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High-temperature diffusion of major elements may obscure the records of early and peak metamorphic stages in granulites, while trace elements are more likely to preserve these records due to their lower diffusion rates. Thus, using calibrated REE-based thermobarometers has proved essential for reconstructing these key stages, drawing considerable attention and application from scholars. However, the precision of these thermobarometers depends on including both major and trace elements from coexisting minerals to define the correlation coefficients (A, B, and D) among mineral pairs, indicating that the elemental composition of these pairs can affect the results. Our study examines the mafic-ultramafic granulites in the southern granulite terrain, India, employing integrated methods such as petrography, mineral chemistry, phase equilibrium modeling, and REE-based thermobarometers. We aim to determine their metamorphic conditions and evolutionary history and to identify potential challenges in using REE-based thermobarometers. The garnet, clinopyroxene, and orthopyroxene in the mafic-ultramafic granulite samples display homogeneous compositional profiles, with pronounced Fe-Mg diffusion zones at the interfaces between garnet and clinopyroxene. Conversely, the profiles of trace elements within garnet and clinopyroxene are better preserved. Investigations into Fe-Mg exchange and randomly selected mineral pairs significantly influence the accuracy of REE-based thermobarometers. Fe-Mg exchange can increase in coefficient A, while decreasing coefficient B for light rare earth elements (LREEs) and increasing it for heavy rare earth elements (HREEs), ultimately resulting in over-estimations when calculating REE-based thermobarometers. For example, selecting major compositions with an Ex (= (X Mg C − X Mg 0) / X Mg 0 × 100 % ; where X Mg C is the value after Fe-Mg exchange, X Mg 0 is the value before Fe-Mg exchange; X Mg = Mg / (Fe 2 + + Mg) ) value of ∼10 for calculation using the REE-in-Grt-Cpx thermobarometer will result in pressures and temperatures being ∼10 kbar and 30–40°C higher than the true values. Random pairing, such as selections based solely on the core or rim of minerals with changes in trace elements, can severely impact the distribution coefficient D, resulting in substantial discrepancies in thermobarometric calculations and potentially producing anomalous results. Thus, to minimize the impact of these factors, it is necessary to first analyze the profiles of major and trace elements in coexisting minerals before applying the REE-based thermobarometers to evaluate the P-T conditions of granulites. Based on this analysis, major element compositions less affected by Fe-Mg exchange (such as avoiding the selection of major compositions at the boundaries of minerals) and in relative equilibrium in trace element compositions among coexisting minerals (same growth periods) should be selected for pairing. Furthermore, integrating additional methods should also be considered when applying the REE-based thermobarometers, to prevent the misinterpretation of the P-T conditions obtained. [ABSTRACT FROM AUTHOR]

The P–T paths of the exhumation of Precambrian granulite complexes at craton boundaries usually include two stages: subisothermal decompression and a decompression–cooling stage with a more gently sloped P–T path. Our goal is to understand the possible causes of the change in the slope of the P–T exhumation path of the Central Zone (CZ) of the Limpopo granulite complex, South Africa, located between the Kaapvaal and Zimbabwe cratons. For this purpose, rocks (mainly, metapelites) were studied in various structural settings within the Central Zone, i.e., in dome structures, regional cross folds, and in local and regional shear zones. The metapelites are gneisses of similar bulk composition. The rocks contain various amounts of relics of leucosomes composed of quartz–feldspar aggregates with garnet and biotite, and melanocratic domains that are enriched in cordierite and usually mark shear microzones that envelope and/or break garnet porphyroblasts. Study of polymineralic (crystallized melt and fluid) inclusions in the garnet, its zoning with respect to the major (Mg, Fe, and Ca) and some trace (P, Cr, and Sc) elements, fluid inclusions in quartz, as well as phase equilibria modeling (PERPLE_X) showed that the rocks coexisted with granite melts and saline aqueous carbonic fluids ( = 0.74–0.58) at the peak of metamorphism at 800–850°C and 10–11 kbar. Partial melting of the rocks initiated their subisothermal exhumation to 7.5–8 kbar during diapirism of granitic magmas in the Neoarchean (2.65–2.62 Ga). This is reflected in the specific zoning of the garnet grains in terms of the grossular content. A change in the rheology of the rocks as a result of partial removal and crystallization of melt activated the shear zones during further exhumation to 6–5.5 kbar along a decompression–cooling P–T path at 95–100°/kbar, reflecting the slower uplift of the rocks in the middle crust. This process was resumed due to thermal effects and interaction of the rocks with aqueous fluids ( > 0.85) in the Paleoproterozoic (~2.01 Ga). Such a scenario of metamorphic evolution implies that the Limpopo granulite complex in general and its Central Zone in particular resulted from the evolution of an ultrahot orogen, in which vertical tectonic movements associated with diapirism were coupled to horizontal tectonic processes caused by the convergence of continental blocks. [ABSTRACT FROM AUTHOR]

New data on the U–Pb age (SHRIMP-II) and trace element composition (SIMS) of zircon from gneisses of the Khapchan Group of the Khapchan terrane of the Anabar Shield are presented. Zircon grains contain relicts of magmatic zircon, the protolith and source areas of which are difficult to specify. The only zircon in this group with the least altered core preserved the 207Pb/206Pb protolith age of 1971 ± 19 Ma. During granulite metamorphism, the zircon was subjected to the impact of fluid enriched in incompatible elements. The disurbances affected both the U–Pb isotope system (zircon age was "reset" at metamorphic age of 1920–1930 Ma) and composition of zircon, magmatic cores of which were significantly recrystallized in a solid state or dissolved by fluid up to the practically complete disappearance of primary zircon. In both the cases, zircon was sharply enriched in incompatible elements (Ca, Ti, Pb, Sr, Ba, and some others) owing to fluid effect, while preserved cores seemed to be rimmed by a new zircon population (CL-black). The REE distribution patterns in the recrystallized cores acquired a "bird's wing" profile atypical for zircon. When the fluid lost its reactivity, the main part of the zircon grain crystallized, typical of granulite zircon. This zircon population is less enriched in incompatible element than the cores are. The horizontal pattern of HREE distribution is consistently repeated, which indicates the co-crystallization of zircon and garnet. The estimated crystallization temperature of the main part of zircon varies in a narrow range of 800–830°C. All zircon domains in the Wetherill concordia diagram form a single trend with a zero lower intercept and an upper intercept confirmed by concordant cluster with an age around 1920–1930 Ma. This value corresponds to the age of regional Paleoproterozoic granulite metamorphism. A unique feature of zircon from the Khapchan gneisses is that its cores did not retain the age marks of the protolith, but were completely reset during metamorphism both in terms of the U-Pb system and the trace element composition, which can be explained by the extremely high intensity of fluid impact during the granulite facies metamorphism superimposed on the rocks of the Khapchan terrane of the Anabar Shield. [ABSTRACT FROM AUTHOR]

