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Zirconium is one of high field strength elements but its isotope behavior during geochemical processes is still uncertain because of the limited database. While Zr isotopes in magmatic rocks are often used to trace the evolution of magmas through fractional crystallization, it is intriguing how highly heterogeneous Zr isotopes were produced by the growth of zircon during crustal anatexis. We address this issue by in-situ zircon Zr isotope analyses of migmatites from two high-temperature metamorphic terranes in the South Lhasa zone and the North Dabie zone, respectively, in China. The results show highly variable δ94Zr values from −0.30‰ to +0.81‰ and from −0.58‰ to +0.49‰, respectively. In addition to the relict zircon of magmatic origin, two types of newly-grown zircons were identified in terms of their occurrences, trace elements and δ94Zr values. The peritectic zircon, mainly occurring in the in-situ leucosomes, exhibits the highest Nb-Ta-Hf-U contents and variably higher δ94Zr values than those of the relict zircon. The anatectic zircon, mainly occurring in the leucocratic veins, shows higher Nb-Ta-Hf-U contents than and similar δ94Zr values to those of the relict zircon. Model calculations demonstrate that the variable Zr isotope compositions of newly-grown zircons would result from decoupled release of Zr from zircon and non-zircon phases. The Zr supply of the peritectic zircon is mainly derived from the decomposition of Zr-bearing minerals in the in-situ anatectic melt (the non-zircon effect), whereas the Zr supply of the anatectic zircon is mainly from the dissolution of pre-existing zircons in the evolved melt (the zircon effect). The significant Zr isotope variations in the migmatites well illustrate the generation, migration and accumulation of the anatectic melts during the partial melting. Therefore, Zr isotopes can be used as a powerful means for distinguishing between the peritectic and anatectic zircons during crustal anatexis. [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]

Granulite facies metamorphism and crustal anatexis exist in the East Cathaysia Block, the exact timing of granulite facies partial melting and its link with orogenesis have not been well constrained. In this study, we carried out petrography, whole rock geochemistry, and zircon U–Pb dating, trace elements and Hf isotopes analyses on Dazhe gneissic granite and banded migmatite from the Badu Group in southwest Zhejiang province in the East Cathaysia Block. The melts were produced through the dehydration of biotite, such as biotite + quartz + plagioclase = orthopyroxene + K‐feldspar + melt and biotite + quartz + plagioclase + sillimanite = garnet + K‐feldspar + melt. Zircons from these rocks show clear core‐rim structure and yield rim and core concordant ages at 233 Ma and 1.83 Ga, respectively. The zircon rims suggesting the melts and the cores are suggesting the protolith of Dazhe gneissic granite and banded migmatite were crystallized from an evolving magma. The zircon cores and rims have negative εHf(t) = −2.2 ~ −6.3 and εHf(t) = −22.8 ~ −32.4, and they give suggestion of the presence of Neoarchean components. Although the major‐element compositions of the gneissic granite and banded migmatite are slightly different, the trace‐element spider diagram and REE pattern show they are similar, and then we find that the protoliths are A‐type granodiorite/diorite. Combined with the published data, we suggested that the Dazhe gneissic granite and banded migmatite were formed through granulite facies partial melting at 233 Ma, which was promoted by crustal shortening and thickening of the collision orogeny between East Cathaysia Block and an unknown terrane with a NNE trend structure line. The protoliths (granite or granodiorite) of Dazhe gneissic granite and banded migmatite crystallized at 1.83 Ga by reworking of the Neoarchean components of East Cathaysia Block. The Paleoproterozoic (1912–1819 Ma) collisional orogeny and the later intraplate rifting stage are corresponding to the aggregation and breakup of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The Rhodope crystalline massif is an Alpine metamorphic complex exposed across several mountain ranges in southern Bulgaria and northern Greece which has experienced a complex history including continental collision, partial subduction and syn-metamorphic nappe stacking followed by syn- to post-contractional extension. We present new 40Ar/39Ar and fission-track data from samples taken from both sides of the North Rhodopean Detachment that were combined with detailed structural studies to investigate the tectonothermal evolution of the northern Rila Mountains. A migmatite from the hanging wall of the North Rhodopean Detachment yields a 40Ar/39Ar muscovite age of 100.79 ± 0.55 Ma, a zircon fission-track age of 38.6 ± 1.9 Ma, and an apatite fission-track age of 21.4 ± 1.5 Ma. A biotite schist from the footwall of the detachment yields 40Ar/39Ar biotite age of 34.90 ± 0.15 Ma, and zircon and apatite fission-track ages of 35.6 ± 5.6 and 13.3 ± 1.1 Ma, respectively. Our new data give evidence of a multistage exhumation of the study area. Late Early Cretaceous (~ 101 ± 0.6 Ma) cooling of the Variscan high-grade metamorphic basement through 440–400 °C was caused by either erosion of the emplacing thrust sheet, or post-contractional denudation. Fast exhumation along the North Rhodopean Extensional System drove a pulse of increased tectonic denudation and cooling during the Eocene (39–35 Ma). Exhumation of the rocks in the northern part of the Rila Mountains below 110 ± 10 °C during the middle–late Miocene was associated with displacement along a system of normal faults. [ABSTRACT FROM AUTHOR]

The titanium (Ti) concentrations in zircon and quartz and corresponding thermometers have been regarded as powerful monitors that constrain petrogenetically meaningful temperature conditions of crystallization and metamorphism. The precise measurement of trace elements by electron probe microanalyzer (EPMA) is quite challenging as their x‐ray intensities are only slightly higher than the Bremsstrahlung background, leading to significant errors while quantifying the elemental abundances (e.g., Ti‐in‐zircon). We present EPMA‐based protocols for analysing Ti concentrations in zircon and quartz by considering recent analytical and instrumental improvements. High counting times at peak and background positions, simultaneous acquisition of Ti in multiple (three) spectrometers and data processing using the non‐central chi2 test for risk determination in sub‐counting method were employed in Ti‐in‐zircon and Ti‐in‐quartz protocols. Applying these protocols to the Mongolian garnet, San Carlos olivine and NIST 610 glass standards yielded Ti concentrations of 0.60 ± 0.02 wt%, 18 ± 3 ppm and 437 ± 26 ppm (in ±2σ), respectively. The Ti concentrations obtained from these standards are consistent with those published based on high‐precision analytical methods. We use the existing Ti‐in‐zircon and Ti‐in‐quartz thermometers to understand the thermal evolution of various lithologies in the Sandmata Complex, Aravalli Craton (north‐western India). The investigated samples include garnet–biotite gneiss, migmatite gneiss, mafic granulite and Anjana granite. The Ti‐in‐zircon temperatures calculated from the patchy‐zoned zircon cores yield HT–UHT conditions (892–959°C) for garnetiferous granite gneiss, migmatite gneiss and mafic granulite, whereas the zircon overgrowths yield temperatures of 725–871°C. The homogeneous zircon cores from Anjana granite yield temperatures (914–984°C) comparable to zirconium saturation conditions (920–960°C), indicating zircon crystallization from "hot" granitic melt. The oscillatory overgrowths on the zircon core obtain variable temperature conditions for inner overgrowth (811–877°C) and outer overgrowth (714–782°C), suggesting the episodic growth of zircon grains from different magma pulses. Additionally, the application of pressure‐dependent Ti‐in‐quartz thermometry yields quartz recrystallization conditions for garnet–biotite gneiss (430–556°C), migmatite gneiss (423–593°C), mafic granulite (430–679°C) and Anjana Granite (444–533°C). The combination of Ti‐in‐zircon thermometry, Ti‐in‐quartz and conventional thermobarometry demonstrates cooling histories for various high‐grade metamorphic and magmatic rocks in the Sandmata Complex. Based on this study, we emphasize that trace element thermometers can decipher high‐temperature metamorphism, which is otherwise erased in conventional thermometers due to diffusional readjustments during long‐lasting near‐peak and post‐peak metamorphism. [ABSTRACT FROM AUTHOR]

The variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process. Based on geochronology, whole‐rock and mineral chemistry, this paper reveals two different granites in the Northern Qinling migmatite complex, which reveal obvious differences in source region and melting condition. The older granodiorite (402 ± 0.8 Ma) displays typical Na‐rich adakite affinity, i.e., high Na2O/K2O (2.04 to 2.64) and Sr/Y (96 to 117) ratios, they have relative evolved isotopic compositions (εNd(t) = –0.52 to –0.04; zircon εHf(t) = –0.06 to +7.78). The younger leucogranite (371 ± 2 Ma) displays higher SiO2 (72.32 to 73.45 wt%), lower (TFeO + MgO + CaO + TiO2) contents (<2 wt%) and depleted Sr‐Nd‐Hf isotopic compositions (i.e., εNd(t) = +2.6 to +3.0; zircon εHf(t) = +5.94 to +14.12), as well as high 10000 × Ga/Al and TFeO/MgO ratios, indicating that they represent highly fractionated I‐type granites that derived from melting of juvenile crust. The variations in source rocks and melting condition of the two granites indicating a tectonic switch from compression to extension in 400 to 370 Ma, this switch is later than that in the eastern section of the North Qinling, indicating a scissor collision process between the South Qinling and North China Craton (NCC) in Devonian era. [ABSTRACT FROM AUTHOR]

Empirical studies of zircon in migmatites document features compatible with growth during heating at suprasolidus conditions. However, numerical modelling of zircon behaviour suggests that suprasolidus zircon is expected to grow only during cooling and melt crystallization. Here, phase equilibrium modelling coupled with mineral–melt Zr partitioning is used in an attempt to reconcile the observations from migmatites with the predictions of previous numerical models of zircon behaviour in anatectic systems. In general, an equilibrium‐based model that includes Zr partitioning does not allow prograde suprasolidus zircon growth. However, melting of metapelites at temperatures just above the wet solidus may allow limited zircon growth because of the low solubility of zircon in melt coupled with a source of Zr from minor garnet and ilmenite breakdown. Preservation of this zircon requires entrapment in growing peritectic minerals during subsequent heating and further melting. Heating above muscovite exhaustion in metapelites is unlikely to grow zircon because of the progressive increase in zircon solubility as well as an increasing compatibility of Zr in the residual mineral assemblage. The modelled compatibility of Zr in the residue of a metabasite decreases during heating, but an increase in zircon solubility in melt counteracts this; prograde suprasolidus zircon growth in metabasites is unlikely. Infiltration of Zr‐rich melt into a migmatite during open‐system anatexis provides an additional potential mechanism for prograde suprasolidus zircon growth during high‐temperature metamorphism. [ABSTRACT FROM AUTHOR]

