Search

En todas las islas Columbretes aparecen rocas con anfíboles, en muchos casos en fragmentos accidentales dentro de las tobas. Todos ellos son magnesio-hastingsitas, más o menos zonadas y reabsorbidas. Los anfíboles de las islas centrales de la alineación principal N-S, se han formado a menor temperatura y presión que el resto. Las profundidades de formación calculadas son aproximadamente las de la profundidad del Moho para la zona, In all the Columbretes islands there are rocks with amphiboles, in many cases in accidental fragments within the tuffs. All of them are magnesium-hastingsites, more or less zoned and reabsorbed. The amphiboles of the central islands of the main N-S alignment have formed at lower temperature and pressure than the rest. The calculated formation depths are approximately the Moho depth for the area

The Sierra de Guasayán (Eastern Sierras Pampeanas, Argentina) is formed by low to medium grade metamorphic rocks intruded by Cambrian metaluminous (La Soledad quartz-diorite), slightly peraluminous (Guasayán, El Escondido and El Martirizado granodiorite plutons), and strongly peraluminous (Alto Bello granodiorite) granitoids of the Pampean magmatic arc. Chemical compositions of amphibole, plagioclase, biotite, and titanite indicate that these granitoids were emplaced at low pressure (mostly &lt, 3 kbar) and temperature (&lt, 770 °C) under oxidizing conditions (QFM + 1 and QFM + 2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. Mineral assemblages and whole-rock and mineral chemistry of the granitoids from the Sierra de Guasayán indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, and titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, and sillimanite), and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, and magnetite). This hybrid nature is supported by the presence of abundant mafic microgranular enclaves and rapakivi texture and by published zircon Hf-isotope data (εHfi ranging from −4.76 to −0.12). This suggests, in turn, the involvement of hybridization in the genesis of these granitoids, which seems to be a common mechanism operating in the Pampean magmatic arc.

The Baghche Maryam (BM) granitoid body is located in the northern part of the Sanandaj-Sirjan zone (SSZ), NW Iran. The BM intrusion is composed of diorite, monzodiorite, syenite and granite with a calc-alkaline to alkaline affinity. Mafic minerals in the BM rocks are biotite and Amphibole. Amphiboles are calcic (magnesiohornblende). The emplacement pressure average of the BM intrusion for granite and diorite rocks is 2.14 and 2.33+0.6 kbar, respectively. During the evolution of this magmatic system to higher silica contents, there was an increase in the activity of oxygen and a decrease in the temperature and the emplacement depth from the monzogabbro-monzodiorite to granite rocks; this is consistent with the typical evolution of the granitoid rocks. The studied amphibole rims show the calculated higher temperature and pressure and low ƒO2 and H2O content than the core of amphiboles which reflects differences in emplacement depth and crystallization conditions.

Metamorphic evolution of an accretionary wedge can be constrained by a reconstructed P&ndash, T conditions of the oceanic and continental margin fragments. This paper deals with the metamorphic overprinting of the Inner Western Carpathians (IWC) Meliatic Triassic&ndash, Jurassic paleotectonic units after the closure of the Neotethyan Meliata Basin. Medium to high-pressure and lower temperature conditions were estimated by Perple_X pseudosection modelling, combined with garnet&ndash, phengite, calcite&ndash, dolomite and chlorite thermometers and chlorite&ndash, phengite and phengite barometers. The Late Jurassic subductional burial to a maximum 50 km depth was estimated from the B&ocirc, rka Unit continental margin fragments at 520 &deg, C and 1.55 GPa. This is compatible with the metamorphic peak garnet&ndash, glaucophane&ndash, phengite assemblage of blueschist facies in metabasites. The Jaklovce Unit oceanic fragments were subducted to maximum 35&ndash, 40 km at 390&ndash, 420 &deg, C and 1.1&ndash, 1.3 GPa. Metabasalts and metadolerites contain winchite, riebeckite, actinolite, chlorite, albite, epidote and phengite. A glaucophane-bearing metabasalt recorded an intra-oceanic subduction in blueschist-facies conditions. Rare amphibolite-facies metabasalts of this unit indicate the base of an inferred oceanic crust sliver obducted onto the continental margin wedge. The Meliata Unit oceanic/continental margin flysch calciclastic and siliciclastic metasediments suggest the burial to approximately 15&ndash, 20 km at 250&ndash, 350 &deg, C and 0.4&ndash, 0.6 GPa. This is indicated by a newly formed albite, K-feldspar, illite&ndash, phengite and chlorite associated with quartz and/or calcite and dolomite in these rocks. Magnesio-hastingsite to magnesio-hornblende bearing metagabbro with newly formed metamorphic magnesio-riebeckite and actinolite is an inferred detached Meliatic block tectonically emplaced in a Permian salinar m&eacute, lange in the Silica Nappe hanging wall. Reconstructed P&ndash, T paths indicate variable metamorphic conditions from the medium-pressure to high-pressure subduction of the B&ocirc, rka and Jaklovce units to the Meliata Unit shallow burial in an accretionary wedge during Late Jurassic to Early Cretaceous Meliaticum evolution. M&eacute, lange blocks of Meliaticum incorporate different juxtaposed Meliatic paleotectonic units exposed in nappe outliers overlying the IWC Gemeric and Veporic superunits.

