Search

The geologic evolution of the Gondwanide orogen recorded during the late Palaeozoic along the Panthalassan border of Gondwana is related to an active continental margin, though it is still debatable whether it was built by collision or accretion. To disentangle its orogenic processes and provide constraints on the orogen type, we characterize the physicochemical conditions of metamorphism and associated deformation of the Mina Gonzalito Metamorphic Complex from northern Patagonia (41°28’30” S-65°40’30” W). New field mapping and comprehensive petrochronologic analysis constrain the evolution of a thick-skinned fold and thrust belt in a retroarc setting, which is spatially and temporally related to the geometry and kinematics of the right-lateral reverse El Jagüelito ductile shear zone. Metamorphic evolution resulted in a clockwise P‐T‐t-D path reflecting three stages of continuously changing P-T conditions under high-pressure (8.0–9.9 kbar) amphibolite facies (540–680°C) during a single-phase progressive ductile deformation event. Monazite ages ranging from 303 ± 5 to 252 ± 6 Ma account for the single-phase regional tectono-metamorphic event spanning ~ 50 My. Our results, integrated with regional data, led to interpreting the late Palaeozoic Gondwanide orogen developed along the Panthalassan margin of Gondwana as accretionary in advancing-mode. [ABSTRACT FROM AUTHOR]

Granulites exposed in high-grade regional metamorphic belts and exhumed as xenoliths in basaltic pipes are considered as window into the deep crust thus play a key role in constraining models of crustal processes and evolution. Here we present a detailed investigation of the tectono-metamorphic history of the two-pyroxene mafic granulite located in the southern region of the Sonapahar area. This involves conducting monazite chemical dating, analyzing petrological and geochemical characteristics, applying geothermobarometry, performing phase equilibria modeling, and tracing a pressure-temperature (P-T) path. Metamorphic P-T conditions estimated for the mafic granulite using conventional thermobarometer and winTWQ shows temperature in excess of 800°C and pressure of about 8.6 kbar, stand for high temperature granulite facies metamorphism. The metamorphic evolution path obtained from P-T pseudosection suggest a clockwise P-T evolution path, thus signify isothermal decompression and indicate rapid upliftment. Geochemical study of trace and rare earth elements (REE), suggest protolith is of tholeiite basalt in nature that is derived from back arc basin setting near to subduction zone. Additionally, the analyzed rock was examined using primitive mantle-normalized trace element spider diagram. The results indicate an enrichment in large-ion lithophile elements (Th, U, K, Pb) and a depletion in high field-strength elements (Nb, Ta, Ti). The presence of negative anomalies in Nb and Ti, coupled with elevated values of Th, K, and Pb, suggests the possibility of crustal contamination. Monazite chemical data from the studied rock reveals a peak metamorphism age of 521.3 ± 4.20 Ma, which corresponds to the Kuunga Orogeny in the later phase of global Pan-African collision. [ABSTRACT FROM AUTHOR]

The studied Miocene volcanic rocks are observed in the Örenköy, Fındıkköy, and Kızılkaya Tepe regions in and around the Kütahya area. The Örenköy volcanic rocks consist of augite basalt, basaltic andesite and andesite, and show hyalo-microlitic porphyritic and cumulophyric texture, and contain plagioclase (An70-82Ab17-29Or1-2), clinopyroxene (Wo40-44En41-52Fs6-16), orthopyroxene (Wo1-4En64-71Fs27-34) olivine (Fo86-90) and Fe-Ti oxide. The Fındıkköy volcanic rocks include augite trachybasalt, augite basaltic trachyandesite and trachyandesite, and show hyalo-microlitic porphyritic and intersertal texture, and generally contain plagioclase (An58-88Ab12-38Or1-5), clinopyroxene (Wo44-48En38-47Fs8-17), olivine (Fo41-63) and Fe-Ti oxide, while the andesitic ones also contain biotite. The Kızılkaya Tepe volcanic rocks contain augite basalt, augite basaltic andesite and trachyandesite, and exhibit hyalomicrolitic porphyritic, vesicular, intersertal and trachytic texture, and include plagioclase (An53-85Ab14-44Or0-3), clinopyroxene (Wo39-46En41-52Fs8-16), orthopyroxene (Wo2-3En73-75Fs21-25), olivine (Fo52-82) and Fe-Ti oxide. In addition, the pre-eruptive crystallization conditions of the volcanic rocks were estimated using mineral chemistry analyses and thus it was determined that the magmas of the volcanic rocks have evolved by fractionation in magma chambers of the upper continental crust. [ABSTRACT FROM AUTHOR]