We present an analysis of kinetics and pulses of zircon growth in migmatites formed at middle to lower crustal depths beneath a volcanic arc. Migmatites in high‐T metamorphic complexes at active continental margins, such as in the Ryoke Complex of southwest Japan, are thought to have been produced beneath volcanic arcs. Thermal models suggest that melt advection supplies the heat to form such high‐T complexes. We found that zircons in the migmatites of the Ryoke Complex grew in multiple discrete stages by rapid diffusion‐controlled growth. The individual growth pulses can be distinguished using a Gaussian mixture model when the duration of each growth pulse is shorter than 1σ of the analytical error of the zircon age dating, and where the interval between each growth pulse is larger than 2σ of them. This method allows extraction of the growth pulses even when the zircon exhibits incomplete textural evidence for multiple stages of growth. Application of the method to the Ryoke Complex revealed three and four pulses of zircon growth with 3–10 Myr intervals for two migmatite samples respectively in the Mikawa area and three pulses with 2–4 Myr intervals from one migmatite sample in the Yanai area. The detected zircon growth pulses are consistent with previously reported pulses of plutonic activity in the two areas, with the exception of the oldest growth pulse in the Mikawa area. Therefore, the growth pulses are interpreted to be the result of thermal pulses because of melt flux events at lower to middle crustal levels. The inferred intervals of pulsed melt fluxes are similar to those of individual caldera formation in coeval caldera clusters at the surface. [ABSTRACT FROM AUTHOR]

We present new U–Pb ages and Hf and O isotope data for zircon from I-, S- and A-type granites from both the western and eastern edges of the Delamerian Orogen in southeastern Australia. The I-type Tanunda Creek Gneiss contains zircon populations of 507 ± 4 and 492 ± 6 Ma inferred to reflect igneous and metamorphic ages, respectively. The I-type Palmer Granite yielded an age of 509 ± 3 Ma, and the Port Elliot S-type Granite has a magmatic age of 508 ± 7 Ma. Inherited zircon in these granites range from 1092 to 3343 Ma, probably derived from assimilation of Adelaide Group sediments. The Murray Bridge A-type Granite is 490 ± 2 Ma in age and lacks inherited zircon. In the Glenelg River Complex, an S-type migmatite from near Harrow contains a complex zircon population. It is most likely ~500 Ma in age and has inherited zircon of 550–700, 1000–1100 and 2437 Ma, hence matching those from the Kanmantoo Group. From this and detrital zircon ages, we infer that only the Kanmantoo Group extends across the Murray Basin into the Glenelg River Complex. The Wando Tonalite and Loftus Creek I-type granites yielded ages of 501 ± 2 and 486 ± 3 Ma, respectively. Zircon from the Dergholm Granite has suffered Pb loss, and the best age estimate for this granite is 488 ± 5 Ma. Combining all the granite data together, εHft and δ18O in the magmatic zircon range from 5.6 to −10.3 and from 5.8 to 8.1, respectively, and are well correlated. The zircon indicates the same temporal and compositional evolution of granitic petrogenesis across ~300 km of strike, reaffirming the notion that these terranes form part of the same orogen. Westward-directed subduction caused orogenic thickening, heating and increasing amounts of crustal contribution. This was followed by convective thinning of the thickened mantle lithosphere and a return to more primitive magmas lacking significant crustal contributions. It contrasts significantly with inferred granite petrogenesis and tectonic style in the younger Lachlan and New England Fold Belts further east that were not built upon extended cratonic lithosphere. [ABSTRACT FROM AUTHOR]

U–Pb geochronology, Hf isotopes and trace-element chemistry of zircon grains from migmatite of the upper Sutlej valley (Leo Pargil), Northwest Himalaya, reveal a protracted geological evolution and constrain anatexis and tectonothermal processes in response to Himalayan orogenesis. U–Pb geochronology and ϵHf record separate clusters of ages on the concordia plots in the migmatite (1050–950 Ma, 850–790 Ma and 650–500 Ma). The 1050–950 Ma zircon population supports a provenance from magmatic units related to the assembly of Rodinia. A minor amount of Palaeoproterozoic grains were likely derived from the Indian craton. The potential source rock of the 930–800 Ma detrital zircons may be granitoid present in Greater Himalayan rocks themselves and the Aravalli Range, which has 870–800 Ma granitic rocks. The arc-type basement within the Himalayan–Tibet orogen recorded (900–600 Ma) igneous activity, which may depict a northeasterly extension of juvenile terranes in the Arabian–Nubian Shield. The granitoid of 800 Ma may be a potential source for 790 Ma detrital zircons owing to scatter in 206/238 dates. The 650–500 Ma zircon population suggests their derivation from the East African Orogen and Ross–Delamerian Orogen of Gondwana. The Cambrian–Ordovician magmatism during the Bhimphedian Orogeny and observed late Neoproterozoic to Ordovician detrital zircons have been derived to some extent from Greater Himalayan magmatic sources. We found no detrital zircon grains that cannot be explained as coming from local sources. One sample yielded a discordia lower intercept age of 15.6 ± 2.2 Ma, the age of melt crystallization. [ABSTRACT FROM AUTHOR]

The Strandja Massif is one of the important metamorphic Massifs of Türkiye. The Strandja Massif consists of metasedimentary, and metamagmatic rocks such as migmatite, ortho- and paragneiss, metagranite, garnet-mica-schist, calcschist and marbles. For the first time, mineral chemistry analyzes of garnet-mica schists were performed to better understand the degree of metamorphism, and possible P-T conditions were defined in the north-northwest of the Strandja Massif. Based on almandine garnet and Fe-biotite mineral chemistry, garnet bearing mica-schist are affected by lower amphibolite facies metamorphism under 6.1 kbar pressure and approximately 547 °C. Moreover, detrital zircon U Pb dating was performed on 107 points to describe the maximum depositional age of this garnet-mica schist. The youngest zircon 206Pb/238U age obtained as 198 ± 17 Ma (98 % concordant, Th/U = 0.74) and the oldest 206Pb/238U age yielded as 1896.8 ± 33.4 Ma (100.12 % compatible, Th/U = 0.63). Additionally, a zircon U Pb concordia protolith age of 302.33 ± 1.79 Ma was obtained from orthogneisses. In-situ rutile-in garnet U Pb dating shows that garnet-mica schists underwent metamorphism at 119 ± 49 Ma. P-T conditions and age of metamorphism show that these rocks effected by the lower amphibolite facies metamorphism during late Jurassic – early Cretaceous period. [ABSTRACT FROM AUTHOR]

Migmatites can be produced in different stages of orogeny and thus have a great significance to constrain the evolution of an orogenic belt. Migmatites widely occur in the Tongbai orogen, but their formation ages and geological significance have not been well constrained. In this study, a combination of cathodoluminescence (CL) imaging, U-Pb-Hf-O isotopes and trace elements of zircons were carried for migmatites in the Tongbai orogen. Most inherited cores in a melanosome show variable U Pb ages and Hf isotope compositions with high δ18O values, suggesting they might be detrital zircons from its protolith. Whereas other relict cores in this sample have nebulously zoning or no zoning, flat HREE patterns with insignificant Eu anomalies and relatively low formation temperatures, indicating their formation under eclogite-facies conditions. They yield U Pb ages of 228 ± 3 Ma, providing direct evidence for the involvement of Triassic subducted continental materials. The overgrowth rims and some new grown grains in the migmatites show euhedral shapes, low CL luminescence, high Th/U ratios, clear negative Eu anomalies and steep HREE patterns, suggesting they are anatectic zircons formed during partial melting. They yield U Pb ages from 139 ± 2 to 132 ± 1 Ma. Combined with previous studies, we suggest that migmatization mainly occurred at 139–130 Ma in the Tongbai orogen. The anatectic zircons in the leucosomes show much lower δ18O values (5.79 ± 0.23‰ vs. 8.94 ± 0.16‰) and higher 176Hf/177Hf ratios (0.282302–0.282648 vs. 0.281728–0.282504) than the zircons in adjacent melanosomes, suggesting that the leucosomes might be externally sourced. According to a compilation of the geochronological information of migmatite and magmatism, the Tongbai-Dabie-Sulu orogens have a spatial and temporal variation of partial melting and magma activities in the post-collisional stage. These might result from the diachronical tectonic switch and collapse of the orogenic lithospheric keels caused by the subduction and rollback of the Paleo-Pacific slab. • The Tongbai migmatites formed at ca. 139–130 Ma. • There exist spatiotemporal variations of partial melting and magmatism in the Tongbai-Dabie-Sulu orogen. • A diachronous tectonic switch has been documented. [ABSTRACT FROM AUTHOR]

In migmatitic environments the behaviour of the system is controlled by the generation and amount of the anatectic melt. Accordingly, migmatites typically show a genetic linkage between the tectonic deformation and melt migration. We investigated this relationship in Olkiluoto (SW Finland) and identified four phases of ductile deformation, which are distinguished by the multiple folding phases, ductile shear events and cross-cutting features associated with pegmatitic leucosomes and/or a specific type of diatexitic migmatite with feldspar megacrysts. U-Pb LA-MC-ICPMS data on zircon cores and rims from migmatites and cross-cutting pegmatites indicate two distinct metamorphic events associated with melt generation and migration at 1.87-1.84 Ga and 1.82-1.78 Ga. These two migmatitic events suggest that the orogenic evolution of the area was long-lasting and characterized by slow cooling. The structural data and the age constraints presented in this paper support the idea of similar tectonic evolution and metamorphic environment in SW Finland and central E Sweden. [ABSTRACT FROM AUTHOR]