Polymetamorphic units are important constituents of continent–continent collisional orogens, and rift metamorphic assemblages are often overprinted by subsequent metamorphism during subduction and collision. This study reports the metamorphic conditions and evolution of the Dorud–Azna metamorphic units in the central part of the Sanandaj–Sirjan zone (SSZ), Iran. Here, new geothermobarometry results are integrated with 40Ar/39Ar mineral and Th–U–Pb monazite and thorite ages to provide new insight of polyphase metamorphism in the two different basement units of the SSZ, the lower Galeh-Doz orthogneiss and higher Amphibolite-Metagabbro units. In the Amphibolite-Metagabbro unit, staurolite micaschist underwent a prograde P–T evolution from 640 ± 20 °C/6.2 ± 0.8 kbar in garnet cores (M1) to 680 ± 20 °C/7.2 ± 1.0 kbar in garnet rims (M2). Three Th–U–Pb monazite ages of 306 ± 5 Ma, 322 ± 28 Ma and 336 ± 39 Ma from the garnet-micaschists testify the Carboniferous age of M1 metamorphism. In the same unit, the metagabbro records P–T conditions of 4.0 ± 0.8 kbar and 580 ± 50 °C in the (magmatic) amphibole core (Late Carboniferous intrusion) to 7.5 ± 0.7 kbar and 700 ± 20 °C in the amphibole rim indicating a prograde P–T path during subsequent burial (M1). New 40Ar/39Ar dating of white mica from the staurolite micaschist yielded a staircase pattern ranging from 36 ± 12 Ma to 170 ± 2 Ma. This implies polymetamorphism with a minimum Late Jurassic cooling age through the Ar retention temperature of ca. 425 ± 25 °C after M2 metamorphism and a Paleogene low-grade metamorphic overprint (M3), while 40Ar/39Ar white mica dating of garnet micaschist yielded a plateau age of 137.84 ± 0.65 Ma. We therefore interpret the amphibolite-grade metamorphism M2 to have predated 170 Ma and is likely between 180 and 200 Ma. Furthermore, it is overprinted at about 36 Ma under retrogressive low-grade M3 metamorphism (at temperatures of ~350–240 °C) during final shortening and exhumation. In the underlying Galeh-Doz unit, the Panafrican granitic orthogneiss intruded at P–T conditions of 3.2 ± 4 kbar and 700 ± 20 °C, then it was metamorphosed and deformed at 600 ± 50 °C and 2.0 ± 0.8 kbar (metamorphic stage M1) prior to Late Carboniferous intrusion of mafic dikes. 40Ar/39Ar dating of amphibole from the Galeh-Doz orthogneiss gave plateau-like steps between 260 and 270 Ma, representing the age of cooling through ca. 500 °C after the M1 metamorphic event. Interestingly, the results of this study demonstrate polyphase metamorphic histories in both the Galeh-Doz orthogneiss and Amphibolite-Metagabbro units at different P–T conditions and final thick-skinned Paleogene emplacement of these units over the underlying low-grade metamorphic June Complex. Our findings suggest that both units are affected by high-T/low-P Late Carboniferous orogenic metamorphism along with the bimodal magmatism, as result of rifting. We propose that the Early Jurassic amphibolite-grade M2 metamorphism of the SSZ is correlated with the initial subduction of the Neotethyan Ocean. Eventually, the investigated units reflect various stages of a Wilson cycle, from rifting to initiation of the subduction in final plate collision.

Recycling of ultramafic lower crustal cumulates via delamination or foundering is often invoked as a mechanism to return mafic material to the mantle during continental crust formation. These recycled pieces of the lower crust are rarely sampled but are preserved in several locations including the Kohistan and Talkeetna arc sections, Sierra Nevada and Colorado Plateau pyroxenite xenoliths and, as discussed here for the first time, the exhumed Higashi-Akaishi (HA) ultramafic body in Japan. The HA is located in the Besshi region of the Sanbagawa metamorphic belt in southwestern Japan and is dominantly composed of dunite with lesser garnet pyroxenite and harzburgite lenses. Although the petrogenetic history of the HA body is still debated, our new bulk major and trace element compositions, radiogenic isotope data, as well as petrologic and field observations, are consistent with a lower crustal cumulate origin for the HA dunite and pyroxenite, with a later slab-derived fluid overprint. Clinopyroxene and olivine in the foliated HA dunite have compositions consistent with ultramafic cumulates with high Mg#s (Mg# clinopyroxene = 0·94, Mg# olivine = 0·88), high NiO in olivine (∼0·26 wt %) and low-Al clinopyroxene. In addition, the bulk major element chemistry of the HA dunite and garnet pyroxenite follow systematic behavior in Mg# vs SiO2 wt %, similar to those observed in other lower crustal cumulate lithologies and corresponding intrusive lithologies, pointing to different liquid lines of descent for the corresponding melts. Our new thermobarometric estimates (peak pressure–temperature at 2·6 GPa, 713ºC) are consistent with a hot slab surface subduction path, rather than the lower crustal temperatures recorded in arc sections (Kohistan & Talkeetna: 1 GPa, 800ºC). A pervasive slab-fluid influence is also indicated in the HA lithologies by LREE and Ce enrichments and strong Nb and Zr depletions. The trace elements and the pressure–temperature estimates, as well as the thermodynamic modeling results necessitate removal of the HA body from the lower crust and incorporation into cooler portions of a mantle wedge. At lower crustal conditions, the bulk density of the HA lithologies is greater than the background mantle, indicating the feasibility of lower crustal foundering into a mantle wedge where the HA was incorporated in the subduction channel to reach its peak conditions. Hydration of the HA body while in the subduction channel likely provided the change in density necessary to facilitate its rapid exhumation to the surface. Thus, the HA cumulate likely represents a piece of the subduction system that is rarely preserved, as well as a key component in the compositional evolution of the continental crust.

EntraPT is a web-based application for elastic geobarometry freely accessible at the “Fiorenzo Mazzi” experimental mineralogy lab website (www.mineralogylab.com/software). It provides a...

