西准噶尔和布克赛尔古洋盆的厘定--来自和布克赛尔蛇绿混杂岩的锆石U-Pb年代学及地球化学证据  

The Determination of Hoboksar Ancient Oceanic Basin in West Junngar:Evidence from Zircon U-Pb Age and Geochemistry of the Hoboksar Ophiolitic Méllange

作　　者：都厚远 陈家富 

机构地区：[1]东北大学深部金属矿山安全开采教育部重点实验室,沈阳110819 [2]东北大学资源与土木工程学院,沈阳110819 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质学报》2017年第12期2638-2650,共13页Acta Geologica Sinica

基　　金：国家自然科学基金(编号41202161,41672217);高校基本科研业务费(编号N140104003,N140104004)资助的成果

摘　　要：本文对西准噶尔北部先前较少报道的和布克赛尔蛇绿混杂岩进行了系统的野外填图与室内分析测试研究。该套蛇绿混杂岩总出露面积约4km2,岩石组分主要包括蛇纹石化橄榄岩、辉石岩、辉长岩、辉绿岩、玄武岩、硅质岩、大理岩及火山碎屑岩围岩。蛇纹石化橄榄岩作为基质,其它蛇绿混杂岩组分均以断块或断片形式与基质呈不规则的断层接触,为典型的基质包裹团块接触关系。围岩、基质和团块均发生不同程度变形和蚀变,围岩和基质中劈理较为发育。对蛇绿混杂岩中辉长岩团块进行地球化学分析,显示上凸型稀土配分模式,(La/Yb)N为0.48~0.65,具有轻微的Eu负异常,高场强元素(Zr-Lu)以几乎不分异并贴近于MORB为特征,显示该蛇绿岩应为洋中脊(MOR)型。辉长岩团块的LA-ICP-MS锆石U-Pb定年结果为484±3 Ma,说明古洋壳形成于早奥陶世。和布克赛尔蛇绿混杂岩时代与属性的最新厘定,一方面暗示了博什库尔-成吉斯弧与扎尔玛-萨吾尔弧之间应发育一个至少在早奥陶世已经存在的古洋盆,可为西准噶尔北部构造演化研究提供重要线索;另一方面,该蛇绿混杂岩可以与邻区已报道的库吉拜、洪古勒楞等蛇绿混杂岩做很好的对比连接,而与查干陶勒盖蛇绿混杂岩在各项特征上存在某些差异,可以为西准噶尔北部构造缝合带的划定提供新的约束。This study carried out detailed field mapping and indoor analysis of the Hoboksar ophiolitic mélange in northern West Junggar, which was poorly reported. The ophiolitic mélange with an area of about 4 km^2 consists of serpentinized peridotite, pyroxenite, gabbro, dolerite, basalt, chert, marble and andesitic volcanic clastic rocks. Matrix consists mainly of serpentinized peridotite; the other components occur as faulting blocks or fragments and exhibit irregular fault contact with the matrix, being typical of contact relation of fragments enclosed by the matrix. Wall rocks, matrix and fragments have undergone various degrees of deformation and alteration, with foliation well developed within wall rocks and matrix. Geochemical analysis shows that the gabbro fragments of the Hoboksar ophiolitic mélange have slight fractionation between LREE and HREE, with （La/Yb）N of 048-065 and negligible Eu anomalies. HFSE （Zr-Lu） shows no fractionation and is characteristic of near MORB, suggesting the Hoboksar ophiolitic mélange belongs to MOR type. LA ICP MS U Pb dating of zircons from the gabbro blocks yields an age of 484±3 Ma, indicating that the ancient oceanic crust was developed in the Early Ordovician. New determination of time and attributes of the Hoboksar ophiolite mélange not only implies the at least one ancient ocean occurring between Boshchekul Chingiz arc and Zharma Saur arc in the early Ordovician, but also provides an important clue for study of tectonic evolution of northern West Jungger. The Hoboksar ophiolitic mélange correlates well with the reported Kujibai and Hongguleleng ophiolitic mélanges in northern West Junggar, but is different from the Qagan Tolgoi ophiolitic mélange in many aspects. Therefore, this study provides new constraints on the determination of the tectonic suture belt in West Junggar.

关 键 词：西准噶尔 和布克赛尔蛇绿岩 构造混杂 LA-ICP-MS锆石U-PB定年 早奥陶世 

分 类 号：P587[天文地球—岩石学]