A contaminated inclusion is characteristic of deposition and mechanical mixing, in which diamond fragments from diamond paste are mixed with epoxy resin and debris from the polishing process is deposited in inclusion ([12]). Especially, nanometer diamonds in inclusion 4 are enclosed inside the C-Si-O and Zr-Si-O materials, and HRTEM images show that the interface between diamond and host amorphous materials is fully coupled and welded (Figs. Discussion Diamond origin Two diamond-bearing inclusions were exposed in the polished surface, leading to a reasonable suspicion that diamonds are from diamond paste in sample preparation. Several crucial lines of evidence support the indigenous origin of diamond and highly disordered CM, including: (1) the C-Si-O and Zr-Si-O materials, as well as vaterite and aragonite in our sample, are natural materials. Keywords: Ultrahigh-pressure metamorphism; vaterite; diamond; fluid inclusion; migmatite; Dabie-Sulu orogenic belt EN Ultrahigh-pressure metamorphism vaterite diamond fluid inclusion migmatite Dabie-Sulu orogenic belt 1410 1424 15 07/05/22 20220701 NES 220701 Introduction Vaterite, as one of the three polymorphs of CaCO SB 3 sb (vaterite, calcite, and aragonite), is a rare mineral in natural rocks, but biogenic vaterite is remarkably widespread, occurring in human calculi ([37]), pearls ([52]), fish otoliths ([48]), etc. [Extracted from the article]

New data include additional garnet Sm-Nd ages, garnet Lu-Hf ages, new zircon U-Pb ages, and zircon and garnet trace element concentrations. Keywords: Zircon U-Pb; garnet Sm-Nd; migmatite; lower crust; rates of intrusion; duration of metamorphism EN Zircon U-Pb garnet Sm-Nd migmatite lower crust rates of intrusion duration of metamorphism 1116 1132 17 06/01/22 20220601 NES 220601 Introduction and geologic setting Zircon and garnet isotopic dates are widely used for understanding local and orogenic scale processes in magmatic arcs, lower-crustal rocks, and high-grade metamorphic terrains. Garnet occurrences are classified according to [77]: Type 1 garnet occurs in discrete garnet reaction zones, Type 2 garnet forms planar to sub-planar arrays as selvages to trondhjemite veins, and Type 3 garnet are porphyroblasts in diffuse leucosomes. The young zircon ages, rejected from the weighted means for the host and garnet reaction zone overlap with garnet Sm-Nd ages for this sample and others from the Malaspina Pluton ([77]), and metamorphic zircon and titanite in the region ([66]). [Extracted from the article]

The high‐grade Higher Himalayan Crystallines (HHC), located between the South Tibetan Detachment System and Main Central Thrust in the collision zone between the Indo‐Australian and Eurasian plates, have been subject to at least four significant phases of deformation and metamorphism. The earliest of those significantly predates the Cenozoic continent‐continent collision, but has been difficult to date isotopically because of later overprinting. Migmatitic paragneiss from the Badrinath Formation in the Dhauliganga Valley, northern Uttarakhand, some of the highest‐grade rocks in the HHC, preserves direct evidence of mid‐Ordovician metamorphism in the form of 465.8 ± 6.4 Ma zircon overgrowths with extremely low Th/U (0.0038–0.0074). The overgrowths have formed on ca. 2.63–0.71 Ga detrital zircon cores and are themselves overgrown by two generations of Miocene metamorphic zircon with mean Pb/U ages of ca. 21.5 and 18.2 Ma. Monazite from the same sample has a mean Pb/Th age of 19.4 ± 0.2 Ma. The oxygen isotopic compositions of the monazite (δ18O: 7.69 ± 0.08‰) and youngest zircon overgrowths (δ18O: 7.95 ± 0.12, 8.24 ± 0.09‰) are consistent with mineral growth in a metasediment, but either of the two minerals did not grow in isotopic equilibrium with each other, or the original composition of the monazite has not been preserved. If the quartz (δ18O: 13.29 ± 0.11‰) equilibrated with the youngest zircon and its composition has been preserved, then the last episode of zircon growth took place at low temperature, ca. 420°C, after the migmatization. The protolith of the Badrinath migmatite was a Neoproterozoic or Early Palaeozoic metasediment partially melted (and probably migmatized) in the Middle Ordovician. The strong planar foliation currently present in the migmatite is probably the result of mid‐crustal extrusional channel flow and HT decompressional partial melting in the Miocene. [ABSTRACT FROM AUTHOR]

We present zircon and titanite U-Pb ages from granulite-facies transtensional shear zones and a greenschist facies strike-slip shear zone in the Karkkila-Vihti area, West Uusimaa. The zircon rim and titanite ages of c. 1815-1820 Ma from the transtensional shear zones constrain the evolution of the orogenic deformation from compression-dominated to syn-compressional lateral-escape within this part of the Fennoscandian shield while the zircon rim and titanite ages of 1790-1800 Ma give the timing of the late- to post-orogenic low-grade reactivation of the large-scale Somero-Karkkila fault zone. The new age data further constrain the timing of the changes in the crustal deformation style during orogenesis from i) compression-dominated to combined transpression - lateral stretching and escape, to ii) the late- to post-orogenic transition into retrograde conditions. [ABSTRACT FROM AUTHOR]

Several outcrops of migmatitic rocks (metatexite to diatexite) developed in the northern part of the Sanandaj-Sirjan zone (Hamedan, Touyserkan and Boroujerd). Two types of inherited zircons (2590 to 190 Ma) and metamorphic zircons (180 to 160 Ma) are found in the mesosome of migmatites. As the cathodoluminescence images display, inherited zircons are euhedral to subhedral with oscillatory zoning, and are jagged their margins in some cases. Metamorphic zircons as thick form grains are characterized by the lack of magmatic zoning and the presence of ghost texture, growing on the margins of the inherited zircons as a thin sheath. In some cases, metamorphic zircons are found as single crystals without any inherited nuclei. As the structural evidence suggests the process of recrystallization formed metamorphic zircons and their elements were moved under sub-solidus conditions. During migmatization, on one hand, the presence of fluid phase due to partial melting, gave rise to the formation of metamorphic zircons showing oscillating zoning and on the other hand, it has precluded the deformation due to shearing in the internal structure of these phases. Metamorphic zircons, belonging to 180 Ma, and younger are possibly nucleated through the Jurassic period thermaldynamic metamorphism. [ABSTRACT FROM AUTHOR]

Eclogites hosted in sillimanite‐bearing migmatites in the Montagne Noire dome (French Massif Central) have an oceanic protolith and recorded a prograde P–T path from ~19.5 kbar, 700°C to the pressure peak at ~21 kbar, 750°C (pseudosection modelling), suggesting metamorphism in a subduction setting. Subsequent exhumation to low‐P high‐T (LP–HT) conditions (~6 kbar, 730°C) is constrained by the equilibration conditions of the embedding migmatite. In samples of a fresh and a retrogressed eclogite, all zircon crystals but one display similar REE patterns (no Eu anomaly, flat HREE), usually ascribed to crystallization under eclogite‐facies conditions. Yet, the U–Pb apparent ages of zircon crystals from both eclogites spread from c. 360 Ma to a dominant data cluster at c. 315 Ma. The c. 315–310 Ma zircon U–Pb dates obtained from the embedding migmatite are interpreted as the age of crystallization of the partial melt during the LP–HT metamorphic stage. First‐order geological evidence, in particular the sedimentary record, excludes the existence of a subduction zone in the region at this period. Unless calling upon a major reappraisal of the tectonics of the European Variscan orogen, this suggests an ambiguous relation between REE patterns and U–Pb dates in the zircon population. Various scenarios that could account for the observations are discussed. Combining our data with the results of a previously published Sm–Nd dating of garnet, and regional considerations, we consider that 360 Ma is the best approximation of the minimum age of the eclogite‐facies event. We hypothesize that the eclogites formed farther north and were transferred to their present location by lower‐crustal flow. It is inferred that during the subsequent exhumation, eclogite‐facies zircon grains recrystallized and underwent partial to total resetting of their U–Pb system, whereas the REE system remained mostly unmodified. These results caution against the use of REE patterns as the only criterion to associate a specific zircon age with HP metamorphism in eclogites occurring in migmatitic domes. [ABSTRACT FROM AUTHOR]

We report contrasting pressure–temperature–time (P–T–t) paths of migmatites developed in the highest‐grade metamorphic zone (Grt–Crd zone) and the contact metamorphic zone (Crd–Kfs zone) of the Mikawa area, Ryoke belt, southwest Japan to discuss the complex P–T–D–t evolution of the middle crust that experienced pulsed granitoid intrusions. In the Grt–Crd zone, sillimanite‐grade high‐T metamorphic condition prevailed from ca. 97 to 87 Ma, followed by cooling to ~500 °C, ~4 kbar. The intrusion of gneissose granitoids below the Grt–Crd zone isobarically reheated the Grt–Crd zone rocks again to the sillimanite‐grade high‐T condition at ca. 84 Ma. This was followed by ca. 71–70 Ma contact metamorphism. Ductile deformation that formed and folded the foliation of migmatites started before ca. 89 Ma and continued at least until ca. 84 Ma in the Grt–Crd zone. On the other hand, ca. 74 Ma age of the Crd–Kfs zone migmatite developed around the Inagawa Granodiorite in addition to ca. 70 Ma age of a syn‐tectonic pegmatite vein revealed that the intrusion of "75–69 Ma granitoids" caused partial melting and locally triggered low‐strain ductile deformation in their contact aureoles. Comparison with other areas of the Ryoke belt suggests that plutono‐metamorphic evolution of the Mikawa and Aoyama areas are similar with each other in that ca. 80 Ma reheating events (i.e., contact metamorphism) are observed, while absence of separate reheating event postdating peak metamorphism in the Yanai area is a rather uncommon feature in the Ryoke belt. [ABSTRACT FROM AUTHOR]