In the Chhotanagpur Gneissic Complex (CGC) of Eastern India a suite of mafic and ultramafic rocks occurs as sills, dykes and enclaves within porphyritic granitoid pluton. These mafic and ultramafic rocks and host porphyritic granitoids were emplaced in a post-collisional setting around 998 ± 10 Ma ago. Field occurrence, petrology and mineral chemistry of the mafic–ultramafic rocks have been studied. Both the mafic (Pl + Hyp + Di + Hbl + Bt + Mag + Spn ± Ol ± Spl) and ultramafic rocks (Di + Hyp + Bt ± Hbl ± Ol ± Pl ± Spl ± Ep ± Spn) are composed of same minerals but in different modal proportions. Plagioclase, clinopyroxene, orthopyroxene, amphibole, biotite and rarely olivine and spinel are important primary minerals of mafic–ultramafic suite. Primary amphiboles, biotites and pyroxenes show their affinity with shoshonitic lamprophyres. Chemically these rocks are similar to the kentallenite (of appinite suite) and are enriched in both compatible (Fe, Mg, Ni, and Cr) and incompatible (K, Ba, Rb, and LREE) elements and show crust-like trace element patterns. Crystallization of clinopyroxene before labradorite and presence of primary hornblende and biotite suggest high water content while biotite–magnetite–sphene assemblage suggests high fO2 of the magma. Liquidus temperature (975–1088°C) of the parental magma of the mafic–ultramafic rocks was obtained by two-pyroxene thermometer. The pressure (2.9–5.7 kbar) and near-solidus temperature (782–819°C) of crystallization were determined using the amphibole–plagioclase geothermobarometry. Similar range of values of pressure, temperature and fO2 values were obtained using other thermobarometers. High H2O and fO2 (>NNO buffer) of the magma are characteristics of convergent setting. The mafic–ultramafic rocks of the suite probably crystallized from a magma which had high SiO2 (48.16–67.64 wt%), high CaO (3.01–11.73 wt%), high K2O (1.34–4.49 wt%) and low TiO2 (0.04–2.71 wt%) contents and intermediate Mg# (46.73 and 59.78).

We investigated the microstructures and geochemistry of pseudotachylytes found within the ophiolitic peridotites and gabbros from the Moncuni area (Lanzo Ultramafic Massif, Western Alps). The pseudotachylytes preserve dry glass and pristine microlites. The presence of garnet and the static development of eclogite-facies assemblages in local hydrated domains indicate that pseudotachylytes experienced subduction conditions of 600 °C and 2.1 GPa. Samples were investigated using optical and scanning electron microscopic imaging as well as electron backscatter diffraction, Raman and IR spectroscopy, single-crystal X-ray diffraction and microprobe analysis. Based on the analysis of the pseudotachylytes and associated wall-rocks, we suggest that the Moncuni body can be regarded as representative for the rheological behaviour during subduction of seismically active, dry, lithosphere. The data is organised in 8 folders termed Figure X, where X is the figure number in the primary publication. One folder is titled Supplements containing 5 subfolders equivalent to the supplementary material in the primary publication. Detailed information about the files and methods used is given in a readme file.

O nordeste do Cinturão Dom Feliciano compreende rochas gnáissicas tonalíticas de afinidade cálcico-alcalina médio-K, de fácies anfibolito, e rochas graníticas póstranscorrentes de afinidade cálcico-alcalina alto-K e alcalina. Com o objetivo de obter dados a respeito das condições de formação destas rochas, métodos geotermobarométricos com base na química mineral e de rocha total foram aplicados. A química mineral dos anfibólios das rochas gnáissicas (Fe-hornblenda a Fetschermakita) registrou uma mudança nas condições de pressão que foi interpretada como tendo um núcleo ígneo, com temperaturas, pressões e profundidades, respectivamente, de 710 a 760 °C, 3,4 a 3,9 kbar e 12 a 14 km; e uma borda metamórfica de 690 a 760 °C, 4,8 a 7,7 kbar e 18 a 28 km. A química mineral dos anfibólios dos granitos (Mg-hornblenda) registrou temperaturas de 659 a 759 e pressões de 3,2 a 5,0 kbar, com profundidades de 11 a 18 km. As temperaturas obtidas com base no teor de Zr na titanita registraram eventos entre 607 a 881 °C, que foram interpretados, em conjunto com observações petrográficas, como tendo tanto uma origem magmática (700 – 881 °C), quanto pós-magmática (

