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The Fuping area lies in the middle part of the Trans‐North China Orogen, which is a critical region for understanding the metamorphic–tectonic evolution of this orogenic belt in the Precambrian. The newly discovered orthopyroxene‐bearing semipelitic granulite in this area is a coherent stratigraphic unit, among which three generations of metamorphic mineral assemblages (peak, post‐peak and cooling retrograde) have been identified based on petrographic observation and mineral chemical analysis. The peak metamorphic mineral assemblage mainly consists of porphyroblastic garnet plus matrix minerals including biotite, plagioclase, orthopyroxene, quartz as well as accessory minerals including pyrite, monazite, zircon and apatite. Geothermobarometry calculations and phase equilibria modelling confirm that the representative samples record different P–T conditions and metamorphic stages due to retrogressive metamorphism, with the highest P–T conditions reaching high‐P granulite facies. The retrieved clockwise metamorphic P–T paths pass from 12.5 to 13.5 kbar/855–880℃ (peak stage) through 8.5–11 kbar/850–886℃ (post‐peak stage) and to a speculative cooling phase (retrograde stage), reflecting near isothermal decompression (ITD) followed by near isobaric cooling (IBC). This P–T path is interpreted to reflect a subduction and/or collision event followed by a rapid exhumation. Secondary ion mass spectrometry (SIMS) U–Pb dating on metamorphic monazite and zircon yielded metamorphic ages ranging from 1,825 to 1,815 Ma, possibly constraining a retrograde metamorphic age. Therefore, the semipelitic granulite in the Fuping area records the subduction/collision event between the Eastern and Western Blocks of the North China Craton during the Late Palaeoproterozoic. [ABSTRACT FROM AUTHOR]

The Eoarchean Isua supracrustal belt (ISB) has been interpreted as one of the earliest records of subduction processes, leading to the conclusion that a plate tectonic geodynamic system was likely operating since the early Archean. However, proposed tectonic models remain difficult to evaluate as our understanding of the metamorphic and structural evolution remains fragmentary. Here, we present a metamorphic study of the supracrustal rocks of the ISB. We used petrographic and microstructural observations, phase equilibria, isopleth geothermobarometry, and conventional thermometry to explore the prograde, peak, and retrograde metamorphic evolution of the northeastern ISB. Our results show that the ISB records a syn‐tectonic, amphibolite facies metamorphic event (M1) with peak conditions of 550°C–600°C and 0.5–0.7 GPa. M1 was followed by a static, lower amphibolite facies metamorphic event (M2; <540°C and <0.5 GPa). Published constraints suggest that M1 and M2 occurred in the late Eoarchean (>3.5 Ga) and the Neoarchean (<2.9 Ga), respectively. These events are partially overprinted by late low temperature (<500°C) retrogression (M3) that is most intensely developed in the northeastern part of the belt; it typically overprints some peak mineral phases while preserving the peak fabric. Our findings are consistent with spatially homogeneous syn‐tectonic amphibolite facies metamorphism and macroscale folding. Such features are predicted by a heat‐pipe tectonic model. Therefore, our findings permit the interpretation of the ISB as a record of early nonuniformitarian tectonic processes. Key Points: The Isua supracrustal belt (ISB) records three tectono‐metamorphic eventsPetrographic observations and geothermobarometry show no clear metamorphic gradients in the ISBSyn‐tectonic metamorphic records are consistent with heat‐pipe model predictions for the evolution of the belt [ABSTRACT FROM AUTHOR]

This article presents textures, mineral chemistry, and geothermobarometric data for the southeastern Pinheiro Machado Complex rocks (PMC), eastern domain of the Dom Feliciano Belt, Rio Grande do Sul, Brazil. The PMC is composed by comagmatic intrusions of quartz diorite, tonalite, and granodiorite with medium‐ to fine‐grained equigranular and medium‐grained inequigranular textures with subordinate alkali‐feldspar macrocrystals. Partial melting features are observed in the comagmatic as melt pools and melt films. Amphibolite xenoliths also occur, presenting sharp‐angled to rounded contacts with the intrusions and evidences of partial assimilation, marked by mafic schlierens. Electron probe microanalyzer punctual analyses were used to classify amphibole, plagioclase, biotite, epidote, and titanite, as well as for the calculations of the crystallization P–T conditions. Amphiboles consist of pargasite for the comagmatic intrusions, and Mg‐hornblende for the amphibolite. Plagioclase ranges from oligoclase to andesine (An15‐40) in both units. Biotite corresponds to annite, with Fe/(Fe + Mg) > 0.3. The epidote has mostly magmatic characteristics in the comagmatic intrusions, with pistacite content 25–30%. Titanite has two distinct textures, titanite I is well formed, subhedral to euhedral, with up to 3 mm; while titanite II is anhedral with size >1 mm and rounded shapes, being both chemically homogeneous. The estimated P–T conditions for the amphibolite crystallization, using plagioclase‐hornblende geothermometer are 650–850°C and 3.62–4.95 kbar, whereas the conditions from the comagmatic intrusions are 714–871°C and 4.44–6.10 kbar. In the mineral phases there is a prevalence in the recrystallization field between subgrain rotation (SGR) and grain boundary migration (GBM) in submagmatic flow. These new data indicate that possibly at the end of PMC crystallization, late magmatic fluids caused re‐equilibrium of mineral phases, mainly in biotite and feldspars. Finally, we suggest that the PMC is the result of continuous and repeated comagmatic intrusions in a continental magmatic arc setting at a depth of 20–30 km in an amphibolitic continental crust. [ABSTRACT FROM AUTHOR]

The pressure dependence of the exchange of Cr between clinopyroxene and garnet in peridotite is applicable as a geobarometer for mantle-derived Cr-diopside xenocrysts and xenoliths. The most widely used calibration (Nimis and Taylor Contrib Miner Petrol 139: 541–554, 2000; herein NT00) performs well at pressures below 4.5 GPa, but has been shown to consistently underestimate pressures above 4.5 GPa. We have experimentally re-examined this exchange reaction over an extended pressure, temperature, and compositional range using multi-anvil, belt, and piston cylinder apparatuses. Twenty-nine experiments were completed between 3–7 GPa, and 1100–1400 °C in a variety of compositionally complex lherzolitic systems. These experiments are used in conjunction with several published experimental datasets to present a modified calibration of the widely-used NT00 Cr-in-clinopyroxene (Cr-in-cpx) single crystal geobarometer. Our updated calibration calculates P (GPa) as a function of T (K), CaCr Tschermak activity in clinopyroxene a CaCrTs cpx , and Cr/(Cr + Al) (Cr#) in clinopyroxene. Rearranging experimental results into a 2n polynomial using multiple linear regression found the following expression for pressure: P GPa = 11.03 + - T K ln (a CaCrTs cpx) × 0.001088 + 1.526 × ln Cr # cpx T K where Cr # cpx = Cr Cr + Al , a CaCrTs cpx = Cr - 0.81 · Cr # cpx · Na + K , with all mineral components calculated assuming six oxygen anions per formula unit in clinopyroxene. Temperature (K) may be calculated through a variety of geothermometers, however, we recommend the NT00 single crystal, enstatite-in-clinopyroxene (en-in-cpx) geothermometer. The pressure uncertainty of our updated calibration has been propagated by incorporating all analytical and experimental uncertainties. We have found that pressure estimates below 4 GPa, between 4–6 GPa and above 6 GPa have associated uncertainties of 0.31, 0.35, and 0.41 GPa, respectively. Pressures calculated using our calibration of the Cr-in-cpx geobarometer are in good agreement between 2–7 GPa, and 900–1400 °C with those estimated from widely-used two-phase geobarometers based on the solubility of alumina in orthopyroxene coexisting with garnet. Application of our updated calibration to suites of well-equilibrated garnet lherzolite and garnet pyroxenite xenoliths and xenocrysts from the Diavik-Ekati kimberlite and the Argyle lamproite pipes confirm the accuracy and precision of our modified geobarometer, and show that PT estimates using our revised geobarometer result in systematically steeper paleogeotherms and higher estimates of the lithosphere‒asthenosphere boundary compared with the original NT00 calibration. [ABSTRACT FROM AUTHOR]

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The Sarmeshk granitoid pluton is located in southeast of the Urumieh-Dokhtar magmatic zone in the Kerman province. Based on petrographic studies, the granitoid consist of three rock type of diorite, granodiorite and monzogranite. They are mainly composed of plagioclase, alkali-feldspar, quartz, amphibole and biotite. Mineral chemistry of diorite, granodiorite and monzogranite indicate that the feldspars are orthoclase and oligoclase-andesin in composition. The calcic amphiboles have magnesiohornblende composition that is feature of I-type granite. The biotites with Fe/ (Fe+Mg)>0.33 are magnesio-biotites. The amounts of Al2O3, TiO2 and Mg# in amphiboles indicate crust and mantle mixing in the formation of Sarmeshk granitoid magma. Thermobarometer studies indicate that the pressure of hornblende crystallization in the Sarmeshk intrusion is about 1 to 2 Kbar and have been formed in the depth of 5.8 km. The thermometer of the hornblende- plagioclase reveal temperatures of 650-750 °C for the intrusion. The composition of hornblendes suggests their formation in high oxygen fugacity condition, which is in accordance with their mineralogical characteristics and active continental margin tectonic setting of Sarmeshk granitoid pluton.

Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnet-bearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610–690 °C and 6.5–10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720–750 °C and 13.4–14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630–730 °C and 3.8–7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438–398 Ma.

