东准噶尔卡拉麦里辉长岩斜锆石U-Pb年代学及其构造意义

卡拉麦里蛇绿岩带是东准噶尔重要的组成部分，该蛇绿岩带沿卡拉麦里山呈NWW向展布，延伸约400 km，主要由橄榄岩、辉长岩、斜长花岗岩和少量的硅质岩组成。选取蛇绿岩带西段呈团块状出露的辉长岩斜锆石进行了LA-ICP-MS锆石 U-Pb 测年得出，辉长岩谐和年龄为（434.4±2.7） Ma（MSWD=0.87），加权平均年龄为（436.4±2.5） Ma（MSWD=0.59），属早志留世。截至目前，该年龄是卡拉麦里蛇绿混杂岩中测得的最早年龄，标志着卡拉麦里洋盆在早志留世就已经开始拉张形成，即在扎河坝—阿尔曼太蛇绿岩所代表的洋盆闭合前，卡拉麦里洋盆就已经存在。

Baddeleyite U-Pb Geochronology and Tectonic Significance of the Gabbro in Kalamaili,Eastern Junggar

The Kalamaili ophiolite belt is an important component of East Junggar.It extends along the Kalamaili Mountains in NWW direction, extending about 400 km.It is an important tectonic unit in the region. The opening and closing of oceanic separation represented by the ophiolite belt is of great significance to the tectonic evolution of the whole east Junggar region.Previous studies on the age of ophiolite have mainly come from the fossil age of siliceous rocks and the zircon U-Pb age of diabase, gabbro and baddeleyite granite. However,there are few reports on the age of baddeleyite in ophiolite.The Kalamaili ophiolite is mainly composed of peridotite,gabbro,plagiogranite and a small amount of siliceous rock, controlled by the Kalamaili fault, which makes gabbro appear as tectonic block and accompanied by peridotite.Gabbro belongs to the large class of silica-unsaturated rocks. Baddeleyite coexists steadily with pyroxene and olivine, while zircon belongs to silica-saturated, supersaturated minerals and gabbro. The crystallization of baddeleyitee is earlier than that of zircon, which is more representative of the true age of formation of rocks. Therefore, in this study, more than 200 baddeleyite were selected from fresh gabbro exposed in massive form in the western part of ophiolite belt, and 80 of them were selected to make targets and take transparent, reflective and cathodoluminescent photographs.Since baddeleyites are black in the cathodoluminescent photographs, LA-ICP-MS U-Pb dating was carried out at the selected testing sites of the transparent and reflective photographs, and 16 years of good harmony were obtained.Age data ranged from 431 Ma to 444 Ma. The harmonic age of rock ²⁰⁷Pb/²³⁵U-²⁰⁶Pb/²³⁸U is （434.4+2.7）Ma (MSWD=0.87) and the weighted average age of ²⁰⁶Pb/²³⁸U is （436.4+2.5）Ma (MSWD=0.59) calculated by ISOPLOT software. The two ages are consistent within the error range, indicating that the gabbro was formed in early Silurian.Up to now, this age is the earliest one found in the Karamari ophiolitic melange, which indicates that the Karamari oceanic basin began to stretch and form in the early Silurian.That is, the Karamari oceanic basin existed before the closure of the oceanic basin represented by the Zhaheba-Aermantai ophiolite in the north of the basin.