Este trabalho apresenta dados de petrologia, química mineral e de geotermobarometria das rochas do Complexo Pinheiro Machado na região de Monte Bonito, domínio oriental do Cinturão Dom Feliciano. Os dados foram obtidos a partir de estudos petrográficos e análises químicas em minerais das rochas de composição expandida do Complexo Pinheiro Machado: quartzo dioritos, granodioritos, tonalitos e sienitos, além dos xenólitos de composição anfibolitíca.A interpretação dos dados mostra uma similaridade de composição química das fases em diferentes rochas, sugerindo uma associação de intrusões co-magmaticas. Os demais dados e aspectos petrográficos mostram evidências de fusão parcial das rochasco-magmáticas, as quais foram colocadas através de multi-intrusões, causando fusão e reequilíbrio das fases minerais precoces. Nesta dissertação é apresentada uma breve descrição sobre as técnicas analíticas utilizadas, além de revisões teóricas sobre a utilização do par Hb-Plgna geotermobarometria e as principas feições em microescala. Por fim, as interpetações e considerações realizadas foram compiladas no artigo denominado “Mineral chemistry and geothermobarometry of the SE Pinheiro Machado Complex: implications for the evolution of the eastern domain of the Dom Feliciano Belt, Brazil”, no qual são interpretados os dados obtidos e são realizadas ponderações sobre os processos e condições de cristalização do Complexo Pinheiro Machado, e consequente evolução do domínio leste do Cinturão Dom Feliciano. This paper presents petrology, mineral chemistry and geothermobarometry datas of the Pinheiro Machado Complex rocks in the region of Monte Bonito, eastern domain of Dom Feliciano Belt. The data were obtained from petrographic studies and chemical analysis of minerals from the Pinheiro Machado Complex expanded rocks: quartz diorites, granodiorites, tonalites and syenites, as well as amphibolite xenolites. Interpretation of the datashows a similarity in the chemical composition of the phases in different rocks, suggesting an association of co-magmatic intrusions. The other data and petrographic aspects show evidence of partial melting of the co-magmatic rocks, which were placed through multi-intrusions, causing melting and rebalancing of the early mineral phases. This dissertation presents brief description of the analytical techniques used, as well as theoretical reviews on the use of the Hb-Plg pair in geothermobarometry and the main features in microscale. Finally, the interpretations and considerations were compiled in the article entitled “Mineral chemistry and geothermobarometry of the SE Pinheiro Machado Complex: implications for the evolution of the eastern domain of the Dom Feliciano Belt, Brazil”, which the data obtained are interpreted and weightings are carried out on the processes and conditions of crystallization of the Pinheiro Machado Complex, and consequent evolution of the eastern domain of the Dom Feliciano Belt.

Made available in DSpace on 2021-06-26T02:53:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01. Added 1 bitstream(s) on 2021-07-15T15:24:38Z : No. of bitstreams: 1 S2317-48892020000400305.pdf: 26294169 bytes, checksum: 3b4bed20279677010df866c15a908eec (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The area is located at the northern boundary of the Guaxupe Complex, which corresponds to the northern domain of the Socorro-Guaxupe Nappe, in the Southern Brasilia Orogen, close to the Varginha Shear Zone. This study integrates petrography, mineral chemistry, optimized geothermobarometry, and trace elements thermometry data, aiming to define and characterize the metamorphic conditions and the P-T path of the granulitic rocks from the northern portion of the Guaxupe Complex. In the area, the Guaxupe Complex consists predominantly of ortho-derived rocks represented by granulitic gneisses (orthopyroxene gneisses) of felsic to mafic composition with clinopyroxene, garnet, amphibole, biotite, and rare rutile. The calculated pressure and temperature conditions record metamorphic peak around 1,078 degrees C and 14.8 kbar, compatible with ultra-high temperature metamorphism conditions, marked by grt + cpx + opx + pl +/- qtz +/- rt mineral assemblages, and granulite facies re-equilibration in the sillimanite stability field at P-T conditions of 930 to 800 degrees C and 13.5 to 11.0 kbar. The results are compatible with deeper portions of the lower crust involved in a continental collision and suggest a clockwise P-T path, typical of crustal thickening zones, followed by near-isothermal decompression during tectonic exhumation. Univ Estadual Paulista, Rio Claro, SP, Brazil Univ Estadual Paulista, Rio Claro, SP, Brazil CAPES: 001

Resumen El volcán Cerro Bravo (VCB) es un volcán compuesto ubicado en la Cordillera Central de Colombia. Durante los 50 ka de evolución del volcán la actividad eruptiva ha variado entre erupciones plinianas y emisiones efusivas. Actualmente, el cráter se encuentra ocupado por un domo que representa la última fase eruptiva de la erupción más reciente. El domo presenta una mineralogía típica de rocas andesíticas-dacíticas, con cristales de plagioclasa, anfíbol y piroxeno. La composición del anfíbol evidencia condiciones de cristalización entre 1 y 3,5 kba, de 800 a 950°C, de -5,3 a -6,8 fO2, y de 5,1 a 6,8 H2O wt.% en el fundido, mientras que en el piroxeno evidencia condiciones de 914 ±97°C y 18,5 ±9,2 Kba. Con base en estos resultados y en las relaciones mineralógicas, se puede establecer una historia de cristalización de la siguiente manera: Augita y enstatita fueron los primeros minerales en cristalizar (>20 - 30 km). Posteriormente hubo un ascenso hacia una cámara magmática ubicada entre 4,6 y 13,2 km donde comenzó la cristalización del anfíbol (a la base de la cámara cristalizó pargasita, y al techo edenita y magnesihornblenda). La disminución en la temperatura, presión y el contenido de calcio durante el ascenso del magma favorecieron la cristalización de labradorita, la cual fue variando hasta andesina. Los microlitos que hacen parte de la masa fundamental son evidencia de las últimas fases de cristalización producto de la descompresión magmática. Este estudio muestra las condiciones de cristalización que representan la última fase eruptiva de la erupción más reciente del VCB. Abstract Cerro Bravo is a composite volcano located in the Central Cordillera of Colombia. Throughout its 50 ka of evolution, this volcano has been characterised by having successive explosive to effusive phases. At present, the crater hosts a dome that represents the last eruptive phase of the last eruption. The dome has a typical mineralogy of andesite-dacite rocks with plagioclase, amphibole and pyroxene crystals. The amphibole composition allow us to constrain the melt crystallisation conditions at 1 to 3.5 kba, 800 to 950°C, -5.3 to -6.8 fO2, and 5.1 to 6.8 H2O wt.%, while the piroxene composition at 914 ±97°C y 18,5 ±9,2 Kba. Based on these results and the mineralogical configuration, it is possible to establish a crystallisation history as follows: Augite and enstatite were the first formed minerals (>20 - 30 km). After that, the magma ascended up to a magma chamber located between 4.6 and 13.2 km from the surface where the amphibole crystallisation started (pargasite at the base of the chamber and edenite and magnesiohornblende at the top). The drop in temperature and pressure also promoted the crystallisation of labradorite that transitionally changed to andesine. Plagioclase microlites in the groundmass are evidence of the last crystallisation phase close the surface, as a result of magmatic decompression. This study shows the crystalisation conditions that represent the last eruptive phase of the last eruption of the Cerro Bravo volcano.