The results of detailed petrological studies of mafic granulites from the Yubileinaya (Alakit-Markha field) and Novinka (Upper–Muna field) kimberlite pipes, where retrograde metamorphic P–T paths were reconstructed for the first time using mineral geothermobarometry, are provided. These P–T paths demonstrate subisobaric transition of the rocks from the P–T conditions of low-grade granulite facies to low-grade amphibolite facies at the depth of the middle crust. It was found that the compositions of garnet, clinopyroxene, and orthopyroxene depend on the adjacent mineral, reflecting the different closure temperatures of the exchange mineral reactions. The higher temperatures are determined using a two-pyroxene geothermometer, while the lower ones are found by application of garnet–clinopyroxene and garnet–orthopyroxene geothermometers. Phase equilibria modeling showed the thermodynamic conditions of the low-grade amphibolite facies: 540°C, 0.76 GPa, lgfO2 = QFM + 1.7 (Yubileinaya pipe); 530°C, 0.72 GPa, lgfO2 = QFM + 2.2 (Novinka pipe). The stability of the granulite paragenesis of garnet + clinopyroxene + orthopyroxene + plagioclase under such P–T conditions is a poorly known phenomenon reflecting a deficit of aqueous fluid during the crystallization of gabbroids and their subsequent cooling in the deep segments of cratons. [ABSTRACT FROM AUTHOR]

Geological examples of the development of thermal dome structures in the Svecofennian belt demonstrate the relationship between plutonic and metamorphic events and metamorphic strengthening towards the core parts of the structures. The corresponding 2D geological model has been created to make a quantitative assessment of the effect of mantle magmas temperature at the base of the crust and the formation of the diapiric cores surrounded by high-temperature areas with a degree of granulite facies metamorphism. Modeling shows that there is a possibility of melting of the lower crust in the presence of a water fluid under the influence of mantle magmas. After melting, there occurs an ascent of partially molten material towards the upper crustal levels. An absorbed aqueous fluid changes to hydrous melt, thus lowering its viscosity and density. The ascending height of high-temperature cores is determined by the depth of viscous-to-elastoplastic transition in the crustal matter rheology. These materials ascend to upper levels in a partially molten state in the process of overthrusting due to "collisional" tectonics.

The Diwani hills are located SE of Balaram–Abu Road in the Banaskantha district of north Gujarat. The crystalline rocks of the Diwani hill area are a diverse assemblage of Precambrian metamorphic and igneous rocks. These rocks are petrologically more complex and date back to the Aravallis or earlier. The mineralogical assemblages such as grt–sp–opx–qz of these rocks indicate their origin in anhydrous or dry conditions, implying metamorphism under pyroxene granulite facies. These granulitic rocks were subjected to Delhi orogenic deformation and were later intruded by the Erinpura granite. Textural and microstructural relationships, mineral chemistry, P – T – X pseudosection modelling and the oxidation state of pelitic granulites from the Diwani hill area of north Gujarat are all part of the current approach. The winTWQ program and pseudosection modelling in the NCKFMASHTO model system utilizing Perple_X software were used to restrict the P – T evolution of these pelitic granulites. The unification of these estimates shows that the pelitic granulites reached their pressure and temperature maxima at 8.6 kbar and 770 °C, respectively. The oxygen fugacity (log f O2) versus temperature computations at 6.2 kbar revealed log f O2– T values of −13.0 and 765 °C, respectively. The electron microprobe dating of monazite grains separated from the granulites of the Diwani hills yields ages ranging from 769 Ma to 855 Ma. The electron microprobe dating presented here from the Diwani hills provides evidence for a Neoproterozoic (Tonian) metamorphic event in the Aravalli–Delhi Mobile Belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coeval TTG and sanukitoid magmatism between 2.22 and 2.06 Ga. • Subduction setting between 2.22 and 2.06 Ga is similar to modern plate tectonics. • Arc migration revealed by OIB-type and E-MORB magmatism at ca. 2.15–2.14 Ga. Transitioning tectonic regimes from stagnant lid to plate tectonic models is still challenging. This tectonic transition appears to be diachronic in different old cratonic blocks worldwide. One key point to address tectonic models in early Earth is the appearance of the TTG-sanukitoid associations, which are interpreted as the products of melting oceanic slabs and melting of the hydrated mantle wedge in supra subduction zones. Although typical of the Archean, this association persists until the Paleoproterozoic in some cratonic remnants of South America. The Minas-Bahia Orogen (MBO) is one of the most extensive Paleoproterozoic belts of Brazil, cropping out in the São Francisco Craton but also as reworked thrust slices within surrounding Neoproterozoic belts. Here, we explore the southern part of MBO, bringing new geochemical, U-Pb zircon geochronology (LA-ICP-MS) and Nd and Sr isotopic data of the Juiz de Fora Complex that constitutes the external magmatic arc system of this Siderian to Orosirian orogen. Granodioritic to tonalitic orthogranulites with TTG geochemical signatures, crystallization ages of ca. 2.21 and 2.14 Ga, with positive εNd i (+2.9 to + 5.9) and 87Sr/86Sr i ratios between 0.7022 and 0.7045; Quartz-dioritic to granodioritic orthogranulites with sanukitoid composition, displaying crystallization ages between ca. 2.21 and 2.18 Ga, with near-chondritic εNd i values of −2.43 to + 0.39, and 87Sr/86Sr i ratios between 0.7076 and 0.7179. Integrating the new data with previously published analyses allows us to envisage a comprehensive tectonic evolution model starting in an intra-oceanic setting and progressively evolving to a continental magmatic arc environment along the Rhyacian period. Integrated geochronology data indicates coeval and continuous generation of TTG and sanukitoid magmas for 160 Myr. Initially, with more juvenile contribution (ca. 2.22–2.15 Ga), that evolves progressively to a more mature stage (2.15––2.06 Ga). Additionally, two groups of mafic rocks, with ages of ca. 2.16 (OIB-like) and ca. 2.14 Ga (E-MORB), fill the gap between these two stages and possibly reflect arc migration and upwelling of the asthenosphere. Finally, data suggests the operation of plate tectonic processes since the Rhyacian, within this accretionary segment of the MBO, that ultimately resulted in the building of the São Francisco Paleocontinent. [ABSTRACT FROM AUTHOR]

The composition and interrelations of oxides (minerals of the spinel supergroup, corundum, ilmenite, rutile) and silicates (garnet, sillimanite, orthopyroxene, cordierite) are studied in metapelitic granulites of the Bunger Hills. It is shown that the Fe–Mg–Zn spinels (XSpl 0.17–0.52) from the matrix and inclusions in garnet are depleted in Cr and, by the Zn content, are subdivided into two groups: Zn-poor (<3 wt % ZnO) and Zn-bearing (7–20 wt % ZnO) spinels, which belong to intermediate members of the hercynite–gahnite series. The mutual aggregates of hercynite (including Zn-poor) and quartz are observed. In addition to the individual grains in the matrix, the Zn-bearing spinels (Zn‑bearing hercynite and gahnite with up to 30 wt % ZnO) form inclusions in ilmenite and rutile. The spinel grains are associated with subparallel corundum–magnetite–ilmenite intergrowths, which formed as a result of exsolution of a high-temperature titanomagnetite solid solution, as well as ilmenite with rutile lamellae, which probably originated after the decomposition of a high-temperature Fe–Ti phase (armalcolite). An intriguing feature of the mineral composition of the studied granulites is related to the presence of the flame-like exsolutions of Ti-bearing magnetite and ulvöspinel (XUsp 0.55–0.78), which occur as regular intergrowths with ilmenite, corundum, and acicular rutile. The calculated temperatures of the Usp–Ilm equilibrium are 950–1250°C. Ulvöspinel is associated with orthopyroxene containing 7–9 wt % Al2O3, the temperature of crystallization of which could reach 930–1010°C according to a Grt–Opx thermobarometry. The clockwise P–T path of metamorphism, which relies on the results of mineral thermobarometry and isochemical phase diagram modeling, demonstrates a synchronous increase in temperature and pressure up to the peak values (T of >1000°C, P of ~10 kbar) at the prograde stage and isothermal decompression up to 6–7 kbar and further isobaric cooling at the retrograde stage. [ABSTRACT FROM AUTHOR]

