Search results for "ELT"
showing 10 items of 2198 documents
Coupled silicon-oxygen isotope fractionation traces Archaean silicification
2011
International audience; Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa.The δ30Si and δ18O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (-0.64‰ 30Si 18O 30Si and δ18O values as high as + 0.81‰ and + 15.6‰, r…
The Late Cretaceous Klepa basalts in Macedonia (FYROM) – Constraints on the final stage of Tethys closure in the Balkans
2017
The waning stage(s) of the Tethyan ocean(s) in the Balkans are not well understood. Controversy centres on the origin and life-span of the Cretaceous Sava Zone, which is allegedly a remnant of the last oceanic domain in the Balkan Peninsula, defining the youngest suture between Eurasia- and Adria-derived plates. In order to investigate to what extent late-Cretaceous volcanism within the Sava zone is consistent with this model, we present new age data together with trace-element and Sr–Nd–Pb isotope data for the Klepa basaltic lavas from the central Balkan Peninsula. Our new geochemical data show marked differences between the Cretaceous Klepa basalts (Sava Zone) and the rocks of other volca…
Geochemical constraints on basalt petrogenesis in the Strait of Sicily Rift Zone (Italy): Insights into the importance of short lengthscale mantle he…
2020
Igneous activity from the late Miocene to historic time (most recently 1891 CE) in the Strait of Sicily has created two volcanic islands (Pantelleria and Linosa) and several seamounts. These volcanoes are dominated by transitional (ol + hy-normative) to alkaline (ne-normative) basaltic lavas and scoriae; volcanic felsic rocks (peralkaline trachyte-rhyolite) crop out only on Pantelleria. Although most likely erupted through continental crust, basalts demonstrate no evidence of crustal contamination and are geochemically similar to oceanic island basalts (OIB). Despite their isotopic similarities, there are considerable compositional differences with respect to major and trace element geochem…
GEOCHEMICAL CONSTRAINTS ON THE ORIGIN OF CALCALKALINE AND ALKALINE MAGMAS OF THE EASTERN TRANS-MEXICAN VOLCANIC BELT
1988
Se presentan datos de elementos mayores, elementos trazas y tierras raras de rocas calco-alcalinas y alcalinas de la parte este del cinturón volcánico transmexicano (TMVB), así como conclusiones acerca de su origen y de su significado tectónico. Las andesitas y dacitas muestran características geoquímicas que descartan su derivación de los magmas basálticos por el proceso de cristalización fraccionada. Las distribuciones gráficas de los elementos LIL y HFS son interpretadas como indicadoras de la formación de magmas en el manto superior modificado por procesos de subducción. Las riolitas se interpretan como resultado de la fusión parcial de la corteza continental.
Metamorphism and melting of picritic crust in the early Earth
2014
Abstract Partial melting experiments with models of Archean oceanic crust (MAOC; with 11, 13 and 15 wt.% MgO) are used to investigate the role of metamorphism and melting of primary picritic compositions in the formation of TTG-like melts and continental crust on the early Earth. The approach investigates the possibility that the average early crust composition was comparatively MgO-rich and evolved to lower magnesium content during the secular cooling of the Earth. High-pressure partial melting experiments indicate a transition of melt compositions from aluminous basaltic melts in MAOC 15 to predominantly tonalitic melts in MAOC 11 and higher melting temperatures with increasing magnesium …
Geochemical heterogeneities in magma beneath Mount Etna recorded by 2001-2006 melt inclusions
2015
We present a geochemical study on olivine and clinopyroxene-hosted melt inclusions (MIs) from 2001 to 2006 Etna basaltic lavas and pyroclastites. Three MI suites are distinguished on the basis of trace element fingerprinting. Type-1 MIs (from 2001 Upper South and 2002 Northeast vents) share their trace element signature with low-K lavas erupted before 1971. Critical trace element ratios (e.g., K/La, Ba/Nb), along with Pb isotope data of Type-1 MIs provide evidence for a heterogeneous mantle source resulting from mixing of three end-members with geochemical and isotopic characteristics of EM2, DMM, and HIMU components. Type-1 MIs composition does not support involvement of subduction-related…
MORB-type neon in an enriched mantle beneath Etna, Sicily
1997
Abstract Noble gas elemental and isotopic compositions were determined for five CO 2 –CH 4 samples collected around Etna, Sicily, to investigate the geochemical features of the mantle beneath the volcano. The samples contain mantle-derived noble gases. The measured helium isotopic ratios ( 3 He/ 4 He) vary between 5.9 and 6.4 times atmospheric ratio ( R a =1.4×10 −6 ), which are comparable to the ratios of olivines (6.1–8.2 R a ) in the lavas of the same volcano [1]. Neon in the samples is enriched in both 20 Ne and 21 Ne ( 20 Ne/ 22 Ne 9.95–10.7, 21 Ne/ 22 Ne 0.030–0.037), indicating derivation from the mantle. The δ ( 20 Ne/ 22 Ne)/ δ ( 21 Ne/ 22 Ne) values are identical with that of mid-…
Experimental calibration and implications of olivine-melt vanadium oxybarometry for hydrous basaltic arc magmas
2018
The strong dependence of vanadium partitioning between olivine and silicate melt (DVOl-M) on redox conditions (fO2) can be used as sensitive oxybarometer in magmatic systems. Here we extend the experimental database on DVOl-M, obtained so far at high temperatures (mainly above 1250 °C), to lower temperatures that are typical for island-arc basalts. Crystallization experiments were performed using a composition from Mutnovsky volcano (Kamchatka), and the investigated temperature, pressure, and oxygen fugacity ranges were 1025–1150 °C, 0.1 and 0.3 GPa, and ΔQFM of –0.5 to +3.2, respectively. The water content in melts ranged from 0.6 to ∼6.5 wt% H2O. The data demonstrate a strong negative cor…
Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from K Ar dating, chemical …
2019
Highlights • Volcanic activity of Harrat Uwayrid (NW Arabia) lasted from 8.2 to 0.3 Ma. • Alkali olivine basalts are followed by basanites, tephrites and tephriphonolites. • Sr-Nd-Pb isotopic ratios of all volcanic rocks suggest a PREMA source. • Different degrees of partial melting of amphibole-garnet-spinel lherzolite • Lithospheric mantle source rather than asthenosphere or plume-type mantle Abstract The volcanic field of Harrat ar Rahah-’Uwayrid (NW Saudi Arabia) consists of an older plateau basalt sequence that overlies Cambrian sandstone and younger cinder cones with smaller flows that are concentrated in the central part of this field. Petrographic and whole rock geochemical data ind…
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…