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The Wager shear zone is an ∼450-km long zone of high strain hosted within Proterozoic and Archean rocks of the Rae domain in northwestern Hudson Bay, Nunavut. New field mapping and microstructural analyzes, combined with titanite and apatite geochronology, define the style, kinematics, and timing of Proterozoic ductile deformation. The results indicate that the Wager shear zone accommodated high-temperature deformation between ca. 1.75 and 1.74 Ga with post-kinematic cooling through apatite U–Pb closure (425–530 °C) at ca. 1705 Ma. These new data show that the Wager shear zone was last active later than inferred in previous work, at a time when the western Churchill Province was undergoing lithospheric delamination and exhumation following the terminal collisional events in the western portion of the Trans-Hudson Orogen. [ABSTRACT FROM AUTHOR]

U–Th–Pb zircon geochronology is an essential tool for quantifying the emplacement, differentiation and thermal evolution of crustal magmatic systems. However, the power of U–Pb zircon dates can be enhanced through complementary characterization of mineral texture and geochemistry, as this permits more detailed interpretations of geochronological datasets than conventionally achieved. Our approach to better relating zircon dates and geological processes consists of a multi-method analytical workflow, including cathodoluminescence imaging (CL), in situ LA-ICPMS/EPMA zircon geochemistry, U–Pb zircon ID-TIMS geochronology, and solution ICPMS zircon Trace Element Analysis (U–Pb TIMS-TEA). These methods are here applied to zircon from the Bergell Intrusion, a composite Alpine pluton preserving a ~ 10 km mid-crustal transect. Hand samples of tonalite, granodiorite and hybridized granitoid each record 250–700 kyr of autocrystic zircon growth. Bergell zircons are ubiquitously zoned with ca. 10 4 –10 6 yr growth histories, as evidenced by ID-TIMS analysis of microsampled fragments from single crystals. U–Pb TIMS-TEA data exhibit compositional trends on multiple spatiotemporal scales, including the handsample -scale, representing in situ differentiation at the emplacement level (e.g., Th/U); lithology -scale, defining trajectories corresponding to the production of tonalitic versus granodioritic magmas (Lu/Hf); and pluton -scale, indicating increasingly-evolved melts over ~1.6 Myr of pluton assembly (Zr/Hf). These absolute TIMS-TEA temporal trends are corroborated by relative LA-ICPMS/EPMA core-to-rim geochemistry. We compare records of trace element evolution from TIMS-TEA, Bergell whole-rock geochemistry, and a global compilation of whole-rock geochemical data. These findings support zircon compositional evolution as a robust indicator of differentiation at local and crustal scales, and provide key empirical constraints on melt differentiation and cooling timescales in the middle crust. [ABSTRACT FROM AUTHOR]

We report isotope dilution thermal ionization mass spectrometry (ID-TIMS) and laser ablation split stream inductively coupled plasma mass spectrometry (LASS) U Pb data for a suite of widely available reference apatites: Fish Canyon Tuff, Mount Dromedary, TEMORA 2, and Duluth Complex anorthosite. We apply different common-Pb correction strategies to the U Pb data sets: (1) anchoring to a Stacey and Kramers (1975) model Pb composition; (2) unanchored 2-D 238U/206Pb-207Pb/206Pb isochron regressions; and (3) unanchored 3-D 238U/206Pb-207Pb/206Pb-204Pb/206Pb isochron regressions. The different common-Pb corrections yield consistent dates within each ID-TIMS and LASS data set, with 3-D regression method producing the highest precision isochrons. FCT apatite produces an ID-TIMS 3-D isochron age of 28.8 ± 3.7 Ma with (207Pb/206Pb) i = 0.851 ± 0.021. Mount Dromedary apatite yields an ID-TIMS 3-D isochron age of 98.4 ± 0.5 Ma with (207Pb/206Pb) i = 0.839 ± 0.003. TEMORA 2 apatite has an ID-TIMS 3-D isochron age of 402 ± 7 Ma and (207Pb/206Pb) i = 0.839 ± 0.008. Duluth Complex anorthosite apatite yields an ID-TIMS 3-D isochron age of 1077 ± 9 Ma with (207Pb/206Pb) i = 0.849 ± 0.046. The MSWDs associated with isochrons calculated from both the ID-TIMS and LASS data sets are larger than expected for a single age population, revealing complexities that are otherwise not captured by 2-D isochron methods. In the case of FCT apatite, the ID-TIMS data indicate significant heterogeneity in the initial Pb ratio ((207Pb/206Pb) i = 0.845–0.856), invalidating this sample as a viable reference apatite for high-precision geochronology. Additionally, the common-Pb compositions of TEMORA 2 and Duluth Complex anorthosite apatites calculated using the ID-TIMS data deviate from bulk Earth Pb evolution models beyond 2σ uncertainty. The data emphasize the utility of unanchored age regressions in generating the highest fidelity apatite U Pb dates. Further, TEMORA 2 and Duluth Complex apatite ages are both younger than their corresponding zircon U Pb ages, highlighting the need to independently verify the ages of prospective reference apatites. [ABSTRACT FROM AUTHOR]

• Zircon and titanite in xenoliths document Eocene metasomatism of the Wyoming craton lower crust. • Metasomatism by hydrous and carbonated fluids linked to subduction of the Shatsky conjugate and Farallon slab beneath the northern margin of the craton. • Metasomatism, slab foundering, and heating triggered partial loss of the Wyoming craton lithosphere. New zircon and titanite U-Pb and trace-element data from minette- and kimberlite-hosted lower crustal xenoliths from near the northern margin of the Wyoming craton document multiple periods of metasomatism from 62 to 50 Ma. Metasomatism was either coincident or preceded eruption of the host magmas by up to 14 Myr (eruption dated at 52 Ma and 48 Ma based on new zircon U-Th/He data). Thus, fluid/melt interactions were not solely related to magmatic entrainment and eruption. Accessory mineral trace element data reveal metasomatism by fluids from multiple sources, including water and carbonatite potentially sourced from the subducted Farallon slab. These metasomatic episodes are interpreted to reflect pan-lithospheric hydration events that weakened the deep cratonic lithosphere and facilitated partial removal following rollback and foundering of the Farallon plate. The new data corroborate previous suggestions that subduction-related metasomatism may be a key requisite for the destruction of otherwise stable cratons. [ABSTRACT FROM AUTHOR]