Western metamorphic belt in Thailand elongated in North-South direction has been grouped into the Chiang Mai-Lincang belt. As part of this metamorphic belt, the Lan Sang National Park located in the west of Tak Province is an affected area from northwest-southeast striking Mae Ping fault. Along the fault zone, rock formations have been strongly deformed, yielding steep foliation and lineation. Based on petrographic study, these rocks are mainly characterized by gneisses showing very fine- to coarse-grained textures which consist of quartz, plagioclase, K-feldspar, biotite, pyroxene, and chlorite. Calc-silicate and impure marble are partly interlayered in these gneisses; they are composed of calcite, quartz, feldspar, pyroxene, and garnet. Moreover, granitic gneiss, which cuts into the host gneisses and calc-silicate, appears to have a similar composition of gneiss. Based on geothermobarometry, these rocks should have undertaken high-grade metamorphism of lower amphibolite facies with P-T (pressure-temperature) ranges of 570-590 °C and 5.8-8.1 Kbar for gneiss. These rocks appear to have several evolution stages. Sedimentary protoliths of gneisses and calc-silicate may have situated in the area prior to regional metamorphism. Subsequently, dikes and veins crosscut into these gneissic and calc-silicate rocks before later metamorphism appears to have continued and reached the ductile-brittle stage. [ABSTRACT FROM AUTHOR]

The study area belongs to the Singhbhum metamorphic belt of Jharkhand, situated in the eastern part of India. The spatial distribution of the index minerals in the pelitic schists of the area shows Barrovian type of metamorphism. Three isograds, viz. garnet, staurolite and sillimanite, have been delineated and the textural study of the schists has revealed a time relation between crystallization and deformation. Series of folds with shifting values of plunges in the supracrustal rocks having axial-planar schistosity to the folds have been widely cited. Development of these folds could be attributed to the second phase of deformation. In total, two phases of deformation, D1 and D2, in association with two phases of metamorphism, M1 and M2, have been lined up in the study area. Chemographic plots of reactant and product assemblages corresponding to various metamorphic reactions suggest that the pattern of metamorphic zones mapped in space is in coherence with the temporal-sequential change during prograde metamorphism. The prograde P–T evolution of the study area has been obtained using conventional geothermobarometry, internally consistent winTWQ program and Perple_X software in the MnNCKFMASHTO model system. Our observations suggest that the progressive metamorphism in the area is not related to granitic intrusion or migmatization but that it was possibly the ascending plume that resulted in the M1 phase of metamorphism followed by D1 deformation. The second and prime metamorphic phase, M2, with its possible heat source generated by crustal overloading, was preceded by D1 and it lasted until late- to post-D2 deformation. [ABSTRACT FROM AUTHOR]

Based on a detailed electron probe microanalysis of the composition and zoning of coexisting minerals (garnet, clinopyroxene, and plagioclase), we have studied the P-T conditions of formation of high-pressure (HP/UHP) rocks of the Maksyutov eclogite- blueschist complex in the South Urals. We have established its periodic evolution and have determined the specific thermodynamic parameters of mineral formation at each stage of its geodynamic history, from the conditions of crystallization of the protolith to the final stages of retrograde greenschist metamorphism. The new analytical data on the composition of coexisting phases confirm the high-pressure formation of eclogites present as numerous lenses, boudins, and interlayers among blueschist and feldspar-mica schists in the lower part of the complex. Thermobarometric calculations of metamorphism parameters were performed for the Grt + Cpx ± Pl + Qz paragenesis using a Grt-Cpx geothermometer and a Pl-Cpx-Qz geobarometer. Garnet in eclogites of the Maksyutov Complex, being conservative to changes in the conditions, has a direct, reverse, or inverse chemical zoning. Under equilibrium of garnet with omphacitic clinopyroxene, this zoning records conjugate progressive and regressive paths reflecting the thermodynamic conditions at the certain stages of the terrane evolution. Based on the data obtained, we have recognized at least four P-T stages of progressive metamorphic transformations of the Maksyutov Complex: (1) >800-910 °C/~2.5-3.5 GPa; (2) 540-790 °C/2.0-3.5 GPa; (3) 410-690 °C/1.1-2.5 GPa; and (4) 310-520 °C/1.0-1.2 GPa. The estimated P-T parameters of the conjugate regressive stages of metamorphism are as follows: (1) 870-625 °C/3.5-2.5 GPa; (2) 745-615 °C/3.5-2.0 GPa; (3) 690-550 °C/1.5-1.0 GPa; and (4) 590-460 °C/1.2-0.6 GPa, respectively. The age data for the certain stages, along with the parameters of metamorphism, form a single P-T-t path of the complex, which determines the position of the gradient of the metamorphic field during the complex exhumation. [ABSTRACT FROM AUTHOR]

The orientation of 76 mineral inclusions represented by olivine (25 inclusions), pyrope (13 inclusions), and magnesiochromite (38 inclusions) was measured in 16 diamond samples from the major primary diamond deposits of Yakutia: Mir, Udachnaya, Internatsionalnaya, Aikhal, and Yubileynaya kimberlite pipes. The novelty of the study is that it provides a special purposeful approach to selection of samples containing not only olivine inclusions that have been extensively studied in the most recent years after the publication of the book Carbon in Earth (2013). The present collection accounts for more than 25% of all samples studied across the world and includes the most typical mineral inclusions of the predominant peridotitic paragenesis in almost all known kimberlites. Both this experiment and similar studies conducted by foreign colleagues in 2014-2019 have found no inclusions whose orientation meets the epitaxial criterion. Only single magnesiochromite inclusions in three diamonds demonstrate an orientation close to the regular one. A significant correlation between the carbon isotope composition and the mineral composition of inclusions of peridotitic and eclogitic paragenesis diamonds as well as the lack of a correlation with other properties may be considered one of the geochemical features. However, given the numerous published and proprietary data demonstrating the complex diamond growth history and, in some cases, wide variations in the composition of mineral inclusions in different zones, along with the difference in their morphology, the authors a believe that syngenetic and protogenetic inclusions can coexist in the same diamond. This is also confirmed by the discoveries of diamondiferous peridotite and eclogite xenoliths in kimberlites where diamonds are completely enclosed in garnet or olivine. Of particular note is the constant presence of heavy hydrocarbons (rel.%), from pentane (C5H12) to hexadecane (C16H34), that are predominant in fluid inclusions in kimberlite and placer diamonds as well as in pyrope and olivine of diamondiferous peridotite xenoliths. [ABSTRACT FROM AUTHOR]

An effective method for identifying the tectonic-magmatic causes of metamorphism is the reconstruction and analysis of P–T–t paths, which can be used to develop a model of rock evolution with time in the "pressure–temperature–time" coordinates. This approach is most widely used in interpreting the development of orogens with a polycyclic history, where different types of metamorphism are combined in contrasting geodynamic settings. The progress in this direction in recent years is due to the improvement of the instrumental base, precision methods for the study of matter – in situ local microanalysis and dating of zonal metamorphic minerals, and the computing apparatus of geothermobarometric procedures using multi-equilibria. The article discusses these issues on the example of geological complexes of various geodynamic nature, which are typical for different types of metamorphism. Reaction microtextures, chemical zoning in minerals, geochronological dating as well as the trajectory of the Р-Т paths provide evidence for the polymetamorphic history. A generalized P-T diagram was built using data on well-studied metamorphic complexes, which are characterized by the simultaneous presence of prograde and retrograde segments of a P-T path. Diagnostic P-T-t paths characteristic of rocks formed in zones of active tectogenesis—under collision, extension and in shear zones of the earth's crust—have been established. This paper discusses some of the ambiguous interpretations of P-T-t paths in areas with simultaneous manifestation of different metamorphic processes, which requires further research. [ABSTRACT FROM AUTHOR]

Monazite dating in metapelites is an emerging method to investigate polymetamorphic areas. A protocol for Th–U–Pb dating of monazite by electron microprobe was adopted for a JEOL JXA-8530F. It was applied to the Variscan and Early-Alpine metamorphic Austroalpine Oetztal-Stubai Complex (OSC). In the Alpeiner Valley in the Stubai region, the Schrankogel complex is the eastern succession of the Central Metabasite Zone. In this part, metabasites are alternating with metapelites. In 4 samples from micaschist lenses, dominantly Carboniferous monazite isochrone ages at 335 ± 4 Ma, 320 ± 4 Ma; 319 ± 4 Ma and 319 ± 4 Ma were obtained. The micaschist samples with diverse modal compositions and variable bulk rock Ca contents of calculated assay, display distinct monazite microstructures, as quantified by automated SEM-MLA (mineral liberation analysis) routines. Clusters of small monazite could indicate new crystallization and yielded isochrones at 313 and 304 Ma. In contrast, corona structures of apatite and allanite around large monazites with isochrones between 350 and 315 Ma suggest a decomposition during decreasing temperature. Garnets in metapelitic assemblages display growth zonations with low pyrope contents in the cores and pyrope-rich rims. A prograde metamorphism with high pressure amphibolite-facies peak conditions at ~ 12 kbar and ~ 680 °C, and a post Pmax path with decompression to 4 kbar and 640–600 °C was estimated from the micaschists and from zoned Ca-amphiboles in retrogressed amphibolitized eclogites. The P–T path entered the monazite stability field during the decompression. This signals a Carboniferous age of the metamorphism. A minor population in one sample is composed of sporadic Permian single monazite ages. A Cretaceous monazite population is lacking. In the wide parts of the Austroalpine basement with Carboniferous-to-Cretaceous mica mixing ages, monazite age populations allow to discriminate a distinct Permian metamorphic event. [ABSTRACT FROM AUTHOR]