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.

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 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.

The Paleoproterozoic metapelites within the major collisional orogenic belts of the North China Craton are generally characterized by clockwise metamorphic P-T-t paths. Here we report the case where an isobaric cooling followed by a final decompression is defined from high grade metapelites in the Jingshan Group at the southern part of the Jiao-Liao-Ji belt. The earlier prograde trajectory is constrained to be considerable heating with slight pressure increase to the peak metamorphism of 7.9–9.2 kbar at 763–770 °C by integrated methods of petrology, geothermobarometry and P-T-X pseudosection, suggesting an anticlockwise P-T path. Zircon and monazite geochronology combined with previous data suggests that the prograde metamorphism probably commenced at 1.90–1.85 Ga, followed by a slow isobaric cooling at mid-crustal level during 1.85–1.80 Ga and a final exhumation to upper crustal level presumable at 1.60–1.70 Ga. The defined P-T-t path seems to contrast with previously reported clockwise P-T-t paths. In the light of available geological evidence and recent numerical modelling, these contrasting P-T-t paths are reconciled by a tentative geodynamic model in which orogenic collapse and hot exhumation of the orogenic root during 1.90–1.85 Ga resulted in isothermal decompression of the granulites with clockwise P-T paths and triggered the prograde metamorphism for those regions displaying anticlockwise P-T paths. The pressure increase in the prograde trajectory of anticlockwise P-T path may be related to the sinking of upper-middle crustal materials to compensate for the contemporaneous ascend of the hot orogenic root. Subsequently, rocks of these contrasting P-T paths experienced a common slow isobaric cooling during 1.85–1.80 Ga. The 1.95–1.90 Ga metamorphic ages that are common in the Paleoproterozoic khondalitic rocks elsewhere in the NCC are absent in our samples can be ascribed to the high-temperature metamorphism related to this orogenic collapse and subsequent slow cooling. Therefore, our new data further supports that the JLJB is a long-lived collisional orogenic belt with post-orogenic extension at 1.90–1.85 Ga and subsequent slow cooling during 1.85–1.80 Ga. Hence, this study provides new metamorphic constraint on the post-orogenic evolution of the JLJB and insights into the mechanism of generating contrasting P-T-t paths in regional metamorphic orogens.

Compositional zoning in garnet, mineral inclusions and the application of the Zr-in-rutile thermometry on rutile inclusions in garnet in combination with conventional geothermobarometry and thermodynamic modelling allows a reconstruction of the prograde pressure-temperature evolution in felsic and mafic high-pressure granulites from the Moldanubian Zone, Bohemian Massif, Lower Austria. Most garnets in these rocks show homogeneous core compositions with high grossular contents (~30 mol%), while their rim zones have a markedly reduced grossular content. Rutile inclusions in the grossular rich garnet cores have low Zr concentrations (400 to 1300 ppm) indicating a formation temperature of ~810–820 °C which implies that the garnet host grew at these temperature conditions as well. Based on numerous polycrystalline melt inclusions, high Ti-biotite relics and a generally high Ti concentration in garnet cores, the peritectic biotite breakdown reaction is considered to be responsible for a first garnet growth, now observed as high-grossular garnet cores. The corresponding pressure is estimated to be in the range of 1.6 to 2.5 GPa, based on experimentally determined biotite breakdown reactions, thermodynamic modelling and the occurrence of high-Ti biotite in garnet cores. Rutile inclusions in low-Ca garnet rims contain significantly higher Zr concentrations (1700 to 5800 ppm) resulting in ultrahigh temperatures of ~1030 °C. Similar temperature as well as corresponding pressure estimates of 1000 ± 50 °C and 1.60 ± 0.10 GPa were obtained by geothermobarometry and thermodynamic modelling using garnet rim and re-integrated ternary feldspar compositions. These high pressure and ultrahigh temperature conditions are well known from literature for these granulites. The proposed two-phase garnet growth is not only seen in different temperatures obtained from rutile inclusions in garnet core and rim areas, but also in discontinuous trace (Cr, Ga, P, Ti, V, Zr) and heavy rare earth element profiles across garnet porphyroblasts, implying a different reaction mechanism for garnet rim growth. This second phase of garnet growth must have occurred during near isobaric heating to the ultrahigh temperature peak, most likely even at slightly lower pressures compared to the garnet core growth. By applying a binary Fe-Mg diffusion model to strongly zoned garnet grains a maximum timescale of 5–6 million years was estimated for the exhumation and cooling process, assuming a linear cooling path from 1000 °C at 1.6 GPa to 760 °C at 0.8 GPa. This short-lived ultrahigh temperature event corresponds to cooling and exhumation rates of 40–50 °C Ma−1 and 5.3–6.6 mm y−1, respectively.