Cenozoic tectono‐magmatism in Iran is widely considered to be related to subduction of the Neo‐Tethys Ocean. We employed whole‐rock and mineral geochemistry and isotopic data of intrusive rocks from Tafresh, central Urumieh‐Dokhtar magmatic arc, to evaluate the role of the mantle in magmatism, to assess the timing of emplacement, and to interpret the tectonic setting. Rock compositions range from gabbro or gabbro‐diorite (plagioclase + pyroxene ± olivine), to diorite (plagioclase + amphibole ± pyroxene), to granodiorite (quartz + plagioclase + K‐feldspar + amphibole + biotite), exhibiting high‐alumina calc‐alkaline affinity. Major oxide and trace element variations vary systematically from less to more evolved rocks suggesting a major role for fractional crystallization processes. Zircon LA‐ICP‐MS U–Pb ages of major rock types are in the range of 24–19 Ma, whereas those of gabbroic dikes are ~17.5 Ma. ԐNd values range between −1.8 and 3.7, and (87Sr/86Sr)i is narrowly restricted to 0.705–0.706, suggesting a common mantle source. The enrichment in light rare earth element (REE) enrichment and flat heavy REE patterns couple depletion of Nb–Ta–Ti indicate that subducting oceanic crust had interacted with the overlying mantle wedge. High‐alumina, mid‐Mg# Tafresh plutonic rocks formed from hydrous melts from which Ca‐pyroxene and magnetite crystallized earlier than plagioclase, whereas late‐crystallizing zircon nucleated while magma traversed through lithospheric mantle and Cadomian crust. Modelling of isotope and incompatible‐element patterns suggests the contribution of no more than ~5% molten sediment or other crustal components in Tafresh magma, at a developmental stage before most plagioclase and amphibole had crystallized. The Miocene Tafresh plutons originated during the final stages of subduction, before the collision between the Arabian and Eurasian plates. [ABSTRACT FROM AUTHOR]

Reconstructions of the tectonometamorphic architectures of orogenic systems rely on petrogenetic indicator minerals, such as garnet, to trace the transport of rocks through space and time. We show the results of new garnet Lu-Hf geochronology and inclusion U-(Th-)Pb geochronology from exhumed midcrustal metamorphic rocks exposed in the Kanchenjunga region of the eastern Nepalese Himalaya. Garnet in three of the five specimens analyzed yielded pre-Himalayan Lu-Hf dates of ca. 292-230 Ma, which contrasts with Himalayan-aged inclusions therein. Garnet in these specimens either grew entirely during the Early Permian opening of the Neo-Tethys Ocean or grew partly during Cambrian-Ordovician orogenesis and partly during the Cenozoic. The remaining two specimens yield Lu-Hf ages of ca. 50 Ma, which are some of the oldest recorded dates for Himalayan metamorphism. The apparent discordance between the geochronological techniques highlights a potential issue with interpretations that rely on single-geochron-method inclusion records. These results further show that some pressure-temperature determinations used in Himalayan models may not be Himalayan in age. [ABSTRACT FROM AUTHOR]

Abstract: Laser-ablation split-stream (LASS) analysis—high-speed, high spatial-resolution, simultaneous isotopic and elemental analysis—enables petrochronology at a new level, through the interpretation of isotopic dates combined with elemental abundances and/or isotopic tracers. This contribution begins with an introduction to petrochronology, presents a new LASS technique using dual multi-collector–single-collector inductively-coupled plasma mass spectrometry, and offers examples of how this technique is used to decipher the evolution of rocks with complex geologic histories. [Copyright &y& Elsevier]

Abstract: An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛ Hft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth''s mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure. [Copyright &y& Elsevier]

Abstract: The Ama Drime Massif is a north–south trending antiformal structure located on the southern margin of the Tibetan Plateau that is bound by the Ama Drime and Nyönno Ri detachments on the western and eastern sides, respectively. Detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the Ama Drime detachment to document spatial and temporal patterns of deformation. Deformation temperatures estimated from quartz and feldspar microstructures, quartz [c] axis fabrics, and two-feldspar geothermometry of asymmetric strain-induced myrmekite range between ∼400 and 650°C. Micro- and macro-kinematic indicators suggest west-directed displacement dominated over this temperature range. Mean kinematic vorticity estimates record early pure shear dominated flow (49–66% pure shear) overprinted by later simple shear (1–57% pure shear), high-strain (36–50% shortening and 57–99% down-dip extension) dominated flow during the later increments of ductile deformation. Exhumation of the massif was accommodated by at least ∼21–42km of displacement on the Ama Drime detachment. Samples from the Nyönno Ri detachment were exhumed from similar depths. We propose that exhumation on the Nyönno Ri detachment during initiation of orogen-parallel extension (11–13Ma) resulted in a west-dipping structural weakness in the footwall that reactivated as the Ama Drime detachment. [ABSTRACT FROM AUTHOR]