Trace-element concentrations in olivine and coexisting garnets included in diamonds from the Akwatia Mine (Ghana, West African Craton) were measured to show that olivine can provide similar information about equilibration temperature, diamond paragenesis and mantle processes as garnet. Trace-element systematics can be used to distinguish harzburgitic olivines from lherzolite ones: if Ca/Al ratios of olivine are below the mantle lherzolite trend (Ca/Al < 2.2), they are derived from a harzburgitic mantle source, and syngenetic garnets are without exception subcalcic G10 garnets. For harzburgitic olivines that cannot be identified this way, Na and Ca contents can be used: olivine inclusions with < 60 µg/g Na and Na/Al < 0.7 are all harzburgitic, whereas those with > 300 µg/g Ca or > 60 µg/g Na are lherzolitic. Conventional geothermobarometry indicates that Akwatia diamonds formed and resided close to a 39 mW/m2 conductive geotherm. A similar value can be derived from Al in olivine geothermometry, with TAl-ol ranging from 1020 to 1325 °C. Ni in garnet temperatures is on average somewhat higher (TNi-grt = 1115–1335 °C) and the correlation between the two thermometers is weak, which may be not only due to the large uncertainties in the calibrations, but also due to disequilibrium between inclusions from the same diamond. Calcium in olivine should not be used as a geothermobarometer for harzburgitic olivines, and often gives unrealistic P–T estimates for lherzolitic olivine as well. Diamond-hosted olivine inclusions indicate growth in an extremely depleted (low Ti, Ca, Na, high Cr#) environment with no residual clinopyroxene. They are distinct from olivines from mantle xenoliths which show higher, more variable Ti contents and lower Cr#. Hence, most olivine inclusions in Akwatia diamonds escaped the refertilisation processes that have affected most mantle xenoliths. Lherzolitic inclusions are probably the result of refertilisation after undergoing high-degree melting first. Trivalent cations appear to behave differently in harzburgitic diamond-hosted olivine inclusions than lherzolitic inclusions and olivine from mantle xenoliths. Some divalent chromium is predicted to be present in most olivine inclusions, which may explain high concentrations up to 0.16 wt% Cr2O3 observed in some diamond inclusions. Strong heterogeneity of Cr, V and Al in several inclusions may also result in apparent high Cr contents, and is probably due to late-stage processes during exhumation. However, in general, diamond-hosted olivine inclusions have lower Cr and V than expected compared to mantle xenoliths. Reduced Na activity in depleted harzburgites limits the uptake of Cr, V and Sc via Na–M3+ exchange. In contrast, Al partitioning in harzburgites is not significantly reduced compared to lherzolites, presumably due to uptake of Al in olivine by Al–Al exchange. [ABSTRACT FROM AUTHOR]

On the base of petrology, the Mirabad- Chehel Khane granitoid, east of Bouin-Miandasht, dominantly consists of syenogranite, monzogranite, alkali granite and granodiorites. The main minerals of these rocks are quartz, alkali feldspar (Orthoclase), plagioclase (Albite - Oligoclase), biotite, ± amphibole with minor amount of allanite, zircon, titanite, apatite, ± tourmaline. The biotite from the granites are Fe-rich type (annite) and primary magmatic in origin. The composition of the biotites studied principally falls in the calc-alkaline subduction related I-type granite on the tectonomagmatic discrimination diagrams, which stand on their major element oxides. Which is consistent with the nature of their host rocks. The studied amphiboles are classified as calcic (ferro-hornblende) which points to the I-type nature of the granitoid. The tourmaline composition plots on the schorl - foitite field. The temperature for the alteration, on the base of chlorite composition from the syenogranite, is estimated around 350°C and from the monzogranite rocks about 341°C. Based on the application of Al-in amphibole, a 3 Kbar pressure was determined for the syenogranite unit corresponding to the depth of 8-11 Km for the emplacement of the pluton. Hornblende- plagioclase thermometer shows 694 to 700°C for the equilibrium of these two minerals.

Introduction Khoy ophiolite at the global scale is in the middle part of the Alp-Himalaya orogenic belt and it is extended over 3900 Km2 which indicates remnant Neotethys oceanic lithosphere in the Mesozoic era (Kananian et al., 2010). In this paper, in addition to a review of previous investigations about Khoy ophiolite, we will try to determine the nature and kind of minerals, origin and partial melting rate as well as the equilibrium pressure and temperature of harzburgites from the Eastern Metamorphic Complex of Khoy ophiolite. Materials and methods Thin sections microscopy studies were carried out following field investigations. EPMA analysis was carried out with using a Superprobe JEOL, JXA 8200 Microprobe unit at the state of WDS and under condition of 15kv accelerating voltage, 10nA current beam, 1µm beam diameter and collection of natural and synthetic standards for calibration. Results The study area is located at the NW of Iran and north of the Khoy city in the west Azarbaijan province. This area is part of the ophiolitic complex of NW Iran and belongs to its Eastern Metamorphic Complex. This metamorphic zone has large tectonically segments of the metamorphic ophiolites which mainly include serpentinized peridotites with associated metagabbros. There are three types of peridotitic rocks in this area which are: Lherzolites, harzburgites and dunites. Lherzolites are composed of olivine (60-70%), orthopyroxene (10-30%) and clinopyroxene (~10-20%) with minor amounts (~2%) of Cr-spinel mineral. Harzburgites are composed of olivine (70-80%), orthopyroxene (10-20%) and clinopyroxene (~5%) with minor amounts (~2%) of Cr-spinel mineral. Dunites are composed of olivine (90-95%), orthopyroxene (5-10%) with minor amounts (~1-2%) of Cr-spinel mineral. Composition range of olivines is between Fo89.46 Fa10.37 to Fo89.86 Fa10.0 as well as NiO content range is 018-046 (wt %). The calculated Mg# of olivines is 0.90 and the composition of olivines in Fo-Fa diagram is plotted in forsterite field. The end-members composition of clinopyroxenes is between En44.159 Wo46.910 Fs4.323 Ac1.459 to En46.803 Wo49.589 Fs4.786 Ac2.081. The calculated Mg# of clinopyroxenes is 0.91. The composition of clinopyroxenes in En-Wo-Fs (Morimoto et al., 1988) diagram is plotted on a diopside field. The plot of clinopyroxenes on Na versus Cr diagram (Kornprobst et al., 1981) indicates that the studied harzburgits are formed in the oceanic setting. Moreover, the Mg# versus Al2O3 in the clinopyroxenes is an indication of their relation to the Abyssal peridotites (Johnson et al., 1990). The end-members composition of orthopyroxenes is between En86.022 Wo2.491 Fs9.368 to En87.314 Wo6.719 Fs10.474. The calculated Mg# of orthopyroxenes is 0.90. The composition of orthopyroxenes in En-Wo-Fs diagram is plotted on an enstatite field. The plot of orthopyroxenes on Mg# versus Al2O3 diagram indicates their relation to Abyssal peridotites (Johnson et al., 1990). Compositions of spinels in the studied harzburgites indicates that they are high-Al type with Mg# and Cr# 0.67-0.72 and 0.19-0.26, respectively. Their TiO2 content are 0.01-0.11(Wt %) and Al2O3 content are 44.009-49.894 (Wt %). In Cr# versus Mg# diagram, spinels are plotted on the Abyssal peridotites field and indicate that the host peridotite has experienced 10-15% partial melting. In addition, using the equation F%=10Ln (Cr/Cr+Al) spinel+24) (Hellebrand et al., 2001) 7.6-10.4 (average 9.7%), the partial melting degree was obtained that means a slow spreading rate for the study area. Using the Cr# versus Mg# diagram, alpine I-type, abyssal and back arc setting for the studied harzburgites are determined. PTMAFIC Software (Soto and Soto, 1995) is used for orthopyroxene (single pyroxene), clinopyroxene-olivine, and orthopyroxene-clinoproxene thermometry. Based on these thermometers, overall temperatures of 1100 ±100 °C are estimated for the equilibrium stage of the minerals. For pressure estimation, the Cr content in clinopyroxene (Nimis and Taylor, 2000) barometer is used. Using this calibration and temperatures from single pyroxene thermometer a pressure of ~22±2.4 Kbar for equilibrium clinopyroxene and associated minerals in the studied harzburgites was estimated. Discussion Mineral chemistry studies indicate that these harzburgites may be related to oceanic settings. Moreover, the high Mg# in orthopyroxenes and clinopyroxenes and the high Fo% in olivines are indications of their tectonite origin. Calculation of partial melting degree using spinels compositions indicate that they are experienced 7.6-10.4 partial melting. In this regard, they are consistent with the partial melting degree in the Atlantic and Indian oceans. The spreading rate studies indicate that harzburgites are produced in the region with slow spreading rate. Their tectonic setting is more consistent with MOR peridotites. Based on geothemobarometry studies an overall ~1100±100°C temperature and ~22±2.4Kbar pressure are estimated which are consistent with mantle spinel lherzolite facies. Acknowledgements The author would like to thank the reviewers for the constructive comments which greatly contributed to the improvement of the manuscript. References Hellebrand, E., Snow, J.E., Dick, H.J.B., and Hofmann, A.W., 2001. Coupled major and trace elements as indicators of the extent of melting in mid-ocean ridge peridotites. Nature, 410(6829): 677–681. Johnson, K.T.M., Dick, H.J.B., and Shimizu, N., 1990. Melting in the oceanic upper mantle: an ion microprobe study of diopsides in abyssal peridotites. Journal of Geophysical Research, 95(B3): 2661-2678. Kananian, A., Ataei, M., Mirmohammadi, M., and Emamalipour, A., 2010. Petrography, mineral chemistry and genesis of Aland and Gheshlagh Chromite deposits, Khoy ophiolite (NW of Iran). Iranian Journal of Crystallography and Mineralogy, 18(3): 369-380. (in Persian with English abstract) Kornprobst, J., Ohnenstetter, D., Ohnenstetter, M., Ohnenstetter, M., 1981. Na and Cr contents in Cpx from peridotites: a possible discriminant between subcontinental and sub-oceanic mantle. Earth and Planetary Science Letters, 53(2): 241-254. Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K., and Gottardi, D., 1988. Nomenclature of pyroxenes. American Mineralogist, 73(1-2): 1123-1133. Nimis, P., and Taylor, W.R., 2000. Single clinopyroxene thermobarometry for garnet peridotites. Part I. Calibration and testing of Cr-in-Cpx barometer and an enstatite-Cpx thermometer. Contributions to Mineralogy and Petrology, 139(5): 541–554. Soto, J.I., and Soto, V.M., 1995. PTMAFIC: software package for thermometry, barometry and activity calculations in mafic rocks using IBM-compatible computer. Computers and Geosciences, 21(5): 619-652.