Mineral inclusions in diamonds play a critical role in constraining the relationship between diamonds and mantle lithologies. Here we report the first major and trace element study of mineral inclusions in diamonds from the Karowe Mine in north-east Botswana, along the western edge of the Zimbabwe Craton. From a total of 107 diamonds, 134 silicate, 15 oxide, and 22 sulphide inclusions were recovered. The results reveal that 53% of Karowe inclusion-bearing diamonds derived from eclogitic sources, 44% are peridotitic, 2% have a sublithospheric origin, and 1% are websteritic. The dominant eclogitic diamond substrates sampled at Karowe are compositionally heterogeneous, as reflected in wide ranges in the CaO contents (4–16 wt%) of garnets and the Mg# (69–92) and jadeite contents (14–48 mol%) of clinopyroxenes. Calculated bulk rock REEN patterns indicate that both shallow and deep levels of the subducted slab(s) were sampled, including cumulate-like protoliths. Peridotitic garnet compositions largely derive from harzburgite/dunite substrates (~90%), with almost half the garnets having CaO contents

This work reconstructs the metamorphic evolution recorded in the cobbles of the Ponteranica Formation to be compared with the evolutions of the basements of the central Southern Alps and of the clasts of Aga and Vedello and Dosso dei Galli conglomerates. The Ponteranica Formation is part of the lower volcano-sedimentary cycle of the Permian sequences of the western Orobic basin. These sequences cap the Variscan basement in which different tectonometamorphic units were recognized and contoured. We sampled all the crystalline rock types preserved as clasts such as different types of metapelites, meta-intrusives, granitoids, and tourmalinites and reconstructed the relative chronology of the superposed equilibrium assemblages. Only for metapelitic rocks the PT paths were reconstructed on the ground of mineral chemical analyses and geothermobarometry. The cobbles of the Pontereanica Formation record two types of metamorphic evolution. In Type 1 cobbles, the M1 metamorphic assemblage is characterised by white mica, biotite, garnet, staurolite, ± kyanite and is interpreted as the result of the record of the Variscan collision. This assemblage is followed by M2 assemblage characterised by white mica, chlorite, ± biotite that represents the Variscan exhumation. In type 2 cobbles, relict andalusite and possible cordierite characterise the pre-M2 metamorphic re-equilibration that developed under a high thermal regime. The PT paths recorded in cobbles are consistent with the tectono-metamorphic evolutions recorded in the basement units suggesting that during the deposition of conglomerates, the type of tectono-metamorphic units exposed to erosion were equivalent to that presently exposed in the Orobic Alps.The evolution of type 1 cobbles is similar to the evolution recorded in the clasts of Aga and Vedello conglomerates, whereas the clasts of Dosso dei Galli Conglomerate recorded only the effects of the Variscan tectonic burial. The occurrence of tourmalinite cobbles may imply an age up to Upper Permian / Lower Triassic for the Ponteranica Formation. In this view, the age of the Permian conglomerates of central Southalpine decreases westward with the increase of the thermal maturity of the metamorphic imprints recorded in clasts. These observations are consistent with a westward migration of the extensional tectonics responsible for the basin opening.

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 ( 140 km.

Mafic magmas are common in back-arc basin, once stalled in the crust, these magmas may undergo different evolution. In this paper, compositional and textural variations of plagioclase as well as mineral-melt geothermobarometry are presented for basalts erupted from the central Mariana Trough (CMT). These data reveal crystallization conditions and we attempt a reconstruction of the magma plumbing system of the CMT. Plagioclase megacrysts, phenocrysts, microphenocrysts, microlites, olivine, spinel, and clinopyroxene have been recognized in basalt samples, using BSE images and compositional features. The last three minerals are homogeneous as microphenocrysts. Mineral-melt barometry indicates that plagioclase crystals crystallized and eventually grew into phenocrysts and megacrysts in mush zone with depth of 5–9 km, in which the normal zoning plagioclases crystallized in the interval of various batches of basic magma recharging. Plagioclase megacrysts and phenocrysts were dissolved and/or resorbed, when new basic magmas injected into the mush zone near Moho depth. It is inferred that magma extracted from the mush zone, and adiabatically ascended via different pathways. Some basaltic magmas underwent plagioclase and clinopyroxene microphenocrysts crystallization in low-pressure before eruption. Plagioclase microlites and outermost rims probably crystallized after eruption.

The Anrakhai Metamorphic Complex (AMC), located in the SE part of the Chu-Ili Mountains of Southern Kazakhstan in the western part of Central Asian Orogenic Belt, exhibits occurrences of HP metamorphic rocks in the form of eclogites and garnet clinopyroxenites with peak metamorphic conditions of 750–850° and 15–19 kbar estimated with both conventional geothermobarometric methods and phase diagram modeling. P-T estimates as well as intimate field relations evidently imply a common metamorphic history for eclogites and garnet clinopyroxenites of the AMC. These high-pressure, medium temperature eclogite facies P-T conditions are indicative of a collision or subduction tectonic setting. Major and trace element geochemistry suggests that they probably had a common magmatic origin as part of a suite of differentiated tholeiitic intrusions. Furthermore, distinctive mineral and chemical compositions of these eclogites and garnet clinopyroxenites correspond to the Fe-Ti type of ultramafic rocks suggesting that they may have been derivatives of intraplate tholeiitic melts, introduced into continental crust before HP metamorphism.

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.

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, wh...

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages. The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

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.