In situ apatite U-Pb petrochronology and Sr-Nd isotope geochemistry requires well-characterized and matrix-matched references materials (RMs), yet only a few suitable apatite RMs are currently available. To ameliorate this issue, we determined the U-Pb, Sm-Nd, and Sr isotopic and elemental compositions of a suite of prospective apatite RMs using isotope dilution (ID) TIMS and laser ablation (LA) ICP-MS. The two RMs, from Morocco (MRC-1) and Brazil (BRZ-1), are cm-sized and available in significant quantities. The U-Pb ID-TIMS data yield an isochron age of 153.3 ± 0.2 Ma for MRC-1. This age is consistent with laser ablation split stream ICP-MS (LASS) analyses that produce an isochron age of 152.7 ± 0.6 Ma. The weighted mean of ID-TIMS analyses for 143Nd/144Nd analyses is 0.512677 ± 3, for 147Sm/144Nd is 0.10923 ± 9, and for 87Sr/86Sr is 0.707691 ± 2. The range and mean of TIMS Sm-Nd isotopic data are reproducible by LA-ICP-MS, but laser ablation Sr data are consistently offset towards more radiogenic values. For BRZ-1 apatite, ID-TIMS U-Pb analyses are dispersed, but a subset of the data yields a coherent age intercept of 2078 ± 13 Ma. The vast majority of LASS spot transects across the apatite produce an isochron that define a younger age of 2038 ± 14 Ma. We interpret this as incorporation of cryptic, younger altered domains within BRZ-1. Discordant U-Pb spot analyses are associated with chemically distinct cracks, likely a result of fluid infiltration. The weighted means of ID-TIMS analyses of BRZ-1 yield 143Nd/144Nd = 0.510989 ± 5, 147Sm/144Nd = 0.10152 ± 8, and 87Sr/86Sr = 0.709188 ± 3. The distribution of Nd isotopic compositions of this RM measured by LA-MC-ICP-MS analyses are comparable to TIMS analyses. By contrast, 87Sr/86Sr measurements by LA-ICP-MS are inaccurate and exhibit large uncertainties, but this RM can be useful for empirically correcting in situ 87Sr/86Sr measurements. The data indicate that MRC-1 apatite may serve well as a U-Pb, Sm-Nd, and Sr RM, whereas BRZ-1 apatite has the most potential as a Sm-Nd RM. These potential RMs provide new benchmarks for in situ apatite chemical analyses and inter-laboratory calibrations. • Two prospective reference apatites from Morocco and Brazil characterized for in situ petrochronology and isotope geochemistry • U-Pb, Nd, and Sr isotopic compositions established using isotope dilution TIMS and laser ablation ICP-MS • Morocco apatite (MRC-1) yields consistent U-Pb dates and Nd and Sr isotopic compositions • Brazil apatite (BRZ-1) has uniform Nd compositions, but heterogeneous U-Pb dates and imprecise Sr compositions • Laser ablation Sr isotope measurements can be calibrated against apatite RMs with different Sr, Ca, P, and REE contents. [ABSTRACT FROM AUTHOR]

Re-examination of specimens collected across the Qomolangma Formation exposed in the summit pyramid on Mount Everest confirms a complex, multi-deformational history. Two pre-Oligocene deformational events are recorded within the calcite-dominated rocks from the main summit (8848 m). The first event is characterized by an R XZ of ~1.3–1.4 in detrital quartz grains, which increases to ~1.6 after the second event. The finite strain recorded in calcite in the same rocks is higher with an R XZ of ~2.7–2.8. The deformation in the main summit appears to have been accommodated dominantly through grain boundary sliding in calcite in a slightly constrictive environment with a vorticity of >0.81. Deformation in the South Summit (8750 m) contrasts with that of the top and is instead interpreted to reflect Miocene movement along the Qomolangma detachment with no earlier deformation preserved. U–Pb geochronology on synkinematic rutile indicates that movement on the structure occurred at 16.3 ± 5.0 Ma. Rocks within the Qomolangma Formation in the summit pyramid of Mount Everest appear to record the basic history of the Himalaya with early deformation likely related to crustal thickening and later, more spatially restricted deformation reflecting the Miocene extrusion of the metamorphic core. • Rocks at the summit of Mount Everest record a multi-stage deformation history. • The deformation record across the summit pyramid on Mount Everest varies spatially and temporally. • The Qomolangma detachment fault at the South Summit was active ca. 16.3 ± 5 Ma. [ABSTRACT FROM AUTHOR]

The Maures–Tanneron Massif and the Corsica–Sardinia Block are two segments of the southern European Variscan belt that separated during the Late Oligocene–Miocene due to the opening of the Western Mediterranean basin. Correlation between the two regions, based mainly on petrologic similarities, is still debated. However, there are no detailed structural and petrochronological constraints on their potential relationships. In northern Sardinia there is well-documented evidence for a dextral transpressive shear zone that initiated after the first stage of frontal collision. In the Maures–Tanneron Massif, despite recognition of an important episode of transpressive deformation, it is still unclear which structures were active during this tectonic regime. We investigate in detail the kinematic of flow, finite strain and the timing of the deformation of the Cavalaire "Fault" (CF), a major ductile shear zone in the Maures–Tanneron Massif. In contrast to previous models, we argue that the CF is a transpressive shear zone characterized by a prevalent component of pure shear, while in-situ monazite geochronology reveals that the CF is initiated at ~ 323 Ma. The new data presented here, based on a multidisciplinary approach document, for the first time, the vorticity of the flow, finite strain and timing of this sector of the East Variscan Shear Zone, a regional-scale shear zone that characterized the Southern European Variscan belt during the late Carboniferous. [ABSTRACT FROM AUTHOR]

The products of Cenozoic continental arc magmatism in Iran provide an outstanding natural laboratory for investigating subduction-related processes. Here we present whole rock, Sr Nd isotopic, zircon U–Pb–Hf age, and mineral composition data for Cenozoic intrusive rocks from the Natanz area, central Urumieh–Dokhtar magmatic arc (UDMA), with a view to re-evaluate spatial–temporal variations in arc magmatism, magma petrogenesis and mantle source characteristics. The suite investigated in this study ranges from less evolved (gabbro) to highly evolved (granite) rocks with calc-alkaline affinity and an age range from 23.2 to 19.7 Ma. Their εNd (t) values vary from −0.32 to 2.73, initial 87Sr/86Sr values range from 0.7049 to 0.7075, and zircon εHf (t) values range from −2.2 to +8.9. Combined modelling of trace element and isotopic data suggests that the most mafic Natanz magmas could have formed through ∼5% melting of a source comprising 99% depleted mantle +1% sediment, with the melts modified subsequently by ∼3% contamination by Cadomian upper crustal components. We postulate that Natanz magmatism originated during a flare-up event instigated by retreat of the subducted slab prior to or in conjunction with the collision between the Arabian and Eurasian plates. The spatial–temporal associations in central UDMA (i.e., 33° 30′ N to 34° N) mirror three distinct flare-up episodes that occurred between 57 and 36 Ma, 26–15 Ma, and < 10 Ma; these events have not been reported previously from the northwestern and southeastern portions of the UDMA. Our results argue against any lull in magmatic activity in central UDMA during Eocene to Miocene times. • Radiometric dating yield 23.2 to 19.7 Ma for Natanz host rocks. • A flare-up event occurred in response to retreat of the subducted slab. • ∼5% melting of a batch (i.e., 99% DMM + 1% sediment) mixed by ∼3% upper crust. [ABSTRACT FROM AUTHOR]

