Geochemical Features, Age, and Tectonic Significance of the Kekekete Mafic‐ultramafic Rocks, East Kunlun Orogen, China

Abstract:The Kekekete mafic‐ultramafic rocks are exposed in the Kekesha‐Kekekete‐Dawate area, which are in the eastern part of the East Kunlun Orogenic Belt It outcrops as tectonic slices intruding tectonically in the Paleoproterozoic Baishahe Group and the Paleozoic Nachitai Group. The Kekekete mafic and ultramafic rocks is located near the central fault in East Kunlun and lithologically mainly consists of serpentinite, augite peridotite, and gabbro. The LA‐ICP‐MS zircon U‐Pb age of the gabbro is 501 ± 7 Ma, indicating that Kekekete mafic‐ultramafic rocks formed in the Middle Cambrian. This rock assemblage is relatively poor in SiO2 and (Na2O+K2O) but rich in MgO and SFeO. The chondrite‐normalized REE patterns of the gabbro dip slightly to the right; the primitive mantle and MORB‐normalized spidergrams of trace elements show enrichment of large‐ion lithophile elements (Cs, Rb, Ba, etc.) and no differentiation of high field strength elements. The general dominance of E‐MORB features and the geochemical characteristics of OIB suggest that the Kekekete mafic‐ultramafic rocks formed in an initial oceanic basin with slightly enriched mantle being featured by varying degrees of mixing of N‐MORB depleted mantle and a similar‐OIB‐type source. From a comprehensive study of the previous data, the author believes that the tectonic history of the East Kunlun region was controlled by a geodynamic system of rifting and extension in the late stages of the Neoproterozoic to early stages of the Early Paleozoic and this formed the paleo‐oceanic basin or rift system now represented by the ophiolites along the central fault in East Kunlun, the Kekekete mafic‐ultramafic rocks and Delisitan ophiolite.