and fracture geometries, and kinematic patterns. Synkinematic mineralisations evolved progressively from epidote–prehnite, sericite–chlorite–calcite, chlorite–hematite, hematite–zeolite–calcite, to quartz–calcite. K–Ar geochronology constrains brittle deformation to discrete localisation events spanning from the Carboniferous to the Late Cretaceous. Multiscalar geometrical modelling at scales of 100, 10, and 1 m helps constrain the extent and size of the deformation zones of each deformation episode, with D2 structures exhibiting the greatest strike continuity and D1 features the most localised. Overall, the approach highlighted here is of great utility for unravelling complex brittle tectonic histories within basement volumes. It is also a prerequisite to constrain the dynamic evolution of the petrophysical properties of basement blocks. [ABSTRACT FROM AUTHOR]

The Re–Os geochronometer has been widely applied for determining the depositional ages of organic-rich rocks and constraining the key time points of petroleum systems, and PGE can provide important information about the presence or absence of extraterrestrial materials in organic-rich sedimentary strata or the hydrocarbon source of a petroleum system. However, due to the extremely low mass fractions, precise determinations of Re–Os–PGE elemental and Os isotopic compositions in organic-rich geological samples (ORGS) remain challenging. In this study, we present an improved two-stage column protocol for the separation and purification of Re–PGE from the sample matrix and interfering elements for ORGS, after Os was separated by CCl4 solvent extraction. In the first step, cation exchange resin (AG50W-X8, 200–400 mesh) was used to separate Re and PGE collectively from the sample matrix and primarily remove interfering elements (particularly Cd, Zr, and Hf). In the second step, LN resin was used to further remove the remaining interfering elements (e.g., Zr and Hf) and to separate Re from PGE (Ir–Ru–Pt–Pd). After these two steps of purification, the Re and PGE mass fractions were determined using MC-ICP-MS (multi-collector inductively coupled plasma-mass spectrometry) and Q-ICP-MS (quadrupole-inductively coupled plasma-mass spectrometry), respectively. To verify the method, three organic-rich reference materials (RMs) (Shales: USGS SBC-1 and USGS SGR-1b; Crude oil: NIST RM 8505) were determined using the procedure, and the analytical results are in good agreement with the literature data. This method is the first report to use LN resin to separate Re and PGE from each other, such that it is allowed to use MC-ICP-MS to measure Re with high precision for Re–Os dating purposes, while using ICP-MS for rapid measurements of PGE (Ir, Ru, Pt and Pd) simultaneously with in-run monitoring of interfering elements for PGE mass fraction determinations. [ABSTRACT FROM AUTHOR]

Known from over 50 Triassic localities worldwide, beetles were a significant component of the early Mesozoic paleofauna. Beetle fossils are particularly diverse in the Late Triassic (Norian) Cow Branch and Walnut Cove formations (Solite deposit) of Virginia and North Carolina, with 100 distinct morphotypes sorted from approximately 1000 specimens. The diversity of the Solite Coleoptera is documented, the 100 beetle morphotypes are informally described, and comparisons are made with other beetle communities through geologic time. In comparison with modern beetle communities, the Solite fauna shares two remarkable similarities. First, the distribution of Solite beetle body sizes matches that of some modern beetle communities, with the majority of specimens in both groups measuring between 2 and 4 mm in length. Second, the vast majority of the 100 Solite morphotypes (84%) are known from only a single specimen. This pattern somewhat follows the species abundance distribution of modern animal communities, in which a community is comprised of only a few common species and many rare species. In contrast, the Solite beetle fauna differs markedly from those of other Triassic and Early Jurassic deposits, both in the composition of higher taxa present, as well as in the lack of shared taxa between sites. The uniqueness of the Solite taxa, including the remarkable diversity, demonstrate the importance of the Solite Konservat-Lagerstätte in understanding the evolutionary history of Order Coleoptera. [ABSTRACT FROM AUTHOR]

The central Inner Mongolia, located at the intersection of the northern margin of the North China Craton (NCC) and the Central Asian Orogenic Belt, is crucial for deciphering the Late Palaeozoic tectonic evolution associated with the subduction and closure of the Palaeo‐Asian Ocean (PAO). Our study focused on petrology, detrital zircon LA–ICP–MS U–Pb geochronology and whole‐rock geochemistry for the Late Carboniferous to Permian sandstones within the Shuanmazhuang, Dahongshan, Naobaogou, and Laowopu formations in Siziwang Banner, central Inner Mongolia. This comprehensive analysis shed light on the dynamic interplay between the NCC and the South Mongolia Block. Detrital zircon U–Pb ages in investigated samples mainly cluster between 250 and 2650 Ma, with significant peaks at 2.4–2.5 Ga, 1.8–2.0 Ga, 400–430 Ma, and 250–320 Ma, respectively. The geochemistry data are characterized by SiO2 contents (56.29–77.95 wt. %), Na2O / K2O ratios (0.45–1.58) and SiO2/Al2O3 ratios between 4.33 and 7.44. Moreover, they exhibit the slight enrichment in large ion lithophile elements (Rb and Ba) and the depletion in high field strength elements (Nb, Ta, Th, and U). These facts indicate that the sedimentary detritus predominantly originates from felsic sources, probably deriving from the Late Carboniferous–Permian continental island arc‐related intermediate‐acid igneous rocks, the Late Ordovician‐Silurian magmatic rocks in the Bainaimiao arc and the basements of the NCC. Furthermore, our present results also suggest that during the Early–Middle Permian, accelerating oceanic crust subduction triggered significant magmatic events in Siziwang Banner, leading to rapid uplift and the erosion of arc magmatic rocks, as well as the abundant corresponding sediments. Subsequently, the gradual convergence and eventual collision between the NCC and the Southern Mongolian Block took place at the end of the Permian, representing final closure of the PAO. [ABSTRACT FROM AUTHOR]