Stable zirconium (Zr) isotopes have become the focus of attention as potential tracers of magma crystallization and differentiation processes. However, the effects of partial melting, especially disequilibrium melting, on Zr isotope fractionation remain unclear. Here we report in-situ zircon U Pb ages, major and trace elements, and Zr Hf isotope data for the migmatites in the eastern Gangdese arc, South Tibet. The leucosomes from the metatexite and diatexite migmatites are generally concordant with the foliation of the paleosome and display diffuse and gradational contacts with the melanosomes, indicating that they are in-source leucosomes. Zircon in the paleosome, the protolith of the migmatites, have U Pb age of 361 ± 2 Ma and low 176Hf/177Hf ratios of 0.282399–0.282482. They exhibit intragrain variation in δ 94/90Zr values, increasing from the core (−0.10 ‰ to +0.36 ‰) to the rim (+0.14 ‰ to +0.55 ‰) domains. The negative correlation between δ 94/90Zr values and Zr/Hf ratios suggests preferential incorporation of light Zr isotopes during the crystallization of the zircon in the protolith. Most zircon in the leucosomes from the metatexite and diatexite migmatites exhibit distinct overgrowth rims around the inherited cores. The inherited cores have consistent U Pb ages (ca. 360 Ma), trace elements, and Hf isotopic compositions (0.282362–0.282449) with zircon in the paleosome, indicating in situ partial melting. The inherited cores display δ 94/90Zr values ranging from −0.12 ‰ to +0.31 ‰, consistent with the zircon core domains in the paleosome. The overgrowth rims have U Pb ages of ca. 102 Ma and display higher 176Hf/177Hf ratios (0.282592–0.282900) and δ 94/90Zr values (+0.01 ‰ to +0.63 ‰) than their inherited cores. The elevated 176Hf/177Hf for the overgrowth rims resulted from the retention of unradiogenic 177Hf in the residue due to limited zircon dissolution and more release of radiogenic 176Hf to the melts because of the garnet breakdown, indicating disequilibrium melting. The elevation of δ 94/90Zr for the overgrowth rims relative to the inherited cores was not caused by the disequilibrium melting of other Zr-bearing minerals but was mainly controlled by the Zr isotopic composition and dissolution degree of the zircon in the protolith. The preferential melting of isotopically heavy zircon rims would elevate the δ 94/90Zr values in the melts relative to their zircon-bearing protoliths. Crustal anatexis may be another important mechanism contributing to the Zr isotope fractionation during crustal differentiation. • The 361 Ma granitic gneiss underwent crustal anatexis at 102 Ma in the Gangdese arc. • Zircon Zr Hf isotope disequilibrium occurred during crustal anatexis. • Garnet breakdown and limited dissolution of zircon caused Hf isotope disequilibrium. • Zr isotope fractionation depended on the dissolution degree of the protolith zircon. • Preferential dissolution of high δ 94/90Zr zircon rim elevate the melt's δ 94/90Zr. [ABSTRACT FROM AUTHOR]

Geological investigations of a part of the crystalline basement in the Baltic Sea have been performed on a drill core collected from the depth of 1092–1093 m beneath the Phanerozoic sedimentary cover offshore the Latvian/Lithuanian border. The sample was analyzed for geochemistry and dated with the SIMS U–Pb zircon method. Inherited zircon cores from this migmatized granodioritic orthogneiss have an age of 1854 ± 15 Ma. Its chemical composition and age are correlated with the oldest generation of granitoids of the Transscandinavian Igneous Belt (TIB), which occur along the southwestern margin of the Svecofennian Domain in the Fennoscandian Shield and beneath the Phanerozoic sedimentary cover on southern Gotland and in northwestern Lithuania. It is suggested that the southwestern border of the Svecofennian Domain is located at a short distance to the SW of the investigated drill site. The majority of the zircon population shows that migmatization occurred at 1812 ± 5 Ma, with possible evidence of disturbance during the Sveconorwegian orogeny. [ABSTRACT FROM AUTHOR]

To understand the crustal growth of the Qinling orogenic belt and the Mesozoic continental interaction between the North China and Yangtze blocks, it is critical to study the South Qinling accretionary complex belt, which is an important part of the Qinling orogen. Based on detailed zircon U–Pb geochronology and Hf isotopic compositional analyses of the Madao complex, this study presents constraints on the migmatization and tectonic evolution of the South Qinling orogenic belt during the Mesozoic. Zircons from leucosome samples of migmatites were found to have weak oscillatory zoning, and one sample yielded a weighted mean age that reflects the time at which the regional tectono‐thermal event initiated the anatexis (210–217 ± 2 Ma). The Hf isotopic compositions indicate that the Madao migmatites were derived from the ancient middle–Late Palaeoproterozoic crust. Zircons from mesosome samples of the migmatites that varied in age from the Palaeozoic to Neoproterozoic exhibited core‐rim textures with magmatic cores (256–1,329 Ma), indicating that they were derived from multiple sources with sedimentary protoliths. Of the 55 analysis spots on the overgrowth rims that yielded 206Pb/238U ages of 200–233 Ma, 40 analyses yielded a weighted age of 211.5 ± 1.0 Ma, indicating the time of anatexis due to the regional tectono‐thermal event. Combined with previously reported Mesozoic data from the South Qinling belt, these results suggest that the migmatites were probably controlled by post‐orogenic extension driven by Mesozoic orogenesis and a prolonged melting episode (from ~200 to 233 Ma). This study reinforces the interpretation that the continental crust in the South Qinling belt may have experienced complex interactions with asthenospheric mantle material during the Mesozoic. [ABSTRACT FROM AUTHOR]

Migmatite in the Sulu ultra‐highpressure (UHP) terrane is an ideal sample to provide information on anatexis during the exhumation of the deeply subducted continental crust. The studied migmatite is composed of the leucosome and melanosome with strongly ductile shear deformation. Petrographic observations clearly show an anatexis process, for example, cuspate and triangular K‐feldspars in triple junction and along grain boundaries, felsic veinlets and pockets mainly consisting of K‐feldspar + quartz + plagioclase ± biotite. The zircon grains of the migmatite have a core‐rim structure: the inherited magmatic core and the anatectic overgrowth rim. The inherited cores exhibit oscillatory zonings in the cathodoluminescence (CL) images and display strong heavy rare earth element (HREE) enrichment with clearly positive Ce and negative Eu anomalies. The inherited cores have an upper intercept U‐Pb age of 814 ± 45 Ma with εHf(t) values of −5.6 to ‐10.6 (mean = −8.5 ± 0.8, n = 16). Thus, protolith of the migmatite is a mid‐Neoproterozoic granitic rock. The overgrowth rims exhibit a typical anatexis genesis, that is, a bright homogeneous luminescence in the CL images, very low Th/U ratios (<0.02) with low U (<100 ppm) and Th (<1 ppm) contents, and lower total REE and Y contents with lower (Gd/Lu)N ratios and higher Hf/Y ratios than the inherited cores. They are Late Triassic with ages ranging from 211 to 234 Ma (mean = 223 ± 8 Ma), which, combined with previous studies on the Sulu UHP terrane, suggests that the anatexis occurred during the early exhumation stage. They have higher Ti‐in‐zircon temperatures ranging from 760 to 813°C (mean = 791 ± 16°C) than the pre‐anatexis zircon (244 ± 5 Ma and 739°C), suggesting a 'hot' exhumation. They have εHf(t) values of −17.6 to −14.5 (mean = −15.5 ± 0.6) which are lower than the estimated value (~12.0) on the crustal evolution array, suggesting an addition of crustal fluid during the anatexis. The anatexis also dramatically affected the zircon Lu–Hf isotopic system, that is, 176Yb/177Hf and 176Lu/177Hf isotopic ratios are markedly decreased but initial 176Hf/177Hf ratios are increased from the inherited magmatic cores to the anatectic rims. Thus, we propose that the anatexis plays a critical role in the exhumation of the UHP metamorphic rocks. The anatexis could lubricate the subducted slices and further facilitate their buoyant rise from the mantle depth to the crustal level. [ABSTRACT FROM AUTHOR]

Orthopyroxene-bearing felsic gneiss occurs as foliation-parallel layers and bands together with aluminous granulite, mafic granulite, and quartzofeldspathic granulite in the Chilka Lake migmatite complex of the Proterozoic Eastern Ghats Belt, India. The rock was classified previously as charnockite which underwent granulite-facies metamorphism. Field and textural features of this rock show evidence of the partial melting of a biotite-bearing greywacke protolith. Orthopyroxene with/without garnet and cordierite were produced with K-feldspar as peritectic phases of incongruent melting of presumed metaluminous sediments. Fluid-inclusion data suggest the presence of high-density CO2-rich fluids during peak metamorphism, which are similar to those found in associated aluminous granulite. Whole-rock major and trace element data show wide variability of the source materials whereas REE distributions show enriched LREE and flat HREE patterns. Zircon grains from representative samples show the presence of inherited cores having spot dates (SHRIMP) in the range c. 1790–3270 Ma. The overgrowth on zircon was formed predominantly during c. 780–730 Ma and sporadically during c. 550–520 Ma. Some neoblastic zircons with c. 780–730 Ma ages are also present. U-rich dark zones surrounding cores appear partially metamictised, but spot ages from this zone vary within c. 1000–900 Ma. The <1000 Ma ages represent metamorphism that mirrors the events in associated aluminous granulite. The sources of metaluminous sediments are speculative as the rock compositions are largely modified under granulite-facies metamorphism and partial melting. Considering the accretionary tectonic setting of the Eastern Ghats Belt during the c. 1000–900 Ma time frame, a greywacke-type protolith for the migmatite complex has been proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The migmatite records the evolution of the Dabie orogen from Triassic to Cretaceous. • The upwelling asthenosphere provided a heat source for the Triassic metamorphism. • The migmatite is the product of multiple anatexis of the subducted continental crust. The Dabie orogen underwent a 'complete' orogenic cycle from Triassic collisional orogeny to Early Cretaceous tectonic collapse. Zircons of the migmatite in the North Dabie terrane recorded the processes from Triassic granulite-facies metamorphism to Early Cretaceous anatexis. Three types of zircon are recognized in the migmatite: the Neoproterozoic inherited magmatic zircon, the Triassic metamorphic zircon, and the Late Jurassic–Early Cretaceous anatectic zircon. The Neoproterozoic inherited magmatic zircons suggest the protolith of the migmatite has a tectonic affinity with the Yangtze Craton (YC). The Triassic metamorphic zircon domains have variable ε Hf (t) values from −4.1 to 3.6 and low δ18O compositions ranging from −4.36‰ to −0.30‰. The anatectic zircon domains have clearly negative ε Hf (t) values of −19.8 to 0.8 (mostly less than −10.0) and relatively high δ18O values from −4.24‰ to 3.49‰. Based on the chronological and isotopic data of migmatite and the results of previous studies, the Triassic granulite-facies metamorphism was closely related to the asthenosphere upwelling after the slab break-off during the orogenic stage, and the Early Cretaceous anatexis respond to widely heat event during the collapse stage of orogen. [ABSTRACT FROM AUTHOR]

