Search results for "Protolith"
showing 10 items of 65 documents
Detrital footprint of the Mozambique ocean: U–Pb SHRIMP and Pb evaporation zircon geochronology of metasedimentary gneisses in eastern Madagascar
2003
Abstract The southern East African Orogen is a collisional belt where the identification of major suture zones has proved elusive. In this study, we apply U–Pb isotopic techniques to date detrital zircons from a key part of the East African Orogen, analyse their possible source region and discuss how this information can help in unravelling the orogen. U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) and Pb evaporation analyses of detrital zircons from metasedimentary rocks in eastern Madagascar reveal that: (1) the protoliths of many of these rocks were deposited between ∼800 and 550 Ma; and (2) these rocks are sourced from regions with rocks that date back to over 3400 Ma, with…
Thermo-mechanical role of a Cambro-Ordovician paleorift during the Variscan collision: the NE margin of the Bohemian Massif
2001
Abstract The Stare Město (SM) belt (NE margin of the Bohemian Massif) represents a preserved example of an intracontinental Cambro-Ordovician rift that has been shortened during the Variscan orogeny. The rifted sequence consists of gabbroic intrusions and a leptyno-amphibolite complex of Cambro-Ordovician protolith age. The latter suffered medium pressure, granulite facies, Cambro-Ordovician metamorphism associated with extension in a continental protorift. The Variscan tectonometamorphic event is manifested by convergent orogenesis with syn-convergent intrusion of a Carboniferous tonalitic sill, high temperature–medium pressure compressional deformation of gabbros and high temperature meta…
The Adamawa-Yadé domain, a piece of Archaean crust in the Neoproterozoic Central African Orogenic belt (Bafia area, Cameroon)
2017
Abstract New field observations, ages and geochemical data are presented for the Adamawa-Yade domain, forming part of Central African Orogenic Belt in Cameroon. This belt delineates the northern margin of the Congo craton and is part of the Braziliano/Pan-African orogenic system, which was formed during amalgamation of the West Gondwana continent at the end of the Neoproterozoic. U–Pb dating indicates that the protoliths of some orthogneisses from the Adamawa-Yade domain were emplaced during three distinct periods. Tonalite-Trondhjemite-Granodiorite (TTG) suites in the Makenene area intruded at ca. 3.0–2.5 Ga, and were affected by partial melting at ca. 2.08–2.07 Ga, during the Eburnean oro…
Zircon ages, geochemistry and Nd isotopic systematics for the Palaeoproterozoic 2.3–1.8 Ga Kuilyu Complex, East Kyrgyzstan – The oldest continental b…
2017
Abstract Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and …
Archaean to Neoproterozoic magmatic events in the Kaoko belt of NW Namibia and their geodynamic significance
1998
Abstract Age relationships in the N–S trending Neoproterozoic (Pan-African) Kaoko belt of northwestern Namibia are still poorly constrained. U–Pb and Pb–Pb zircon age determinations by single grain evaporation, conventional multigrain fraction analyses and ion microprobe (SHRIMP) from a profile along the E–W Hoanib River reveal various episodes of zircon growth, ranging from late Archaean to late Neoproterozoic. From the eastern part of the profile we report crystallization ages of gneiss protoliths from 2645 to 2585 Ma, the oldest ages so far found in Namibia. Sm–Nd isotope data suggest the involvement of still older crustal material in the generation of these gneisses. A thermal event at …
Hf isotope compositions of Mediterranean lamproites: Mixing of melts from asthenosphere and crustally contaminated mantle lithosphere
2010
Abstract Mediterranean lamproites from Spain, Italy, Serbia and Macedonia are mantle-derived ultrapotassic volcanic rocks that occur exclusively in postcollisional, extension-related geodynamic settings within the Alpine–Himalaya orogenic belt. Previous studies inferred them to be multi-component melts, originating by mixing of several mantle end-members: (1) provenance-controlled crust-contaminated mantle component(s), (2) an ultra-depleted mantle component, and (3) a component ultimately derived from the convecting mantle. Hf isotope ratios of Mediterranean lamproites reported here cover a large range of eHf values from 0 to −15, for less variable eNd −2 to −13, providing further evidence…
U–Pb zircon geochronology and Hf–Nd isotopic systematics of Wadi Beitan granitoid gneisses, South Eastern Desert, Egypt
2015
Abstract Migmatitic granitoid gneisses are widespread in the southern Eastern Desert of Egypt, but their formation ages are poorly understood. They consist of granitoid gneiss ranging in composition from tonalite to granodiorite, with a distinct calc-alkaline chemical character. Zircons from three migmatitic gneiss samples from Wadi Beitan were dated on SHRIMP II and yielded magmatic emplacement ages of 719 ± 10, 725 ± 9 and 744 ± 10 Ma, respectively, indicating that the gneiss protoliths are Neoproterozoic. The zircons yielded eHf(t) values of − 4.8 to + 12.5 and corresponding Hf crustal model ages ranging from 824 to 1753 Ma. These data indicate the involvement of both juvenile and older …
Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kedougou Inlier, eastern Senegal, West Africa
1997
Abstract The Palaeoproterozoic Kedougou basement in the Mako area in eastern Senegal consists of four major rock complexes: 1) high-grade amphibolitic and gneissic rocks occuring as large xenoliths (the Sandikounda amphibolite-gneiss complex); 2) voluminous bimodal volcanic rocks (the Mako volcanic-plutonic complex); 3) the Sandikounda layered plutonic complex; and 4) trondhjemitic to calc-alkaline intrusive granitoids (the Laminia-Kaourou plutonic complex). Zircons from xenoliths of the Sandikounda amphibolite-gneiss complex yielded ages of ∼2200 Ma, which are slightly older than those of the Mako Supergroup volcanic rocks. These xenoliths also have ɛNd(t) values ranging from +2.4 to +4.1.…
Pan-African high-pressure metamorphism in the Precambrian basement of the Menderes Massif, western Anatolia, Turkey
2001
The Menderes Massif is made up of Pan-African basement and a Paleozoic to Early Tertiary cover sequence imbricated by Late Alpine deformation. The Precambrian basement comprises primarily medium- to high-grade schists, paragneisses, migmatites, orthogneisses, metagranites, charnockites, and metagabbros. High-pressure relies in the Pan-African basement are divided into two groups: eclogites and eclogitic metagabbros. The mineral assemblage in the eclogites is omphacite (Jd 44)-garnet-clinozoisite-rutile. The eclogites occur as pods and boudinaged layers in the basement schists and paragneisses. Inclusions found in the cores of the garnets indicate a medium-pressure protolith. The eclogitic m…
Structural and thermal history of poly-orogenic basement: U-Pb geochronology of granitoid rocks in the southern Menderes Massif, Western Turkey
2004
Ion microprobe U-Pb dating of granitoid rocks from key structural outcrops of the Menderes Massif in western Turkey provides an important constraint to the thermal and deformational history of a structurally complex metamorphic belt within the Alpine chain. Crystallization ages of two granite protoliths, derived from the weighted means of rim ages and the ages of homogeneous prismatic zircon grains, are 541 +/- 14 Ma and 566 +/- 9 Ma, whereas the cores of zoned pyramidal and short-prismatic zircon grains range from Palaeoproterozoic to Neoproterozoic in age. These ages indicate that amphibolite- to gramilite-facies metamorphic rocks in much of the Menderes Massif were deformed, metamorphose…