Search results for "Mafic"
showing 10 items of 126 documents
Source composition, fractional crystallization and magma mixing processes in the 3.48–3.43Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swazilan…
2016
Abstract The ca. 3480–3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200–3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis. In c…
Carboniferous high-potassium I-type granitoid magmatism in the Eastern Pontides: The Gümüşhane pluton (NE Turkey)
2010
The Gumushane pluton, a high-K calc-alkaline I-type granodionte/granite complex, forms an important component of the pre-Liassic basement of the Eastern Pontides (NE Turkey) In its eastern part, the pluton shows a compositional zonation ranging from biotite-hornblende granodiorite in the NW through biotite-hornblende granite to leucogranite/granophyre in the SE Numerous mafic microgranular enclaves (up to similar to 40 cm in diameter) suggest the former presence of globules of mafic melt during crystallization Emplacement of the pluton occurred during the latest Early Carboniferous, as shown by the 320 +/- 4 Ma Ar-40-Ar-39 bionte/homblende and 324 +/- 6 Ma LA-ICP-MS U-Pb zircon ages. In Har…
Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline Province
2004
Geological mapping and diamond exploration in northern Quebec and Labrador has revealed an undeformed ultramafic dyke swarm in the northern Torngat Mountains. The dyke rocks are dominated by an olivine-phlogopite mineralogy and contain varying amounts of primary carbonate. Their mineralogy, mineral compositional trends and the presence of typomorphic minerals (e.g. kimzeyitic garnet), indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite. Recognized rock varieties are aillikite, mela-aillikite and subordinate carbonatite. Carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene. In contrast, mela-aillikites are richer …
The demir kapija ophiolite, Macedonia (FYROM): A Snapshot of subduction initiation within a back-arc
2013
The Demir Kapija ophiolitic complex in southern Macedonia–FYROM (Former Yugoslav Republic of Macedonia) represents the southernmost exposure of the Tethyan Eastern Vardar ophiolitic unit in the Eastern Mediterranean. It consists of a mafic volcanic sequence (pillow basalts, sheeted dyke diabases and gabbros) that was subsequently intruded by island arc magmas with and without adakitic affinity. The mafic volcanic sequence is characterized by slightly increased ratios of large ion lithophile elements to high field strength elements (LILE/HFSE), flat rare earth element (REE) patterns, radiogenic 143Nd/144Nd (up to 0·51272) and high TiO2 contents (which reflect Pl + Ol + Cpx fractionation). Th…
New constraints on granulite facies metamorphism and melt production in the Lewisian Complex, northwest Scotland
2018
The research carried out for this study was part of YF's Master Thesis at the Institute of Geoscience, Johannes Gutenberg University, Mainz, which provided the funding for fieldwork and laboratory analyses. TJ acknowledges support from Open Fund GPMR210704 from the State Key Lab for Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. In this study we investigate the metamorphic history of the Assynt and Gruinard blocks of the Archaean Lewisian Complex, northwest Scotland, which are considered by some to represent discrete crustal terranes. For samples of mafic and intermediate rocks, phase diagrams were constructed in the Na2O-CaO‐K2O‐FeO‐MgO‐Al2O3-SiO2-H2O-T…
The composition of fluids stored in the central Mexican lithospheric mantle: Inferences from noble gases and CO2 in mantle xenoliths
2021
We present the first isotopic (noble gases and CO2) characterization of fluid inclusions coupled to Raman microspectroscopy analyses in mantle xenoliths from Central Mexico, a geodynamically complex area where the Basin and Range extension was superimposed on the Farallon subduction (terminated at 28 Ma). To characterize the isotopic signature of the Central Mexican lithospheric mantle, we focus on fluid inclusions entrapped in mantle xenoliths found in deposits of the Joya Honda maar (JH), a Quaternary monogenetic volcano belonging to the Ventura Espiritu Santo Volcanic Field (VESVF) in the state of San Luis Potosí (central Mexico). Thirteen ultramafic plagioclase-free xenoliths were selec…
Zircon age and occurrence of the Adaatsag ophiolite and Muron shear zone, central Mongolia: constraints on the evolution of the Mongol–Okhotsk ocean,…
2005
The Adaatsag ophiolite in eastern Mongolia is situated in the Mongol–Okhotsk suture zone, which extends from central Mongolia through Transbaikalia to the Sea of Okhotsk and separates the Siberian and Amurian (Mongolian) plates. The ophiolite sequence passes upwards from serpentinite melange and serpentinized dunite and harzburgite, through layered gabbro (with leucogabbro pegmatite dykes), wehrlite and clinopyroxenite, to isotropic gabbro and leucogabbro, sheeted mafic dykes, and olivine-rich basaltic lavas, overlain by red chert and meta-clastic sediments. A single-zircon mean 207 Pb/ 206 Pb evaporation age of 325.4 ± 1.1 Ma for a leucogabbro pegmatite dyke records the time of igneous cry…
Zircon ages of metamorphic and magmatic rocks within peridotite-bearing mélanges: Crucial time constraints on early Carboniferous extensional tectoni…
2013
Abstract We dated and geochemically characterized peridotite-bearing melanges in the Chinese South Tianshan and within the Main Tianshan Shear Zone. The Yushugou-Tonghuashan melange in the Chinese South Tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite (predominantly lherzolite) massif with a high-grade metamorphic terrane (ca. 10 km long; protolith age ≥ ca. 445–466 Ma). Metamorphic zircons of a mafic granulite (eNd(t) = 5.0) yielded a weighted mean 206Pb/238U age of 341 ± 8 Ma that we interpret as the time of granulite-facies metamorphism. The youngest zircon rims of an intermediate granulite (eNd(t) = − 4.3) have a mean age of 332 ± 13 Ma that records a …
Anatectic amphibole and restitic garnet in Variscan migmatite from NE Sardinia, Italy: insights into partial melting from mineral trace elements
2014
We report results of a laser-ICP-MS investigation of trace element contents in the main constituent minerals of an amphibole-bearing migmatite from the Variscan orogen in northeastern Sardinia. The migmatite is associated with migmatised orthogneiss and Al-silicate-bearing pelitic migmatites. The protolith of the amphibole-bearing migmatite was a mid-Ordovician igneous rock of intermediate composition characterised by a biotite + plagioclase + quartz assemblage. The migmatite consists of mesosomes and tonalitic (or, less frequently, granodioritic) leucosomes, characterised by amphibole crystals (potassian ferropargasite) up to 2 cm in size. The tonalitic leucosomes are made up of quartz, pl…
Phase equilibrium constraints on a deep crustal metamorphic field gradient: metapelitic rocks from the Ivrea Zone (NW Italy)
2011
The metamorphic rocks of the Ivrea Zone in NW Italy preserve a deep crustal metamorphic field gradient. Application of quantitative phase equilibria methods to metapelitic rocks provides new constraints on the P–T conditions recorded in Val Strona di Omegna, Val Sesia and Val Strona di Postua. In Val Strona di Omegna, the metapelitic rocks show a structural and mineralogical change from mica‐schists with the common assemblage bi–mu–sill–pl–q–ilm ± liq at the lowest grades, through metatexitic migmatites (g–sill–bi–ksp–pl–q–ilm–liq) at intermediate grades, to complex diatexitic migmatites (g–sill–ru–bi–ksp–pl–q–ilm–liq) at the highest grades. Partial melting in the metapelitic rocks is consi…