Dur’ngoi ophiolite in East Kunlun, Northeast Tibetan plateau: Evidence for paleo-Tethyan suture in Northwest China

Abstract

The A'nyemaqen (阿尼玛卿) ophiolite belt along the southern margin of the East Kunlun (昆仑) Mountains marks the suture formed by the closure of paleo-Tethys. The Dur'ngoi ophiolite in the eastern part of this belt consists of meta-peridotite, mafic-ultramafic cumulates, sheeted dikes and basaltic lavas. The meta-peridotites consist of dunite, harzburgite, lherzolite, feldspar-bearing lherzolite and garnet-bearing lherzolite and contain residual spinel with Cr # [100×Cr/(Cr+Al)] ranging from 30 to 57 and Mg # [100×Mg/(Mg+Fe 2+ )] ranging from 50 to 75, indicating an Al-and Mg-rich series. The meta-peridotites have a relatively narrow range of composition with Mg # of 89.2-92.6, Al 2 O 3 contents of (1-4) wt.% and slightly depleted chondrite normalized REE patterns, indicating that they represent relict mantle material that has undergone intermediate to low degrees of partial melting. Garnets in the lherzolite are andradite, enriched in Ca and Fe and depleted in Mg and Al (And=95-97, Pyr=0.3-5, Gro=0-3), indicating a metamorphic origin. The cumulate rocks mainly consist of dunite, wehrlite, pyroxenite and gabbro. A well-layered gabbro-pyroxenite complex is defined by modal variations in plagioclase and pyroxene. Blocks of garnet-pyroxenite or rodingite are locally present in the meta-peridotites. Garnets in the cumulate rocks are grossular (Gro=69-90, And=9-19, Br=1-12), also metamorphic origin. The diabase dikes are moderately depleted in LREE [(La/Sm) N =0.5-0.8] and HREE resulting in slightly convex chondrite-normalized patterns with slightly positive Eu anomalies (δEu=1.1-1.3). The basaltic lavas have REE patterns similar to those of MORB with (La/Sm) N ratios of 0.5-1 and small negative Eu anomalies. They appear to have been derived from a depleted mantle source and to have undergone little or no differentiation during crystallization. SHRIMP U-Pb dating of zircons from the basalts yields 206 Pb/ 238 U ages of 276-319 Ma (average 308.0±4.9 Ma). The Dur'ngoi ophiolite is interpreted as a dismembered fragment of paleo-oceanic crust emplaced during closure of the paleo-Tethyan Ocean basin. Three other suites of oceanic lavas are recognized in the area: island arc volcanic (IAV) rocks, possible back arc basin (BAB) basalts and possible post-collisional volcanic (PCV) and plutonic rocks. The distribution of these rocks suggests north-directed subduction. Opening of the A'nyemaqen oceanic basin started at least as early as Late Carboniferous (308 Ma) and the basin probably closed during the Early Triassic. The IAV formed in Late Permian (260 Ma), the BAB in Early-Middle Triassic, and the PCV in Late Triassic. Several large scale, ductile, sinistral strike-slip fault zones, extending hundreds to thousands kilometers, formed along or north of the suture during the Early-Late Triassic, e.g., they are the south margin fault zone of East Kunlun (200-220 Ma), the Altyn Tagh fault (220-230 Ma), and the North Qaidam fault zone (240-250 Ma). These strike-slip faults were probably generated by oblique subduction and closure of the...

Zircon U–Pb geochronology, geochemical and Sr–Nd–Hf isotopic compositions of the Triassic granite and diorite dikes from the Wulonggou mining area in the Eastern Kunlun Orogen, NW China: Petrogenesis and tectonic implications

“…R2 plot, they plot primarily in the late-orogenic granitoid field. Because the Proto-Tethys closed during the Early Devonian (Bian et al, 2004;Harrowfield and Wilson, 2005;Jiang et al, 1992;Pan et al, 1996;Reid et al, 2005;Roger et al, 2003;Sengör, 1987;Xu et al, 2003;Yang et al, 1996;Yang et al, 2009;Yin and Harrison, 2000), we suggest that during the Anisian, the EKO may still have been affected by the post-collision deformation between the South Kunlun belt and Middle Kunlun belt, which formed late-orogenic granitoids such as the Balugou granite dike.…”

“…Previous work has revealed that the EKO has undergone at least two stages of orogeny that are closely related to the consumption of the Proto-Tethys (Neoproterozoic to Early Devonian) and Paleo-Tethys (Carboniferous to Late Triassic) oceans (Bian et al, 2004;Harrowfield and Wilson, 2005;Jiang et al, 1992;Pan et al, 1996;Reid et al, 2005;Roger et al, 2003;Sengör, 1987;Xu et al, 2003;Yang et al, 1996;Yang et al, 2009;Yin and Harrison, 2000). The collision between the EKO and the BH-SG is thought to have been a soft collision, which accounts for the lack of significant crustal thickening in the East Kunlun (Yin and Zhang, 1997).…”

Petrogenesis and tectonic implications of Triassic mafic complexes with MORB/OIB affinities from the western Garzê-Litang ophiolitic mélange, central Tibetan Plateau

“…It is interesting that the composition of most lavas from these ophiolites is characterized by MORBs and minor OIBs in composition and a distinct lack of IATs and BONs, which is inconsistent with most ophiolites (Robinson and Zhou, 2008;Zhang et al, 2008b). The generation and tectonic nature of these ophiolites are poorly understood, and previous studies have proposed diverse models for determining these factors, including oceanic spreading, back-arc spreading and mantle plume activity (Bian et al, 2004;Guo et al, 2007;Jian et al, 2009a;Yan et al, 2005;Yang et al, 2009;Zhang et al, 2008b). A lack of knowledge of the petrogenesis, mantle sources and geodynamic setting of mafic-ultramafic rocks from these ophiolites is the main reason for such uncertainty and controversy.…”

Geochemistry, zircon U–Pb ages and Sr–Nd–Hf isotopes of an Ordovician appinitic pluton in the East Kunlun orogen: New evidence for Proto-Tethyan subduction

“…Ocean during the Late Permian to Early Triassic (Guo et al, 2007;Yang et al, 2009), with the formation of a large-scale granitoid belt (Fig. 1b;Huang et al, 2014;Xiong et al, 2014).…”

“…Numerous studies on the Paleo-Tethyan ophiolites in the A'nyemaqen suture zone have been carried out (Fig. 2a), with the conclusion of the Paleo-Tethyan ocean opened as early as Carboniferous (Chen et al, 2001;Bian et al, 2004;Yang et al, 2009). However, recent studies have shown that large amounts of Cambrian ophiolite fragments are also present in the A'nyemaqen suture zone (Fig.…”