The Zambezi Belt in southern Africa has been regarded as a part of the 570–530 Ma Kuunga Orogen formed by a series of collision of Archean cratons and Proterozoic orogenic belts. Here, we report new petrological, geochemical, and zircon U-Pb geochronological data of various metamorphic rocks (felsic to mafic orthogneiss, pelitic schist, and felsic paragneiss) from the Zambezi Belt in northeastern Zimbabwe, and evaluate the timing and P-T conditions of the collisional event as well as protolith formation. Geochemical data of felsic orthogneiss indicate within-plate granite signature, whereas those of mafic orthogneiss suggest MORB, ocean-island, or within-plate affinities. Metamorphic P-T estimates for orthogneisses indicate significant P-T variation within the study area (700–780 °C/6.7–7.2 kbar to 800–875 °C/10–11 kbar) suggesting that the Zambezi Belt might correspond to a suture zone with several discrete crustal blocks. Zircon cores from felsic orthogneisses yielded two magmatic ages: 2655 ± 21 Ma and 813 ± 5 Ma, which suggests Neoarchean and Early Neoproterozoic crustal growth related to within-plate magmatism. Detrital zircons from metasediments display various ages from Neoarchean to Neoproterozoic (ca. 2700–750 Ma). The Neoarchean (ca. 2700–2630 Ma) and Paleoproterozoic (ca. 2200–1700 Ma) zircons could have been derived from the adjacent Kalahari Craton and the Magondi Belt in Zimbabwe, respectively. The Choma-Kalomo Block and the Lufilian Belt in Zambia might be proximal sources of the Meso- to Neoproterozoic (ca. 1500–950 Ma) and early Neoproterozoic (ca. 900–750 Ma) detrital zircons, respectively. Such detrital zircons from adjacent terranes possibly deposited during late Neoproterozoic (744–670 Ma), and subsequently underwent high-grade metamorphism at 557–555 Ma possibly related to the collision of the Congo and Kalahari Cratons during the latest Neoproterozoic to Cambrian. In contrast, 670–627 Ma metamorphic ages obtained from metasediments are slightly older than previous reports, but consistent with ∼680–650 Ma metamorphic ages reported from different parts of the Kuunga Orogen, suggesting Cryogenian thermal events before the final collision. Image 1 • 2655 ± 21 Ma and 813 ± 5 Ma magmatic ages related to within-plate magmatism under continental rift setting. • 557–555 Ma high-grade metamorphism related to Neoproterozoic collision of the Congo and Kalahari Cratons. • Variation in peak P-T suggests the belt might be a suture zone with discrete crustal blocks. • Neoarchean, Paleoproterozoic, Mesoproterozoic, and early Neoproterozoic detrital zircons. • The detrital zircons were derived from proximal sources such as the Kalahari Craton and the Lufilian Arc. [ABSTRACT FROM AUTHOR]

In the Variscan Bohemian Massif, (ultra-)potassic plutons are conspicuously associated with the high-grade, lower crustal/upper mantle Gföhl Unit (Moldanubian Zone). They can be subdivided into two contrasting groups: (1) coarse amphibole–biotite melagranite to quartz syenite with conspicuous K-feldspar phenocrysts (the 'durbachite suite'), and (2) essentially equigranular biotite–two-pyroxene quartz syenites to melagranites (the 'syenitoid suite'). The latter suite, represented by the Tábor and Jihlava plutons, is characterized by an originally 'drier' mineral assemblage orthopyroxene + clinopyroxene + Mg-biotite + plagioclase + K-feldspar + quartz, with accessory zircon, apatite, ilmenite, monazite and/or rutile + chromite. The rich assemblage of both rock-forming and accessory minerals allows testing of numerous geothermobarometers. The resulting P–T data are mutually consistent; they document emplacement of the parental magmas at mid-crustal levels (~5 kbar/19 km for Tábor and 7–8 kbar/26–30 km for Jihlava) and record near-isobaric crystallization from at least 1170 °C to the solidus. New Isotope-Dilution Thermal Ionization Mass-Spectrometry (ID-TIMS) U–Pb ages for zircon (336.9 + 0.6 Ma) and rutile (336.8 + 0.8 Ma) from the Tábor Pluton, together with previously published ages from the Jihlava Pluton, provide temporal constraints for the emplacement and rapid cooling of the syenitoids below c. 600 °C. This supports the hypothesis of post-tectonic emplacement of a hot and dry melt (>1200 °C?) into an essentially consolidated orogenic crust. The two syenitoid plutons have comparable, crust-like radiogenic isotope signatures (87Sr/86Sr 337 = 0.7114–0.7133, ε337 Nd = −6.8 to −8.0). This, in context of whole-rock geochemical variation and K-feldspar Pb isotopic compositions, is consistent with generation from a strongly enriched lithospheric mantle source. Shortly before melting, the local orogenic mantle was most likely modified by deep subduction and relamination of felsic crustal material of the Saxothuringian provenance, transformed to the felsic high-pressure granulites common in the Moldanubian Zone. In the subsequent evolution of the two-pyroxene syenitoid plutons, crystal fractionation and accumulation played a key role, unlike in the durbachite suite itself, where magma mixing with leucogranitic melts was much more important. Structural relations inside and around the (ultra-)potassic plutons (~343–335 Ma) suggest that – besides different depths and specific processes of magma emplacement – these plutons track different kinematic histories and evolutions of regional strain fields in their high-grade country rocks in this crucial period of the Variscan Orogeny. Unlabelled Image • Bt–two-Px syenites-melagranites (Tábor and Jihlava) intruded Variscan orogenic root. • ID-TIMS U–Pb ages of post-tectonic Tábor Pluton (Zrn 336.9 ± 0.6, Rt 336.8 ± 0.8 Ma) • Enriched orogenic mantle source, contaminated by subducted/relaminated felsic crust. • ~1200 °C melt crystallized Cpx → Opx, Pl, Phl, Ap, Zrn, Rt, Chr → Kfs, Qtz at 8–5 kbar. • (Ultra-) potassic plutons are superb indicators of tectonic events in the Variscan Orogeny. [ABSTRACT FROM AUTHOR]

Exhumation and tectonomagmatic processes of the granitoid from Sulawesi were discussed using petrochemistry (e.g. petrographic and major element compositions) and geothermobarometry data (mineral chemistry data). Detailed petrographic observations were conducted to determine the mineral composition, texture, and structure of the granitoid rocks, whereas the whole rock composition were determined using XRF method, and the mineral chemistry was analyzed using Electron Microprobe Analyzer (EPMA). The granitoids are classified as calc-alkaline, metaluminous I-type. Pressures of 0.91 to 1.2 kbar and emplacement depths of 3.2 to 4.3 km at temperatures of 677 - 729°C were estimated for Mamasa Pluton. Whereas Masamba Pluton was emplaced at pressures of 2.3 to 2.8 kbar, temperatures of 756 - 774°C, and emplacement depths of 8.2 to 10 km. Moreover, Lalos-Toli and Sony Plutons were emplaced at temperatures of 731 to 736°C and 601 to 609°C, respectively. The pressures varying from 3.1 to 3.3 kbar and 3.2 to 3.4 kbar, equate to an emplacement depth of 11.3 and 11.6 km, respectively. Gorontalo Pluton emplaced at temperatures of 662 - 668°C with the pressure range from 2.6 to 2.7 kbar, is equivalent to 9.3 km deep. Varied oxidation state (ranging from -14 to 19) is inferred from the mineral assemblages, showing a strong association with highly oxidized I-type series granitic rocks. The exhumation rate estimation shows that Mamasa and Masamba Plutons were exhumed respectively at a rate of 0.37 and 1.6 mm/year, whereas Lalos-Toli and Sony Plutons at 1.4 and 2.7 mm/year, respectively. Gorontalo Pluton located in the Northern Sulawesi Province was exhumed at 0.42 mm/year. The rapid exhumation rate of Sony Pluton is attributed to the active vertical movement of Palu-Koro Fault Zone which has been active since Pliocene. It shows that faulting may play an important role in differential exhumation of intrusive bodies in the orogenic belt. [ABSTRACT FROM AUTHOR]