The geology of New York City (USA) consists primarily of metasedimentary rocks that were deformed during the series of orogenies between ca. 470 Ma and ca. 300 Ma that culminated in the amalgamation of Pangea. The rocks in New York City play a key role in understanding the tectonic history of these orogenies because they lie at a critical location at the boundary between the Northern and Southern Appalachian Mountains. The primary question addressed here is where these metasedimentary rocks originated prior to the assembly of Pangea. Through detrital zircon and whole-rock Nd isotope analyses, we show that all the metasedimentary rocks of New York City, mapped as the Manhattan Schist and the Hartland Group, are primarily derived from Laurentia as indicated by detrital zircon populations dominated by 1200-900 Ma grains and εNd values between -7 and -13. The results presented here do not necessitate an exclusively Laurentian source for the detrital material found in New York City, but the data strongly suggests protoliths represent sedimentary units that are primarily derived from the Laurentian margin. Another important result from this study is the limited contributions from any rift volcanics and/or Gondwanan material(s). There is some subtle variability across our zircon sample suite, but there is no convincing evidence for major changes in bulk provenance signal that would be consistent with derivation from vastly different continental sources for these rocks. The shared provenance signal observed here is counter to the previous suggestions that a major terrane boundary, often called Cameron's Line, exists in New York City, separating Laurentian rocks from those of a Gondwanan affinity. [ABSTRACT FROM AUTHOR]

The Samba Cu deposit is located in pre-Katangan Supergroup basement metavolcanic rocks of the Central African Copperbelt in Zambia. To better understand the formation of the Cu deposit, we use geochronologic, geochemical, and S isotopic data obtained for the deposit's host rocks and sulfide minerals. Laser ablation-inductively coupled plasma-mass spectrometric (LA-ICP-MS) dating of zircon from host rocks, including quartz-sericite schist and biotite-sericitechlorite schist, yields ages of 1967 ± 17 Ma and 1960 ± 20 Ma, which are interpreted as the crystallization ages of the original volcanic rocks. Re-Os analyses of molybdenite intergrown with chalcopyrite constrain sulfide deposition to 548.1 ± 7.5 Ma and 524.1 ± 7.3 Ma, which correspond to the timing of the Cu mineralization. LA-ICPMS U-Pb analyses of metamorphic rutile from the biotite-sericite-chlorite schist yield a U-Pb age of 508.3 ± 6.6 Ma, which is interpreted to represent the age of regional metamorphism. The new data suggest that the Cu mineralization at Samba was synchronous with the Lufilian orogeny. [ABSTRACT FROM AUTHOR]

The Precambrian Southern Granulite terrane of south India has a crustal evolution history broadly bracketed between the late Archean and Cambrian with records of polyphase deformation, metamorphism, and magmatism. The Southern Granulite terrane comprises distinct crustal blocks bounded by shear/suture zones that have been variably correlated with supercontinent fragments including Madagascar, Sri Lanka, Africa, Eastern Ghats, and Antarctica. However, the timing and mechanism of assembly of different crustal blocks within the Southern Granulite terrane and its linkages with counterparts in East Gondwana are highly debated. This study aimed to unravel the complex crustal evolutionary pattern of the terrane by generating robust zircon U-Pb/Hf isotopic data from basement charnockites, gneisses, granitoids, and alkaline intrusive units from the central part of Southern Granulite terrane and comparing these results with similar data from different East Gondwanan terranes. The study identified four distinct crustal growth episodes in the Madurai block: (1) Neoarchean-early Paleoproterozoic, (2) Rhyacian-Orosirian, (3) late Tonian, and (4) Ediacaran-Cambrian. Analysis of zircon Hf isotope data revealed that the first two events are marked by juvenile magmatic signatures, whereas the latter two are distinctly associated with intense reworking and remelting of older crust with no significant juvenile input. Our new results combined with existing data from other Gondwanan terranes suggest a common Paleoproterozoic ancestry for the Southern Granulite terrane and its corresponding Gondwanan fragments, proposing a revision to the existing geodynamic models. [ABSTRACT FROM AUTHOR]