The Madurai Block which forms the central crustal block in the Precambrian Southern Granulite Terrain, south India preserves crustal evolution history with record of multiple magmatic and metamorphic episodes ranging from early Archaean to late Neoproterozoic. Documenting the precise chronology and tectonothermal evolution of these events are of paramount importance to correlate with other crustal blocks in Southern Granulite Terrain as well as to link with other continental fragments of East Gondwana. The present study focuses on hitherto unreported location within a key section of Madurai Block along the transcrustal Suruli Shear Zone known as Kambam Ultrahigh temperature Belt. This belt is noticeable for the proliferous occurrence of HT-UHT metapelites with an overall clockwise P-T trajectory. Samples of Garnet-Spinel granulite, Cordierite-Spinel granulite and associated Granite gneiss were subjected to detailed petrographic, thermobarometric and geochronologic analysis. Combined petrography, mineral reaction, geothermobarometry and pseudosection modelling of the granulite samples reveals HT-UHT metamorphic conditions with clockwise P-T path demonstrating significant decompression and cooling. LA-ICPMS U Pb dating of zircon, monazite and rutile phases within these samples constrain the timing of metamorphism as well as cooling. U Pb zircon ages of ~2500 Ma from the granulites points to new evidences for Paleoproterozoic high-grade metamorphism in the area where monazite U Pb ages at ~593 and ~ 557 Ma throw light into the imprints on ~36 Ma prolonged Neoproterozoic thermal event attributed to Pan African collisional orogeny. LA-MC-ICPMS Hf isotopic record from zircon cores point to the role of significant juvenile crustal melting/anatexis during Paleoproterozoic. In addition, numerous whispered metamorphic episodes are also identified evincing the polydeformed evolutionary history of these rocks. The ca. ~432 Ma cooling age record from rutile estimates an average cooling rate of ~3 °C/Ma over a time period of ~125 Ma, classifying Madurai block as a classic slow cooled granulite terrain with long lived UHT orogenic history. The results also bring to the fore the importance of Kambam Ultrahigh temperature belt and Suruli Shear zone which can be projected as a major terrain boundary within Southern Granulite Terrain.

The Luswishi Dome forms part of the Neoproterozoic Lufilian Arc which hosts copper-cobalt ores of the Central African Copperbelt. We report new data from a study that combines observations from drill core logging, petrographic and chemical analyses, geothermobarometry and phase equilibria modelling. Drill core logging identifies lithostratigraphic units which are partially correlated with the Katanga Supergroup based on the occurrence of regional markers. The Nguba Group constrained by the presence of glacial tillite includes variably deformed, carbonaceous shales, and carbonates. An underlying sequence of quartzites , metapelites , calc-silicates, meta-sandstones, shales, dolomites and gabbros is partially correlated with the Roan Group. Overprinting relationships of structures in drill core provide evidence for possible polyphase deformation. Early deformation generated folds which were overprinted by faults and later by brecciation caused by hydrofracturing during later deformation, and subsequently metasomatism . Petrographic examinations reveal porphyroblast-inclusion-matrix relationships which indicate that the area experienced at least two penetrative ductile deformation events, D1 and D2, which are in turn overprinted by brittle structures at D3 and later phases. Thermobarometry calculations identify peak metamorphic conditions of 580–600 °C with maximum pressures of ~7 ± 1 kbar. Integrating thermobarometry with pseudosection modelling allows reconstruction of clockwise P-T-d paths consistent with consumption of epidote , chlorite, muscovite , quartz and low Ca-plagioclase to form biotite , garnet , high Ca-plagioclase and aluminosilicates . These observations suggest Barrovian intermediate P/T -type metamorphism which can be attributed to a tectonic scenario of burial under geothermal gradients of ~20–25 °C/km prior to uplift and erosion. These data complement previous models of regional metamorphism by crustal thickening during the Lufilian orogeny .

The Malinche Pumice II is a fallout deposit produced by a Plinian-type eruption during the Pleistocene-Holocene at La Malinche volcano. La Malinche (4461 masl) is an active stratocone located in central Mexico, in the Trans-Mexican Volcanic Belt province. It is 26 km to the NE of the City of Puebla and 22 km to the SE of the City of Tlaxcala. The Malinche Pumice II was produced by one of the largest explosive eruptions of this volcano, involving a dacitic magma (63.6–65.3 wt% SiO2, anhydrous basis) with a mineral assemblage of plagioclase + amphibole + Fe Ti oxides and ± biotite phenocrysts. Larger plagioclase crystals are up to 1.2 mm in diameter, with resorbed margins and complex zoning (An26 to An43), whereas microcrysts are euhedral with homogeneous composition (An42 to An55). Amphibole is mainly magnesio-ferri-hornblende (Mg# = 0.65–0.82) and lesser amounts of pargasite. Geothermometry performed using Fe Ti oxides yields an average temperature of 873 ± 2 °C and oxygen fugacity of 1.8 units above the NNO buffer. Amphibole geothermobarometry yields a lower temperature (809 ± 19 °C) and a pressure of 230 ± 100 MPa, assuming 4.4 wt% of H2O. Considering an average density of 2650 kg/m3 for the upper crust in central Mexico, the storage region of the Malinche Pumice II dacitic magma was located at 8 ± 2 km depth. Biotite could be antecrystic or xenocrystic in origin, based on its reacted texture, large sizes (0.85–2 mm), and reaction rims. Similarly, pargasite that provides higher temperature estimates (900 ± 18 °C) and low anorthite plagioclase (An26) could also be antecrysts or xenocrysts. The Plinian eruption was likely triggered by an input of a hotter and deeper magma batch that overpressurized the dacitic magma system that eventually provoked vesiculation and fragmentation. The eruption shifted to a hydromagmatic style because of external water's entrainment that decreased the vesicularity of pumice. Our results are in good agreement with recent seismicity recorded at depths of ~7 km probably associated with activity of the Malinche's magmatic system.