Clinopyroxene–liquid geothermobarometry is a widely used tool for estimating the conditions under which mafic magmas are stored before they erupt. However, redox variability, sector zoning and disequilibrium crystallization present major challenges to the robust estimation of magma storage conditions. Moreover, most recent studies seeking to address these challenges have focused on clinopyroxenes from alkalic systems and are thus of limited use for understanding clinopyroxenes from the tholeiitic systems that dominate global magma budgets. Here we combine observations on natural clinopyroxenes from the 2014–2015 Holuhraun lava in Iceland with observations on experimental clinopyroxenes synthesized during high-pressure, high-temperature experiments on the same lava in order to investigate clinopyroxene–liquid equilibria in tholeiitic systems and optimize of geothermobarometric strategies. Natural clinopyroxenes from the 2014–2015 Holuhraun lava are sector zoned, with { 1 - 11 } hourglass sectors being enriched in the enstatite–ferrosillite component at the expense of all other components with respect to { hk 0 } prism sectors. In contrast with observations on clinopyroxenes from alkalic systems, sector zoning in clinopyroxenes from the 2014–2015 Holuhraun lava is characterized by differences in Ca and Na contents as well as in Ti and Al contents. The products of crystallization experiments performed at 100–600 MPa and 1140–1220 °C on a powdered starting glass at two sets of melt H2O content–oxygen fugacity conditions (∼0·1 wt % H2O and close to the graphite-oxygen redox buffer, and 0·5–1·0 wt % H2O and approximately one and half log units above the quartz–fayalite–magnetite redox buffer) demonstrate that clinopyroxene crystals from nominally equilibrium experiments can preserve strongly disequilibrium compositions. The compositional systematics of experimental clinopyroxenes are consistent with the presence of sector zoning. Furthermore, the magnitude of compositional variability increases with decreasing melt H2O content and increasing deviations of experimental temperatures below clinopyroxene liquidus temperatures (i.e. degrees of undercooling sensu lato), indicating that kinetic processes play a key role in controlling clinopyroxene compositions, even under notionally equilibrium conditions. Few published analyses of experimental clinopyroxene crystals may thus represent truly equilibrium compositions. Stoichiometric calculations on natural and experimental clinopyroxenes show that Fe3+ is a major constituent of clinopyroxenes from tholeiitic magmas under naturally relevant oxygen fugacity conditions. They also show that Fe3+ is most likely incorporated as Ca- and Al- bearing Ca–Fe-Tschermak's component rather than Na-bearing aegirine component at oxygen fugacities up to one and a half log units above the quartz–fayalite–magnetite buffer. Elevated oxygen fugacities are thus less likely to compromise clinopyroxene–liquid geothermobarometry than previously thought. Guided by our experimental results, we combined published descriptions of clinopyroxene–liquid equilibria with geothermobarometric equations to develop an internally consistent and widely applicable method for performing geothermobarometry on tholeiitic magmas that does not require equilibrium zones to be selected a priori. Applying this method to natural clinopyroxene crystals from the 2014–2015 Holuhraun lava that formed under low but variable degrees of undercooling (perhaps 25 °C or less) returns values in excellent agreement with those from independent methods (232 ± 86 MPa, 1161 ± 11 °C). Robust estimates of magma storage conditions can thus be obtained by performing clinopyroxene–liquid geothermobarometry on tholeiitic magmas when disequilibrium is suitably accounted for. [ABSTRACT FROM AUTHOR]

The Cumbres Calchaquíes Range forms part of the Famatinian metamorphic basement of the Eastern Sierras Pampeanas. The sedimentary protoliths of the metamorphic sequence were deposited in a marine basin alongside the western margin of Gondwana during the Neoproterozoic. New petrologic, geochemical and thermobarometric data give insight into the evolution of the sedimentary basin, its sediment source area, its later metamorphic overprint and its regional relationship to other parts of the Famatinian basement. The metamorphic series studied here consists of banded schists and gneisses and rare calcsilcate-rocks and migmatites that have been reworked by mid-to deep-crustal metamorphic and tectonic processes. The bulk rock compositions indicate shale, wacke, marl and litharenitic protoliths. The metamorphosed clastic sediments have major and trace element compositions indicating a continental granitoid-dominated source area with low sediment recycling. Low SiO 2 /Al 2 O 3 ratios suggest a relatively low maturity of the sedimentary protoliths. Therefore, the Cumbres Calchaquíes section represents a sequence of turbidity currents with progressive shallowing of the depositional environment, as indicated by quartz- and carbonate-rich sediments. The overall data are consistent with the geodynamic environment of a basin adjacent to a continental magmatic arc as the most probable scenario. Whereas the sedimentary protoliths of the metamorphic basement in the Sierra de Ancasti and Sierra de Aconquija, located ca 100–300 km south of the study area are interpreted as originating in an evolving back-arc basin, our results from the Cumbres Calchaquíes region indicate a sedimentary source in a felsic continental arc with no significant influx of basic rocks. The Famatinian metamorphic evolution of the Cumbres Calchaquíes rocks is of typical Barrow-type, culminating in partial melting of the metasediments. Conventional thermobarometry combined with thermodynamic models (pseudosections) reveal a prograde evolution reaching peak conditions of ca 665 °C/6.1 Kbar. This implies a geothermal gradient of ca 35 °C/km, which is slightly higher than the average for continental crust and suggests a period of crustal thinning, as known from back-arc basins, or additional heat supply by voluminous intrusions. • The metamorphic series studied here consists of banded schists and gneisses. • The bulk rock compositions indicate shale, wacke, marl and litharenitic protoliths. • Thermobarometry reveals peak conditions of ca 665 °C/6.1 Kbar. • This implies a geothermal gradient of ca 35 °C/km. [ABSTRACT FROM AUTHOR]

The Eastern Nigerian terrane forms the eastern flank of the Trans-Saharan Orogenic Belt within the Benin-Nigerian Shield. We report new petrological and P–T data of metamorphic rocks (migmatitic gneisses with subordinate granite gneiss, meta-quartz diorite, and meta-ultramafic rock) from Obudu in the southeastern flank of the Benin-Nigerian Shield for unraveling the tectono-metamorphic signatures of the eastern margin of the Trans-Saharan Orogenic Belt. The migmatized pelitic gneiss contains a peak mineral assemblage of plagioclase + rutile + garnet + biotite + K-feldspar + quartz ± liquid, based on which the peak metamorphic conditions are constrained as 850–890 °C and 9–10 kbar using phase equilibria modeling, optimal thermobarometry, and garnet-biotite geothermometry. Retrograde conditions were also estimated for a plagioclase + quartz + garnet + biotite + cordierite + rutile + sillimanite assemblage as 3.8 kbar/590 °C to 6.8 kbar/780 °C. The peak condition under granulite facies confirmed a marked increase of metamorphic grade from the greenschist facies in the western Benin-Nigerian Shield through the middle-upper amphibolite facies in the north-central Nigerian terranes to the granulite facies in the eastern part of the Benin-Nigerian Block. The results presented in this study are the first evidence of granulite-facies metamorphism from the easternmost parts of the Benin-Nigerian Shield. The clockwise path obtained in this study might suggest a continent-continent collisional setting for the evolution of this region related to the closure of the Goiás-Pharusian Ocean and the formation of the Trans-Saharan Orogenic Belt. [ABSTRACT FROM AUTHOR]

The paper presents detailed data on the mineralogy, chemical composition, geothermobarometry, and U–Pb zircon isotopic dating of peraluminous sapphirine-bearing crystalline schists, which occur in association with biotite–garnet–sillimanite gneisses, hypersthene–plagioclase–potassic feldspar and high-K hypersthene orthogneisses, and Ti-rich and subalkaline metabasites of the Kilegir Formation of the Daldyn Group at the Anabar Shield. In contrast to known granulites of the Daldyn and Upper Ananbar groups, the rocks of this association are enriched in K, Rb, Ba, Th, and LREE and have elevated (La/Yb)n. Thermobarometric studies of these rocks yielded the P–T parameters of the origin and evolution of the sapphirine-bearing granulites in the Anabar Shield, with peak values of UHT metamorphism in the ranges of T = 920–1000°C at P = 9–11 kbar. Isotope-geochronological data indicate that the rocks underwent a polymetamorphic evolution. The detrital zircon cores yielded ages of 3.36, 2.75, 2.6, and 2.5 Ga. Later overprinted metamorphic transformations of the detrital zircon formed rims, which are dated at 2.4, 2.3, 2.2, and 1.8 Ga. The timing of formation of the aluminous metasedimentary and associated metamagmatic rocks is estimated in the range of 2.5 to 2.4 Ga. A potential eroded source of the detrital zircons could be hypersthene plagiogneisses and metabasites of the Daldyn Group (whose premetamorphic age was no younger than 3.3 Ga) and products of their metamorphism (dated at about 2.7 Ga), and perhaps, also Na–K granites with an age of about 2.6–2.5 Ga, which still have not been found in the area but known at other shields and are enriched in radioactive (K, Th, and U) and trace elements. An additional source of clastic material for the aluminous sediments could be the two-feldspar magmatic rocks of rhyolite composition found in association with the gneisses and having the same model age. [ABSTRACT FROM AUTHOR]

