Search results for "Mafic"
showing 6 items of 126 documents
Os isotopes and highly siderophile elements (HSE) in the Ligurian Ophiolites, Italy.
2000
The Os isotopic and highly siderophile element (HSE) concentration systematics of the upper mantle have been the focus of much recent interest. However, little systematic study has addressed the combined HSE and Os isotopes in mantle rocks from MOR ophiolites. The Ligurian ophiolites in northern Italy represent an important class of ophiolites representing, like Zabargad or the Galicia margin, crust with clear ocean ridge affinity floored by older mantle with arguably more continental affinities [Rampone et al., J. Petrol. 36, 18–105, 1995; Rampone et al., Contrib. Mineral. Petrol. 123, 61–67, 1996]. We have studied a suite of 15 geochemically and geologically well characterized mantle peri…
Tectono-Magmatic Evolution, Age and Emplacement of the Agardagh Tes-Chem Ophiolite in Tuva, Central Asia: Crustal Growth by Island arc Accretion
2004
Publisher Summary The Agardagh Tes–Chem ophiolite in Tuva, Central Asia, is part of the Central Asian Mobile Belt which formed during subduction–accretion processes lasting from the early Neoproterozoic to the late Palaeozoic. The Agardagh Tes–Chem ophiolite marks the northwestern border of the Tuva–Mongolian Massif (TMM), which comprises several intrusive and metamorphic complexes. These complexes consist of metatonalites, gneisses, migmatites, amphibolites, marbles, quartzites, low-grade metasedimentary rocks and minor ultramafic lenses, and radiometric ages range between 536 and 464 Ma. Field observations suggest that the southwestern part of the Tes–Chem unit represents the lower to int…
Geochemistry, geochronology and isotope geology of Nakfa intrusive rocks, northern Eritrea: products of a tectonically thickened Neoproterozoic arc c…
2001
Abstract The north-south-trending Neoproterozoic volcano-sedimentary plutonic associations in northern Eritrea are part of the Nubian Shield. The Nakfa intrusive rocks range in composition from gabbro to syeno-diorite to granite and alkaline syenite and intrude supracrustal rocks of volcanic and sedimentary origin. All granitoid rocks are metaluminous or slightly peraluminous and have typical I-type chemical signatures. The calc-alkaline intrusive rocks and the alkaline syenites have geochemical characteristics (e.g. low Nb values) typical of arc intrusives and plot as volcanic arc granites on various discriminant diagrams. Single zircon evaporation Pb-Pb ages and conventional multigrain U-…
Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano
2014
We use volatiles in melt inclusions and nominally anhydrous phenocrysts, with volcanic gas flux and composition, and textural analysis of mafic inclusions to estimate the mass of exsolved vapour prior to eruption at Soufriere Hills Volcano (SHV). Pre-eruptive andesite coexists with exsolved vapour comprising 1.6–2.4 wt% of the bulk magma. The water content of orthopyroxenes indicates a zone of magma storage at pressures of approximately 200–300 MPa, whereas melt inclusions have equilibrated at shallower pressures. Inclusions containing >3 wt% H2O are enriched in CO2, suggesting flushing with CO2-rich gases. Intruding mafic magma contains >8 wt% H2O at 200–300 MPa. Rapid quenching is accompa…
Corundum Anorthosites-Kyshtymites from the South Urals, Russia: A Combined Mineralogical, Geochemical, and U-Pb Zircon Geochronological Study
2019
Kyshtymites are the unique corundum-blue sapphire-bearing variety of anorthosites of debatable geological origin found in the Ilmenogorsky-Vishnevogorsky complex (IVC) in the South Urals, Russia. Their mineral association includes corundum-sapphire, plagioclase (An61&ndash
Ultra-high temperature metamorphism recorded in Fe-rich olivine-bearing migmatite from the Khondalite Belt, North China Craton
2018
International audience; We document the first occurrence of Fe‐rich olivine‐bearing migmatitic metapelite in the Khondalite Belt, North China Craton. Petrological analyses revealed two exotic assemblages of orthopyroxene+spinel+olivine and orthopyroxene+spinel+cordierite. Phase relation modelling suggests that these assemblages are diagnostic of ultra‐high temperature (UHT) metamorphism in the Fe‐rich system, with temperatures from 1,000 to 1,050°C at 0.6 GPa. U–Th–Pb SIMS analyses on zircon reveal a similar age of c. 1.92 Ga for the olivine‐bearing migmatite and an adjacent gabbronoritic intrusion that is therefore identified as the heat source for the UHT metamorphism. These results, coup…