陆内“滞后”弧岩浆岩特征及其地质意义:来自西准噶尔乌尔禾北早二叠世岩浆作用的证据

发布时间：2018-10-11 15:42

【摘要】：产于西准噶尔哈拉阿拉特山南麓的"滞后"弧岩浆岩,由乌尔禾中基性岩墙群和白杨河组玄武岩组成,二者构成一完整陆相火山机构,并呈角度不整合覆于下二叠统佳木河组陆相磨拉石建造之上。中基性岩墙群岩性主要为辉绿岩、辉绿玢岩和辉长闪长岩,其LA-ICP-MS锆石U-Pb年龄为(283.6±2)Ma(MSWD=0.57,95%置信度)、(286.3±4.0)Ma(95%置信度,MSWD=0.32)、(286.5±5.6)Ma(MSWD=0.3,95%置信度)。白杨河组玄武岩LA-ICP-MS锆石U-Pb年龄为(283.3±3.1)Ma(MSWD=0.45,95%置信度),均属早二叠世。二者具有相似的与岛弧俯冲相关的地球化学性质,属钙碱性中低钾系列,富集轻稀土,δ_(Eu)异常不明显,富集K、Ba、Sr等大离子亲石元素,而高场强元素Nb、Ta强烈亏损,Zr、Hf适度亏损,正的ε_(Nd)(t)值和相对低的初始~(87)Sr/~(86)Sr比值表明源区为亏损地幔。该岩浆岩形成于洋盆关闭,即沟弧盆体系消失之后,时代"滞后"于造山后沉积记录,表明西准噶尔晚古生代俯冲作用结束的最终时限应为早二叠世晚期。根据准噶尔地区滞后型岩浆岩区域性分布特点,推断其产地的连线区为天山—塔里木板块与西伯利亚板块最终深部俯冲的接合部位。
[Abstract]:The "lag" arc magma, which occurs at the southern foot of the Hara Arrate Mountains in West Junggar, is composed of the Wuerhe Middle basic Rock-Dike Group and the Baiyanghe formation basalt, which constitute a complete continental volcanic mechanism. The angle-unconformities are overlaid on the lower Permian Jiamuhe formation. The LA-ICP-MS zircon U-Pb age is (283.6 卤2) Ma (MSWD=0.57,95% confidence), (286.3 卤4.0) Ma (95% confidence, MSWD=0.32), (286.5 卤5.6) Ma (MSWD=0.3,95% confidence). The LA-ICP-MS zircon U-Pb age of basalt in Baiyanghe formation is (283.3 卤3. 1) Ma (MSWD=0.45,95% confidence), which belongs to early Permian. They have similar geochemical properties related to island arc subduction and belong to the calc-alkaline medium low potassium series. They are rich in light rare earth elements, 未 _ (Eu) anomaly is not obvious, and rich in large ion lithophile elements, such as K _ (Eu), Sr, etc., while the high field strength element Nb,Ta is severely depleted and the Zr,Hf is moderately depleted. The positive 蔚 _ (Nd) (t) value and the relatively low initial ~ (87) Sr/~ _ (86) Sr ratio indicate that the source region is a depleted mantle. The magmatic rock formed Yu Yang basin closed, that is, after the disappearance of the trench arc basin system, the epoch "lagged" behind the post-orogenic sedimentary record, indicating that the final time limit for the end of the late Paleozoic subduction in West Junggar is the late early Permian. According to the regional distribution characteristics of lagging magmatic rocks in Junggar area, it is inferred that the connecting area between Tianshan-Tarim plate and Siberian plate is the junction of deep subduction.
【作者单位】：长安大学地球科学与资源学院;国土资源部岩浆作用成矿与找矿重点实验室;
【基金】：国家自然科学基金项目(41273033,40534020) 中央高校基金项目(310827153407) 中国地质调查局项目专项(基[2010]矿评01-01-05),基[2012]02-020-015)
【分类号】：P588.1

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