Azufral is one of the most touristic, but also one of the most explosive active volcanoes of SW-Colombia. Although no historical eruptions have occurred, the potential thread is inferred from the predominance of dacitic pyroclastic units and lava domes since the Holocene. This paper presents new stratigraphical and compositional data of the uppermost and thickest proximal pyroclastic deposits exposed on the current inner and outer SE crater rim. The studied eruption units correspond to parallel and low-angle cross-bedded vitric-crystalline to lithic-crystalline tuffs. The absence of interbedded paleosols or epiclastic deposits indicates continuous eruptive activity throughout the studied succession. Criteria for stratigraphic package division at proximal sites includes erosive contacts, marked changes in grain sizes, and ballistic-bearing horizons. Each package comprises several bedsets consisting of two to three beds of distinctive lithofacies associations suggesting deposition from diluted pyroclastic density currents. Temporary partial or total conduit obstruction conditions could also be inferred from the presence of ballistic horizons. Petrographical and geochemical analyses from a type-bedset with fresh, poorly to moderately vesicular rhyolitic glassy particles and the mineral association Pl + Amp + Bt + Fe-Ti oxides ± Qz microcrysts suggest the presence of juvenile material. Textures and mineralogy of glassy ash particles are the same as those in large ballistic blocks, which are dacitic in whole-rock composition. Geochemical analyses suggest that magma evolution was mainly controlled by Pl + Amp + Bt + Py + Fe-Ti oxides fractionation and magma recharge events. All Pl and Amp microcrysts in the studied juvenile ash and ballistics can be grouped into two populations: (i) unzoned microcrysts and (ii) zoned microcrysts. Zoned microcrysts have evolved and partially corroded cores, coated by a more Mg-rich (Amp) or An-rich (Pl) mantle, and followed by an outermost Fe-rich (Amp) or Ab-rich (Pl) rim that broadly overlaps with the composition of the unzoned microcrysts. Textures, mineral composition, and pre-eruptive conditions obtained from similar-sized Amp, Pl and Fe-Ti oxide microcrysts within the juvenile ash and a juvenile ballistic provide evidence of complex crystallization paths before final decompression and eruption. • Dacitic vulcanian explosions lead to hazardous proximal surges. • Comparing fresh glassy ash and ballistics helps to discern the juvenile or accessory provenance of pyroclasts. • Crystal populations unravel hints on the subvolcanic context. • Co-existing microcrysts had at least two different crystallization paths. • Magma recharge took place before eruption. [ABSTRACT FROM AUTHOR]

Abstract The Além Paraíba Shear Zone (APSZ) is composed of subvertical mylonites trending ENE/WSW with subhorizontal stretching lineation indicative of dextral movement. In the western part of the area mapped in this paper the shear zone, defined as an elongated body of mylonites, dies out. This constrains the possible displacement along the zone. The mylonites are of relatively high metamorphic grade, product of deformed orthogneisses, granulites, paragneisses and associated syn-tectonic granitoids. These rocks reached granulite facies conditions at temperatures and pressures in excess of 850 °C and 8 kbar. Geothermobarometric results indicate that the progressive ductile deformation related to the shear zone occurred under amphibolite facies conditions at temperatures of 714 ± 23 °C to 562 ± 38 °C and pressures between 7.1 ± 0.8 kbar and 4.3 ± 1.1 kbar. Zircon U-Pb dates by LA-ICPMS were obtained from three samples, one from a mylonitic orthogneiss with age 583.6 ± 7.1 Ma, one from a mylonitic paragneiss with age 591.5 ± 6.1 Ma, and one from a pegmatitic vein that cuts the mylonites obliquely and yields an age of 597.7 ± 9.4 Ma. Monazite crystals from the mylonitic orthogneiss were also analyzed by LA-ICPMS U-Pb, resulting in a spread of concordant dates ranging from 611 to 553 Ma. Taking these data together, we estimate the age of peak metamorphism to be between 595 and 590 Ma. The age of the monazite crystals suggests continuous crystallization and/or re-equilibration after the metamorphic peak, probably catalyzed by the activity of the shear zone and/or fluid migration under amphibolite facies conditions. Since the APSZ affects a 535 Ma granite, we argue that the shear zone was probably active in the time span between 580 and 530 Ma, after metamorphic peak conditions but still at relatively high temperatures. The temporal coincidence with the main collision in the Ribeira Orogen supports the idea that the shear zone is the result of oblique collision. Highlights • Textures showed that the mylonites are of medium to high temperature. • Geothermoberometry indicated retrograde mylonitization in the amphibolite facies. • Taking the data together the age of the metamorphic peak is estimated at 595-590 Ma. • The zone was probably active in the time span between 580 and 530 Ma. [ABSTRACT FROM AUTHOR]

The Craters of Meke Lake and Acıgöl are located in the district of Konya Province border and 6 km southeast of Karapinar. Compared with petrographical signatures, craters formed during the final stage of volcanism that effective in Plio-Quaternary comprise basalt-andesite and andesitic rocks and are found around the Meke crater, whilst the andesite and trachyandesite lithologies have been observed in Acıgöl. Volcanics formed by the main mineralogical composition plagioclases (Meke An56-80; Acıgöl An46-68), pyroxene (Meke Wo37-51, Acıgöl Wo40-48), amphibole and biotite are observed as mafic components. In Meke volcanics, these mafic components are accompanied by olivines (Fo70-85). The major element oxides of the rocks outcropping in the region show values the values of 51.32-64.88% SiO2, 1.16-3.09 K2O%, 2.39-3.92% Na2O, MgO 1.2-3.39%, 14.24-17.85% Al2O3, 0.18-0.35% P2O5, 5.59- 9.46%CaO, 0.09 to 0.15%MnO and the 5.17 to 10.21%Fe2O3. The Harker-type variation diagrams suggested that more basic characters of major oxides are observed in the rocks cropping out around the Meke Lake. MORB-normalized trace element patterns reflect strongly LILE enrichment and slightly HFSE depletion. The petrographic and geochemical studies indicate that the volcanic rocks of Meke and Acıgöl are characterized by the continental arc setting and the calcalkaline to alkaline in nature. The petrographic, geochemical and geothermobarometric studies indicate that Acıgöl and Meke volcanics crystallized under respectively 1093-1107 °C-0.9-1 kb and 1133-1141 °C - 4.7-5.3 kb conditions. Meke and Acıgöl are characterized by the continental arc setting and the calc-alkaline in natüre. [ABSTRACT FROM AUTHOR]

Highlights • The amphibolite of the Inyoni Shear Zone records clockwise P-T paths. • The metamorphic age ranges from 3260 to 3217 Ma. • Subduction and later tectonic exhumation might operate. Abstract Geothermobarometry and phase equilibria modeling were conducted for garnet-bearing amphibolite of the Inyoni Shear Zone (ISZ), southwestern Barberton Greenstone Belt, South Africa. The prograde (M1), metamorphic peak (M2) and retrograde (M3) metamorphic P-T conditions were estimated to be ∼560 °C/∼8 kbar, 660–730 °C/7–9.5 kbar and 570–630 °C/5–6 kbar, respectively. The amphibolite records clockwise P-T paths, and the metamorphic peak P-T conditions belong to the medium P/T facies series. The retrograde segment of the P-T path documents near isothermal decompression which may reflect relative fast exhumation. The estimated apparent geotherm is 20–30 °C/km. SIMS U-Pb dating of metamorphic zircon suggests that the metamorphism of the ISZ amphibolite have occurred during ∼3.26–3.22 Ga, and the metamorphic peak might occur at ∼3.24 Ga. Furthermore, 40Ar/39Ar dating of hornblende indicates that the cooling stage might occur at ∼3.20 Ga. It is anticipated that the protolith of the amphibolite of the ISZ may have been involved in a subduction-like tectonic process along with the TTG plutons and was metamorphosed during 3.26–3.22 Ga, then uplifted from within the surrounding TTG plutons at ∼3.20 Ga. [ABSTRACT FROM AUTHOR]

Abstract An Early Permian >VEI 6 eruption (ca. 42 km3) deposited an ash flow tuff into the Chemnitz Basin (southeastern Germany), which exhibits typical characteristics of a Snake River-type ignimbrite. The peculiarity of the Planitz ignimbrite are well-preserved vitroclastic domains with fresh minerals, which provide a unique opportunity for investigation of a relatively crystal-poor (~20 vol% crystals) magmatic system of Late Paleozoic Central Europe. Combined textural and chemical analyses on whole rock, glass shards and mineral phases were acquired to unravel the physical characteristics of the vitrophyre and the pre-eruptive evolution of its multistage magma system. The greyish-black vitrophyre is classified as a well-sorted coarse ash flow tuff (95 vol% of crystals <2 mm) with predominant cuspate and microvesicular fabrics in the groundmass. The latter comprise colorless glass shards; subordinately, brown glass shards (≤1 vol%). The felsic modal mineralogy comprises Ab-rich plagioclase (~7 vol%) followed in abundance by sanidine (~5 to 6 vol%) and quartz (~2 vol%), whereas the ferromagnesian cumulate fragments are dominated by pyroxene (3 to 4 vol%). Bulk ignimbrite composition corresponds to a peraluminous rhyolite that shows characteristics of crustal assimilation by pronounced negative Nb and Ta anomalies. The ferromagnesian silicates have compositions indicating crystal growth in alkaline to calc-alkaline magma (diopside, augite, annite) as well as peraluminous one (siderophyllite). Some glomerocrysts contain alkaline diopside with high Mg-numbers from 80 to 84 and plagioclase with An-content from 44 to 56 mol%, which are evidence for input of mafic melts in the Planitz magma reservoir. Oscillatory zonation in plagioclase crystals points to a repetition of this process. Melt inclusions in pyroxene (57 to 67 wt% SiO 2) indicate the presence of intermediate to acidic magmas in mid crustal reservoirs. Thermo- and barometry calculations based on pyroxene suggest crystallization depths around 25 km for lower crustal dry magma, whereas the occurrence of biotite, sanidine and quartz has been interpreted as entrained material from a rhyolitic cap of an upper crustal batholithic reservoir at depths around 6 km. A genetic connection between the Planitz vitrophyre and the intracaldera Rochlitz ignimbrite of the North Saxon Volcanic Complex, as it was suggested in previous studies, is unlikely because (1) biotite in the Planitz vitrophyre is Fe-rich annite showing AlIV-Mn exchange trends, whereas the Rochlitz biotite is siderophyllite with Fe Mg substitution and (2) the Planitz vitrophyre lacks textures like granophyric intergrowth, which are abundant in the Rochlitz ignimbrites. During and after deposition of the ash flow tuff (≤ 30 m thick), high-temperature processes like moderate welding compaction and formation of lithophysae were followed by high-temperature perlite formation and glass hydration. The latter was associated with depletion of Na and K in colorless glass shards when compared to the whole rock composition. Moreover, the hydration reduced Mg, Fe, and Ca in evolved brown glass shards. Highlights • First description and classification of a SR-type ignimbrite in Late Paleozoic Central Europe • The well-preserved ignimbrite allows insights into the complex SiO 2 -rich intraplate volcanism • Combined textural and chemical analyses unravel the dynamics of a multi stage magma reservoir [ABSTRACT FROM AUTHOR]