Migmatite, generated from anatexis or partial melting, links metamorphism with magmatism and can be used to investigate the source of magmas. Zircon and titanite, as refractory minerals in migmatite, can illuminate both the conditions of partial melting and the sources of associated granites. Mesozoic granitoids in the Jiaodong Peninsula, eastern China, have been studied extensively for their origins as partial melts of the lower continental crust. However, Jurassic metamorphism and partial melting of their hypothesized parent rocks have rarely been reported and discussed. In this study, we investigated the morphology, interior structure, U-Pb geochronology, and trace element compositions of zircon and titanite from diverse migmatites in the Yantai-Rushan area of the Jiaodong Peninsula. For leucosomes, inherited metamorphic and magmatic (or anatectic) zircon cores yield Paleoproterozoic ages, indicating a North China affinity; in contrast, anatectic zircon domains with high rare earth element concentrations show Jurassic ages of 160–154 Ma. For mafic melanosomes, metamorphic zircon and titanite yield ages of 154–149 Ma and c. 150 Ma, respectively; in contrast, two inherited metamorphic zircons record Triassic ages, suggesting an affinity with the ultrahigh-pressure rocks in the Sulu orogen. For granites, the oldest age of anatectic zircons is 175 Ma. Altogether, these data demonstrate a long-lived (c. 25 Myr), Jurassic, metamorphic-anatectic event in the Jiaodong Peninsula. These new findings prove that three lithotectonic units—the Jiaobei terrane, Sulu orogen, and preexisting granites in the Jiaodong Peninsula—were all sources for protracted Jurassic partial melting. This study deepens our understanding of the links between metamorphism and magmatism in demonstrating the diverse rock types that simultaneously source granites. • A Jurassic metamorphic-anatectic event was identified in the Jiaodong Peninsula of eastern China. • Rocks of North and South China block affinity were co-involved in the Jurassic partial melting. • This provides robust evidence for multiple origins of Jurassic and later granitoids. [ABSTRACT FROM AUTHOR]

Partial melting of ultrahigh‐pressure (UHP) metamorphic rocks is common during collisional orogenesis and post‐collisional reworking, indicating that determining the timing and processes involved in this partial melting can provide insights into the tectonic evolution of collisional orogens. This study presents the results of a combined whole‐rock geochemical and zirconological study of migmatites from the Sulu orogen in eastern China. These data provide evidence of multiple episodes of crustal anatexis and geochemical differentiation within the UHP metamorphic rocks. The leucosomes contain higher concentrations of Ba and K and lower concentrations of the rare earth elements (REE), Th and Y, than associated melanosomes and granitic gneisses. The leucosomes also have homogenous Sr–Nd–O isotopic compositions that are similar to proximal (i.e. within the same outcrop) melanosomes, suggesting that the anatectic melts were generated by the partial melting of source rocks that are located within individual outcrops. The migmatites contain zircons with six different types of domains that can be categorized using differences in structures, trace element compositions, and U–Pb ages. Group I domains are relict magmatic zircons that yield middle Neoproterozoic U–Pb ages and contain high REE concentrations. Group II domains represent newly grown metamorphic zircons that formed at 230 ± 1 Ma during the collisional orogenesis. Groups III, IV, V, and VI zircons are newly grown anatectic zircons that formed at 222 ± 2 Ma, 215 ± 1 Ma, 177 ± 2 Ma, and 152 ± 2 Ma, respectively. The metamorphic zircons have higher Th/U and lower (Yb/Gd)N values, flat heavy REE (HREE) patterns with no significantly negative Eu anomalies relative to the anatectic zircons, which are characterized by low Th/U ratios, steep HREE patterns, and negative Eu anomalies. The first two episodes of crustal anatexis occurred during the Late Triassic at c. 222 Ma and c. 215 Ma as a result of phengite breakdown. The other two episodes of anatexis occurred during the Jurassic period at c. 177 Ma and c. 152 Ma and were associated with extensional collapse of the collision‐thickened orogen. The majority of Triassic anatectic zircons and all of the Jurassic zircons are located within the leucosomes, whereas the melanosomes are dominated by Triassic metamorphic zircons, suggesting that the leucosomes within the migmatites record more episodes of crustal anatexis. Both metamorphic and anatectic zircons have elevated εHf(t) values compared with relict magmatic zircon cores, suggesting that these zircons contain non‐zircon Hf derived from material with more radiogenic Hf isotope compositions. Therefore, the Sulu and Dabie orogens experienced different episodes of reworking during the exhumation and post‐collisional stages. [ABSTRACT FROM AUTHOR]

Meta-pelitic rocks with interlayers of meta-psammites within the inner thermal aureole of the Alvand plutonic complex (Sanandaj-Sirjan Zone (SaSZ), western Iran) underwent partial melting; generating various types of migmatites. The mesosome of the Hamedan migmatites is classified into two groups: (1) cordierite-rich and Al-silicate-poor mesosomes and (2) cordierite-poor, Al-silicate-rich groups. Leucosomes are also variable, ranging from plagioclase-rich to K-feldspar-rich leucosomes. Mineral-chemical studies and thermobarometric estimations indicate temperature and pressure of 640–700°C and 3–5 kbar, respectively, for the formation of mesosomes. U–Pb zircon geochronology on 214 grains from the mesosome of migmatites indicates ages of 160–180 Ma (ca ~170 Ma) for zircon metamorphic rims and variable ages of 190–2590 Ma for the inherited detrital zircon cores. Inherited core ages show various age populations, but age populations at 200–600 Ma are more frequent. The age populations of the detrital zircons clarify that the provenance of the younger zircon grains (200–500 Ma) was more likely the Iranian plate, whereas the older grains (600 Ma to >2.5 Ga) may be sourced from both northern Gondwana (such as Arabian-Nubian Shield) and the neighbouring, old cratons like as Africa. We suggest that magmatic activities, especially mafic plutonism at ~167 Ma, are the main triggers for the heat source of metamorphism, partial melting, and migmatization. In contrast to a presumed idea for a Cretaceous regional metamorphic event in the NW parts of the SaSZ, this study attests that the metamorphism should be older and can be associated with Jurassic magmatic pulses. [ABSTRACT FROM AUTHOR]

The Early Palaeozoic geology of the South China Craton (SCC) is characterized by an Early Palaeozoic intracontinental orogen with folded pre-Devonian strata and migmatites, MP/MT metamorphic rocks and Silurian post-orogenic peraluminous magmatic rocks in both the Yangtze and the Cathaysia blocks. In this contribution, we present new zircon U–Pb ages and Hf isotope data for detrital zircons from the Neoproterozoic to Silurian sedimentary sequences in the southeastern Yangtze Block. Samples from Neoproterozoic rocks generally display a major peak at 900–560 Ma, whereas samples from Lower Palaeozoic rocks are characterized by several broader peaks within the age ranges 600–410 Ma, 1100–780 Ma, 1.6–1.2 Ga and 2.8–2.5 Ga. Provenance analysis indicates that the 900–630 Ma detritus in Cryogenian to Ediacaran samples was derived from the Late Neoproterozoic igneous rocks in South China that acted as an internal source. The occurrence of 620–560 Ma detritus indicates the SE Yangtze was associated with Late Neoproterozoic arc volcanism along the north margin of East Gondwana. The change of provenance resulted in the deposition of 550–520 Ma and 1.1–0.9 Ga detrital zircons in the Cambrian–Ordovician sedimentary rocks. The ε Hf(t) values of these detrital zircons are similar to those of zircons from NW Australia–Antarctica and South India. This change of provenance in the Cambrian can be attributed to the intracontinental subduction between South China and South Qiangtang, and the convergence of India and Australia when East Gondwana finally amalgamated. [ABSTRACT FROM AUTHOR]

Abstract The Early Paleozoic orogeny in the South China Block was accompanied by crustal anatexis, as indicated by the voluminous granites and migmatites. Here we report on the migmatite-granite suite within the Neoproterozoic biotite gneiss of the Baiyunshan Domain, which has directly recorded the process of anatectic melt formation, segregation and extraction. The crystallization of leucosome in migmatite was dated at ca. 438 Ma by U–Pb analysis of zircon, and the granitic vein that intruded the migmatite was dated at ca. 433 Ma. Petrological and geochemical data suggest that anatexis resulted from fluid-present melting of the biotite gneiss at low temperature and pressure conditions (~650–700 °C and ~4–6 kbar). The leucosome mainly consists of plagioclase + K-feldspar + quartz and has positive Eu anomaly (Eu/Eu* = 1.70–2.89), which is attributed to feldspar accumulation. This means that some melt has been extracted from the migmatite, and the granitic veins are likely to represent these extracted melts since they have similar trace element compositions and zircon Lu Hf isotopes to the leucosomes. The degree of partial melting and chemical differentiation to generate the migmatite and the granitic veins are revealed by mass balance calculations. Calculations suggest that the primary melt could be a result of ~40 wt% melting of the Baiyunshan biotite gneiss, and fractionated melt (~24–26 wt%) was extracted from the deeper sections to form the intrusive veins. Combined with regional dating results, it is suggested that the crustal anatexis in the Wuyi-Yunkai orogen started no later than 465 Ma with a duration of >55 Myr. Generation of the granitoids and migmatites are a result of water-fluxed melting and linked to extra heat from mantle magmas provided to the middle-lower crust. Highlights • A suite of migmatite-granitic vein is well-preserved in the Baiyunshan Domain. • Dating constrains migmatization and granite intrusion to ~438 Ma and ~433 Ma, respectively. • Leucosomes are feldspar accumulation, granitic veins are extracted interstitial melt. • Crustal anatexis lasted over 55 Myr requiring intense heat flux from the mantle. [ABSTRACT FROM AUTHOR]

