碎屑重矿物组成对南天山白垩纪—新近纪剥蚀去顶过程的指示  

Compositions of Detrital Heavy Minerals and Their Implications for Cretaceous—Neogene Erosion and Unroofing Process of South Tianshan

作　　者：李双建[1] 石永红[1] 王清晨[1] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029

出　　处：《地质学报》2006年第2期217-226,共10页Acta Geologica Sinica

基　　金：国家重点基础研究发展规划"973"项目(编号G1999043303)资助的成果。

摘　　要：通过对天山南缘库车坳陷内白垩系—新近系砂岩中碎屑石榴子石的电子探针分析,可以将石榴子石分为3部分,分别是高锰铝榴石组份的石榴子石、与西南天山高压变质岩中石榴子石组成相似的石榴子石和富铁镁铝榴石组份的石榴子石。与白垩系相比,古近系和新近系砂岩中的富锰铝榴石组份的石榴子石所占比例减少,而富铁镁铝榴石组份的石榴子石含量增加。白垩系砂岩中含有高压变质岩来源的多硅白云母和蓝闪石,而且与西南天山高压变质岩中石榴子石组成相似的碎屑石榴子石在白垩系中含量也较高,而随着地层时代的变新,与西南天山高压变质岩中石榴子石组成相似的碎屑石榴子石在地层中的含量减少。根据现今南天山水系的分析,西南天山高压变质岩在最高隆起带以北,已经不能向库车坳陷提供物源。这些研究结果说明,古近纪和新近纪以来,南天山逆冲带与西南天山含高压变质岩体的古生代俯冲杂岩之间存在差异隆升,南天山的快速隆升遮挡了西南天山高压变质岩对库车坳陷的物质贡献。According to electronic microprobe analysis, the detrital garnets in Cretaceous-Neogene sandstones trom Kuqa depression, south margin of Tianshan, can be divided into three parts： the garnets with high spessartine component, the garnets whose composition are similar with that from high-pressure metamorphic rocks in westsouthern Tianshan, and the garnets with high almandine and pyrope. Comparing to that in Cretaceous, the proportion of garnets rich in spessartine reduces in Neogene sandstones, while the proportion of garnets with high almandine and pyrope increases. The phengitic mica and blue amphibole derivated from high-pressure metamorphic rocks can be found in Cretaceous sandstone. The proportion of detrital garnets whose components are similar with that from high-pressure metamorphic rocks in westsouthern Tianshan is higher in Cretaceous and becomes less and less with the updating of formation. According to the distribution of present water system in south Tianshan, the high-pressure metamorphic rocks in southwest Tianshan are located in the north of the highest uplift zone, which cannot become provenance for Kuqa depression. The study results show that different uplift occurred from Tertiary between south Tianshan thrust and Paleozoic subduction complex with high-pressure metamorphic rocks in it. Fast uplifting of south Tianshan shelters the contributions of highpressure metamorphic rocks in southwest Tianshan to Kuqa depression.

关 键 词：重矿物 剥蚀 物源 南天山 库车坳陷 

分 类 号：P546[天文地球—构造地质学]