The Central Mackenzie Valley (CMV) area of Northwest Territories is underlain by Precambrian basement belonging to the North American Craton. The potential of this area to host kimberlitic diamond deposits is relatively high judging from the seismologically-defined lithospheric thickness, age of basement rocks (2.2-1.7 Ga) and presence of kimberlite indicator minerals (KIMs) in Quaternary sediments. This study presents data for a large collection of KIMs recovered from stream sediments and till samples from two study areas in the CMV, the Horn Plateau and Trout Lake. In the processed samples, peridotitic garnets dominate the KIM grain count for both regions (> 25% each) while eclogitic garnet is almost absent in both regions (< 1% each). KIM chemistry for the Horn Plateau indicates significant diamond potential, with a strong similarity to KIM systematics from the Central and Western Slave Craton. The most significant issue to resolve in assessing the local diamond potential is the degree to which KIM chemistry reflects local and/or distal kimberlite bodies. Radiogenic isotope analysis of detrital kimberlite-related CMV ilmenite and rutile grains requires at least two broad age groups for eroded source kimberlites. Statistical analysis of the data suggests that it is probable that some of these KIMs were derived from primary and/or secondary sources within the CMV area, while others may have been transported to the area from the east-northeast by Pleistocene glacial and/or glaciofluvial systems. At this stage, KIM chemistry does not allow the exact location of the kimberlitic source(s) to be constrained. [ABSTRACT FROM AUTHOR]

The Diavik Diamond Mine in the NWT of Canada has produced in excess of 100 million carats from 3 kimberlite pipes since mining commenced in 2002. Here, we present new findings from deep (>400 m below surface) mining, sampling and drilling work in the A154N kimberlite volcano that require a revision of previous geological and emplacement models and provide a window into how the sub-continental lithospheric mantle (SCLM) below Diavik was sampled by kimberlite magmas through time. Updated internal geological models feature two volcanic packages interpreted to represent two successive cycles of explosive eruption followed by active and passive sedimentation from a presumed crater-rim, both preceded and followed by intrusions of coherent kimberlite. Contact relationships apparent among the geological units allow for a sequential organization of as many as five temporally-discrete emplacement events. Representative populations of mantle minerals extracted from geological units corresponding to four of the emplacement events at A154N are analyzed for major and trace elements, and provide insights into the whether or not kimberlites randomly sample from the mantle. Two independent geothermometers using clinopyroxene and garnet data indicate similar source depths for clinopyroxenes and G9 garnets (130-160 km), and suggest deeper sampling with time for both clinopyroxene and garnets. Harzburgite is limited to 110-160 km, and appears more prevalent in early, low-volume events. Variable ratios of garnet parageneses from the same depth horizons suggest random sampling by passing magmas, but deeper garnet sampling through time suggests early preferential sampling of shallow/depleted SCLM. Evaluations of Ti, Zr, Y and Ga over the range of estimated depths support models of the SCLM underlying the central Slave terrane. [ABSTRACT FROM AUTHOR]

The Jurassic Victor kimberlite (Attawapiskat Field) was emplaced into an area of the central Superior Craton that was affected by a lithosphere-scale thermal event at ~1.1 Ga. Victor diamonds formed ca. 400 million years after this event, in a lithospheric mantle characterized by an unusually cool model geotherm (37-38 mW/m2; Hasterok and Chapman 2011). The bulk of Victor diamonds derives from a thin (<10 km thick) layer that is located at about 180 km depth and represents lherzolitic substrates (for 85% of diamonds). Geothermobarometric calculations (average pressure and temperature at the 1 sigma level are 57 ± 2 kbar and 1129 ± 16 °C) coupled with typical fluid metasomatism-associated trace element patterns for garnet inclusions indicate diamond precipitation under sub-solidus (lherzolite + H2O) conditions. This conclusion links the presence of a diamond-rich lherzolitic layer in the lithospheric mantle, just above the depth where ascending melts would freeze, to the unusually low paleogeotherm beneath Attawapiskat, because along an average cratonic geotherm (40 mW/m2) lherzolite in the presence of hydrous fluid would melt at depths >140 km. [ABSTRACT FROM AUTHOR]

Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnet-bearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610-690 °C and 6.5-10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720-750 °C and 13.4-14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630-730 °C and 3.8-7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438-398 Ma. [ABSTRACT FROM AUTHOR]

The anatomy of the plumbing system of active volcanoes is fundamental to understand how magma is stored and channeled to the surface. Reliable geothermobarometric estimates are, therefore, critical to assess the depths and temperatures of the complex system of magmatic reservoirs that form a volcano apparatus. Here, we developed a novel Machine Learning approach (named GAIA, Geo Artificial Intelligence thermobArometry) based upon Feedforward Neural Networks to estimate P-T conditions of magma (clinopyroxene) storage and migration within the crust. Our Feedforward Neural Network method applied to clinopyroxene compositions yields better uncertainties (Root-Mean-Square Error and R2 score) than previous Machine Learning methods and set the basis for a novel generation of reliable geothermobarometers, which extends beyond the paradigm associated to crystal-liquid equilibrium. Also, the bootstrap procedure, inherent to the Feedforward Neural Network architecture, permits to perform a rigorous assessment of the P-T uncertainty associated to each clinopyroxene composition, as opposed to the Root-Mean-Square Error representing the P-T uncertainty of whole set of clinopyroxene compositions. As a test, we applied GAIA to assess P-T conditions of five Italian volcanoes (Somma-Vesuvius, Campi Flegrei, Etna, Stromboli, Volcano), which are among the most dangerous volcanic centres in Europe. The results on the depths of the plumbing systems are in excellent agreement with those obtained with independent geophysical and geodetic surveys, and provide further evidence to current models of volcano plumbing systems consisting of physically-separated reservoirs interconnected by a network of conduits channelling magma en route to the surface. The results on the magma (clinopyroxene crystallization) temperatures are also in agreement with other estimates, albeit obtained considering - mainly but not only - thermodynamically-based clinopyroxene-liquid geothermometers. GAIA can set robust estimates of magma storage, segregation, and ascent conditions within the plumbing system of active volcanoes, helping to unravel P-T variations, if any, during their eruptive history and providing robust clues to volcanic hazard assessment. • Pressure and temperature are critical to assess volcano plumbing systems. • Machine Learning methods offer novel strategies to geothermobarometry. • GAIA is a new Deep Learning-based, clinopyroxene-only geothermobarometer. [ABSTRACT FROM AUTHOR]

Susong metamorphic complex is located at the southernmost end of Dabie orogenic belt, and is one of the important components of the orogenic belt. Due to the relatively low degree of metamorphism and relatively little information of metamorphic evolution, the construction of metamorphic P-T path has challenged geologists for many years, which restricts the full understanding of the formation mechanism of Dabie orogenic belt. The detailed petrographic, mineralogical and thermodynamic evaluation of garnet-plagioclase amphibolite, which was a typical rock from Susong metamorphic complex, were carried out. the results show that this kind of rocks has four metamorphic stage mineral assemblages including Ts+Ep+Qz+Rt, Grt+Pl+Ts+Qz+Ep+Rt, Pl+Ts+Qz+Mag and mainly Chl+Qz, and the corresponding temperatures and pressures are 591 ℃-620 ℃, 606 ℃-636 ℃, 600 ℃-619 ℃ and 400 ℃-500 ℃, and 0.48-0.56 GPa, 1.01-1.12 GPa, 0.79-0.91 GPa and 0.1-0.3 GPa, showing a metamorphic P-T pattern of near-isothermal pressure lift→near-isothermal pressure reduction→temperature reduction and depressurization. The establishment of this P-T path indicates that Susong metamorphic complex experiences rapid subduction and exhumation in the early stage, and slow uplift in the late stage, suggesting that Susong metamorphic complex, as the leading edge block of Yangtze plate, subducts rapidly under the dragging action of the oceanic plate, returns rapidly due to the buoyancy of the plate fragments, stays at the upper crustal level for a long time, and then rises slowly to the surface. [ABSTRACT FROM AUTHOR]

The Ibaré Lineament is a shear zone that sections the Western portion of Sul-riograndense Shield, affecting the orthogneissic rocks of Santa Maria Chico Granulitic Complex, acting as a conduct for hydrothermal fluids. The studied hydrothermal mineralogy reflects a propylitic alteration paragenesis that is composed of Fe-clinochlore, epidote, albite, calcite and quartz, typical low-pressure paragenesis (< 2,000 bar). This mineral association reflects an equilibrium in a neutral to slightly alkaline pH. Using the new approach for chlorite geothermometry, an average formation temperature of 274°C was obtained, compatible with the stability of polytype IIb chlorite and with the irregular textures of twinning in calcites. The fluid inclusions in quartz establish a low-salinity system (2.45 wt.% NaCl eq.) and an average temperature of 175°C. The obtained temperatures are interpreted as a continuum cooling model with meteoric fluids entrance. The system pressure is evaluated from isochores, reaching an average value of 1,560 bar. This is the first temperature and pressure estimate to the Ibaré Shear Zone, which enabled the establishment of a shallow hydrothermal system (epithermal) with fluid interaction from magmatic and meteoric sources, confirmed by the behavior of carbon and oxygen stable isotopes, which indicated an the origin from mixed sources. [ABSTRACT FROM AUTHOR]