The aegirine end-member (NaFe3+Si2O6) in clinopyroxenes resulted from incorporation of Fe3+ into the mineral structure. Its presence affects the accuracy of reconstruction of the P-T conditions in the high-grade metamorphic rocks and allows the evaluation of the redox conditions of their formation. The content of this end-member in clinopyroxenes is usually estimated using crystal chemical recalculations of microprobe analyses. However, in some publications on eclogites, the comparison of microprobe-based recalculations with Mössbauer data revealed significant difference between the measured and calculated Fe3+/ΣFe ratios, which can significantly affect the results of geothermometry. This paper presents the results of the Mössbauer spectroscopy measurements of clinopyroxene fractions separated from three samples of garnet–clinopyroxene granulites from the Udachnaya kimberlite pipe. The ratios Fe3+/ΣFe = 0.22–0.26 measured in the clinopyroxenes correspond to 6–10 mol % aegirine. These estimates are in good agreement with the values obtained for the same clinopyroxenes by the recalculation of microprobe analyses using the charge balance method. Following this conclusion, we believe that crystal chemical recalculations of microprobe analyzes of clinopyroxenes from non-eclogitic rocks make it possible to correctly estimate the Fe3+ content in them. Similar recalculation of microprobe analyses of clinopyroxenes in crustal xenoliths from other localities, as well as from ferrobasalts of the continental flood basalts provinces, ferrodolerite dikes, and gabbroid xenoliths (similar in bulk chemical composition to many lower–middle crustal xenoliths) revealed significant amounts of previously unaccounted aegirine (up to 13 and 4–9 mol %, respectively), which holds the potential for deciphering redox conditions in many rocks. [ABSTRACT FROM AUTHOR]

Lenses of eclogites (the Tulepsai complex) that formed at the peak of metamorphism at P = 15 kbar and T = 700–750°C and experienced decompression at 12 kbar (granulite-facies metamorphism) are located among the amphibolite sequences in the Eastern Mugodzhar Zone. The insignificant difference between the age of zircon cores, which, we believe, formed under the conditions of the eclogite-facies metamorphism (374 ± 4 Ma) at depths of 50–60 km (?) and the age of their rims (372 ± 6 Ma) formed during the isothermal decrease in pressure up to 12 kbar (25–35 km?) may indicate a rapid uplift of eclogites from considerable depths. Rutile extracted from eclogites yields a U–Pb age at 360 ± 2 Ma and reflects a later stage of rock transformation at 630–690 ± 40°C. The Maksyutov eclogite–glaucophane–schist and Tulepsai complexes are structural analogs of similar age and compose the lower allochthons on different branches of the Magnitogorsk synform. The complexes were formed in a similar geodynamic setting at the arc–continent collision. [ABSTRACT FROM AUTHOR]

The Lewisian Complex in northwest Scotland presents a record of the transition from the Neo-Archean to the Paleoproterozoic. However, this record is complicated by a long and varied history after peak metamorphism that has erased and/or partially reset much of the early history of the rocks. Such overprinting is a common feature of Archean granulites and poses a substantial problem when trying to understand the tectonic processes that were active prior to the onset of modern plate tectonics. By combining careful petrography with phase diagram modeling and a range of exchange thermometers we obtain the peak and retrograde temperature history of the Lewisian Complex from a single, well-preserved, representative sample of garnet-bearing mafic granulite. We present the application of high-resolution electron probe microanalysis (HR-EPMA) to characterize sub-micrometer orthopyroxene exsolution lamellae in clinopyroxene. We discuss ways to mitigate issues associated with HR-EPMA including surface contamination, beam drift, standards, and the need to correct for secondary fluorescence effects. The resulting compositions from our HR-EPMA analyses provide an independent measure of the retrograde temperature conditions and can also be used to back-calculate the compositions of clinopyroxene in the peak assemblage. We obtain peak metamorphic conditions for the Lewisian of >11 kbar and >1025 °C, and constrain subsequent metamorphic overprints to 850 °C (Grt-Cpx), 590 °C (Opx-Cpx), and 460 °C (Mag-Ilm). These peak and retrograde temperatures span the range of those found in the literature. Whereas recent phase equilibrium studies assume equilibrium among all preserved high-T minerals, this study considers microstructural and mineral-chemical evidence for corona formation that reflects post-peak decompression with partial equilibration at ~850 °C, as recognized in some earlier studies. [ABSTRACT FROM AUTHOR]

• Rutile U-Pb ages from granulites of south India cluster between 422 to 458 Ma and estimates cooling rates of 2–6 °C/Ma. • The terrane has undergone slow-cooling subsequent to regional scale metamorphism. • Calculated cooling rates from other East Gondwanan terranes (≤7 °C/Ma) suggest similar cooling history. • The terranes underwent coeval exhumation preferably by surface erosion. The Precambrian Southern Granulite Terrane of south India figures prominently in the East African collisional orogen, linked to the assembly of the East Gondwana supercontinent along with Sri Lanka, Madagascar, Antarctica, and Africa. While the timing of this collision and associated magmatic-metamorphic processes are well constrained, the mechanisms governing the cooling and exhumation of these terranes remain uncertain. This study focuses on U-Pb rutile ages derived from granulites in the Southern Granulite Terrane and attempts to extract the cooling history of the terrane. Our new U-Pb rutile ages cluster between 422 to 458 Ma, postdating regional metamorphism and indicating an extended cooling period of ∼ 35 Ma whereas trace element signatures suggest their formation during granulite facies metamorphism with temperatures reaching up to ultrahigh-temperature conditions. Calculated cooling rates using these rutile U-Pb ages range between 2–6 °C/Ma similar to the cooling rate of ≤ 7 °C/Ma from other East Gondwanan terranes. Based on these results it is proposed that the coeval exhumation of these terranes was assisted by surface erosion after the final assembly of the East Gondwana supercontinent. [ABSTRACT FROM AUTHOR]

In this study, we present evidence for the stable coexistence of sapphirine + quartz and the compositional characteristics of the sapphirine-bearing granulites from Kothuru in the Eastern Ghats Mobile Belt (EGMB), India. The study area is an integral part of the Precambrian terrane in the western part of EGMB and is characterized by the granulite facies rocks comprising mainly of pelitic granulites such as charnockites, enderbites, leptynites, khondalites and gneisses, and sapphirine-spinel-quartz-bearing rocks. The chemistry of the minerals present in the assemblage has been examined using the electron probe micro analyser to infer their occurrence and distribution in various reaction textures observed during the petrographic study. The peak and post-peak history of the sapphirine-bearing granulites of Kothuru section have been constrained in the NCKFMASHTO system showing decompressional P-T path of high-grade metamorphic rocks through the intersection of the isopleth contours of various mineral phases present. The proposed P-T path with a steep isothermal decompression retrograde trajectory may be attributed to the over-thrust processes. The results obtained from the petrographic study of the mineral assemblages along with their textural relationship, mineral chemistry, especially Fe3+/FeTotal ratio and pseudosection modelling reveal that the studied segment has arrested promising ultra-high temperature metamorphic signatures and is tectonically distinct from those reported in the adjacent areas. [ABSTRACT FROM AUTHOR]

