Search results for "Adakite"

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…

Geochemical signature of Paleozoic accretionary complexes of the Central Asian Orogenic Belt in South Mongolia: Constraints on arc environments and c…

2006

Abstract We report a reconnaissance geochemical and Nd-isotopic study for 33 metaigneous and metavolcaniclastic rocks from the ca. 470 to 290 Ma old Gurvan Sayhan, Zoolen, Nemegt Uul, Bayanleg-Hatuu, and Tseel mountain ranges in southern Mongolia, in order to infer tectonic environments, test a recently proposed multiple terrane model, and explore the late-stage development of the southern Central Asian Orogenic Belt (CAOB). Samples from the Gurvan Sayhan and the Zoolen ranges have a predominantly intermediate, calc-alkaline composition; they display LREE enrichment, excess abundances of fluid-soluble elements, and low concentrations of high-field strength elements. These data, in combinati…

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 …

Emergence of blueschists on Earth linked to secular changes in oceanic crust composition

2015

The oldest blueschists—metamorphic rocks formed during subduction—are of Neoproterozoic age1, and 0.7–0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago2. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa−1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface3. Here we show that the absence of blueschists in the ancient geological rec…

Post-collisional adakite-like magmatism in the Ağvanis Massif and implications for the evolution of the Eocene magmatism in the Eastern Pontides (NE …

2011

In the Anatolia, the Caucasus and northwest Iran, the Eocene epoch is characterized by widespread basic to acidic magmatism, whose temporal and spatial evolutions and origin are poorly understood. In this paper, we provide geochronological and geochemical data on a suite of Early Eocene intrusions from northeast Turkey and discuss their origin within a regional tectonic framework. Post to late-collisional, moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude Permo-Triassic low-grade metamorphic rocks in the southern part of the Eastern Pontides very close to the Neo-Tethyan Izmir-Ankara-Erzincan suture. In places, the intrusives display…

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…

Partial Melting and Counterclockwise P T Path of Subducted Oceanic Crust (Sierra del Convento Melange, Cuba)

2007

Tectonic models for accretion of the Central Asian Orogenic Belt

2007

The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic–Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian–Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with…

Evolution of a Permian intraoceanic arc–trench system in the Solonker suture zone, Central Asian Orogenic Belt, China and Mongolia

2010

Abstract The identification of a fossil arc–trench system from the ophiolite-decorated Solonker suture zone in the southernmost Central Asian Orogenic Belt (CAOB) enables us to constrain the timing of pre-subduction extension (ca. 299–290 Ma), subduction initiation (ca. 294–280 Ma), ridge–trench collision (ca. 281–273 Ma) and slab break-off (ca. 255–248 Ma) in the Permian. A fraction of proto-arc crust (ca. 45 km long, up to 8 km wide) is preserved as a volcanic–plutonic sequence and is juxtaposed against a wide (ca. 30–80 km) forearc melange. This proto-arc crust comprises two distinct magma series, island arc tholeiite (IAT) and mid-ocean ridge basalt (MORB), both of which have strong sup…

Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for conti…

2008

Abstract We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), hi…