The garnet-muscovite geothermometer and garnet-muscovite-Al2SiO5-quartz (GMAQ) geobarometer have been empirically calibrated under P-T conditions of 1-12 kbar and 460-760 ºC using natural metapelitic rocks. The chemical compositions of the calibrant muscovite are in the ranges of Fe=0.03-0.21 atoms, Mg=0.02-0.32 atoms and AlVI=1.62-1.96 atoms, respectively, on the 11-oxygen basis per formula unit. The garnet-muscovite thermometer yields similar temperature estimates to the well calibrated garnet-biotite thermometer within error of ±55 °C, and successfully discriminates the systematic temperature change of the different zones of either the prograde or inverted metamorphic terranes or thermal contact aureoles. The six formulations of GMAQ barometry yield similar pressure estimates to the well calibrated GASP barometer within error of ±1.2 kbar, and plot the Al2SiO5-bearing metapelite into the correct stability field of the Al2SiO5 polymorphs. Moreover, the GMAQ thermobarometers show that the pressure is almost constant for every thermal contact aureole within limited geographic region, which reflects geological condition. The random errors are estimated to be of ca. ±60 °C and ±1.4 kbar for the geothermometer and geobarometer, respectively. A spreadsheet for applying GMAQ geothermobarometry is supplied in the Electronic Supplementary Materials. [ABSTRACT FROM AUTHOR]

Abstract Quaternary eruptions from an intraplate multistage magma reservoir of the Aragats stratovolcano in western Armenia formed pyroclastic density currents and fallouts deposited in an area around 2,000 km2, comprising six ignimbrite units and three fallout deposits. Published K/Ar and Ar/Ar age data allow for a distinction between older (Calabrian, 1.8–0.90 Ma) and younger (Middle Pleistocene, 0.75–0.65 Ma) ignimbrites. The detailed characterization of the crystal-poor to crystal-rich, trachyandesitic to rhyolitic ignimbrite sequence deciphers the pre-eruptive magmatic conditions. It also contributes to the understanding of Plinian eruptions of the largest volcanic complex in the Lesser Caucasus. The chemical variation of pumice fragments reveals the conditions of both, homogeneous and mingled heterogeneous magma systems. The phenocryst assemblage of the older crystal-poor units (Ab-rich plagioclase + amphibole ± pyroxene) indicates growth in a cooler hydrous magma chamber, whereas the partially resorbed phenocrysts of the younger crystal-rich units (An- to Ab-rich plagioclase + pyroxene) suggest growth in a superheated magma chamber fueled by mafic, mantle-derived melts. In the younger units, external (e.g. sieve fabrics) and internal phenocryst textures have been generated by decompression and convection during ascent. With the older units, the chemical variation in amphibole from core to the narrow break-down rim reveals magma ascent from a deep (13 km depth) to a shallow (up to 8 km) level. Tracking the p-T paths of cumulate fragments (pyroxene, plagioclase) in the younger units, we estimate the depth of the anhydrous crystal-rich magmatic chamber at around 25 km. Based on the composition of clinopyroxene cumulates, we propose a multi-stage evolution of melts from subalkaline and tholeiitic to calc-alkaline composition. The pronounced high Zr content and Zr/Hf ratios of the entire Upper Pliocene to Quaternary post-collisional magmatism could be attributed to partial melting of an enriched mantle source in the Lesser Caucasus. Highlights • Revised Aragats ignimbrite lithostratigraphy • Combined textural and chemical analyses unravel the Aragats magma system • Contribution to the knowledge on dynamics of Lesser Caucasus intraplate magmatism [ABSTRACT FROM AUTHOR]

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Abstract: Two phengite–garnet‐bearing metapelites from the Nevado‐Filábride Complex, Betic Cordillera, one from the Ragua unit (sample 23085) and the other (sample 23098) from the Calar Alto unit, were studied in detail to elucidate their metamorphic evolution. We calculated various P–T pseudosections for different O2 and H2O‐CO2 contents and Fe3+/Fe2+ ratios with PERPLE_X . On the basis of the compositions of the garnet core and the highest Si content in potassic white mica, different peak pressures of 12.7 ± 0.7 kbar at 525 ± 10°C (23085) and 17.4 ± 1.2 kbar at 526 ± 17°C (23098) resulted (errors refer to an estimated 1σ range). The suggested clockwise P–T loop was followed in both cases by another loop caused by a reheating process. On the basis of garnet rim compositions, peak temperatures of 596 ± 10°C at 10.7 ± 1.4 kbar (23085) and 629 ± 11°C at 8.5 ± 0.7 kbar (23098) resulted, supported by Zr‐in‐rutile thermometry (23085: 591 ± 11°C; 23098: 607 ± 10°C). In situ dating of monazite (23085) with the electron microprobe yielded ages between c. 48 and 14 Ma. On the basis of the monazite composition and histogram analysis, two age populations with mean ages of 40.2 ± 1.7 (1σ) and 24.1 ± 0.8 Ma could be defined. Low Y2O3 contents (<0.6 wt%) in monazite point to its formation after initial growth of garnet. The older generation was therefore assigned to the formation of the garnet core and the early P–T loop. The younger monazite population was related to the late P–T loop. A geodynamic scenario is hypothesized that assigns the Eocene metamorphism to subduction of a continental margin to depths of 50–65 km, followed by exhumation in an exhumation channel accompanied by mixing of slices of different rock types including mantle rocks. This process ended with stacking of such slices causing reheating of the studied rocks in the Early Miocene. The noted time gap of c. 15 Ma between subduction and nappe stacking is similar to the continent–continent collisional orogeny of the Himalaya. [ABSTRACT FROM AUTHOR]

Carboniferous biotite granite, Late Permian hornblende granite, and Triassic biotite-hornblende granite, all of which belong to the Eastern Granite Belt, expose in the Wang Nam Khiao area, Nakhon Ratchasima, northeastern Thailand. The Carboniferous biotite granite is dominated by quartz, K-feldspar, plagioclase, and biotite. The Late Permian hornblende granite contains dominant assemblages of plagioclase, quartz, K-feldspar, hornblende, and minor amount of biotite, while the Triassic biotite-hornblende granite consists of quartz, plagioclase, K-feldspar with small amounts of biotite, and hornblende. The REE patterns with steep decrease from light to heavy REE together with the LILE (e.g. K, Sr) enrichment and depletion of some particular HFSE (e.g. Nb, Ti) indicate low degree of partial melting. Mineral chemistry of biotite and hornblende in the granites reflects crystallization from hydrous calc-alkaline arc-derived magmas possibly formed by subduction. Amphibole-plagioclase thermometry and Al-in-hornblende barometry indicate that the Late Permian hornblende granite and the Triassic biotite-hornblende granite may have equilibrated at 3.0–5.8 kbar/700–820 °C and 2.0–3.2 kbar/600–750 °C, respectively, in the middle-upper crust (about 10–15 km depth). Zircon U-Pb geochronology of the Carboniferous biotite granite, Late Permian hornblende granite and Triassic biotite-hornblende granite yielded intrusion ages of 314.6–284.9 Ma, 253.4 Ma, and 237.8 Ma, respectively, which implies multiple episodes of arc-magmatism formed by Palaeo-Tethys subduction beneath Indochina Terrane during Late Carboniferous/Early Permian, Late Permian and Middle Triassic. [ABSTRACT FROM AUTHOR]

Here, we present a compilation of 44 metamorphic pressure-temperature (P-T) estimates from 31 localities in the Svecofennian province of eastern and central Sweden. Based on these P-T estimates, which were obtained using the average P-T method of the computer programme THERMOCALC, we calculated an apparent metamorphic field gradient of 54 ± 4 °C/km for the Svecofennian province. This is typical for low-medium P/T (Buchan) metamorphism and supports tectonic models that imply Svecofennian crustal growth by accretion of volcanic arc systems. In general, estimated P and T conditions range from 0.2 to 0.6 GPa and from 400 to 800 °C, respectively; i.e., from greenschist to granulite facies conditions. Metamorphic grade is generally higher, reaching upper amphibolite or granulite facies in northern and southwestern parts of the Svecofennian province, whereas metamorphism in Bergslagen was at greenschist to lower amphibolite facies conditions. The higher metamorphic temperatures recorded by rocks in the southwestern part of the province might relate to magmatic activity associated with the Transscandinavian Igneous Belt (TIB). Higher pressure, epidote amphibolite facies metamorphic conditions in the western part of the province probably reflect Sveconorwegian overprinting. Finally, local upper amphibolite and granulite facies conditions probably reflect contact metamorphism. [ABSTRACT FROM AUTHOR]

In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined “El Triunfo Complex” located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at ~ 650 °C and ~ 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of ~ 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian (~ 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from ~ 457 to ~ 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of the amphibolite have E-MORB characteristics and were derived from a depleted mantle source younger than the Rodinia-type basement. Inasmuch as similar amphibolites also occur in the Ediacaran metasedimentary rocks as dykes or lenses, Late Neoproterozoic magmatism in a rift setting is suggested. Hence, the geologic record of the El Triunfo Complex includes evidences for Rodinia assemblage, Tonian circum-Rodinia subduction, and breakup during the Late Neoproterozoic. Metamorphism, and partial melting are interpreted in terms of a convergent margin setting during the Ordovician. The results place the southern Chiapas Massif along with Oaxaquia and similar Northern Andes terranes on the NW margin of Gondwana interpreted as the extension of the Famatinian orogen that evolved during the closure of the Iapetus Ocean. [ABSTRACT FROM AUTHOR]