Qimanyuter Ophiolite Melange And Its Tectonic Significance, Western Kunlun Mountain, NW China

Based on the 1/250000 mapping work of Yutian and Bolike sheets, an Early Paleozoic ophiolite melange has been found in western Kunlun mountain and named as Qimanyuter Ophiolite melange(QOM). This ophiolite melange is exposed along the north flank of Kunlun Mountains, from south of Pulu-Liushui village Yutan county to south of Nuer of Ciler county. Qimanyuter ophiolite melange crops out 1-3 km in width and extends EW-NEE about 50 km, parallels to the Kunlun Mountains. Qimanyuter Ophiolite melange is composed mainly of serpentinite (metapyrolite), peridotite, bedded gabbro, grbbro, diabase sheet and pillow-like and massif basalt as well. Associated sedimentary rocks with this ophiolite melange include silicalite, dark gray silicalite and thin-bedded limestone. The geological, geochemical and geochronological features regarding to this ophiolite melange and related blocks to its both north and south sides have been investigated in this thesis. As a consequence of this research the tectonic evolution process of western Kunlun mountain has been discussed.The Qimanyuter Ophiolite melange takes role as a tectonic boundary separating South Kunlun Massif from North Kunlun Massif.. The lower member of typical ophiolite suit is exposed at outsides of the Qimanyuter Ophiolite melange and in between, there distribute the basalt, deep sea limestone and silicalites. These different litho-members contact to each other with ductile shear zones. All these ductile shear zones are characterized by northward thrusting.The U-Pb dating on zircons from the bedded gabbro of the Qimanyuter Ophiolite melange gives an age of 526 ?1 Ma(Early Cambrian). It agrees with the fact that the gabbro is intruded by Late Ordovician granitic pluton.The Pre-Sinian basement strata exposed in the North Kunlun Massif are Later Archean -Neoproterozoic Milan Group, Changcheng System Kaqiang Group, Jixian System Liushui Formation and Qingbaikou System Sulu Formation. The South Kunlun Massif is composed of Jixian System Alamasi Group. All these rocks aforementioned are mainly parametamorphic rocks. Milan, Kaqiang and Alamasi Group underwent high-grade metamorphism of amphibolite facies, together with weak migmatism. They share the same geochemistry and total REE and many other chracters. This suggests that the paleo-ocean represented by QOM, separating the South Kunlun Massif from North Kunlun Massif, might be a smaller ocean basin other than a bigger one.The Lower Paleozoic continent marginal sedimentary strata in the North Kunlun Massif are Sinian-Cambrian Alajiaoyi Group and Ordovician Pishigaisayi Formation. The former is composed of high maturity flysch deposit, the later consist of continental shelf deposit such as carbonate and slate and sandstone. These rocks implies that they might form at passive continental margin.The Lower Paleozoic strata in the South Kunlun Massif are Kulafuhe Group of Cambbrian-Ordovician. They consists of metamorphic detrital rocks, limestone, magnetite-bearing basalt, quartzite(meta-silicalite), which suggests that they might form at activecontinent margin. The geochemical characteristics of volcanic and detrital rocks do indicate that they might form at an active marginal environment such as island arc etc.Associated with the Qimanyuter Ophiolite Suit, there are lots of Early Paleozoic granitic plutons. They form a relatively complete granite belt. The granite belt can be divided into three sub-belts: the southern, middle and northern sub-belt, younging fromsouth to north. In terms of their geological and geochemical characteristics as well as the ages of these plutons, these three sub-belts from south to north are interpreted as syn-subductional, syn-collisional and post-collisional plutons respectively.Composed of quartz diorite and quartz monzonite, the syn-subduction plutonic rocks are confined only to the South Kunlun Massif. The zircon U-Pb ages of three major plutons are 481 Ma, 461 Ma and 452 Ma respectively.Syn-collisional plutonic rocks aie composed of granodiorite and adamellite, whi...