At perhaps the coarsest scale of consideration, the rock cycle operates through fluxes associated with tectonic uplift and erosion, which are generally balanced by subsidence/subduction and the burial of mineral materials that leads to volumetric balance among the principal rock reservoirs. At Earth's surface, net rates of transfer are manifest as the reduction of areas of older rocks during erosional destruction as well as during burial by younger units. Because exposure of continental crust comprises some finite space, decrease of older rock area by erosion and/or burial must be largely balanced by an increase in area of new sedimentary and volcanic successions. Here, we examine relations between the lateral extents of rock units exposed across North America-their lithology, elevation, and the age of formation-to determine rates of geologic "repaving" that are recorded in the age and area of rocks making up the surface of the continent. Moreover, because deposition occurs at lower elevations, one might expect that subsequent episodes of uplift and/or burial would serve to increase the average elevation of currently exposed sedimentary lithosomes. Because plutonic and metamorphic rocks form at depth and are only exposed along orogenic belts and across shields after extended intervals of uplift and/or erosion, one might expect basement rocks to be initially exposed at higher elevations, and that subsequent erosion would decrease elevation with increasing age. Therefore, processes giving rise to associations between outcrop lithology, extent, and elevation may serve as measures of continentscale rates of rock cycling. We combine data from the 1 arc-minute global relief model with data from the Geological Society of America's 2005 Geologic Map of North America to assess the actuality and significance of first-order relations among the lithologies, areas, ages, and elevations of rock bodies now exposed across the North American continent and how these may shed light on deep-time rates of rock cycling. Areas of the 23,642 mapped North American lithosomes make up a lognormal frequency distribution (mode = 121 km²). This distribution reflects both natural (lateral extents of individual map units must be limited in space) and anthropogenic (cartographers must render map units within limited range of sizes) causes. Contiguous, lateral associations of the major rock types suggest that the spatial occurrence of volcanic and sedimentary rock bodies is largely independent of the proximity of other rock types, but exposures of plutonic and metamorphic lithosomes are intimately associated in space and thus comprise the "crystalline basement" exposed in cores of younger orogens and across the Canadian Shield. Unlike sedimentary and volcanic rocks that "attain their age" when formed at Earth's surface, plutonic and metamorphic units are "born" at depth and therefore must have reached some antiquity prior to first exposure. As a result, the ages of volcanic and sedimentary exposures span the full range of ages represented by all lithologies, while those of plutonic and metamorphic suites are more abbreviated and older. Median ages of North American volcanic, sedimentary, plutonic, and metamorphic exposures are 482 Ma, 306 Ma, 1695 Ma, and 2467 Ma, respectively. Although the areal extent of sedimentary rock decreases with increasing age, elevation increases. This change is interpreted as reflecting progressive tectonic uplift from initial accumulation at lower elevations. In contrast, the surfaces of exposed volcanic, plutonic, and metamorphic lithosomes become lower in elevation with increasing age. This change reflects both the erosional lowering of lithosome surfaces as well as the progressive exhumation of larger areas of crystalline basement. Exposed rock area exhibits a power law decrease with increasing age. This change reflects the progressive destruction of older units and their burial by younger units. A simple "repaving" model in which 0.8% area is uplifted and eroded per million years is in good agreement with observed relations of map age versus area, the rate of which is equivalent to the resurfacing of the North American continent every 63 m.y. or -56 times over the past 3.5 Ga. The rate of decrease in map area of exposed rocks with increasing age evident in both geologic map data and repaving models is about three times the rate of decrease in total sediment volume as determined from stratigraphic data and repaving models. The decrease in the areas of exposed rock units is primarily the result of burial by younger units rather than erosive destruction. [ABSTRACT FROM AUTHOR]

Knowledge of the late Mesozoic topography and drainage system of the Tibetan Plateau is essential for understanding the Cenozoic tectonic dynamics of the plateau. However, systematic analyses of the pre-Cenozoic surface uplift history and sediment-routing systems of the Tibetan Plateau remain sparse. Here we present new results for paleocurrents and U-Pb detrital zircon geochronology from the Lanping Basin, a key junction in the southeastern (SE) Tibetan Plateau, and integrate multidisciplinary data sets to constrain sediment provenance and reconstruct paleotopography and its drainage system throughout the Cretaceous. Our results indicate that mid- to Late Cretaceous (ca. Albian-Santonian) tectonically induced surface uplift occurred in the SE Tibetan Plateau, leading to the build-up of an extensive topographic barrier, and resultant rain shadows in the interior of east Asia. Superimposition of this topographic pattern by uplands in the eastern margin of Asia meant that the Cretaceous topography of east Asia was characterized by an enclosed paleo-relief pattern that was high in both the east and west, with drainage from the east and west to the south, contrasting with previously proposed configurations. This topographic pattern interrupted the atmospheric circulation pattern and generated widespread intracontinental desertification and drainage network evolution in east Asia. Our study constrains a key part of the late Mesozoic growth of the Tibetan Plateau prior to the Cenozoic collision between India and Eurasia and will improve our understanding of the paleoclimate, atmospheric circulation, and modern drainage system evolution of the east Asian continent. [ABSTRACT FROM AUTHOR]