An integrated study using cathodoluminescence (CL) images, U–Pb geochronology, and Hf isotopic characterization of zircons was performed on migmatites from the Yuka terrane to provide insights into the timing and nature of the protoliths, metamorphism, and partial melting of these rocks. Zircon grains separated from the migmatites have three distinct domains. Residual zircon cores in samples YKT01 and YKT02 exhibit oscillatory zoning, high Th/U ratios (0.10–0.79), steep heavy rare earth element (HREE) patterns, and mean ages of 936 ± 5 Ma and 927 ± 11 Ma, respectively, indicating that they are igneous in origin and record Neoproterozoic magmatism during the Grenvillian Orogeny. CL‐grey cores record an ultrahigh‐pressure (UHP) peak metamorphism age of 435 ± 5 Ma and have low Th/U and 176Lu/177Hf ratios, weak negative Eu anomalies, and relatively flat HREE patterns. The CL‐bright rims have steep HREE patterns with lower middle rare earth element (MREE) concentrations but higher HREE concentrations compared with the metamorphic cores and a weighted average age of 422 ± 4 Ma, which records the timing of melt crystallization. The migmatites incorporate garnet relicts coexisting with fluid inclusions and hydrous minerals like peritectic phengite and peritectic large anhedral poikilitic tourmaline in the leucosomes. Peak temperatures are less than 750°C, suggesting that the anatectic melts may be derived from melting of felsic gneiss in the presence of water. The timing of melt crystallization is ca. 13 Ma later than UHP metamorphism, indicating that the partial melting took place during the exhumation stage. The metamorphic zircon cores have higher 176Hf/177Hf(t) ratios than the residual magmatic cores, which provides powerful evidence for the generation of the metamorphic zircons through the incorporation of internal high Hf minerals other than zircon in a closed system. Anatectic rims with lower 176Hf/177Hf(t) ratios but higher 176Lu/177Hf ratios than metamorphic cores suggest that the main formation mechanism is dissolution‐reprecipitation of pre‐existing zircons. In conclusion, the elevated 176Hf/177Hf(t), TDM2 age and decreasing 176Lu/177Hf(t) ratios in the metamorphic and anatectic domains imply that the new zircons in some migmatites and granites may not reflect the Hf isotope compositions of their source rocks, accounting for the variable Hf isotope compositions in S‐type granites. [ABSTRACT FROM AUTHOR]

Highlights • We present geochronological data of a transition between Mozambique Belt and the Unango-Marrupa Complex. • Phanerozoic sediments of the Selous-Mandawa-Ruvuma Basin mask the basement exposures. • The area is intruded by granitoids with ages between 790 ± 8.7 Ma and 614 ± 8.1 Ma. • An orthogneiss with a protolith age of 1056 ± 19 Ma occurs as inlier in SE Tanzania. • Metamorphic reworking in SE Tanzania occurred between 606 ± 6.6 and 560 ± 37 Ma. • An alkali granitic pluton postdate metamorphism and intruded the area about 554 ± 3.9 Ma. Abstract We present geochronological and petrological data of orthogneisses, granitoids, and supracrustal rocks from SE Tanzania to characterize the transition zone between the Mesoproterozoic Unango-Marrupa Complex and the Neoproterozoic Mozambique Belt. Geochronological data (U-Pb zircon; LA-ICP-MS) indicate that the emplacement of orthogneisses (protolith) and granitoids in SE Tanzania occurred in Stenian, Cryogenian, and Ediacaran Periods. The magmatic emplacement ages are determined between 1056 ± 19 Ma and 554 ± 3.9 Ma. No older ages that that were determined. The Stenian orthogneisses (biotite granitic gneiss dates at 1056 ± 19 Ma and the associated migmatites, charnockites, amphibolite) represents Mesoproterozoic magmatic inliers in the Neoproterozoic rocks and the extension of the Unango-Marrupa Complex in SE Tanzania. Supracrustal rocks (marble and calc-silicate, garnet-biotite (hornblende) gneisses, quartzo-feldspathic gneisses, graphite schists, and quartzites) are interlayered with granitoids dated between 790 ± 8.7 Ma and 614 ± 8.1 Ma. The supracrustal rocks represent the upper part of the Mozambique Belt (Eastern Granulites/Cabo-Delgado nappes), and are possibly relics of continental shelf sedimentary deposits of the Mozambique Ocean. Upon assessing metamorphic ages (U-Pb zircon) in SE Tanzania we determined the Ediacaran metamorphic event dated between 606 ± 6.6 and 560 ± 37 Ma, which reworked the Stenian – Cryogenian crusts. The U-Pb zircon metamorphic ages are supported by a precise U-Th-Pb monazite metamorphic age at 589 ± 5 Ma obtained from a biotite garnet gneiss rock sample (amphibolite facies). The Ediacaran metamorphism in SE Tanzania was followed by the emplacement of biotite alkali granite at 554 ± 3.9 Ma, which probably marks crustal relaxation and extension after metamorphism as the result of collision or accretion. Magmatic rocks of the Mozambique Belt in SE Tanzania were emplaced during the East African Orogeny. Metamorphic reworking occurred during the final amalgamation of Gondwana between 600 and 500 Ma (Kuunga Orogenic Cycle) in line with tectono-magmatic history of the neighbouring Unango-Marrupa Complex, the Ubendian Belt, and the Irumide-Southern Irumide Belt. [ABSTRACT FROM AUTHOR]

Abstract The goal of this paper is to use the structural, metamorphic and geochronological record from the migmatitic core of the Naxos dome (Greece) and its associated subdomes to address the internal dynamics of a partially molten orogenic root. U-Pb ages from ca. 24 to 16 Ma and textures of zircon in the migmatites suggest successive dissolution and precipitation cycles with a period of 1 to 2 Ma , interpreted as the timescale of convective instabilities in a ca. 20 km thick partially molten layer. Dimensional analysis indicates that convection of this root requires a viscosity lower than 1018 Pa·s, consistent with viscosity values expected for partially molten felsic rocks. Structural analysis and U-Pb geochronology of deformed granitic dikes rooting in the migmatites record the subsequent development of the Naxos dome by diapirism from ca. 16 to 13 Ma. The size of the first order migmatite dome on Naxos (5 × 12 km) requires that the unstable layer at the onset of diapirism was 5 to 10 km thick and presented a moderate viscosity contrast with its envelope. From this analysis we propose that the Naxos migmatite dome documents a two stage dynamic evolution for the partially molten root of the Aegean belt characterized by (1) crustal scale convection for at least 8 Ma and (2) diapirism for about 3 Ma during progressive thinning of the collapsing orogenic crust. Graphical abstract Unlabelled Image Highlights • Naxos migmatite domes and subdomes denote a gravitationally unstable orogenic root. • U-Pb zircon ages are consistent with dissolution-precipitation cycles of 1 to 2 Ma. • U-Pb ages of dikes indicate that dome development occurred in about 3 Ma. • Convection of a 20 km thick molten crust requires a viscosity lower than 1018 Pa·s. • Diapirism involves a 5–10 km unstable layer and occurred during orogenic collapse. [ABSTRACT FROM AUTHOR]

A melt contamination model is presented to explain the formation of "I-type" granitic rocks, based on studies of migmatitic mafic granulites from the Hidaka Metamorphic Belt (Japan). Analysis of apatite and zircon from leucosomes and mesosomes of the migmatites reveals grain-scale Nd and Hf isotope heterogeneities of >10 epsilon units, inconsistent with closed-system anatexis. We interpret this marked isotopic variability to instead reflect hybridization between metasedimentary-derived partial melts and interlayered mafic granulite horizons during extraction of silicic melt from the lower crust. This open-system melt-rock interaction induces local isotopic modification of the mafic granulites and shifts the Hf isotope signature of the anatectic melt to more radiogenic values, similar to those of hornblende-bearing (I-type) granitic rocks emplaced into the Hidaka sequence at higher crustal levels. This study shows that the generation of broadly I-type granitic magmas does not require extreme temperatures to extensively melt meta-igneous rocks, nor is the direct input of mantle magma essential. Mineral-scale isotopic heterogeneities in such magmas reflect derivation from contrasting crustal sources and the rate and mechanism of magma transfer through the granulitic lower crust. [ABSTRACT FROM AUTHOR]

The Th/U ratios of zircon crystals are routinely used to help understand their growth mechanism. Despite the wide application of Th/U ratios in understanding the geological significance of zircon U--Pb ages, the main controls on the Th/U ratio in metamorphic zircon are poorly understood. Here, phase equilibria modelling coupled with solubility expressions for accessory minerals are used to investigate the controls on the Th/U ratios of suprasolidus metamorphic zircon in an average amphibolite facies metapelite composition. We also present a new database of metamorphic Th/U ratios in zircon from Western Australia. Several factors affecting the Th/U ratio are investigated, including the bulk rock concentrations of Th and U, the amount of monazite in the system, and open v. closed system behaviour. Our modelling predicts that the main controls on the Th/U ratio of suprasolidus metamorphic zircon are the concentrations of Th and U in the system, and the breakdown and growth of monazite in equilibrium with zircon. Furthermore, the relative timing of zircon and monazite growth during cooling and melt crystallization has an important role in the Th/U ratio of zircon. Early grown zircon near the peak of metamorphism is expected to have elevated Th/U ratios whereas zircon that grew near the solidus is predicted to have relatively low Th/U ratios, which reflects the coeval growth of monazite during cooling and melt crystallization. Our modelling approach aims to provide an improved understanding of the main controls of Th/U in metamorphic zircon in migmatites and hence better apply this geochemical ratio as a tool to assist in interpretation of the genesis of metamorphic zircon. [ABSTRACT FROM AUTHOR]

