Search results for "mantle wedge"
showing 10 items of 32 documents
Igneous petrology, zircon geochronology and geochemistry of multiply emplaced granitoid bodies from the Palaeoproterozoic Usagaran domain in central …
2019
Abstract This study reports igneous petrology, zircon ages and geochemistry for Palaeoproterozoic I-type granitic, granodioritic, Qtz-monzonitic, Qtz-monzodioritic and monzodioritic rocks from the Usagaran domain of southwestern Tanzania. These rocks can be subdivided into three groups according to their age, T-t evolution and geochemistry. The oldest group is made up of amphibolite-facies calcic-alkalic gneisses, ranging in age between ∼1984 and ∼1910 Ma, which have been divided into two subgroups regarding their T-t evolution. The first subgroup shows a constant increase in T, and the second subgroup first shows a decrease in T, followed by an increase in T. The second group consists of a…
Geochemistry of ultramafic and mafic rocks from the northern Central Asian Orogenic Belt (Tuva, Central Asia) - constraints on lower and middle arc c…
2021
Abstract The Agardagh Tes-Chem complex (ATCC) in Tuva, Central Asia (50.5°N, 95°E) exposes a rare mafic to ultramafic crust-mantle fragment that developed within a late Neoproterozoic (~570 Ma) intra-oceanic island arc system that was accreted to the Tuva-Mongolian microcontinent during the formation of the Central Asian Orogenic Belt. Residual mantle rocks (harzburgites and dunites) are highly refractory with high Cr# (0.59–0.83) and intermediate Mg# (0.46–0.52) in spinel and experienced high degrees of total melt extraction (up to 25%). In ultramafic cumulate rocks (wehrlites and pyroxenites), Cr# and Mg# in spinel are distinctly lower (0.22–0.45 and 0.34–0.37), and rare earth element (RE…
Is there a global carbonate layer in the oceanic mantle?
2021
co-auteur étranger; International audience; Previous modeling of carbonate subduction by high‐pressure experimentation has allowed to propose scenarios for bulk carbon return to the mantle, but the detailed transfer mechanisms have seldom been studied. We monitored carbonate – silicate reactions by combining high‐pressure experiments and synchrotron‐based x‐ray diffraction. Carbonates break down at moderate pressure and high temperature and CO2 is trapped at grain boundaries. Further isothermal compression yields melting, which may control continuous carbon introduction, first in the mantle wedge, and next, away from the wedge. Carbon presence has been discussed in a variety of magmatic con…
The imprint of subduction fluids on subducted MORB-derived melts (Sierra del Convento Mélange, Cuba)
2011
International audience; Major and trace element signatures and Sr-Nd-Pb isotope data for muscovite (Ms)-bearing amphibolite blocks and associated muscovite-bearing trondhjemite and quartz-muscovite rocks from the Sierra del Convento melange (eastern Cuba) indicate that Proto-Caribbean oceanic crust underwent wet partial melting processes during Mesozoic subduction and after accretion to the upper plate. Trace element normalized patterns of Ms-bearing amphibolites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE) and evidence variable trace element transfer from the Proto-Caribbean subducting slab to the mantle wedge. Ms-bearing trondhjemites show LREE…
Whole-rock Nd–Hf isotopic study of I-type and peraluminous granitic rocks from the Chinese Altai: Constraints on the nature of the lower crust and te…
2017
Abstract The nature of the lower crust and tectonic setting of the Chinese Altai in the early to middle Paleozoic are still hotly debated. Decoupling between zircon Hf and whole-rock Nd isotopic systems for granites results in different interpretations for the above issues. In order to solve the problem, whole-rock Nd–Hf isotopic analyses were conducted on representative early to middle Paleozoic I-type granite and strongly peraluminous granites and rhyolites from the Chinese Altai. The I-type granites show metaluminous to weakly peraluminous feature and have eNd(t) values ranging from − 2.2 to + 0.8 and eHf(t) from + 3.9 to + 12.9, respectively. The strongly peraluminous granites and rhyol…
Noble-gas signature of magmas from a heterogeneous mantle wedge: The case of Stromboli volcano (Aeolian Islands, Italy)
2014
Abstract We report on the variation of the elemental (He, Ne, and Ar) and isotopic (He and Ar) compositions of olivine- and clinopyroxene-hosted fluid inclusions hosted in lavas, pyroclastics, and cumulate xenoliths from the last 60 ka of the eruptive history of Stromboli volcano, Italy. Samples belong to (i) the present-day activity as represented by shoshonitic (SHO) basalts, i.e., pumices with low porphyritic (LP) content and high porphyritic (HP) scoriae; (ii) the subalkaline versus alkaline products erupted at Stromboli during its subaerial history among the extreme magmatic series, i.e., calc-alkaline (CA) and potassic (KS); and (iii) the only known ultramafic cumulates (San Bartolo w…
Late Cretaceous lithospheric extension in SE China: Constraints from volcanic rocks in Hainan Island
2015
Abstract Petrological, geochemical and in-situ zircon U–Pb dating and Hf-isotope analyses have been carried out on a suite of basalt–andesite–rhyolite volcanic rocks exposed in the Liuluocun area, Hainan Island, SE China. Zircon analyses show that these volcanic rocks crystallized in the Early Cretaceous (ca. 102 Ma). The basalts are characterized by low MgO contents and mg-numbers but high rare earth element, high field strength element and large ion lithophile element contents and Nb–Ta negative anomalies. They have relatively uniform Sr–Nd isotope compositions with e Nd (t) values of − 4.09 to − 3.63. The andesites show enrichment of high field strength element and rare earth element wit…
The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism
1990
Volcanism extending over 11 Ma is represented in the rocks of the Nevados de Payachata region, culminating in the formation of two large composite stratocones within the last 500 000 years. Chemically distinct mafic magmas are erupted at a number of parasitic centers. These cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones. Two distinct trends are defined by the intermediate and evolved rocks; a high LILE (large ion lithophile element), TiO2 and Ce/Yb lineage among the youngest rocks (including the two major stratocones), and a more typical calc-alkaline trend among the older (>1 Ma) rock type…
Effects of Rayleigh number length thickness of continent on time of mantle flow reversal
1998
Abstract Numerical experiments are carried out to study the effects of continents on the structure of thermal convection in the mantle. The mantle is modelled by a viscous fluid occupying a horizontally extended rectangular 2-D region of aspect ratio 10:1. Continents are treated as thick rigid heat-conducting plates placed in the mantle, with free-slip and with no-slip conditions. Continents restrict the heat release from the underlying mantle; the mantle material heats up and becomes lighter; as a result, a hot upwelling flow replaces downwelling. We calculate the characteristic time τ of this restructuring for various values of model parameters and obtain analytical approximations for τ a…
Constraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism
2008
[1] Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from southern Italy (seven Aeolian Islands, Mt. Vulture, Etna, Ustica, and Pantelleria) range from 2.3 to 7.1 Ra. Importantly, the phenocryst 3He/4He correlate well with whole rock Sr isotopic composition (0.70309–0.70711), reflecting the mixing of two sources. A significant contribution of He from crustal contamination is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr (and a…