Tin mineralization at Mayo-Darlé in the Cameroon Volcanic Line is associated with highly evolved anorogenic ferroan granite magmatism with a pervasive hydrothermal overprint. Mineralization occurs as cassiterite-quartz-muscovite stockwork and disseminated in quartz-mica and quartz-topaz greisen in low-Ca alkali feldspar granite with a composition near the 1 kbar haplogranitic thermal minimum. The trace element composition of zircon indicates elevated temperature (880 ± 55 °C) and very low oxidation state below the quartz-fayalite-magnetite buffer. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) identifies a partly disturbed U-Pb system for igneous zircon (U and Th contents >1000 ppm) but defines Tera-Wasserburg concordia ages and common-lead-corrected weighted 206Pb/238U ages of about 54 Ma, similar to a previous 87Rb/86Sr vs 87Sr/86Sr regression with a date of 56.1 ± 1.7 Ma (MSWD = 58; n = 9) and an initial 87Sr/86Sr ratio of 0.7085 ± 0.0035 (2 s). Hydrothermal cassiterite gives a pooled LA-ICPMS Tera-Wasserburg concordia age of 56.7 ± 0.6 Ma on two samples (each about 20 points, MSWD = 0.54 and 1.3). These new age data define a period of early Cenozoic intraplate calc-alkalic felsic magmatism as a precursor to abundant Oligocene to Recent alkali basalt volcanism along the Cameroon Volcanic Line. Geochemical and Sr–Nd–Hf isotopic data suggest that the granitic rocks from Mayo Darlé were largely derived by partial melting of Mesoproterozoic basement and modified by strong differentiation, all likely powered by heat (and possibly fluids) from the mantle. The Tertiary age of the rare-metal magmatism sets this system apart from the widespread Late Neoproterozoic to Early Paleozoic rare-metal pegmatites and granites in the Pan-African collisional belts of Africa, and also from the anorogenic Mesozoic ring complexes in Central Nigeria. [Display omitted] • Tin mineralization is associated with anorogenic alkali feldspar granite magmatism. • Igneous zircons yield a partially disturbed U-Pb age of 54 Ma. • Zircon trace elements indicate very low oxidation state. • Hydrothermal cassiterite gives a pooled U-Pb concordia age of 56.7 ± 0.6 Ma. • Cassiterite proves to be suitable for U-Pb dating of highly evolved granite systems. [ABSTRACT FROM AUTHOR]

Magmatic suites provide the keys to evaluate the growth and reworking of continental crust. Late Cretaceous to Pleistocene convergence in the Urumieh–Dokhtar magmatic arc (UDMA) of Iran produced continental-arc magmatism that traces the transition from subduction to collision. The extent and origin of some magmatic segments in the SE UDMA remain poorly understood. The Oligocene (31 to 25 Ma) Jiroft plutonic rocks here investigated encompass the compositional spectrum from gabbro to granodiorite. Zircon εHf (t) (−1.3 to +8.1), whole rock εNd (t) (+0.8 to +3) and δ56Fe (0.07‰ to 0.16‰) are intermediate between values of depleted mantle and arc-related magmas, and indicate low degrees of oxidization of metasomatized mantle. Modelling indicates that the trace element patterns of Jiroft parental melts can be closely replicated by 4% partial melting (i.e., F = 4%) of a mantle source which was metasomatized by 2% of sediment melt. The parental melt fits well with a model pattern of ∼97% batch melt (i.e., 98% DM + 2% sediment at F = 4%) and contaminated with ∼3% upper crustal components. The 31–25 Ma magmas of the SE UDMA formed before the main collision event (< 20 Ma) between Arabia and Iran, in conjunction with changing tectonic regime from extensional to compressional. Compilation of the Cenozoic magmatic front (i.e., UDMA) and rear-arc (NE Iran and Alborz–Azerbaijan) data reveals variable degrees of crustal cannibalization during the flare-up episodes. We find that individual segments of the UDMA experienced different geodynamics conditions, further documenting the diachronous collision and correspondingly non-uniform crustal thickening across the UDMA. • Radiometric dating yield 31 to 25 Ma for Jiroft host rocks. • Batch includes 4% partial melting of DMM metasomatized by 2% of sediment melt. • ∼97% batch melt contaminated with ∼3% upper crust components. • The δ56Fe values show fractional crystallization and low degrees of oxidization. • A flare-up event likely occurred in response to retreat of the subducted slab. [ABSTRACT FROM AUTHOR]

Accessory phosphate minerals, such as monazite and xenotime, are commonly used as geochronometers to provide timing constraints on tectonometamorphic events recorded by the host rocks within which they occur. However, the formation and recrystallization of accessory minerals, and their interaction with major mineral phases, are still poorly understood. As a consequence, linking ages obtained from accessory minerals to the metamorphic pressure-temperature (P-T) paths obtained primarily from major mineral phases, such as garnet, remains challenging. While there have been studies that have advanced our understanding of the behaviour of various accessory minerals through thermodynamic modelling, limited examples are available to test their reliability in natural metamorphic rocks. This study incorporates phosphate minerals into one of the most commonly used thermodynamic data sets for phase equilibria modelling. This refined methodology is tested by modelling the detailed P-T-time (t) paths for rocks from two different regions of the Himalaya, one subsolidus and one that experienced suprasolidus conditions. The results obtained from our integrated models yield direct information on the behaviour of monazite and xenotime growth/breakdown along the calculated P-T paths. This allows us to tie different age populations obtained from the accessory minerals directly to the P-T paths derived from major mineral phases and facilitates a refined understanding of the P-T-t histories of those rock specimens. • Phosphate minerals are modelled with silicate minerals using thermodynamic modelling approach. • Results yield direct information on behavior of monazite and xenotime along calculated P-T path. • Robust tool to link the ages from those minerals to the P-T path to get a well constrained P-T-t paths. • Provides insight into the trace element partitioning and equilibrium between garnet and monazite. • This approach aids in better understanding of the metamorphic evolution of the studied rocks. [ABSTRACT FROM AUTHOR]