The structure of the Central Asian Orogenic Belt (CAOB) is determined by a combination of Neoproterozoic and Paleozoic paleoceanic and island-arc complexes and blocks with Precambrian basement. The Dzabkhan terrane, one of the largest blocks in the central segment of the CAOB, was initially considered as a microcontinent with an Early Precambrian basement. It included the Baidarik, Tarbagatai, Songino and proper Dzabkhan terranes, which are attributed to the Early Precambrian "cratonic" terranes. At present, the Early Precambrian complexes were established only in the northwestern Baidarik terrane and the Ider complex of the Tarbagatai terrane. Their folded structure was formed at ~ 1855 Ma, which is typical of the basement of ancient Northern Eurasia craton. The Early Proterozoic charnockitoids of the Baidarik terrane with an age of 1854 ± 5 Ma contain granulite-facies xenoliths. Previously, these xenoliths were considered as belonging to the Bumbuger Complex, which hosts the charnockitoid massif. However, zircons from two-pyroxene granulite xenoliths yielded an age of 1850 ± 4 Ma, which almost coincided with the age of 1854 ± 5 Ma determined for host charnockites. These data showed that charnockitoids generated at the lower crustal depth brought up the fragments of the Early Proterozoic lower crust to the amphibolite-facies metamorphic zone. The obtained new age data on zircon (2413 ± 12 Ma) extracted from two-pyroxene quartz diorite (enderbite) xenolith in these charnockitoids provided new insight into Early Proterozoic granulite facies metamorphism, which reflects the stages of the lower crustal growth in the geological evolution of the Early Precambrian complexes of the Baidarik terrane. [ABSTRACT FROM AUTHOR]

• Zircons from studded crustal xenoliths do not record the age peak at 1.9 Ga. • Sodalite was found in mafic granulite xenoliths of the Yakutian kimberlite province. • Superplumes triggered the crustal growth and reworking at 2.7 and 1.9 Ga. • There is no collision zone between the Daldyn and Markha terranes. The tectonic framework of the Siberian craton is still under debate. It is generally assumed that the Markha and Daldyn terranes collided at 2.2–2.1 Ga and the final assembly of the Siberian craton occurred at 1.9–1.8 Ga. However, previous study on zircons from xenoliths of the Zapolyarnaya pipe, which is located in the Upper Muna kimberlite field and close to the boundary between the Markha and Daldyn terranes, do not show tectonothermal evidence younger than 2.7 Ga. To clarify the tectonothermal evolution of the Siberian craton, we present U-Pb ages and Hf isotope data of zircons from crustal xenoliths in the Novinka and Komsomolskaya Magnitnaya kimberlite pipes in the Upper Muna field. The zircon ages confirm only one major tectonothermal event at 2.7 Ga in the Upper Muna field, which doubts the existence of the collision zone between the Markha and Daldyn terranes. The middle-lower crust beneath the Upper Muna field is mainly composed of mafic and intermediate granulites and experienced long-term cooling. The negative values of ε Hf (2.7) suggests ignorable addition of juvenile component during partial melting of the Paleoarchean crust at 2.7 Ga. Compared with crustal xenoliths from other kimberlite pipes in the Yakutian diamondiferous province, the crust of the Anabar province shows vertical and lateral heterogeneity and the absence of a relationship between the crustal reworking degree and the main collision zones. We propose that the widespread 2.7 and 1.9 Ga tectonothermal events in the Anabar tectonic province were associated with the episodic rise of superplumes, which not only caused the crustal growth and reworking but also facilitated collision and amalgamation of terranes. [ABSTRACT FROM AUTHOR]

Granulite complex on the left side of the Bol. Kuonamka River, below the mouth of the Khapchan River, is composed of melanocratic and mesocratic orthopyroxene–clinopyroxene crystalline schists and leucocratic orthopyroxene and orthopyroxene–clinopyroxene plagiogneisses. The granulites formed after mafic to felsic volcanoplutonic rocks with rare sedimentary interlayers. In terms of chemical composition, the mafic and ultramafic rocks correspond to pyroxenites, gabbronorites, and gabbro-diorites of the tholeiite series. The plagioschists and plagiogneisses were formed after rocks similar to diorites, tonalities, and trondhjemites or their volcanic analogs, and are distinguished by increased contents of Ba, Zr, Y, REE, Nb, and Ta. The concordant U-Pb age of zircon from the diorite protolith of orthopyroxene–clinopyroxene plagioschists is 2095 ± 10 Ma. The Lu-Hf isotopic composition of the zircon (εHf (T) = 6.5–12, THf(DM) = 1.98–2.22 Ga) indicates the correspondence of its source to the Paleoproterozoic depleted mantle. Two-pyroxene plagiogneisses with a concordant U-Pb zircon age of 2030 ± 17 Ma were formed after tonalites of the calc-alkaline series. They are characterized by well-pronounced negative Ti, Nb, Ta, P anomalies characteristic of subduction magmatism. All studied rocks of the Khapchan Belt have positive εNd(T) values from +2.3 to +4.2 and are interpreted as a juvenile suprasubduction complex. It is assumed that the subduction of oceanic crust of this age is associated with the formation of eclogitic diamond, which was noted earlier and widespread in placer deposits in the northeastern Siberian platform. [ABSTRACT FROM AUTHOR]

Abstract The area is located at the northern boundary of the Guaxupé Complex, which corresponds to the northern domain of the Socorro-Guaxupé Nappe, in the Southern Brasília Orogen, close to the Varginha Shear Zone. This study integrates petrography, mineral chemistry, optimized geothermobarometry, and trace elements thermometry data, aiming to define and characterize the metamorphic conditions and the P-T path of the granulitic rocks from the northern portion of the Guaxupé Complex. In the area, the Guaxupé Complex consists predominantly of ortho-derived rocks represented by granulitic gneisses (orthopyroxene gneisses) of felsic to mafic composition with clinopyroxene, garnet, amphibole, biotite, and rare rutile. The calculated pressure and temperature conditions record metamorphic peak around 1,078°C and 14.8 kbar, compatible with ultra-high temperature metamorphism conditions, marked by grt + cpx + opx + pl ± qtz ± rt mineral assemblages, and granulite facies re-equilibration in the sillimanite stability field at P-T conditions of 930 to 800°C and 13.5 to 11.0 kbar. The results are compatible with deeper portions of the lower crust involved in a continental collision and suggest a clockwise P-T path, typical of crustal thickening zones, followed by near-isothermal decompression during tectonic exhumation.