Fossil scales from gar fish are made of bioapatite and are common in the continental sedimentary record from the Cretaceous to the present, prompting interest in using these fossil scales as geochemical archives. We investigated the diagenetic characteristics of the two different components of gar scales: ganoine, which has similarities to tooth enamel, and bone. We examined microscopic textural characteristics, spatially resolved trace element patterns, and apparent gar scale ages using the (U-Th)/He and U-Th-Pb systems, in modern scales as well as fossil scales from Cretaceous to Paleogene age strata in the North American Williston and San Juan Basins. Structural and textural characteristics of modern and fossil gar scales suggest that ganoine is more resistant to diagenetic alteration than bone. Trace element concentrations in fossil bone are at least an order of magnitude higher than in ganoine and can be spatially heterogeneous, indicative of a complex and prolonged diagenetic history. Trace element concentrations in fossil ganoine often decrease systematically with distance from the ganoine surface, which may be consistent with a fossilization model in which trace element concentrations are controlled by an inwardly propagating recrystallization front. However, (U-Th)/He dates of ganoine are substantially younger than expected based on basin thermal histories and compared to conventional detrital apatite (U-Th)/He dates from the same localities. The ganoine (U-Th)/He dates are also older than a few Ma for only the lowest effective uranium concentrations. We interpret the young (U-Th)/He dates and the date-effective uranium pattern to be indicative of either protracted or late-stage incorporation of trace elements, which is inconsistent with a recrystallization front model alone. The young (U-Th)/He dates may also reflect microstructurally-controlled low helium retentivity in gar scale ganoine, although this does not explain the observed date- effective uranium systematics. Late-stage incorporation of trace elements is supported by the U-Th-Pb systematics of ganoine, which require addition of U and Th at a time significantly later than the depositional age. Late-stage, or protracted, diagenetic uptake of parent nuclides in gar scale ganoine contrasts with recent studies of bioapatite from conodont elements, which instead appear to exhibit late-stage parent nuclide loss. We conclude that the (U-Th)/He system in gar scale bioapatite is not currently useful as a chronometer and suggest that applications of other trace element proxies to gar scale bioapatite be approached with caution. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that thermal models clearly demonstrate that crustal magma bodies should solidify rapidly upon emplacement. Small plutons can cool below the solidus in thousands of years, while even large plutons require hundreds of thousands of years, but not more than a million years. However, recent U-Pb zircon geochronological data contradict these results, strongly suggesting that magmatic systems are often characterized by protracted events. Therefore, a conceptual framework that reconciles thermal models and the geochronology data is necessary. The Devonian foreland magmatism of the Sierra de San Luis is made up of two distinctive suites, the Monzonite suite (<65 wt.% SiO2) and the Granite suite (>65 wt.% SiO2), both emplaced at ca. 3.7 kbar. Classification of the studied Devonian granitoids is debatable because they have a hybrid I- to A-type granite signature. Based on a robust geochronological U-Pb zircon dataset we corroborate the development of a protracted magmatic activity with three major crystallization events for this Devonian magmatism: 391 ± 1, 384 ± 1, and 379 ± 2 Ma. Considering these geochronological data, we postulate the presence of a deep mush reservoir, where a prolonged magmatic activity, permitted the prolonged crystallization of antecrysts (ca. 395–384 Ma). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber located at shallow levels, where zircon autocrysts crystallized (ca. 379 Ma). Age spectra reported within individual samples support the idea of a massive migration of magma when conditions were favourable (e.g. thermally matured crust). Individual crystallization ages recorded by monazites hosted in two-mica granites are comparable to those obtained from zircons, supporting the presence of a long-lasting hot source. Additional geochronological data indicate that a later thermal event (ca. 353 Ma) could have partially affected some areas of the Devonian magmatic zircons promoting Pb loss, with subsequent partial resetting of the isotopic clock. [ABSTRACT FROM AUTHOR]

Modern analogues of Archaean charnockite are important because they facilitate investigations into processes of early crustal formation and tectonic transition. Herein, we present the results of the petrography, geochemistry, and isotope geochronology of Late Neoarchean charnockites in the Daqingshan terrane at the northern margin of the North China Craton. The sources, petrogenesis, and tectonic implications of the samples obtained are determined based on their geochemical characteristics. Charnockites mainly exhibit magnesian and calc–alkaline characteristics; furthermore, they contain high amounts of light rare-earth elements, with slightly positive Eu anomalies. Analysis of zircon U–Pb dating using a sensitive high-resolution ion microprobe reveals that Hademengou–Xiwulanbulang (HDMG–XWLBL) charnockites were emplaced during the (i) Late Neoarchean (ca. 2500 Ma), with zircon εHf(t) values ranging from 1.57 to 7.81; (ii) single-stage model ages (TDM1) from 2529 to 2637 Ma; and (iii) two-stage model ages (TDM2) from 2710 to 2820 Ma. A comparative study has performed on the petrography, geochemistry, and geochronology of charnockite and granulite shown that the parent magma of the charnockites is the product of the partial melting of granulite. Combining our results with geological data pertaining to the Archaean structural evolution of the Daqingshan terrane, we speculate that the Late Neoarchean HDMG–XWLBL charnockite was formed during a subduction-related thermo-tectonic event in the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