The Zafarghand pluton, having ~10 km2 of outcrop exposure, lies within the central Urumieh–Dokhtar magmatic arc (UDMA) in Iran, of ~34 Ma age. Zafarghand plagioclase is albitic, with amphibole and chlorite being the distinctive mafic minerals. Although productive porphyry Cu deposits (PCDs) occur nearby, Zafarghand and its immediate neighboring plutons are sub-productive. Values of SiO 2 and K 2 O span a narrow compositional range from 69 to 73 wt% and 2.2 to 3.5 wt%, respectively, corresponding to granodiorite or granite and calc-alkaline in affinity. εNd (t) values are ranging from ~0 to +1.2, a diagnostic range for the mantle-dominant melts. The Sr Nd isotopic values are significantly lower and higher than those of slab melting- and crust melting adakites, respectively. The 34 Ma age of Zafarghand plutons make them to be the oldest Cu porphyry deposits yet to be found in the UDMA, in which mineralization had occurred during a mature, late stage of subduction (pre -collisional). We propose multi-stage refertilizing of Cu in lithospheric mantle beneath the UDMA, negligibly during Eocene to Early Oligocene slab roll-back accompanied by middle to rather high f O 2 context, and dominantly, during the Middle–Late Miocene slab break-off, the latter significantly tapping into influxing of asthenosphere mantle melt. Buffering of f O 2 at a sufficiently high level (and not partial melting of slab or thickened crust) is the most plausible explanation for forming Late Eocene–Oligocene sub-productive (–and non-adakitic) Zafarghand Cu-bearing plutons. • Radiometric dating yield ~34 Ma for Zafarghand host rocks • The oldest hitherto known porphyry copper deposit in the UDMA • ~96 % mantle-derived magma with contributions of ~4 % upper crustal material • Multi-stage refertilizing of Cu in lithospheric mantle beneath the UDMA • Change in f O 2 (not melting of slab or thickened crust) as the reason for PCDs [ABSTRACT FROM AUTHOR]

A detailed understanding of the tectonomagmatic processes that produced and deformed the thick and geographically widespread volcanic successions exposed across much of the southern Andes is only beginning to emerge. Findings from this study reveal that the Abanico Formation in the Principal Cordillera of central Chile (35°S latitude) provides an unprecedented (64+ m.y.) record of volcanism and crustal deformation related to South America's subduction margin and growth of the southern Andes. Here, we utilized detailed field mapping and U-Pb and 40Ar/39Ar geochronology to document the stratigraphy and structure of the Abanico Formation in the upper Río Tinguiririca drainage, thereby clarifying the tectonomagmatic history of the Principal Cordillera. The Abanico Formation exceeds ~3.6 km in composite thickness and is composed primarily of intra-arc deposits, including intermediate to mafic lavas, block-and-ash flows, volcaniclastic sedimentary deposits, and rhyodacitic tuffs. The lower Abanico Formation (ca. 75-37 Ma) records the slow accumulation (~46-49 m/m.y.) of volcanic and volcaniclastic strata within an arc platform without obvious structural control. In contrast, the upper Abanico Formation (ca. 37-11 Ma) preserves volcanogenic rocks intercalated with thick intervals of epiclastic accumulations synorogenic with crustal deformation. Well-dated growth strata and a system of dextral-reverse faults indicate that transpressive crustal shortening occurred in the Principal Cordillera from the late Eocene to the middle Miocene. Collectively, results from this study demonstrate that the Abanico Formation spans far more time (Late Cretaceous--Miocene) than long assumed (Eocene--Oligocene) and thus significantly revises the geologic record of arc magmatism in the Principal Cordillera. The data also reveal a previously unrecognized transpressive component to Andean orogenesis near 35°S latitude, plausibly tied to oblique plate convergence during the Cenozoic. [ABSTRACT FROM AUTHOR]

In the Caledonides of northern Scotland temperatures of metamorphism ( T m) and deformation ( T d) progressively increase structurally up section in the Moine thrust sheet at the foreland edge of the Scandian (mid Silurian) orogenic wedge. However, the thermal history of the structurally overlying, more hinterland positioned thrust sheets is less well known. This study focuses on determining T d and T m for both the central/upper part of the Moine thrust sheet and the lower part of the overlying Sgurr Beag thrust sheets in the middle of the Northern Highlands Terrane. Preserved microstructures and quartz c-axis fabric opening angles in the Moine and Sgurr Beag thrust sheets imply T d of 460 °C to 605 °C ± 50 °C. Thermobarometry and pseudosection-based P-T constraints, indicate T m of ∼550–680 °C at 4.8–7.2 kbar in the Moine thrust sheet and T m of ∼620 °C at 5.6–7.7 kbar in the Sgurr Beag thrust sheet. Together, T d and T m in the Moine and Sgurr Beag thrust sheets indicate that deformation continued after peak metamorphic conditions in the Sgurr Beag thrust sheet. Monazite and xenotime petrochronology show that T m, and possibly T d, record Precambrian metamorphism. Peak metamorphism is associated with the Knoydartian orogenic event (840-720 Ma), with possible reworking during Scandian thrusting (430-425 Ma). [ABSTRACT FROM AUTHOR]