The Afonso Claudio Intrusive Complex (ACIC) is an inversely zoned pluton that intruded the Aracuai-West Congo Orogen (AWCO) during the orogenic collapse, which lasted from 530 to 480 Ma. It is hosted in orthogneisses of the Pre-collisional Supersuite and paragneisses from Nova Venecia Complex and is mostly constituted by two off-centered mafic cores, composed by monzogabbro and monzodiorite, surrounded by quartz monzonite hills. Mingling and mixing zones were mapped between these rocks, where jotunite and quartz mangerite were locally found. In this study, we present a petrographic, mineral chemistry and geothermobarometric study concerning the most abundant ACIC rocks. These rocks showed emplacement conditions corresponding to middle and lower crust, which are similar to crustal levels estimated for its main host rocks. In addition, the ACIC rocks enclose many host rocks xenoliths, with some of them showing melting evidences. These evidences suggest that the ACIC host rocks were one of the main sources of the ACIC felsic magmas, which contaminated mantle mafic magmas during ACIC evolution. Due to the similarities between the AWCO post-collisional rocks, present work concludes that post-collisional plutons intruded between the middle and lower crust levels and were contaminated by its host rocks during its evolution and cooling, contributing also to the felsic magma sources.

The rheology and the conditions for viscous flow of the dry granulite facies lower crust are still poorly understood. Viscous shearing in the dry and strong lower crust commonly localizes in pseudotachylyte veins, but the deformation mechanisms responsible for the weakening and viscous shear localization in pseudotachylytes are yet to be explored. We investigated examples of pristine and mylonitized pseudotachylytes in anorthosites from Nusfjord (Lofoten, Norway). Mutual overprinting relationships indicate that pristine- and mylonitized pseudotachylytes are coeval and resulted from the cyclical interplay between brittle and viscous deformation. The stable mineral assemblage in the mylonitized pseudotachylytes consists of plagioclase, amphibole, clinopyroxene, quartz, biotite, ± garnet ± K-feldspar. Amphibole-plagioclase geothermobarometry and thermodynamic modelling indicate that pristine- and mylonitized pseudotachylytes formed at 650-750°C and 0.7-0.8 GPa. Thermodynamic modelling indicates that a limited amount of H2O infiltration (0.20-0.40 wt%) was necessary to stabilize the mineral assemblage in the mylonite. Diffusion creep is identified as the main deformation mechanisms in the mylonitized pseudotachylytes based on the lack of crystallographic preferred orientation in plagioclase, the high degree of phase mixing, and the synkinematic nucleation of amphiboles in dilatant sites. Extrapolation of flow laws to natural conditions indicates that mylonitized pseudotachylytes are up to 3 orders of magnitude weaker than anorthosites deforming by dislocation creep, thus highlighting the fundamental role of lower crustal earthquakes as agents of weakening in strong granulites.

To provide new insights into the origin of megacrysts and metasomatism of the subcontinental lithospheric mantle (SCLM), we present a detailed petrographic and geochemical investigation of clinopyroxene-phlogopite xenoliths and clinopyroxene megacrysts from the Grib kimberlite (Arkhangelsk diamond province, Russia). Clinopyroxene megacrysts and clinopyroxene from clinopyroxene-phlogopite xenoliths have similar petrography, major and trace element compositions, and are therefore classified as Cr-rich megacrysts. Geothermobarometry suggests that Cr-rich clinopyroxenes originate from within the SCLM (3.6–4.7 GPa and 764–922 °C). Phlogopite from clinopyroxene-phlogopite xenoliths have low-Ti and -Cr compositions that overlaps with phlogopite megacrysts from the Grib kimberlite. The clinopyroxene-phlogopite rocks within the SCLM are the main source for Cr-rich clinopyroxene and low-Ti phlogopite megacrysts in the Grib kimberlite matrix. Trace element compositions of studied Cr-rich clinopyroxenes have similar geochemical features to clinopyroxenes megacrysts occurrences worldwide and overlap with clinopyroxenes from phlogopite-garnet peridotite xenoliths from the Grib kimberlite. The strong depletion in Ti, Nb, Ta and to a lesser extent in Zr and Hf in clinopyroxene reflects equilibrium with Ti-oxides, such as ilmenite. The clinopyroxene-phlogopite xenoliths could be the final product of metasomatism of garnet peridotites within the SCLM beneath the Grib kimberlite. The calculated equilibrium of clinopyroxene melt compositions suggests that the metasomatic agents were derived from silicate-bearing kimberlite melts. The presence of veinlets infilled with kimberlitic mineral assemblages in clinopyroxene grains suggests that the clinopyroxene-phlogopite rocks experienced intense interactions with kimberlite melt after their formation, but before their entrainment into the host kimberlite magma. This interaction resulted in the formation of high-Ti and -Cr phlogopite and high-Ti clinopyroxene rims, zones and grains with spongy textures. Finally, we propose the sequence of metasomatic events that occurred in the SCLM and the subsequent formation of the Grib kimberlite.

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.

Garnet-bearing aluminous gneisses in the Vasil’kovka area of the Orekhov–Pavlograd zone of the Ukrainian Shield were studied using the THERIAK-DOMINO, THERMOCALC, and WINTWQ software and mineral geothermobarometry methods. The stability fields of parageneses formed at the initial, peak, and post-peak metamorphic stages have been estimated: T = 500–650 °C and P > 7 kbar, T = 800–850 °C and P ≈ 8 kbar, and T = 600–670 °C and P = 4.0–5.5 kbar, respectively. A “clockwise” PT path has been established. Based on the aluminous gneiss, the age of metamorphism is determined as Paleoproterozoic (2014 ± 11 Ma). Unique regularly oriented acicular goethite microinclusions were described in garnet. In contrast to other known oriented Ti-bearing mineral inclusions in garnet, these goethite inclusions suggest not only extremely high P and T values (necessary for the formation of oriented Ti-bearing inclusions) but also a high oxygen fugacity. The obtained data broaden the concepts of the ways and conditions of formation of regularly oriented mineral phases in garnet.