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The presence of nanogranitoids (crystallized melt inclusions showing a granitic s.l. composition) in regionally metamorphosed migmatitic and granulitic terranes was documented for the first time in 2009. This important finding represented a hallmark event for crustal petrologists, demonstrating that the pristine composition of anatectic melts may be preserved and recovered in small objects hosted in peritectic minerals of high-grade metamorphic rocks. Many further occurrences were documented in rocks worldwide, from diverse geodynamic settings, from the Archean to Miocene, and these inclusions turned out to have diverse composition (from silicatic to carbonatitic). Therefore, we propose "nanorocks" as a comprehensive name for these crystallized melt inclusions. In the last decade, many studies demonstrated their utility in characterizing mechanisms of melting and in tracking crustal magma evolution. Although scholars are now able to easily recognize nanorocks in high-grade metamorphic rocks, only a few research groups remelt them by means of experimental devices because of a time-consuming preparation. However, when cutting-edge techniques are applied in addition to more routine ones, nanorocks do open new perspectives in crustal petrology. [ABSTRACT FROM AUTHOR]

The present paper presents new U–Pb and Sm–Nd age data obtained for granulites of the Cheremshanskaya Unit enclosing metamorphosed volcano-sedimentary sulfide ores, in which sulfur isotope mass-independent fractionation (MIF–S) was established. Zircons from orthotectites that cut hosted paragranulites yielded aconcordant U–Pb age of 1866.8 ± 7.6 Ma, reflecting the final stage of granulite metamorphism. The model age (ТND (DM)) of ~3.0 Ga obtained for graphite–sulfide–cordierite (±Bt) and garnet–biotite–orthopyroxene paragneisses indicates that the protolith of sedimentary rocks was formed in the Mesoarchaean. As evidenced from various sources, the Sm–Nd isotopic characteristics of orthotectites differ from those of paragneisses. [ABSTRACT FROM AUTHOR]

In the northern part of the Anabar Shield, orthopyroxene plagiogneisses of the granulite Daldyn Group host lenses of mafic rocks surrounded by melanocratic rims. According to their chemical composition, the mafic rocks correspond to subalkaline gabbro, the plagiogneisses correspond to granodiorites contaminated with mafic material, and the rims are diorites. The orthopyroxene plagiogneisses of granodiorite composition have 147Sm/144Nd = 0.1097, εNd(Т) = 1.6, TNd(DM) = 3.47 Ga and are metamorphosed anatectic granitoids with an age of 3.34 Ga. The mafic rocks have high Zr, Th, and Pb contents, are enriched in REE (ΣREE = 636 ppm), with a high degree of fractionation [(La/Yb)N = 17.73] and a well-defined Eu minimum (Eu/Eu* = 0.51), and have 147Sm/144Nd = 0.099, εNd(Т) = 1.4 and TNd(DM) = 3.65 Ga. It is assumed that these rocks crystallized from melt derived from an enriched mantle (plume) source. Based on U–Pb (SHRIMP-II) dating of 50 zircon grains from the mafic rocks, a group of grains with concordant ages from 3567 to 1939 Ma was distinguished, along with a large number of discordant values. Multiple measurements in zircon grains with discordant age values make it possible to identify seven grains of Eoarchean age, with upper intercepts of the discordia corresponding to 3987 ± 71 to 3599 ± 33 Ma. The Lu–Hf systematics of 14 zircon grains is characterized by εHf(T) = +3.7 and by close values of THf(DM) = 3.95 and = 3.93 Ga (3.99 Ga for the oldest zircon). The Paleoarchean (3.57 Ga) zircons are characterized by negative values of εHf(T) = –5.3 and –6.8, THf(DM) = 3.92–3.98 Ga, and = 4.14–4.24 Ga, which indicate recycling of the preexisting Eoarchean and Hadean continental crust. The younger zircon (3287–2410 Ma) was also formed when the preexisting crust was recycled. [ABSTRACT FROM AUTHOR]

Quartzites and paragneisses of the Archean granulite series of the Anabar Shield (Siberian Craton, Russia) are described geochemically. The Sm-Nd isotope systematics of the rocks and the U-Pb age (SHRIMP II) and geochemistry of zircons from quartzites and paragneisses are studied. Newly formed zircons from quartzites display geochemical characteristics of the magmatic type and were produced by rock anatexis upon granulite-facies metamorphism. The Paleoproterozoic age of the latest detrital zircons, 2250 ± 24 Ma, constrains the maximum age of sedimentary rock deposition. The anatectic rims around detrital zircons were formed ca. 2000 ± 9 Ma ago. The time of deposition of the sedimentary protolith of gneisses and quartzites falls within the age interval of the above-mentioned dates and is tentatively accepted as 2.1 Ga. The presence of Paleoproterozoic metasedimentary rocks in the Daldyn Group implies the tectonic heterogeneity of the series and the existence of Paleoproterozoic rock bodies among the predominant Archean rock sequences.

Type-chemical features of high-titanium magnezium-ferruginous micas of granulites, mafite-ultramafites, alkaline rocks, and carbonatites are considered. It is shown that genetically high-titanium micas are connected only with alkaline rocks and carbonatites. Chemical composition of high-titanium phlogopite-annite can be used at an assessment of Zr-Nb mineralization of metamorphic and magmatic rocks.

Although zircon U-Pb geochronometer has been widely used for dating metamorphism in moderate- to high-grade metamorphic rocks, it is still difficult to link the zircon U-Pb age to pressure and temperature (P-T) conditions. In this study, zircon trace elements and Hf isotopes and REE partitioning between zircon and garnet are adopted to track the formation condition of zircon in the granulites from North Tongbai Orogen, Central China. Combined with previous metamorphic P-T path results, a quantitative integrated anticlockwise P-T-t path was established for Tongbai granulites. These granulites recorded an early low-P heating followed by a dramatic pressure increase. Evidence for the prograde history (M1) is provided by cordierite, orthopyroxene and biotite inclusions in garnet. The prograde metamorphism occurred at around 443±3 Ma, with P-T conditions of ca. 730-820 °C and <6 kbar. The peak metamorphic (M2) condition is >920 °C and 8.5-10 kbar and the peak metamorphism age is ca. 432±4 Ma. At around 419 Ma, the granulites suffered an amphibolite-facies retrograde metamorphism (M3), represented by the replacement of garnet by biotite and plagioclase, and clinopyroxene by amphibole, with metamorphic condition of ca. 700 °C and ca. 7 kbar. The last retrograde metamorphism (M4) is a greenschist-facies overprint with an age of ca. 404 Ma. It is concluded that the metamorphism of Tongbai granulite lasted for more than 40 Ma, including a stage of more than 20 Ma granulite-facies metamorphism. The prolonged granulite-facies metamorphism resulted from the continuous northward subduction of the Shangdan oceanic crust beneath the North Qinling terrane. [ABSTRACT FROM AUTHOR]

The data on the distribution of rare earth elements (REE) in peridotites - abyssal (oceanic) and orogenic (continental), in mafic granulites of the base of the continent crust and gabbro of the base of the oceanic crust, in the oceans (MORB) and continental flood basalts (CFB) are compared. Two types of komatiites - Archean aluminum depleted komatiites (ADK) and Paleoproterozoic Aluminum Undepleted (ANK) have different characteristics of the content and distribution of REE: ADK have a chondritic distribution of REE; ANK-distribution with depletion of light rare earth elements (LREE). Such differences are inherited from the ANK and ADK in continental and oceanic rock groups. Given the early Precambrian formation of the ADK and the ANK, it can be assumed that the differences in the distribution of REE are inherited by the post-Cambrian igneous rocks of the continents and oceans from the early Precambrian. As a consequence, the spatial location of the continents and oceans could in that case remain stable (fixed), beginning with the early Precambrian. [ABSTRACT FROM AUTHOR]

The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km² ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granuliteand amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data. [ABSTRACT FROM AUTHOR]