• Rutile U-Pb data of the amphibolite rocks show the metamorphic age of 56.08 ± 1.13 Ma. • Thermometry data display the peak metamorphism temperatures have been 616 to 674 ˚C. • Protolith of the rocks may be produced in intra-continental back arc basin. Amphibolitic rocks of the Tutak Metamorphic Complex (TMC), in the southern part of the Sanandaj Sirjan Zone (SaSZ), are associated with meta-dolerites, felsic intrusions, mica-schists, and marbles as bodies and interlayers. Rutile grains from an amphibolite (ES-18–1) yield a U-Pb age of 56.08 ± 1.13 Ma (Late Paleocene-Early Eocene) while Zr-in-rutile thermometry indicates peak temperatures ∼ 616 to 674 °C. These data are inferred to reflect the timing of medium-pressure/medium-temperature (MP/MT) amphibolite facies metamorphism in Late Paleocene-Early Eocene rather than upper Cretaceous time in the TMC complex. Geochemically, the amphibolites are from an Nb-enriched basalt-andesite to basalt protolith with sub-alkaline to alkaline affinity. The amphibolites have moderate 87Sr/86Sr (t) ratios (0.702451 to 0.712720), 143Nd/144Nd (t) ratios (0.512122 to 0.512209), positive ƐNd (535 Ma) (3.38 to 5.08) values and two-stage Nd model ages (T DM) between 0.84 and 1.3 Ga. The geochemical trends and (La/Yb) cn > 3, Nb/La > 0.6, Sm/Nd < 0.3, Zr/Y (4.42 to 7.47, avg. 5.72) ratios with moderate 87Sr/86Sr (5 3 5) ratios and positive Ɛ Nd(535 Ma) values indicate that the mafic protoliths of the amphibolites are probably derived from the low partial melting of subcontinental lithospheric mantle in a spinel lherzolite field, with enriched mantle (E-MORB/OIB-like) nature. Subsequently, they experienced minor crustal contamination in the early stages of the development of intra-continental-type back-arc basin (BABB). Lack of subduction signals in the amphibolites with E-MORB/OIB-like features may result from the roll-back of subducting Proto-Tethys oceanic slab during the Cambrian similar to other peri -Gondwana terranes. [ABSTRACT FROM AUTHOR]

Intermontane basins are illuminating stratigraphic archives of uplift, denudation and environmental conditions within the heart of actively growing mountain ranges. Commonly, however, it is difficult to determine from the sedimentary record of an individual basin whether basin formation, aggradation and dissection were controlled primarily by climatic, tectonic or lithological changes and whether these drivers were local or regional in nature. By comparing the onset of deposition, sediment-accumulation rates, incision, deformation, changes in fluvial connectivity and sediment provenance in two interrelated intermontane basins, we can identify diverse controls on basin evolution. Here, we focus on the Casa Grande basin and the adjacent Humahuaca basin along the eastern margin of the Puna Plateau in northwest Argentina. Underpinning this analysis is the robust temporal framework provided by U-Pb geochronology of multiple volcanic ashes and our new magnetostratigraphical record in the Humahuaca basin. Between 3.8 and 0.8 Ma, ~120 m of fluvial and lacustrine sediments accumulated in the Casa Grande basin as the rate of uplift of the Sierra Alta, the bounding range to its east, outpaced fluvial incision by the Río Yacoraite, which presently flows eastward across the range into the Humahuaca basin. Detrital zircon provenance analysis indicates a progressive loss of fluvial connectivity from the Casa Grande basin to the downstream Humahuaca basin between 3 and 2.1 Ma, resulting in the isolation of the Casa Grande basin from 2.1 Ma to <1.7 Ma. This episode of basin isolation is attributed to aridification due to the uplift of the ranges to the east. Enhanced aridity decreased sediment supply to the Casa Grande basin to the point that aggradation could no longer keep pace with the rate of the surface uplift at the outlet of the basin. Synchronous events in the Casa Grande and Humahuaca basins suggest that both the initial onset of deposition above unconformities at ~3.8 Ma and the re-establishment of fluvial connectivity at ~0.8 Ma were controlled by climatic and/or tectonic changes affecting both basins. Reintegration of the fluvial network allowed subsequent incision in the Humahuaca basin to propagate upstream into the Casa Grande basin. [ABSTRACT FROM AUTHOR]

Meta-granites in the Tutak metamorphic Complex (TMC) preserve crucial information about the Late Neoproterozoic tectonic history of the Sanandaj-Sirjan Zone, Iran. This paper employs comprehensive zircon U Pb geochronology, whole-rock geochemistry, and zircon Lu Hf isotopic data to elucidate the protolith, tectonic setting, and evolutionary history of these rocks. Late Neoproterozoic zircon U Pb ages of ca. 575 Ma are taken as the crystallization age for the protolith to the meta-granites, which are intruded by leucogranite with a zircon U Pb age of 543 Ma. Zircon trace element data indicate that the grains have the late magmatic signature extracted from continental crust mafic zircons under oxidizing conditions. The meta-granites have a pronounced high-K-alkaline, peraluminous S-type signature. The meta-granites have zircon ɛHf (t) ranging from −4.2 to +2.3 and the T DM C model ages from 1.3 Ga to 1.7 Ga, suggesting the involvement of Paleoproterozoic crust. The geochemical data indicate that granitic melts in the Sanandaj-Sirjan Zone were produced via partial melting of lower crustal igneous crustal rocks (i.e., amphibolite) and sedimentary sources (i.e., metapelite). Based on the data (e.g., negative anomalies of Ba Nb and enrichments of Rb-Th-Ce and U/Yb, Nb/Yb ratios in zircon), they have been formed in a post-collisional setting related to the convergence of peri-Gondwana terranes and Iranian continental fragments. • The metagranites from TMC have a protolith age of 575 Ma, representing the Late Neoproterozoic age. • The meta-granites have an S-Type signature and formed in a transpressional tectonic regime. • The younger leucogranites with zircon U Pb age of 543 Ma intruded the meta-granites. [ABSTRACT FROM AUTHOR]

