Search results for "Ophiolite"
showing 10 items of 54 documents
A geotraverse across two paleo-subduction zones in Tien Shan, Tajikistan
2017
Abstract We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earli…
Kinematics and U-Pb zircon ages of the sole metamorphics of the Marmaris Ophiolite, Lycian Nappes, Southwest Turkey
2018
In the eastern Mediterranean, the Lycian Nappes are found in the structurally uppermost position in the Anatolide-Tauride belt related to the closure of the Neotethys. In Western Turkey, the Marmaris Ophiolite with the metamorphic sole occupies the uppermost tectonic position in the Lycian belt. The metamorphic sole is represented by discontinuous tectonic slices composed of amphibolites, phyllites, micashists and quartzo-feldspathic micaschists. Zircons from the micashists and quartzo-feldspathic micaschists display dark cores and rims. The cores yield ages between 229 and 175 Ma, inner rims yield ages between 153 and 143 Ma and the outer rims show a concordia age of 96.7 ± 0.79 Ma. In ter…
Zircon ages of the Bayankhongor ophiolite mélange and associated rocks: Time constraints on Neoproterozoic to Cambrian accretionary and collisional o…
2010
Abstract Central Mongolia is geologically characterized by close juxtaposition of an accreted oceanic terrane with an arc-microcontinent collision zone. We present new U–Pb zircon ages and geochemical data for the Bayankhongor ophiolite melange from the oceanic terrane and for a syenite porphyry pluton from the arc-microcontinent zone, providing critical constraints on the regional evolution in late Neoproterozoic to early Cambrian times. An anorthosite (655 ± 4 Ma) associated with layered gabbro, a rodingite (metasomatized layered gabbro) (647 ± 6 Ma), and a high-level isotropic amphibole gabbro (647 ± 7 Ma) yielded the oldest zircon ages for the plutonic part of the ophiolite. A plagiogra…
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…
Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints
2009
Abstract The Samothraki mafic suite in the north-eastern Aegean Sea, Greece, is an ‘in situ’ magmatic complex comprising gabbros, sparse dykes and basalt flows and pillows cut by late dolerite dykes. We have determined the age of the complex by SHRIMP zircon geochronology of a gabbro as 159.9 ± 4.5 Ma (i.e. Oxfordian; early Late Jurassic), which precludes any correlation with the so-called Lesvos ophiolite further south (253.1 ± 5.6 Ma; Latest Permian). Six distinct, hitherto unrecognised, geochemical groups have been identified among the basalts and dolerites of the Samothraki mafic suite on the basis of trace-element and Nd–Sr isotopic characteristics. All groups show the presence of an e…
The Gabal Gerf complex: A precambrian N-MORB ophiolite in the Nubian Shield, NE Africa
1995
We report geochemical and isotopic data for tectonically dismembered units of the Cabal Gerf mafic-ultramafic complex, the largest Neoproterozoic (Pan-African) ophiolite in the Arabian-Nubian Shield and located near the Red Sea in the border region between Egypt and the Sudan. The complex consists of basaltic pillow lavas, sheeted dykes, isotropic and layered gabbros and an ultramafic melange, all in tectonic contact along thrust sheets. Major- and trace-element data, including REE, for the pillow lavas and sheeted dykes are indistinguishable from modem high-Ti N-MORB. Chemical variations in the various rock types can be ascribed to fractionation and accumulation involving olivine, clinopyr…
Neoproterozoic Ophiolites of the Arabian-Nubian Shield
2004
Publisher Summary Ophiolites of mid-Neoproterozoic age are abundant in the Arabian-Nubian Shield (ANS) of NE Africa and Arabia. The ANS ophiolitic mantle was mostly harzburgitic, containing magnesian olivines and spinels that have compositions consistent with extensive melting. Cumulate ultramafics transition upwards into layered gabbro. Several crystallization sequences are inferred from ANS transition zones and cumulate gabbro sections. In all samples studied, olivine and spinel crystallized first, followed by cpx-plag, cpxopx-plag, and opx-cpx-plag. The ANS in NE Africa and W. Arabia is the largest tract of juvenile continental crust of Neoproterozoic age on Earth. The best preserved oph…
Cambrian ophiolite complexes in the Beishan area, China, southern margin of the Central Asian Orogenic Belt
2018
Abstract We present zircon ages and geochemical data for Cambrian ophiolite complexes exposed in the Beishan area at the southern margin of the Central Asian Orogenic Belt (CAOB). The complexes consist of the Xichangjing-Xiaohuangshan and Hongliuhe-Yushishan ophiolites, which both exhibit complete ophiolite stratigraphy: chert, basalt, sheeted dikes, gabbro, mafic and ultramafic cumulates and serpentinized mantle peridotites. Zircon grains of gabbro samples yielded 206 Pb/ 238 U ages of 516 ± 8, 521 ± 4, 528 ± 3 and 535 ± 6 Ma that reflect the timing of gabbro emplacement. The geochemical data of the basaltic rocks show enrichment in large-ion lithophile elements and depletion in the high f…
The Shishkhid ophiolite, northern Mongolia: A key to the reconstruction of a Neoproterozoic island-arc system in central Asia
2005
Abstract The Shishkhid ophiolite is a well-preserved 13 km-thick mafic-ultramafic assemblage which comprises (from bottom to top): mantle tectonites (∼6 km), layered and isotropic gabbro (∼4.5 km), sheeted dykes (up to 0.5 km), a bimodal assemblage of basalt and rhyolite (up to 0.7 km), as well as andesitic pyroclastic rocks (∼2 km). The volcanic rocks are overlain by a 3 km-thick sedimentary sequence showing progressive subsidence of the volcanic edifice after cessation of volcanism. The sedimentary unit is unconformably overlain by Ediacaran-Cambrian platform sediments. SHRIMP U-Pb dating of magmatic zircons from a rhyolite of the lower volcanic unit has yielded a concordant 206 Pb/ 238 U…
Devonian to Permian plate tectonic cycle of the Paleo-Tethys Orogen in southwest China (II): Insights from zircon ages of ophiolites, arc/back-arc as…
2009
Abstract New SHRIMP zircon ages for ophiolites, arc/back-arc assemblages and within-plate igneous rocks constrain the evolution of the Paleo-Tethys Orogen of southwest China. Ophiolites represent remnants of the Paleo-Tethys ocean, which was divided by the Simao terrane into two tracts, the main ocean in the west (current position) and a branch in the east. The main ocean has been inferred to originate from Gondwana break-up in the Early Devonian, and the heritage is preserved as the Changning-Menglian ophiolite (SSZ-type). The oceanic branch is represented by the Ailaoshan (NMORB-type)–Jinshajinag (EMORB-type) ophiolites. Zircons from a diabase and a plagiogranite of the Ailaoshan ophiolit…