The article "Geodigest" provides a summary of various geological events and discoveries. It discusses the A23a iceberg in the South Atlantic Ocean, the discovery of a new species of aetosaur called Garzapelta muelleri, and the rejection of a proposal to declare an Anthropocene epoch. It also mentions recent earthquakes in New York City and Taiwan, highlighting improvements in building structures and emergency response. The article then focuses on important discoveries in Antarctica, including foot bones from extinct terror birds and tracks made by these birds in Argentina. It also discusses a study on lithification in artificial ground and the proposal of a new rock name, plastistone, for sedimentary rocks containing waste plastics. Lastly, the article explores the role of tectonism in the diversification of mammals during the Late Cretaceous. [Extracted from the article]

Evolutionary stasis characterizes lineages that seldom speciate and show little phenotypic change over long stretches of geological time. Although lineages that appear to exhibit evolutionary stasis are often called living fossils, no single mechanism is thought to be responsible for their slow rates of morphological evolution and low species diversity. Some analyses of molecular evolutionary rates in a handful of living fossil lineages have indicated that these clades exhibit slow rates of genomic change. Here, we investigate mechanisms of evolutionary stasis using a dataset of 1,105 exons for 481 vertebrate species. We demonstrate that two ancient clades of ray-finned fishes classically called living fossils, gars and sturgeons, exhibit the lowest rates of molecular substitution in protein-coding genes among all jawed vertebrates. Comparably low rates of evolution are observed at fourfold degenerate sites in gars and sturgeons, implying a mechanism of stasis decoupled from selection that we speculate is linked to a highly effective DNA repair apparatus. We show that two gar species last sharing common ancestry over 100 million years ago produce morphologically intermediate and fertile hybrids in the wild. This makes gars the oldest naturally hybridizing divergence among eukaryotes and supports a theoretical prediction that slow rates of nucleotide substitution across the genome slow the accumulation of genetic incompatibilities, enabling hybridization across deeply divergent lineages and slowing the rate of speciation over geological timescales. Our results help establish molecular stasis as a barrier to speciation and phenotypic innovation and provide a mechanism to explain the low species diversity in living fossil lineages. [ABSTRACT FROM AUTHOR]

Mabel Creek Ridge, in the northern Gawler Craton, is a granulite‐facies domain recording early Mesoproterozoic metamorphism, flanked by less metamorphosed rocks and dissected by crustal‐scale divergent structures. The nature of early Mesoproterozoic events is poorly understood due to the lack of basement outcrop. Calculated metamorphic phase diagrams and geochronology are used to decipher the tectonic regime of a potential gneiss dome. Pressure–temperature (P–T) modelling of metapelites from five drill holes across Mabel Creek Ridge suggests it has experienced conditions of ~6.4–7.4 kbar and 800–850°C and the growth of suprasolidus cordierite after garnet indicates subsequent decompression. In situ U–Pb monazite and Lu–Hf garnet geochronology constrains the granulite‐facies metamorphism of Mabel Creek Ridge to ca. 1600–1560 Ma. In contrast, drill hole GOMA DH4 located to the north of Mabel Creek Ridge records conditions of 2.2–5.4 kbar and 710–740°C at ca. 1520 Ma, with no evidence for 1600–1560 Ma metamorphism. Our new P–T pseudosection results and geochronology data from Mabel Creek Ridge and adjacent crust, coupled with the regional seismic and airborne magnetic data, reveal that Mabel Creek Ridge represents a record of early Mesoproterozoic extension in the Gawler Craton, during which thermally perturbed lower crustal rocks were exhumed within a gneiss dome. Early Mesoproterozoic extension took place within a complex geodynamic regime resulting from the interplay between final Nuna convergence along the margin of northeast Australia at ca. 1600 Ma and subduction to the southwest at ca. 1630–1610 Ma. [ABSTRACT FROM AUTHOR]

Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles. [ABSTRACT FROM AUTHOR]

Granitic rocks forming in the syn- to post-orogenic stages can trace the compositional and structural complexity of the crust beneath an orogenic belt. The Qinling orogenic belt undertook multiple stages of tectonics and magmatism, resulting in the multifaceted evolution and compositional diversity of the crust. In the present study, the Guangtoushan and Miba plutons in South Qinling were chosen to reveal the crustal heterogeneity in study area via isotopic geochemistry and zircon geochronology. The Guangtoushan pluton was emplaced between ~215 Ma and ~202 Ma and the Miba pluton formed at ~213 Ma, as constrained by zircon U-Pb isotopic dating. Granitic rocks of the Miba pluton are characterized by amphibole bearing and homogeneous composition, with relatively depleted Sr-Nd isotopic compositions (initial 87Sr/86Sr values of 0.7060 to 0.7084 and initial εNd values of −5.4 to −9.5) and high Pb isotopic values. The Guangtoushan pluton contains muscovite and complex inherited zircon grains and has variable Sr-Nd isotopic composition (initial 87Sr/86Sr values of 0.7050 to 0.7091 and initial εNd values of −4.5 to −12.9) and low Pb isotopic values. Felsic magmas of the Guangtoushan pluton should be derived mainly from meta-sedimentary rocks beneath South Qinling, while the Miba pluton originated primarily from partial melting of meta-igneous rocks. The compositional diversity recorded in the Early Mesozoic plutons was caused by the heterogeneous crust, and partial melting was induced by heating of the up-welling asthenosphere in a post-collision setting. [ABSTRACT FROM AUTHOR]