Monazite U–Pb and trace-element data were gathered from six high- to ultrahigh-pressure (UHP) samples from the Western Gneiss Region, Norway, using LASS (laser-ablation split-stream ICP-MS) to investigate variations in monazite composition during high-pressure metamorphism. The UHP monazites were found to contain up to 7600 ppm Sr, 110 ppm non-radiogenic Pb, relatively weak negative Eu anomalies, and Y concentrations as low as 500 ppm. Amphibolite-facies monazite that rims the UHP monazite in one sample contains Y concentrations up to 1.6 wt.%, Sr as low as 13 ppm, and no detectable non-radiogenic Pb. The UHP monazite composition (high Sr–Pb) is interpreted to result from growth in the absence of feldspar, possibly aided by increased compatibility of Sr–Pb–Eu 2 + in the monazite crystal structure at high pressure. Sr in monazite as a proxy for feldspar stability may be a useful tool not only in studying high-pressure metamorphism, but also in determining timescales of melting and crystallization, when the amount of feldspar changes over time. [ABSTRACT FROM AUTHOR]

• The Intra Tantato shear zone records both thrusting and normal shear sense activities. • The thrusting event accommodated NE-SW lower crustal shortening at ∼1.9 Ga. • Thrusting is linked to the compressive stage of the Snowbird orogeny. • The Intra Tantato shear zone was reactivated as an extensional structure ca. 1.86 Ga. • The normal-sense activity is linked to regional exhumation. The Intra Tantato shear zone (ITSZ), which occurs within the East Athabasca mylonite triangle in the southern portion of the ∼1.9 Ga Snowbird tectonic zone in northern Saskatchewan, Canada, is a low to high angle, curvi-planar, kilometer-thick mylonite zone hosted within granulite-facies gneiss that records a complex history with both thrust- and normal-sense motion. New field mapping, microstructural analysis, and quartz crystallographic preferred orientations (CPO) detail a composite history for the ITSZ that includes top-to-the-ENE thrusting of the hanging wall over the footwall that is overprinted by normal-sense top-to-the-WSW reactivation. Quartz CPOs further indicate constrictional deformation related to both events and quartz c -axis opening angles define deformation temperatures of ∼750 ± 50 °C for the thrusting event and ∼550 ± 50 °C for the later, normal-sense reactivation. Monazite and garnet geochronology on rocks within and around the ITSZ indicate it may have nucleated along a pre-existing 2.6–2.5 Ga sub-horizontal fabric. This appears to have occurred immediately after the ∼1.920 Ga metamorphic peak of the hanging wall and during the ∼1.905 Ga metamorphic peak of the footwall. Monazite ages from small matrix grains in interstitial positions in specimens that record reactivation kinematics indicate overprinting occurred at ∼1.860–1.830 Ga, contemporaneous with the earliest recorded activity along the nearby Grease River Shear Zone. Overall, this tectonic evolution can be attributed to a crustal thickening process that occurred in the Athabasca mylonite triangle during the Snowbird orogeny at ∼1.9 Ga and during the post-collisional exhumation processes. Moreover, these results show that the lower continental crust can actively accommodate shortening during large-scale collisional events with tectonic units piling up via nappe-stacking processes similarly to what is typically observed in the middle crust. [ABSTRACT FROM AUTHOR]

Gneiss domes in the Pamir (Central Asia) and the Himalaya provide key data on mid- to deep-crustal processes operating during the India-Asia collision. Laser ablation split-stream inductively coupled plasma-mass spectrometry (LASS-ICP-MS) data from monazite in these domes yield a time record from U/Th-Pb dates and a petrologic record from rare earth element (REE) abundances. Seven samples from the Pamir and six samples from the north Himalayan gneiss domes yield almost identical monazite dates of ca. 28-15 Ma. Most monazite has invariant heavy REE (HREE) abundances; two samples, however, have older monazite that records progressive HREE depletion and two samples have younger monazite that records progressive HREE enrichment. These variations in HREE are compatible with increasing garnet abundance--prograde metamorphism-- until ca. 20 Ma, and decreasing garnet abundance thereafter. The change from HREE depletion to enrichment may record a transition from crustal thickening and heating to dome exhumation and cooling. This documentation of synchronous Barrovian metamorphism within domes of Indian crust along the margin of the orogen (Himalaya) and within domes of Asian crust within the core of the orogen (Pamir) is best explained by a plate-scale driving force rather than by local events. We propose that widespread, synchronous thickening was initiated by the resumption of Indian subduction following slab breakoff and then terminated by a second slab-tearing event--both plate-scale events inferred from tomography. [ABSTRACT FROM AUTHOR]

Abstract: The highly fossiliferous sediments of the Tolomosa Formation from Tarija, southern Bolivia, represent one of the most important localities in South America that documents the Great American Biotic Interchange. Over the past several decades, chronostratigraphic studies have indicated a middle Pleistocene age for the Tolomosa Formation from ~1.1 to 0.7Ma. This interval correlates to the Ensenadan South American Land Mammal Age as it is characterized from classic localities in Argentina. Recently, however, a new interpretation based on AMS 14C ages indicates that the fossiliferous sediments from Tarija are latest Pleistocene, i.e., <44ka, and thus of Lujanian age. Here we report a new age of 0.76±0.03Ma (2σ) based on 11 U–Th/Pb and U–Th/He individual determinations from the Tolomosa Formation. This is indistinguishable from the age published from the same ash in 1983, and was originally used to calibrate the magnetostratigraphic section at Tarija. The new age confirms that the age of the Tolomosa Formation is middle Pleistocene, and not latest Pleistocene. The age of the Tarija Fauna has significant implications with regard to the stage of evolution biochronology for Pleistocene fossil mammals in South America, and in particular, the classic and important reference sections in Argentina. [Copyright &y& Elsevier]