Mineral chemistry data as well as petrography provide a comprehensive picture of magma crystallization conditions that support the conclusions based on geochemical data. In addition, the chemical composition of minerals such as clinopyroxene, olivine, biotite, feldspar, and Fe-Ti oxides reflect physicochemical parameters (pressure, temperature, and oxygen fugacity), crystal growth history, and melt origin. The pressure, temperature and oxygen fugacity parameters are estimated from chemical data of various rock-forming minerals to provide information regarding the crystallization of magmas. The essential purposes of present study are to determine the physicochemical conditions (temperature and pressure), to identify the tectonic environment and to propose an emplacement model for Pargeh mafic magmas formation. [ABSTRACT FROM AUTHOR]

We combined compositional analyses, crystal size distributions and geothermobarometry of tephra erupted during the 2021 Tajogaite eruption (La Palma, Spain), focusing on samples collected in November 2021 associated with a period of abundant ash emission characteristic of the second half of the eruption (from October onwards). Magma erupted in November exhibits a more primitive basanitic composition than the earlier magma. Crystallisation temperatures range between ~1100–1160 °C (H2O = 1–3 wt.%) for phenocrysts and microphenocrysts, with corresponding pressures indicating depths from ~10 to ~30 km. Crystal size distribution analysis reveals short (minutes) residence times for plagioclase. Finally, magma ascent velocities (~0.01–0.3 m s−1) suggest acceleration and fragmentation in the shallowest part of the conduit. Our results suggest that the trigger of the November explosive activity can be attributed to complex feedback between gas emission rates, changes in conduit geometry, and magma ascent rate.

We present a reconstruction of the physicochemical conditions of melts in the Pleistocene storage and plumbing system of the Doña Juana Volcanic Complex (SW Colombia): a poorly known, potentially active polygenetic volcano of dacitic composition comprising four major edifices and showing periods of long quiescence. Compositional data for plagioclase, amphibole, pyroxene, and Fe-Ti oxides were combined with new and existing whole-rock data from representative eruptive products, allowing for the implementation of equilibrium tests and geothermobarometry calculations within an established stratigraphic, petrographic, and geochronological framework. Textural and geochemical variabilities of all mineral phases suggest the existence of a trans-crustal magmatic system feeding the Pleistocene eruptions of Doña Juana, and cyclic rejuvenation of a crystal mush following each volcano edifice collapse. The assemblage of different crystal cargos before magma recharge and final eruption is attested by (i) the coexistence of equilibrium and disequilibrium textures and variable compositions in crystals of all studied species, (ii) felsic cores in antecrysts, (iii) mafic overgrowth rims, and (iv) significantly less differentiated microcrysts relative to the composition of meso- and macrocrysts. By integrating multiple mineral-only and mineral-liquid geothermobarometers, after careful textural analyses, we estimate the intensive parameters of the mush–melt interaction zone of the plumbing system in the middle crust, providing a preliminary view of the architecture of a trans-crustal magmatic system in a complex tectonic setting at a previously understudied area of the north-Andean volcanic zone. [ABSTRACT FROM AUTHOR]

Based on the proposed numerical model of the stress-strain state of polymineral rocks, which describes the formation of blastomylonites in the Yenisei Regional Shear Zone (YRSZ) in the Yenisei Ridge, the possibility of local tectonic overpressure exceeding the lithostatic pressure in rocks subjected to shear deformations is shown. For tectonites of the southern (Angara–Kan block) and northern (Isakovka terrane and Garevka complex) segments of the YRSZ, estimates of the maximum overpressure were obtained from 2–3 to 4–5 kbar, which range from 25 to 50% of the lithostatic pressure. It is shown that the excess pressures can be preserved in a local volume on a geological time scale sufficient for their fixation in metamorphic minerals. Model values of overlithostatic pressure in the garnet–amphibole tectonites and geobarometric estimates of peak values during stress metamorphism allow us to offer new evidence for pressure inhomogeneity in natural mineral associations. Using the results of numerical modeling for the evolution of metabasite blastomylonites, it was established that the overpressure at the stage of syn-deformation metamorphism in the shear zone is possible at temperatures up to 600–650°C and not reaching 800°C; the presence of fluid or partial melt prevents the occurrence of overpressure. Magnitudes of excess pressure caused by shear stresses depend on the mineral composition and structure of the rock. [ABSTRACT FROM AUTHOR]