柴北缘西段古近纪物源体系分析

Provenance analysis of the Palaeogene clastic rocks in the western part of northern Qaidam Basin

关键词:  重矿物组合  古近系  物源体系  柴北缘西段

Key words:  heavy mineral assemblage  Palaeogene  provenance system  western part of northern Qaidam Basin

摘要:

沉积区物源分析对研究造山带构造演化、盆地沉积过程及划分油气区带等方面具有重要的意义。为了查明柴达木盆地北缘构造带古近纪物源方向,通过对古近系碎屑岩的碎屑组成、岩屑成分、重矿物组合特征和ZTR指数的研究,并结合前人的研究成果,初步确定古近纪柴北缘西段发育五大主力物源区:(1)牛东物源主要来自阿尔金山东段,重矿物组合以稳定且含量较高的电气石区别于邻区,碎屑组分中以石英和含量较高的长石为特征,岩屑中含有少量的碳酸盐岩岩屑;(2)冷北物源主要来自小赛什腾山方向,重矿物组合中榍石和赤铁矿的含量明显偏高,碎屑组分中以高岩屑为特征;(3)赛西物源主要来自赛什腾山西段,电气石和角闪石含量较高,碎屑组分较为均一,母岩以变质岩和火成岩为主,含少量碳酸盐岩岩屑;(4)赛东物源主要来自赛什腾山东段,其白钛矿含量明显高于邻区,碎屑组分以较高含量的石英和长石为主,岩屑类型主要为变质岩、火成岩和沉积岩岩屑;(5)九龙山物源主要来自九龙山和绿梁山地区,石榴石含量高且稳定,碎屑组分较为均一,母岩以变质岩和火成岩为主,含少量的非碳酸盐岩类沉积岩岩屑。

Abstract:

The provenance analysis of the sediments is considered to be of vital importance to the study of tectonic evolution, basin deposition and the division of petroleum areas in the orogenic zones. In the light of clastic and lithic composition, heavy mineral assemblage and ZTR index, in integration of the previous results of research, five provenances have been distinguished for the Palaeogene clastic rocks in the western part of northern Qaidam Basin. (1) The Niudong provenance is located in the eastern part of the Altun Mountains. The heavy mineral assemblages contain stable and higher contents of tourmaline, which are different from those in the adjacent areas. The clastics dominantly consist of quartz and feldspar with high contents, with minor amount of carbonate rock debris in the lithic fragments. (2) The Lengbei provenance is located in the Lesser Serteng Mountains. The contents of titanite and hematite are remarkably higher in the heavy mineral assemblages, and the clastic components are characterized by higher contents of lithic fragments. (3) The Saixi provenance appears in the western part of the Serteng Mountains, where there exist higher contents of tourmaline and hornblende and uniform clastic compositions. The parent rocks are made up of dominated metamorphic and igneous rocks, with minor amount of carbonate rock debris. (4) The Saidong provenance lies in the eastern part of the Serteng Mountains, where the contents of leucoxene are noticeably higher than those in the adjacent areas. The clastics mainly consist of quartz and feldspar, and the lithic fragments are dominantly composed of metamorphic, igneous and sedimentary rock debris. (5) The Jiulongshan provenance occurs in the Jiulong Mountains and Luliang Mountains. Different from those in the other above-mentioned provenances, the ultra-high contents of garnet and lower contents of magnetite represent the characteristics of the heavy mineral assemblages in the provenance. The clastics are uniform in composition, and the parent rocks are dominantly made up of metamorphic and igneous rocks, with minor amount of noncarbonate rock debris.