• Crystallization of the protolith of the orthogneisses occurred in the Early Cambrian. • The rocks are related to subduction of the Proto-Tethyan beneath the Iranian plate. • The protolith of the rocks probably originated by partial melting of the mafic source. • The crust is thickened and then thinned during Late Neoproterozoic - Cambrian times. A combined U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopic study give new insights into the nature of the protolith, tectonic setting, and petrogenetic history of Cadomian orthogneisses from the Tutak metamorphic complex (TMC), Sanandaj-Sirjan Zone, Iran. U–Pb zircon dates of 535 ± 4 Ma suggest an Early Cambrian crystallization age for the orthogneiss protoliths. Geochemical data indicate that the orthogneisses have I-type, high-K calc-alkaline, and peraluminous signatures. Depletion in Nb, Ta, Ti, Sr, and enrichment in Nd, Th, K, U relative to the primitive mantle, suggest derivation in a subduction zone environment in an active continental margin. Initial 87Sr/86Sr and 143Nd/144Nd ratios vary from 0.7045 to 0.7092 and from 0.5116 to 0.5117, respectively. Moreover, εNd (t) values range from − 2.95 to − 5.29, and two-stage model ages vary from 1.4 to 1.6 Ga. Taken together, these data suggest derivation of TMC orthogneisses from a metasomatic lithospheric mantle with a contribution of a crustal component generated via partial melting of a metabasite (i.e., amphibolite). [ABSTRACT FROM AUTHOR]

Accessory phase geochronology records several phases of metamorphism that affected Moine metasedimentary rocks in the Northern Highlands Terrane of Scotland. Within the Sgurr Beag nappe, monazite and xenotime record initial metamorphism at c. 750 Ma, with later resetting at c. 600 Ma and c. 425 Ma. Monazite, xenotime, titanite and zircon also cryptically record c. 750 Ma and c. 600 Ma metamorphism in the Naver and Ben Hope nappes prior to the dominant 435-415 Ma Scandian orogeny. Textural, geochemical, and isotopic data indicate that c. 600 Ma and c. 425 Ma isotopic resetting in the Sgurr Beag nappe was caused by fluid-mediated dissolution and reprecipitation of monazite and xenotime. The compositions of fluid-altered monazite fall into two distinct trends, with high and low Y+HREE apparently reflecting the distinct timing and temperature conditions of dissolution and reprecipitation. Monazite-xenotime thermometry is applied to constrain the temperatures of fluid alteration. High Y+HREE, low Th/U monazite is related to high temperature (∼650°C) alteration at c. 600 Ma and low Y+HREE, high Th/U monazite is related to lower temperature (∼400°C) reactivity at c. 425 Ma. These data show that the composition of reprecipitated monazite is sensitive to metamorphic conditions during fluid alteration and is therefore useful in understanding the evolution of polyphase metamorphic terranes. These data suggest that a widespread metamorphic or metasomatic event affected northern Scotland at c. 600 Ma, likely related to higher heat flux and magmatic activity during the break-up of Rodinia. Additionally, the now adjacent Sgurr Beag and Moine nappes appear to have contrasting metamorphic records at least until Caledonian orogenesis, which suggests that final regional scale motion on the Sgurr Beag thrust must be of Caledonian age. [ABSTRACT FROM AUTHOR]

The Central Andes are the product of contractional deformation related to subduction of the Nazca plate beneath the South American continent. In this geodynamic setting, thrust belt propagation in the Central Andean retroarc in NW Argentina and southern Bolivia has been linked with the critical wedge model implying progressive eastward migration of the deformation front during the Cenozoic. However, Eocene unconformities and growth strata within the orogenic hinterland of the Eastern Cordillera and Puna Plateau suggest selective reactivation of pre-Andean and Andean faults revealing a pattern of diachronous and spatially disparate range uplifts. The Calchaquí Valley in NW Argentina is characterized by basin-and-range morphology, which is intimately linked with the heterogeneous Neoproterozoic basement, Cretaceous rift structures, and the Cenozoic foreland. In this study, we analyze this complex deformation by reconstructing Cenozoic fault reactivation and sedimentation patterns in the Eastern Cordillera. Detailed structural mapping along the eastern Calchaquí border (Tonco area) reveals five Cenozoic unconformities in the former foreland deposits related to multiple episodes of fault reactivation during the Eocene-to-Pleistocene. A refined chronostratigraphy (U-Pb zircon), new AHe thermochronological data (apatite U-Th-Sm/He), and existing evidence for deformation indicate episodic out-of-sequence deformation and increased Eo-Oligocene (Puna Plateau) to Miocene (Eastern Cordillera) fault displacement apparently controlled by pre-Cenozoic heterogeneities. The coeval eastward propagation of deformation and continuing deformation in the west generally challenge the applicability of the critical wedge model. • Superposed Cenozoic unconformities found in the Tonco Valley. • Exhumation event started at 17 Ma marked by modeled AHe ages. • Multiple reactivations of retro-vergent reverse faults involving basement. • Conciliation between cooling ages and field deformation evidences. • Non-systematic deformation pattern in a NW Argentina. [ABSTRACT FROM AUTHOR]

The Early Jurassic Butcher Ridge Igneous Complex (BRIC) in the Transantarctic Mountains contains abundant and variably hydrated silicic glass which has the potential to preserve a rich paleoclimate record. Here we present Fourier Transform Infrared Spectroscopic data that indicates BRIC glasses contain up to ~8 wt.% molecular water (H 2 O m ), and low (<0.8 wt.%) hydroxyl (OH) component, interpreted as evidence for secondary hydration by meteoric water. BRIC glasses contain the most depleted hydrogen isotopes yet measured in terrestrial rocks, down to δD = -325 ‰. In situ 40 Ar/ 39 Ar geochronology of hydrated glasses with ultra-depleted δD values yield ages from 105 Ma to 72 Ma with a peak at c. 91.4 Ma. Combined, these data suggest hydration of BRIC glasses by polar glacial ice and melt water during the Late Cretaceous, contradicting paleoclimate reconstructions of this period that suggest Antarctica was ice-free and part of a global hot greenhouse., (© 2022. The Author(s).)

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87 Sr/ 86 Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87 Sr/ 86 Sr lava from Savai'i Island, Samoa for detailed analyses of 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87 Sr/ 86 Sr-including the highest observed in an oceanic hotspot lava-encompassing ~30% of the oceanic mantle's total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87 Sr/ 86 Sr variability resulting from magma mixing between a high silica, high 87 Sr/ 86 Sr (up to 0.7316) magma, and a low silica, low 87 Sr/ 86 Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth's mantle.