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Evidence is presented for the localized melting of cordierite–orthopyroxene–biotite metapelites within the Petronella shear zone in the Southern Marginal Zone of the Limpopo Belt of Southern Africa. This process is expressed by the formation of centimetre-scale, K-feldspar-rich, garnet–orthopyroxene-bearing leucosome patches. Structural data indicate that the leucosomes formed after regional peak metamorphic and deformational events, but were syn- to late tectonic with respect to the shear fabric of the host metapelites. Phase equilibria modelling using the PERPLE_X software shows that the leucosomes were produced via fluid-deficient partial melting of the metapelites at temperatures above 900°C and pressures of 6·0–6·5 kbar. Melting reactions involving mainly biotite, plagioclase, quartz and accessory phases (including sulfides) produced peritectic Cr-enriched orthopyroxene, as well as Sc, Y, Cr, P-enriched garnet along with the potassium-rich melt. The melt was segregated around the peritectic minerals into the leucosomes. During near-isobaric cooling, the segregated melts crystallized to produce abundant K-feldspar and Sc, Y, Cr and P-poorer garnet inside the leucosome patches. Partial melt loss from the patches on cooling assisted with the preservation of anhydrous assemblages inside the patches and with re-hydration of the surrounding melanosome, with extensive formation of biotite + quartz±sillimanite assemblages after orthopyroxene and cordierite, as well as late Sc, Y, Cr, and P-free garnet (+sillimanite + quartz) at temperatures down to < 600°C. Field and P–T data suggest a link between the localized melting of metapelites and trondhjemite intrusions that were syn- to late-tectonically injected into the Petronella shear-zone at about 2·67 Ga after the peak metamorphic and deformational event in the Southern Marginal Zone. This link is proven by U–Pb ages for monazites (a weighted average 207Pb/235U age of 2666 ± 4 Ma) from the leucosome patches. The trondhjemites provided additional heat and, probably, also a small amount of fluids, for the leucosome formation. [ABSTRACT FROM AUTHOR]

In this study, we investigate the possible record of a Late Mesoproterozoic paired metamorphic belt in the Aravalli-Delhi Mobile Belt (ADMB), NW India using a suite of supracrustal and metaigneous granulites from the Pilwa-Chinwali granulite terrain at the north-western margin of the ADMB. Using metamorphic reaction textures, mineral chemistry, metamorphic reaction history, geothermobarometric computations and electron microprobe dating of monazite in 5 samples of pelitic granulite, leptynite gneiss, enderbite and charnockite, we have deduced a medium-pressure granulite facies metamorphism ( P between 4.9 and 6.8 kbar, T > 760–815 °C) along a heating-cooling, counterclockwise P-T path between 1.09 and 1.01 Ga. When collated with published metamorphic and chronological constraints and geological settings of the adjoining crustal domains of the ADMB, these findings provide new insights into the developments of two tectonic domains of contrasting thermal gradients at ca. 1.0 Ga, consistent with metamorphic transformations in tectonically thickened middle-lower crustal sections during continental collision to continental subduction and in the root zones of spatially adjacent island arc, as part of the Rodinia supercontinent assembly event. [ABSTRACT FROM AUTHOR]

The Precambrian basement in the region of Cariré, northeast Ceará Central Domain, NE Brazil, comprises essentially dioritic gneisses and granodiorites formed under high-grade metamorphism conditions. The granulites occur frequently as metric bodies or as boudins in mylonitic/cataclastic orthogneiss matrix, within shear zones related to Transbrasiliano Lineament. Geological mapping in this region confirmed a mylonitic foliation trending ∼ N20E and sub vertical dip (∼70°) towards NW or SE. Hornblende, biotite and orthopyroxene crystals define the lineation of the main extensional direction, with sub horizontal S-SW plunge (∼5-10°). Many outcrops show a large variety of structural elements linked to ductile deformation and typical structural elements representing the transition from ductile to brittle domains. Felsic and mafic dykes of various dimensions and both ductilely and brittlely deformed are found frequently. Analysis of kinematic indicators in the lineament shows both dextral and sinistral shear sense, although ductile dextral shear is more frequent. Structures developed in shallower crustal conditions, including micro-shear, tension gashes and faults trending N12E-N20E, show sinistral kinematics. Zircon crystals obtained from felsic dykes, dislocated by faults parallel to the regional trend of the Transbrasiliano Lineament, display four groups of concordant ages, the most recent of which is ca . 460 Ma. Our data suggest that throughout its complex history, the Transbrasiliano Lineament has been reactivated under brittle conditions from the Upper Ordovician onwards. [ABSTRACT FROM AUTHOR]

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810–860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342–337 Ma which corresponds to a fast, nearly isobaric cooling. [ABSTRACT FROM AUTHOR]

Most of granulite terrains worldwide are characterized by large mean grain sizes of 1 mm or more. An important exception are the high-pressure felsic granulites in the Bohemian Massif, the European Variscan belt. There, recrystallization of original coarse-grained ternary feldspar led to formation of a fine-grained (∼100 μm) mixed matrix dominated by plagioclase and K-feldspar. This change occurred at temperatures of ∼850 °C and was probably caused by chemically induced decomposition related to slight cooling and enhanced by deformation during continental collision. The resulting microstructure shows indications of diffusion creep assisted by melt-enhanced grain-boundary sliding. Further on, minor coarsening occurred associated with deformation by dislocation creep and aggregation of mineral phases. Using a thermodynamics-based model of grain size evolution we show that stability of the fine-grained microstructure crucially depends on Zener pinning in the two-phase mineral matrix. Pinning efficiently hinders grain growth, and the small grain size that resulted from the ternary feldspar decomposition can be stable even at high temperatures. The late switch from the grain-size-sensitive creep to dislocation creep is rather difficult to explain by temperature and strain rate (or stress) changes only. However, a simple incorporation of melt solidification can successfully simulate this behavior. Alternatively, the switch and the associated grain size growth can be related to mineral phase aggregation at lower pressure–temperature conditions resulting into a decrease of pinning efficiency. This study suggests that the fine grain size of the Bohemian granulites, in contrast to the common coarse-grained type, stems from abrupt recrystallization during the high-pressure high-temperature conditions, and pinning in the fine-grained matrix. Such a process may in some cases significantly and suddenly reduce the strength of the lower continental crust and allow for its efficient redistribution. [ABSTRACT FROM AUTHOR]

The Hf-Nd isotope systematics was used to determine the genesis of zircons from granulites of the Daldyn Group of the Anabar Shield. Obtained age of magmatic crystallization for biotite-hypersthene crystalline schists and garnet amphibolites agree with position of zircons within terrestrial array. Magmatic genesis of plagiogranite neosome under granulite conditions was established for leucocratic plagiogneisses. [ABSTRACT FROM AUTHOR]