The Ladakh Magmatic Arc (LMA) of trans‐Himalaya was formed due to subduction of the Tethyan Ocean beneath the Eurasian continental plate. This was followed by the Indo‐Eurasian continental collision that gave rise to the Himalayan orogen. In this work, we present results from U–Pb geochronology of zircon of 2 samples from a previously unknown migmatite body within the LMA and one two‐mica granite body that lies adjacent to this migmatite and intrudes the LMA. One sample of mesosome from this migmatite gives a crystallization age of 66.9 ± 1.5 Ma (n = 11 zircon) along with a younger population of zircon (n = 24) giving an age of 62.1 ± 1.3 Ma. This sample also shows the presence of a younger cluster of zircon (n = 7) giving a concordant age of 50.0 ± 2.9 Ma. The other sample of one leucosome contains a cluster of inherited zircon (n = 5) giving a concordant age of 72.86 ± 0.83 Ma. However, the majority of the population (n = 10) gives a concordant crystallization age of 55.31 ± 1.5 Ma. Limited Hf isotopic analysis of the leucosome shows positive εHft values ranging from 7 to 15, comparable to that of the LMA. High and positive εHft values and absence of any Palaeozoic xenocrystic zircon help us infer that the Indian continental crust was not involved in the partial melting and leucosome generation process. Therefore, this event of migmatization predates Indo‐Eurasian collision. By comparing Th/U ratio versus age for both the mesosome and leucosome and their respective age spectra, we infer that this part of the LMA underwent pronounced partial melting between 55 and 60 Ma and generated leucosome till ~50 Ma. The two‐mica granite contains muscovite, indicating its crustal origin. It gives 2 closely spaced age spectra of 38.1 ± 1.1 Ma (n = 7) and 34.31 ± 0.48 Ma (n = 4). This two‐mica granite also contains xenocrysts of Palaeozoic ages. By integrating our studies with earlier works, we infer that this migmatization of the LMA indicates its collision with the Indian plate, prior to Indo‐Eurasian continental accretion, at 55–50 Ma. The two‐mica granite contains xenocrystic material from both the LMA and the Indian continental crust and indicates S‐type granite magmatism related to India–Eurasia continental collision at 35–40 Ma. [ABSTRACT FROM AUTHOR]

Extensive migmatization and large-scale post-collisional intrusions occurred in the Dabie orogen, east-central China, during the Early Cretaceous, characterized by distinct deformation preserved in migmatites in the North Dabie Complex unit. The North Dabie Complex unit can be subdivided into three areas based on detailed field observations: the north of the Tiantangzhai pluton, the Luotian area and the Yuexi area. Banded migmatites crop out in the north of the Tiantangzhai pluton while anisotropically deformed migmatites occur in the Luotian area, and both types coexist in the Yuexi area. Microscopy reveals similar micro-structures are in migmatites from the north of the Tiantangzhai pluton, the Yuexi area and border of the Luotian area, while static recrystallization appears in migmatites from the core of the Luotian area. The Lattice-Preferred Orientation of dynamically recrystallized quartz grains in the migmatites are measured using electron backscattered diffraction, revealing prism slip or slip in migmatite from the north of the Tiantangzhai pluton and the Yuexi area and in one sample from the Luotian area. A Type I crossed girdle is developed in another sample from the Luotian area, indicating top-to-the-SE shearing that developed under greenschist facies conditions. Zircon U-Pb dates from four migmatites reveal that mainly Early Cretaceous ages are from the north of the Tiantangzhai pluton, only four Early Cretaceous ages are from the Luotian area, and all zircons from the Yuexi area record Indosinian metamorphic ages. Although zircon U-Pb results show multiple migmatization events, all samples record a migmatization age of about 132 Ma, suggesting an orogen-scale event at that time. The subsolidus deformation in migmatites indicates that deformation were soon after migmatization. Overall, this study shows that deformation in migmatites of the North Dabie Complex unit occurred somewhat later than the migmatization (~132 Ma) at about 131 Ma. The most likely mechanism for thinning of the thickened crust in the Dabie orogen involved removal of the upper along the detachment fault and ductile adjustment of lower crust during development of the North Dabie metamorphic core complex. [ABSTRACT FROM AUTHOR]

Wuyishan is one of the most important terrains exposing the Precambrian basement of the Cathaysia Block, South China. Conventionally, Paleoproterozoic and Neoproterozoic sequences have been proposed in this terrain, however, the thermal histories affecting each unit within these sequences remain unclear. We report here spot analysis of 448 LA-ICPMS U-Pb zircon and >1600 EMP Th-U-Pb monazite ages for twenty samples, including schist, gneiss, migmatite and amphibolite, from different units within the basement. U-Pb zircon dating yield some concordant Neoproterozoic and/or Early Paleozoic age clusters with a wide spread of Neoarchean to Mesoproterozoic inherited ages (except amphibolite), indicating the formation of the Mayuan/Chencai core in the Early Neoproterozoic (887–827 Ma) and peripheral units in two stages of the Late Neoproterozoic (746–731 Ma and 681–660 Ma). The in-situ EMP monazite analyses give consistent Early Paleozoic ages (440–426 Ma) from inclusions in various host minerals for all but two samples from same locality that are Triassic in age (239–237 Ma). A large population of Early Paleozoic interstitial monazites shows breakdown texture and ages of secondary monazites range from 376 Ma to 358 Ma, conforming with the U-Pb zircon age of the amphibolite (370 ± 5 Ma). A few samples exhibit relict ages of ∼540 Ma from monazite cores. We conclude that the Wuyishan terrain is dominated by Early and Late Neoproterozoic basement sequences related to collisional and continental rifting orogenies, respectively, while the Badu Group in Zhejiang as a Paleoproterozoic protolith. The Neoproterozoic basement incorporating some Early Cambrian detritus, has thoroughly metamorphosed during the Silurian and further affected by the regional fluid-aided metasomatism coeval with the basic magma, now represented by amphibolites, around ∼370 Ma. The EMP monazite dating results for the Wuyishan terrain are quite different from the Yunkai massif where Triassic ages predominate, although the Wuyi-Yunkai metamorphic belt is often referred to as the same orogen in the Cathaysia Block. [ABSTRACT FROM AUTHOR]

The plate affiliation of the North Dabie terrane (NDT) has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zircons and field investigation for migmatite in the NDT was carried out, which reveals participation of crustal rocks of the North China craton (NCC) in the protolith in addition to the more common crustal rocks of the Yangtze craton (YC). The evidence of an NCC affinity for protolith of migmatite in the NDT is the ∼2.5 Ga (2 486±14 and 2 406±26 Ma) magamtic age and ∼1.8 Ga (1 717±79 Ma) metamorphic age in the relict zircon domains because these two age groups are characteristic for the evolution of the NCC. The evidence of a YC affinity for protolith of migmatite in the NDT is the more common 0.7-0.8 Ga (e.g., 787±12 Ma) magamtic zircon age. Mid-Neoproterozoic magmatic age (0.7-0.8 Ga) is a symbol of YC basement rocks. In view of the widely exposed YC crustal components in the NDT, we suggest that the protolith of the NDT is mainly crustal rocks from the YC with minor crustal components from the NCC. The zircon rim domains and new growth grains from all the migmatite samples are characterized by anatectic zircons and have a widely concordant ages ranging from 112.2±2.8 to 159.6±4.3 Ma with several peak values, suggesting a long lasting multistage anatexis. In conclusion, the NDT has a mixed protolith origin of both the YC and the NCC crustal rocks were strongly remoulded by anatexis during orogenic collapse. [ABSTRACT FROM AUTHOR]

An integrated study using cathodoluminescence (CL) images, U-Pb geochronology, and Hf-O isotopic compositions of zircons, and whole-rock geochemistry was carried out on migmatites from the North Dabie terrane in order to constrain the sources and processes of the melt during partial melting and implications for tectonics in the northern Yangtze block. CL imaging revealed that zircon grains in the migmatites occur as either new crystals or overgrowth rims around older inherited cores. The zircons display euhedral in shape with oscillatory or weak zoning and variable Th/U ratios, suggesting that they are of metamorphic origin and grew during partial melting. These zircons have concordia U-Pb ages from 129 ± 2 Ma to 140 ± 4 Ma, indicating partial melting of the North Dabie terrane due to the extension and collapse of the thickened orogenic root in the Early Cretaceous. The metamorphic zircons in two leucosome samples show higher δ18O but lower εHf(t) values than the inherited zircons in the same sample or adjacent melanosome samples, suggesting that the leucosomes were derived from external melt. The large variation of zircon εHf(t) values (-17.9 ± 0.5 to -4.6 ± 0.6) in one leucosome sample implies mixing between outside Hf from external melt and internal Hf from the dissolution-reprecipitation of the inherited zircons. The metamorphic zircons in one melanosome sample have higher 176Hf/177Hf ratios than, but similar δ18O values to those of the inherited zircons in the same sample, providing strong evidence for the generation of the metamorphic zircons by breakdown of a zirconium-bearing phase other than zircon in a closed system. The inherited zircon cores show oscillatory or weak zoning, resorption textures, and overprinting by overgrowth rims, suggesting that they are magmatic zircons inherited from the protoliths. Their U-Pb ages are ca. 450 Ma, providing unambiguous evidence for the presence of early Paleozoic magmatism in the Dabie-Sulu orogen. The inherited zircon cores have εHf(t) values of 8.6-14.0 and depleted mantle model (TDM2) ages of ca. 880-540 Ma, indicating prompt reworking of juvenile crust during their formation. Inherited zircons in two samples (a melanosome and a leucosome) show δ18O values of ~5.3‰, suggesting no involvement of hydrothermal materials. In contrast, inherited zircons in a melanosome sample show δ18O values from 3.22‰ ± 0.24‰ to 5.00‰ ± 0.29‰, with a weighted average of 4.28‰ ± 0.23‰. These values are distinctly lower than the normal mantle zircon values, suggesting the occurrence of Paleozoic low-δ18O magma in the northern part of the Yangtze block. The Paleozoic low-δ18O magma is inferred to have been generated by remelting of preexisting 18O-depleted rocks in a rift setting. Combined with previous geological observation, we proposed a rift setting for the northern Yangtze block during the early Paleozoic, which might have resulted in the final opening of the Paleotethys Ocean along the Qinling-Tongbai-Hong'an orogenic belt. [ABSTRACT FROM AUTHOR]