Aim: The evolutionary interactions between western spadefoot toads (genus Spea) represent a textbook example of character displacement, facilitated by dietary specialization of one Spea species on fairy shrimp (Anostraca) when all three co‐occur. The aim of this study is to understand the covariation between predator (Spea) and prey (Anostraca) range shifts in response to climate change oscillations, and whether biotic interactions can be used to project species distribution models on different time scales when studying species with dietary specialization. Taxon: Amphibia: Spea spp. and Crustacea: Anostraca. Location: North America. Methods: Using multiple modelling techniques, we first estimated the potential distribution of central and western North American fairy shrimp species (Crustacea: Anostraca) and two western spadefoot toad species (Spea bombifrons and Spea multiplicata). We then created a shrimp species richness map by aggregating individual species estimates. Third, we studied the relationship between the probability of spadefoot toad presence and fairy shrimp species richness during the present and Last Glacial Maximum conditions. Finally, we estimated the strength and direction of the co‐occurrence between spadefoot toads and fairy shrimp sampled at the level of entire predicted range and at the regional level (allopatric and sympatric). Results: First, the same abiotic environmental variables shape spadefoot toad and fairy shrimp species' distributions in central and western North America across time. Second, areas of sympatry of Spea bombifrons and Spea multiplicata correspond with dry conditions and higher shrimp richness. Finally, the spatial patterns of predator–prey co‐occurrence are highly variable across geography, forming a spatial mosaic over the species' ranges. Main Conclusion: Predator–prey relationships form a spatial mosaic across geography and species ranges. Including biotic interactions into species distribution estimates for organisms with dietary specialization is highly recommended. Biotic interactions can be projected across different time frames for organisms with dietary specialization as they are likely conserved. [ABSTRACT FROM AUTHOR]

The Zanhuang Complex is situated on the eastern margin of the Trans-North China Orogen, with the Huangcha Pluton being a constituent of this complex. To ascertain the nature of the approximately 2.5-billion-year-old Huangcha Pluton, crucial evidence for understanding its extensional setting was sought through petrogenesis and dating investigations. LA-ICP-MS dating of zircon from the granite yielded an age of (2488 ± 6) Ma. Primarily composed of porphyritic monzonite with sporadic melanocratic enclaves, the Pluton's phenocrysts are predominantly feldspar with minor quartz. The granite exhibits high SiO2 content (72.64%–74.16%) and alkali levels, with Na2O + K2O ranging from 7.59% to 9.07%, classifying it as a shoshonitic series with a slightly peraluminous feature. Enrichment in large-ion lithophile (LIL) elements (Rb, Th, and U) and depletion in Sr, V, Cr, Co, and Ni were observed, with high Rb/Sr and Ga/Al ratios ranging from 0.73 to 2.72 and 2.75 × 10−4 to 3.11 × 10−4, respectively. The rock exhibits high εNd(t) values, ranging from −0.06 to 0.88, with TDM2 ages falling between 2.79 and 2.87 billion years. Zircon grains display 176Hf/177Hf ratios ranging from 0.281266 to 0.281412 and εHf(t) values spanning from 0.96 to 6.18, calculated using the 207Pb/206Pb age. It is suggested that the Huangcha Pluton represents A-type granite formed via anatexis of the Neoarchean TTG in an extensional setting following orogenic processes. The formation of the Huangcha Pluton further corroborates the stabilization of the North China Craton towards the end of the Neoarchean. This finding supports the hypothesis that the North China Craton may belong to the Rae-family cratons, sharing similar magmatic and tectono-metamorphic records around ~2.5 billion years ago. [ABSTRACT FROM AUTHOR]

Magmatic–hydrothermal breccia pipes are widespread in numerous major porphyry and epithermal gold deposits globally, representing significant repositories of metal resources and serving as potential indicators for exploration targeting. More than ten breccia pipes occur in the Central Taihangshan District (CTD) of the North China Craton. Some of these breccia pipes host gold mineralization and are proposed to be related to the adjacent lode gold mineralization. However, the lack of detailed geological constraints make this hypothesis ambiguous. To address this, the present study conducted comprehensive field observations, drill core logging, an in situ sulfur isotope analysis of pyrite, and the 40Ar/39Ar dating of adularia along a 1400 m section of the Tietangdong breccia pipe at Yixingzhai. Three distinct breccia facies were identified at Tietangdong, exhibiting variable proportions across the entire section, including a massive skarn breccia; polymictic, skarn matrix-supported breccia; and polymictic, intrusive rock cement chaotic breccia. Furthermore, adularia 40Ar/39Ar dating indicates a syn-/post-gold mineralization age of 136 ± 1.5 Ma, coinciding with the age of post-breccia felsite dike. The deepest sampled pyrite displays δ34S values of ~2.7‰, strongly indicating a magmatic–hydrothermal signature. These results, when combined with the geological, geochronological, and isotopic studies on the adjacent lode gold mineralization, further suggest a close genetic relationship between the breccia pipes and the lode Au mineralization, paving the way for their utilization as effective indicators for gold targeting within the CTD. [ABSTRACT FROM AUTHOR]