The relative validity and closure temperature of the Zr-in-rutile thermometer for recording UHT metamorphism are process dependent and hotly debated. We present an integrated petrological approach to Zr-in-rutile thermometry including phase equilibrium (pseudosection) modelling in complex chemical systems with updated mineral a-X models and systematic in-situ microanalysis of rutile. This study is centred on high-pressure rutile bearing UHT granulites from Mt. Charles, Napier Complex, Antarctica. P–T phase equilibrium modelling of two garnet bearing granulites (samples 49677, 49701) constrains an overall post-peak near isobaric cooling (IBC) evolution for the Napier Complex at Mt. Charles; from ~ 14 kbar, 1100 °C with moderate decompression to ~ 11 kbar, 800–900 °C. Local hydration on cooling over this temperature range is recorded in a kyanite bearing granulite (sample 49688) with an inferred injection of aqueous fluid equivalent to up to 9 mol% H 2 O from T–MH 2 O modelling. Further late stage cooling to < 740 °C is recorded by voluminous retrograde mica growth and partial preservation of a ky-pl-kfs-bt-liq bearing equilibrium assemblage. Overall, Zr-in-rutile temperatures at 11 kbar (Tomkins et al., 2007) are reset to between 606 °C and 780 °C across all samples, with flat core–rim Zr concentration profiles in all rutiles. However, zircon precipitates as inclusions, needle exsolutions, or rods along rutile grain boundaries are recrystallised from rutiles in qz/fsp domains. Reintegrating the Zr-in-rutile concentration ‘lost’ via the recrystallisation of these zircon precipitates (e.g. Pape et al., 2016) can recover maximum concentrations of up to ~ 2.2 wt% and thus maximum peak temperatures of ~ 1149 °C at 11 kbar. Rutile Nb–Ta signatures and rounded rutile grains without zircon precipitates in hydrated mica domains in sample 49688 provide evidence for fluid-mediated mobility of Zr and Nb during retrograde cooling in hydrated lithologies. Aqueous fluid supplemented excess H 2 O liberated by melt crystallisation, interacting with rutile on cooling of sample 49688 to reset Zr-in-rutile temperatures (606–780 °C) at the Mt. Charles locality. The wide range of geochemical and petrological characteristics of Napier Complex rutile highlights that Zr-in-rutile reintegration and a broad petrological approach are required for successful interpretation of Zr-in-rutile geothermometry for long-lived regional UHT metamorphism. [ABSTRACT FROM AUTHOR]

The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km2 ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granulite- and amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data.

The Porto Nacional Complex in the northern portion of the Goiás Massif, in north-central Brazil, represents a Paleoproterozoic/Archean microcontinent reworked in the Neoproterozoic during the Brasiliano Cycle. This NE-SW-trending belt of high-grade metamorphic rocks consists, predominantly, of orthogranulites in addition to aluminous paragneisses that reached high-grade metamorphic conditions in the granulite facies (∼860 °C and 9 kbar). The zircon U–Pb geochronological results obtained on orthogranulite (enderbite) crystal cores yielded an age of 2.16 Ga, however, the crystal borders present lower values (2.09 Ga). These results represent, respectively, the age of igneous crystals of tonalitic protoliths, and high-grade metamorphism. The zircon crystals of another enderbite sample yielded lower values of about 2.09 Ga, reinforcing the interpretation of metamorphic zircons. The U–Pb geochronological results between 2.09 Ga and 2.10 Ga obtained on monazite from the aluminous paragneisses, coincide with the values obtained for enderbite metamorphic zircon crystals, allowing us to define the high-grade metamorphism age and the formation of igneous protoliths in the Rhyacian. This small age difference demonstrates the metamorphism role contemporary to the magmatism of the tonalitic protoliths of the Porto Nacional Complex, related to the Late-Transamazonian orogeny. The Hf-T DM C model ages suggest two crust formation episodes that gave rise to the following rocks: one from the Siderian (2.40–2.48 Ga) and another from the Neo-Mesoarchean (2.52–3.01 Ga). The positive petrogenetic parameters Ɛ Hf (t) (+3.9 to +5.2) evidence a mantle source derivation for the Siderian material, while the negative and positive petrogenetic parameters Ɛ Hf (t) (−4.6 to +3.3) indicate a mixture between crustal and juvenile material for the Neo-Mesoarchean material. These results allow us to disregard the proposed correlation between this high-grade metamorphic terrain with the Porangatu-Talismã Granulitic Belt, which occurs to the south of this region, whose thermo-tectonic evolution is related to the late Neoproterozoic. On the other hand, there are records of several other Rhyacian similar granulitic terrains, such as the granulites of the Bacajá and Tartarugal Grande in the Amazonian Craton, the Itabuna-Salvador-Curaçá Granulitic Belt in the São Francisco Craton, as well as in the Bakhuis Belt, in Suriname, and Limpopo Belt in the West African Craton. • Porto Nacional Complex represents a Rhyacian high-grade metamorphic terrene in Central-Brzil. • Zircon U–Pb geochronological of orthogranulites results on 2.16 Ga representing the age of igneous protoliths. • Monazite U–Pb from the aluminous paragneisses yielded 2.09–2.10 Ga representing the age of high-grade metamorphism. • Porto Nacional Complex represents an important accretion and continental collisions with collages in the Rhyacian (2.0–2.16 Ga). [ABSTRACT FROM AUTHOR]

The lower continental crust, representing up to 50% of the continental mass, is largely inaccessible, making its composition difficult to constrain. Previous composite models based on geophysical evidence and geochemical data of granulite terrains and xenoliths have proposed varying results, from a mafic, relatively refractory lower crust to an intermediate-felsic, more enriched composition. Here, we investigated the mineralogy and geochemistry of predominantly mafic granulite xenoliths from eastern Australia and the Kola Peninsula, Russia, using an in situ analytical approach that minimises host magma contamination. The resulting xenolith compositions are variably and often strongly depleted in most highly incompatible trace elements, including the heat-producing elements. These xenoliths represent an extremely refractory component of the lower continental crust, likely formed after high degrees of partial melting or crystallisation from a depleted source. A lower crust composed solely of this refractory endmember would be too exhausted in heat-producing elements to satisfy heat-flow constraints. However, a volumetrically significant component of the lower crust is this mafic and refractory material, combined with undifferentiated material and a felsic or metapelitic portion. Using geophysical constraints on proportions of refractory (55%), undepleted (38%) and enriched (7%) components, a new estimate for average lower continental crust that satisfies heat flow limits was calculated, including for elements such as Be, B, Cs, W and Tl, where previous estimates relied on very few data. Finally, we show that because much of the lower continental crust is so refractory and depleted in incompatible elements, it is unlikely to be a reservoir that can balance radiogenic isotope (unradiogenic Pb) and trace element ratios (e.g. Rb/Cs, Nb/Ta) for which bulk silicate Earth departs from chondritic ratios. • Granulite xenoliths are investigated to constrain the composition of the deep crust. • Most of the lower crust is extremely depleted in highly incompatible trace elements. • An updated compositional estimate for the lower crust is presented. • Deep crust has limited potential as a "hidden" reservoir for mass balance issues. • Only ancient delaminated deep crust can contribute significantly to the bulk Earth. [ABSTRACT FROM AUTHOR]

The migmatitic metapelites of the Lapland granulite belt (LGB) in the NE part of the Fennoscandian Shield represent an arc-related greywacke basin metamorphosed in the granulite facies. Detrital zircons from migmatitic metapelites are derived from 1.94 − 2.9 Ga old acid source rocks (U-Pb SIMS ages). The clustering of detrital zircon ages between 1.97 and 2.2 Ga is problematic, because abundant felsic crust of this age is absent in the shield. The metasediments are characterized by Sm-Nd model ages of ca. 2.3 Ga. A younger, 1905 − 1880 Ma population of homogeneous zircons was formed during regional metamorphism. The peak high-grade metamorphism took place at ~1900 Ma and the latest chronological record from subsequent decompression and cooling phase is from ca. 1870 Ma. The norite-enderbite series of the LGB represents arc-magmas, which were intruded into the metasediments at ~1920 − 1905 Ma ago according to zircon U-Pb ages and were probably an important heat source for metamorphism. Older, zoned zircon grains in a quartz norite vein, initial εNd values of 0 to +1 and the continuous spectrum of LILE enrichment in the enderbite-series probably reflect assimilation of metasediments by magmas. Monazite U-Pb ages of migmatitic metasediments in the range 1906 − 1910 ± 3 Ma overlap the late stage of enderbite intrusion and growth of early metamorphic zircons. Garnet-whole rock Sm-Nd ages from leucosomes in the range 1880 − 1886 ± 7 Ma are concurrent with the growth of the youngest metamorphic zircons and probably indicate the crystallization of leucosomes or the influence of a fluid liberated from them. Isotopic and petrologic data reveal that the evolution of Lapland Granulite belt from the erosion of source rocks to the generation of a sedimentary basin, its burial, metamorphism and exhumation took place within ca. 60 Ma.