Migmatites provide a record of melt formation and crustal rheology. In this study we present zircon U-Pb ages and geochemical composition of migmatites from the Foping dome and granites from the Wulong pluton. U-Pb results from migmatite zircons indicate two episodes of partial melting. Rim domains from a leucosome in the Longcaoping area yield an age of ca. 209 Ma. Migmatites collected from the Foping dome yield U-Pb zircon ages of ~ 2910 to ~ 190 Ma, suggesting the involvement of meta-sedimentary source components. Rim domains of the zircons with low Th/U ratios (< 0.1) give ages of ~ 225–190 Ma and the youngest age domains (ca. 195 Ma) are characterized by low contents of heavy rare earth elements, which is related to crystallization of garnet. Magmatic rocks from the Wulong pluton can be subdivided into high Sr/Y and low Sr/Y granites. U-Pb zircon ages vary from 219 to 214 Ma for the high Sr/Y granites and from 214 to 192 Ma for the low Sr/Y granites. High Sr/Y granites have higher Na 2 O and Sr contents than the low Sr/Y granites. They also lack negative Eu anomalies and are depleted in HREE compared to the low Sr/Y granites. Initial 87 Sr/ 86 Sr ratios and ε Nd values of all the samples roughly overlap with those of Neoproterozoic basement rocks exposed in South Qinling. Including previous studies, we propose that the high and low Sr/Y granites formed by melting of thickened and normal crust, respectively. Close temporal-spatial relationship of the high and low Sr/Y granites with the two-stage migmatization events implies variation of crustal thickness and thermal overprints of the orogenic crust in post-collisional collapse. Following the collision of South Qinling and the Yangtze block prior to 219 Ma, partial melting of the deep crust occurred. The melts migrated upwards to form the high Sr/Y granites. This process occurred rapidly and caused collapse of the thickened crust and carried heat upwards, leading to further partial melting within the shallower crust and formation of the low Sr/Y granites. [ABSTRACT FROM AUTHOR]

Cratons, as well as the basement of their marginal orogens, may represent important sites of research regarding the formation and evolution of Archean continental crusts. The Gavião Block is one of the oldest terranes in South America with rocks aged up to 3.6 Ga. Among the Archean units that outcrop in the southern sector of this block is the Santa Izabel Complex, which for the most part is located in the São Francisco Craton, close to its limit with the Araçuaí-West Congo Orogen. This complex has generally been described as comprising ortho- and paraderived rocks that were metamorphosed in high amphibolite facies. Studies in the southern region of this complex have shown the main components: (i) orthogneisses, whose protoliths are the Mesoarchean rocks of the Santa Izabel Magmatic Suite; and (iii) migmatites. and (iv) amphibolitic and metaultramafic enclaves. U-Pb studies (LA-ICPMS and SHRIMP) performed on zircons of the paleosome in metatexites and inherited zircons in migmatites indicate crystallization ages between 3091 ± 24 and 3136 ± 8 Ma for the rocks of the Santa Izabel Magmatic Suite. Inherited zircons aged ca. 3.4 Ga in paleosomes demonstrate the influence of older continental crust in the formation of these rocks. For the Caraguatai Magmatic Suite, the alignment of zircons and monazites suggests a crystallization age around 2.6 Ga. The Rhyacian migmatites were divided into metatexites and diatexites. Diatexites were divided into: (i) discontinuous boudinated early diatexites, which are parallel to stromatic metatexites, composing the gneissic banding. These rocks have diffuse metamorphic banding and features that suggest the action of mylonitization processes; and (ii) late diatexites, forming more continuous bodies, which truncate the gneissic banding. The migmatization occurred in two stages, with time interval between ca. 2.1 Ga and 2.07 Ga. The structural framework reveal the existence of four progressive Rhyacian deformation phases (D n to D n+3 ), and one deformation phase assumed to be Ediacaran (D n+4 ). Gneissic banding is the dominant structure and lithofacies of the Santa Izabel and Caraguatai Magmatic suites, in which metatexites and late diatexites alternate between themselves. This progressive deformation occurred in conditions of high amphibolite facies, with stress fields varying between NW-SE and WSW-ENE. The youngest phase, D n+4 , was associated with distal deformations related to the evolution of the intracontinental Araçuaí-West Congo Orogen with a WSW-ENE stress field. The combined data suggest a complex evolution for the Gavião Block, involving juvenile accretion, crustal reworking, deformation and metamorphism/migmatization from the Paleoarchean to the early Rhyacian. Almost all elements of the evolutionary stages of the Gavião Block can be recognized in the study area, setting it as a natural laboratory to unravel the evolutionary history of this sector of the South American continental crust. [ABSTRACT FROM AUTHOR]

Compositional variability of crustal-derived granites has been attributed to a multitude of processes. Although there has been much discussion on the entrainment of residuum and its effect on granite magma chemistry, the exact nature of what is entrained and when entrainment is efficient remain unclear. We describe the relationship between granulite-facies migmatites and granites in the Sierra de Quilmes, NW Argentina, focusing on how the style of melt segregation affects its ability to disaggregate the source and carry residual minerals, and therefore control granite chemistry. The north-south-trending mountains that define the region known as the Sierras Pampeanas are characterized by variably metamorphosed turbidites of the Neoproterozoic-Cambrian Puncoviscana Formation. Early Ordovician subduction on the western Gondwana margin produced widespread high-T, low-P metamorphism of the turbidites during the Famatinian orogeny (~500-440Ma), resulting in extensive anatexis and granite plutonism. The Tolombón complex of the northern Sierra de Quilmes is a tilted metamorphic sequence in the northern Sierras Pampeanas, providing near-complete exposure from granulite-facies magma source rocks in the SW to granite emplacement levels in amphibolite- and greenschist-facies rocks in the NE. Anatexis is associated with fluid-absent incongruent breakdown of biotite in granulite-facies rocks, evidenced by the presence of peritectic Grt±Crd±Opx. The western Tolombón complex is separated from the Ovejeria complex by a shear zone. The Ovejeria complex is distinguished by a generally higher melt fraction, and is dominated by gradational contacts from metatexites to diatexites and granites. In contrast, in the Tolombón complex, with few examples of diatexites, magmas are more commonly extracted from metatexites, and migrate to feed stocks and plutons at higher crustal levels. Granites derived from diatexites tend to remain close to the source and retain strong compositional similarities to the Puncoviscana Formation protolith, indicating significant mobilization of residuum, and defining the Ovejeria style of granite formation. Granites derived dominantly from melt extraction from metatexites tend to be leucogranites with compositions approaching those of experimental melts, defining the Tolombón style of granite formation. Magma derived through either mechanism undergoes further differentiation, giving rise to the compositionally diverse suite of rocks common to most anatectic terranes. Magmas derived through the Tolombón style of melt extraction are leucocratic and impoverished in light rare earth elements (LREE), Th, and Zr compared with both the sedimentary source rocks and residuum-rich magmas derived through the Ovejeria style of granite formation. The low solubility of zircon and monazite in relatively dry, peraluminous leucogranite melts guarantees that Zr, Th, and LREE behave as compatible elements during dehydration melting of metasedimentary packages. Therefore, neither style of granite formation contributed to the transfer of many of the typical trace elements enriched in the upper crust. Instead, biotite dehydration melting in the Sierra de Quilmes had the opposite effect of typical crustal differentiation, concentrating these trace elements in the residual source, possibly reflecting the lack of a pressure gradient driving extraction of residuum-rich magmas [ABSTRACT FROM AUTHOR]

Crustal anatexis plays a significant role in the processes of orogenic evolution. We carried out a combined study of structure, U-Pb age and trace element on zircons from leucosome-based migmatites in the North Dabie zone to provide information on crustal anatexis during the evolution of the Dabie orogen. Protoliths of the migmatites are Middle Neoproterozoic (ca. 780–710 Ma) magmatic rocks that belong to the South China Block. They underwent a relatively low-T eclogite-facies metamorphism during the Middle to Late Triassic (235–225 Ma) continental subduction and collision. An over-thickened crustal root was formed and the Dabie orogen entered into the stage of post-collisional evolution after the Triassic. The earliest anatexis occurred at ca. 185 Ma; the anatexis in the Jurassic was weak and gentle due to episodic flow of metamorphic fluids with a prolonged interval. Nevertheless, it indicates that the crustal root started to become ductile and unstable at that time. Extensive epsodic anatexis occurred between ca. 160 Ma and 110 Ma. As the anatexis became stronger, more extensive and uninterrupted, the anatectic products changed gradually from low-degree migmatites to high-degree migmatites. The beginning of extensive anatexis at ∼160 Ma marks the beginning of orogenic activation. The duration of ca. 160–145 Ma corresponds to the orogenic activation when the collision-thickened crust still remained, whereas the period of ca. 145–110 Ma is in accordance with the orogenic collapse. The peak period of anatexis (ca. 145–125 Ma) was accompanied by plutonism, high-T granulite-facies metamorphism, extensional uplift and subsequent delamination of crustal root. After that, the anatexis trailed off until ca. 110 Ma. The long lasting multistage anatexis recorded in the migmatites has witnessed the evolution of the Dabie orogen in the postcollisional stage. [ABSTRACT FROM AUTHOR]

Zircon hosted in granite, which crystallized from local pools of anatectic melt among migmatites, in the Rikolatvi structure, Belomorian Mobile Belt, contains minute inclusions of various minerals, biotite and garnet among others. The compositions of the biotite and garnet in the microinclusions differ from those of the same minerals in the granite containing the zircon. The crystallization temperature of the anatectic melt was estimated by the biotite-garnet geothermometer and the composition of the biotite and garnet inclusions at ~800°C. [ABSTRACT FROM AUTHOR]

The Inchope orthogneiss comprises a mesoproterozoic group of variously deformed and migmatised orthogneisses in the Chimoio group. This area is well known for its numerous, small pegmatite deposits with cassiterite and columbite. Zircon U-Pb geochronological and whole rock Sr-Nd isotope data are reported for five Inchope orthogneiss samples. The zircon U-Pb data exhibit one period of crystallization between 1065 and 1053 Ma and two metamorphic ages of 956 Ma and 484 Ma. The Inchope orthogneiss displays evolved Nd isotopic compositions with ɛNdi between −11.7 and −13.3, 87 Sr/ 86 Sri between 0.7117 and 0.7209 and T DM values of between 2.3 and 2.4 Ga. Therefore, the Inchope orthogneiss crystallized in Mesoproterozoic from the paleoproterozoic metapelites along the eastern margin of the archaen Zimbabwean craton. This was followed by pegmatite veins intrusions and Pan-African tectonometamorphic reworking. These features are typical of S-type and calc-alkaline granites in continental margin arcs. [ABSTRACT FROM AUTHOR]