北羌塘地区冬布勒山基性、超基性岩特征及构造意义

Characteristics and tectonic significance of Dongbuleshan basic-ultrabasic rocks in Northern Qiangtang Region

冬布勒山基性、超基性岩产于若拉岗日逆冲断裂带北侧,近东西向展布,岩石组合为超镁铁岩及变质玄武岩,与千枚岩、硅质岩、碳酸盐岩共生,呈岩块状镶嵌于上三叠统若拉岗日岩群砂泥质复理石、中基性火山岩及灰岩中。超镁铁岩浆来自亏损的地幔,并受壳源物质混染;玄武岩贫钾富钠,属钙碱性、碱性系列,为过渡型洋脊玄武岩,它们为蛇绿岩残片,与西侧大横山、弯岛湖蛇绿混杂岩带、东部康特金—岗齐曲蛇绿混杂岩带处于同一构造带,东连金沙江蛇绿岩带,是古特提斯洋壳向北俯冲消减过程中形成的增生楔。

Dongbuleshan basic - ultrabasic rocks, located at the northern of Ruolagongri thrust fault zone, occurred along the east - west direction together with the phyllite, siliceous, and carbonate rocks. They were mosaic in a massive rock early Triassic Ruol- agangri Rock Group flysch sand - mud rocks, intermediate - mafic volcanic rocks and limestone rocks. Ultramafic rocks, derived from depleted mantle, are subjected to the contamination by crustal material; the basalt rocks are poor - K and Na - rich, and belong to calc - alkaline - alkaline series. These transition - mid ocean ridge basahs originated from the fragments of the ophiolite, and belong to the same tectonic zone, together with Dahengshan - Wandaohu ophiolite belt to the west and Kangtejin - Gangqiqu ophiolite belt to the east. They occurred with Jinsha River ophiolite belt to the east. All belong to the aecretionary wedge, which due to the northward sub- duction of the ancient Tethyan oceanic crust.