Mars missions and Martian meteorites revealed how complex the Martian crust is. The occurrence of both alkaline and sub-alkaline igneous rocks of Noachian age (>3.7 Ga) in Gale crater indicates diverse magmatic processes, with sub-alkaline rocks likely formed through the partial melting of hydrous mafic rocks, as commonly observed on Earth. The orbital discovery of excavated evolved igneous rocks scattered in Noachian terrains raise questions about the petrology of the ancient Martian crust, long thought to be basaltic. A possibly evolved crust beneath a mafic cover is supported by geophysical and seismic measurements from the Insight lander that indicate the bulk crust has a lower density than expected if it were homogeneously basaltic. If localized magmatic processes could form evolved terrains, the detection of abundant intermediate to felsic Noachian crustal exposures through remote sensing suggest regional- to global-scale processes that produced evolved crustal component(s) that are now buried below mafic materials. Due to the lack of centimetric to millimetric textural imaging and compositional measurements, the petrology of such crust is ambiguous. Future orbiter, rover, and aerial missions should focus on Noachian exposed regions exhibiting evolved crustal characteristics to unfold the petrology of the Martian crust and its formation. [ABSTRACT FROM AUTHOR]

The southern portion of the eastern North American margin (SENAM) is an archetypical volcanic passive margin formed during Mesozoic rifting. How past magmatic events affect the evolution of the SENAM remains an open question of fundamental importance. To better understand this question, here we construct a high‐resolution 3‐D crustal velocity model from the oceanic side to the continental interior with a combination of multimodal dispersion inversion and full‐waveform ambient noise tomography. Our new model reveals an oceanic‐continental transitional crust over a short horizonal distance of 100–150 km across the SENAM, with a local‐scale lower‐than‐surrounding velocity anomaly directly beneath the transitional crust. Furthermore, the new model shows three intra‐crustal higher‐than‐average velocity anomalies beneath the SENAM continent. We suggest that the magmatism assisted the Mesozoic rifting process to form the narrow ocean‐continent transitional crust along the coastline. The underplating of magma beneath the transitional crust led to a reduction of seismic velocity of the uppermost mantle. In addition, it is probable that the emplacement of the Central Atlantic Magmatic Province caused widespread magmatic intrusions within the continental crust of the SENAM, which were later solidified into intra‐crustal high‐velocity plutons. Our findings provide new insights into crustal modification history at the passive margin. Plain Language Summary: It has been suggested that the emplacement of magma played a key role in the formation and evolution of passive margins. However, how this process evolves during geological time is still unclear. The southern portion of the eastern North American margin (SENAM) preserved many magmatic records, making it an ideal laboratory to study this question. In this study, we constructed a high‐resolution 3‐D crustal velocity model from the oceanic side to the continental interior of the SENAM using a combination of state‐of‐the‐art multimodal dispersion inversion and full‐waveform ambient noise tomography. Our new model reveals two important features within the crust and upper mantle of the SENAM: (a) a sharp increase in crustal thickness over a transitional zone from ocean to continent, and a lower‐than‐surrounding velocity anomaly beneath the eastern margin of the transitional crust; and (b) three higher‐than‐average velocity anomalies within the continental crust. We suggest that the magmatic events assisted a continental rifting at ∼200 Ma in forming the ocean‐continent transitional crust. In addition, the magma associated with the emplacement of Central Atlantic Magmatic Province might have been injected into the continental crust of the SENAM, which subsequently solidified into high‐velocity igneous rocks. Key Points: A high‐resolution 3‐D crustal velocity model is constructed in the southern portion of the eastern North American marginA transitional crust is observed from ocean to continent that was likely formed by a magmatic‐assisted continental riftingThree high velocity anomalies are observed within the continental crust, probably representing magmatic intrusion associated with Central Atlantic Magmatic Province [ABSTRACT FROM AUTHOR]