High-temperature metamorphic rocks are the result of numerous chemical and physical processes that occur during a potentially long-lived thermal evolution. These rocks chart the sequence of events during an orogenic episode including heating, cooling, exhumation and melt interaction, all of which may be interpreted through the elemental and isotopic characteristics of accessory minerals such as zircon, monazite and rutile. Developments in imaging and in situ chemical analysis have resulted in an increasing amount of information being extracted from these accessory phases. The refractory nature of these minerals, combined with both their use as geochronometers and tracers of metamorphic mineral reactions, has made them the focus of many studies of granulite-facies terrains. In such studies the primary aim is often to determine the timing and conditions of the peak of metamorphism, and high-temperature metasedimentary rocks may seem ideal for this purpose. For example pelites typically contain an abundance of accessory minerals in a variety of bulk compositions, are melt-bearing, and may have endured extreme conditions that facilitate diffusion and chemical equilibrium. However complexities arise due to the heterogeneous nature of these rocks on all scales, driven by both the composition of the protolith and metamorphic differentiation. In additional to lithological heterogeneity, the closure temperatures for both radiogenic isotopes and chemical thermometers vary between different accessory minerals. This apparent complexity can be useful as it permits a wide range of temperature and time ( T – t ) information to be recovered from a single rock sample. In this review we cover: 1) characteristic internal textures of accessory minerals in high temperature rocks; 2) the interpretation of zircon and monazite age data in relation to high temperature processes; 3) rare earth element partitioning; 4) trace element thermometry; 5) the incorporation of accessory mineral growth into thermodynamic modeling; and 6) Hf isotopic signature of zircon overgrowths and its use in linking zircon into major metamorphic phase development. [ABSTRACT FROM AUTHOR]

The Pedra Dourada Granulite (PDG) occurs at the southeastern portion of the Araçuaí Belt, north of the town of Ponte Nova. It comprises bodies up to 45 km² inserted into amphibolite-facies gneisses of the Mantiqueira Complex. Motivated by the discrepancy of metamorphic grade with surrounding rocks, this paper presents results of the petrographic and geochemical investigation of the PDG. The unit is comprised of meta-igneous and metasedimentary rocks. Meta-igneous rocks dominate and include felsic granulites (biotite ± garnet-bearing and orthopyroxene-bearing) and subordinate mafic granulites. Metasedimentary rocks are aluminous granulites with Al-rich mineral assemblages (garnet, sillimanite, spinel). Geochemical data show that most of felsic protoliths are peraluminous rocks including granites, granodiorites and diorites of calc-alkaline character, chemically similar to granitoids of convergent tectonic settings. Mafic protoliths are metaluminous rocks comprised of gabbros and subordinate diorites of tholeiitic affinity, compositionally similar to plate margin basalts. Aluminous protoliths may be peraluminous pelitic rocks and wackes, analogous to sediments from convergent environments. The mineral assemblages indicate that these rocks were metamorphosed under medium-P granulite-facies conditions. Coronitic garnet textures suggest a near-isobaric cooling (IBC-path) after metamorphic peak. [ABSTRACT FROM AUTHOR]

The Palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Proterozoic terrains in the NE part of the Fennoscandian Shield concurrently with the accretion of Svecofennian arc complexes at ~1.9 Ga. The belt consists mainly of aluminous migmatitic metagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly into the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas. This is supported by structural and contact relations of metasediments and igneous rocks, and by the lack progressive metamorphic reaction textures in the igneous rock series. The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quartz assemblage at 750 − 850 °C and 5 − 8.5 kbar which lead to formation of a restitic palaeosome and peraluminous granitic melt in metapelites. Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pelitic rocks (650 °C) under the stability field of andalusite coexisting with potassium feldspar (2 − 3 kbar). Cooling was accompanied by the crystallization of the neosomes, often carrying aluminium-rich phases. Postmetamorphic duplexing of the LGB is clearly seen in the distribution of calculated PT conditions.

Highly restitic rocks from the Antananarivo Block in northern Madagascar are investigated in this study in order to unravel processes of HO-rich biotite formation in HT rocks. Polyphase metamorphism and melt migration occurred at 0.6 GPa and 850 °C. Biotite remains stable together with orthopyroxene and makes up to 45 vol% of the rock. In addition, three well-characterised and delimited microdomains having different textural, chemical and petrological characteristics are preserved. Thermodynamic models using the specific bulk compositions of the domains are in agreement with petrological observations. These rocks provide evidence that the lower crust may be strongly heterogeneous, locally associated to the formation of hydrous restites controlled by episodes of melt production and melt escape. This has significant consequences for understanding of the lower crust. [ABSTRACT FROM AUTHOR]

The Glenroy Complex consists of retrogressed monzodioritic granulites (Woodham Orthogneiss) and heterogeneous metasedimentary rocks (Davis Creek Paragneiss). U–Pb zircon dating shows that the Woodham Orthogneiss comprises rocks ranging in age from 121.8 to 126.6 Ma that are correlatives of the geochemically similar Western Fiordland Orthogneiss Worsley Pluton in northern Fiordland. Permian–Jurassic detrital zircon age peaks in the Davis Creek Paragneiss indicate a maximum depositional age of c. 227 Ma, suggesting correlation with George Sound Paragneiss in northern Fiordland and the paleo-Pacific Gondwana margin cover sequence. Metamorphism of the Davis Creek Paragneiss is constrained to 120.6 ± 0.9 Ma by U–Pb dating of low Th/U zircon overgrowths. The McKnee Intrusives were intruded in two discrete episodes at 225.0 ± 2.7 Ma and 137.8 ± 0.7 Ma which, together with their geochemistry, suggests correlation with northern Fiordland Late Triassic and Early Cretaceous Darran Suite plutons. The HiSY Mt Cann Pluton has an age of 113.8 ± 1.0 Ma and is correlated with the Separation Point Granite. The Glenroy Complex and McKnee Intrusives were likely exhumed during at least two stages: initially in the Cretaceous prior to displacement from their northern Fiordland correlatives by the Alpine Fault; and during emplacement as tectonic blocks in the Matakitaki foreland thrust system at the Big Bend. [ABSTRACT FROM AUTHOR]

High-pressure mafic granulites and garnet pyroxenites occur within the South Muya block as boudins or lenses among metamorphic rocks of the Kindikan Group. Their primary minerals crystallized at 670-750 °C and 9.5-12.0 kbar. Granulite metamorphism peaked at 630 Ma, according to LA-ICP-MS U-Pb zircon ages. Judging by their major- and trace-element compositions and Hf isotope ratios in zircons, the South Muya granulites were derived from differentiated within-plate basalts, which, in turn, resulted from melting of juvenile mantle source and Meso- or Paleoproterozoic crust. The events of granulite and eclogite metamorphism in the South and North Muya blocks, respectively, were coeval and the two blocks were spatially close to each other at the onset of Late Baikalian subduction and collision events. [ABSTRACT FROM AUTHOR]