The timing of partial melting in high-grade metamorphic rocks is critical for constraining tectonic histories and processes. However, uncertainties exist about the behavior of monazite and zircon during partial melting, especially about the timing of crystallization with respect to melting reactions. This study is focused on a single sample (16TG143) of finely layered, migmatitic gneiss from the Adirondack Highlands, New York, interpreted to have undergone extensive biotite dehydration melting (i.e., Bt + Pl + Als + Qz = Grt + Kfs + melt). The rock contains one distinct leucosome layer. The non-leucosome (gray gneiss) portion of the migmatite has millimeter-scale sublayers with distinct differences in modes and mineralogy. The layers are interpreted to reflect the differential preservation of reactants and products formed during the forward and reverse progress of the melting reaction. Monazite and zircon modes, and to some degree, texture, composition, and geochronology all vary from layer to layer. Both minerals have up to three domains: ca. 1150 Ma anhedral cores, ca. 1050 Ma monazite mantles/fir tree textured zircon, and ca. 1030 Ma rims. The heterogeneous layered gray gneiss provides robust constraints on the timing of melting (ca. 1050 Ottawan orogenesis), melt crystallization, and post-melting retrogression, in addition to information about earlier metamorphic events. Early-formed monazite and zircon grains were largely dissolved during progressive melting, except where preserved as relicts or inclusions. Monazite mantles and fir tree zircon grains precipitated upon cooling during progressive melt crystallization between temperatures of 800 and 750 °C. Rims are interpreted to have precipitated during subsolidus, solid-state retrogression after ca. 1050 Ma. Correlations between the gneissic layering, melting reactions, and the character of geochronometers emphasize the importance of characterizing the layer-forming and chronometer petrogenesis processes as a critical part of deconvoluting the history of migmatitic gneisses. [ABSTRACT FROM AUTHOR]

Transport properties of silicate melts control magma ocean dynamics on the early terrestrial planets and rocky exoplanets. Here we calculate the viscosity (transport of momentum) of peridotite liquid at potential magma ocean conditions (0–159 GPa, 2,200–6,000 K) using ab initio molecular dynamics simulations. We find that, unlike MgSiO3 or basaltic melts, the viscosity of the highly depolymerized peridotite liquid (a) increases monotonically with pressure without an anomalous drop and (b) is lower than those of other melts over the entire mantle pressure range. Low viscosity would promote fractional crystallization in a less polymerized magma ocean and thus contribute to mantle heterogeneity from its earliest stage. Given the compositional dependence of magma ocean properties, emphasis on multicomponent bulk silicate Earth‐like composition, instead of simple end‐members, are rendered necessary, in order to better understand high‐energy planetary accretion processes and their aftermaths. Plain Language Summary: In the aftermath of impacts, widely envisaged scenarios taking place on early terrestrial planets, the silicate mantle (i.e., rocks) experiences extreme temperatures that lead to extensive melting (i.e., magma ocean) on those planets. According to our supercomputer simulations, the viscosity of a magma depends on its composition, which can be as fluid as water for a silicate Earth‐like composition. Low viscosity entails vigorous convection, promoting fractional crystallization in the magma ocean. In light of this early differentiation process, mantle heterogeneity observed in the present‐day Earth may be remnants of the solidified magma ocean that survived over geologic time. Key Points: The viscosity of peridotite liquid is calculated at probable magma ocean conditions up to 159 GPa and 6,000 KIsothermal viscosities of peridotite liquid increase monotonically with pressure and are constantly lower than those of MgSiO3 liquidLow viscosity points to turbulent mixing in a magma ocean and favors fractional crystallization during its solidification [ABSTRACT FROM AUTHOR]

How and when sedimentary rocks record Earth's magnetic field is complex. Most studies assume a time‐progressive lock‐in mechanism during sediment deposition called depositional remanent magnetization (DRM). However, magnetic minerals can also form in situ, recording a chemical remanent magnetization (CRM) that is discontinuous in time. Disentangling the two mechanisms represents a major hurdle, and differences in their recording efficiencies remain unexplored. Here, our theoretical solutions demonstrate that CRM intensities exceed DRM by a factor of six when acquired in the same magnetic field. Novel experiments growing greigite (Fe3S4) in sediments and subsequent redeposition under identical magnetic field conditions confirm the predicted difference in recording efficiency. Thus, if left unrecognized, CRM leads to overestimated paleointensity and deserves more attention when interpreting Earth's magnetic history from sedimentary records. Recognition of fundamental differences between CRM and DRM characteristics provide a way forward to distinguish the recording mechanisms through routine laboratory protocols. Plain Language Summary: Remanent magnetizations preserved in sedimentary rocks serve as a continuous record of Earth's magnetic field history and play a fundamental role in understanding the Earth system. It is commonly assumed that magnetic minerals align with the magnetic field as a particle settles through the water column, known as a depositional remanent magnetization (DRM). However, diagenesis can lead to chemical growth of magnetic minerals, known as a chemical remanent magnetization (CRM). CRM lacks stratigraphic continuity and can obscure or completely overprint the original magnetization any time after sediment deposition, leading to a magnetic record that is uncorrelated with the age of the rock. Yet, CRMs go largely unrecognized. Theory and experiments in our paper document that CRMs record the magnetic field six times more efficiently than DRMs. Our work provides a way to distinguish the two through routine laboratory protocols. Key Points: Recording efficiency of chemical remanent magnetization (CRM) is six times higher than depositional remanent magnetization (DRM)Undetected chemical remanences lead to overestimated relative paleointensity estimatesComparison of natural and laboratory magnetization and demagnetization behavior help identify chemical remanent magnetizations in sediments [ABSTRACT FROM AUTHOR]