摘要
为了恢复昌都盆地内早石炭世聚煤环境,对马查拉组内碎屑岩微量元素、稀土元素进行测试,结果显示的地球化学特征(La/Yb=10.04~15.62μg/g;La/Th=1.33~3.17μg/g;Hf=4.58~13.90μg/g)表明,该套沉积岩物源为来自被动大陆边缘沿物源区的沉积岩和酸性岛弧源区的花岗岩。马查拉组在Zr–Th、La–Th–Sc、Th–Co–Zr/10构造环境判别图解中的位置(∑REE=193.96μg/g,LREE/HREE=6.29;δEu=0.61;La/Yb=13.17;(La/Yb)N=8.55),说明马查拉组沉积既有活动大陆边缘的特性,又有向大陆岛弧过渡的趋势。马查拉组主体是一套沉积于大陆边缘的浅海–海陆交互环境的沉积岩,层内煤层多发育在海侵体系域内,属于海侵成煤。煤层具有层数多、厚度薄、连续性差、聚煤中心分散的特点。研究区沉积时,其西缘的澜沧江洋盆已经发生俯冲,其聚煤模式属于活动大陆边缘弧后盆地成煤。研究成果既可以细化早石炭世特提斯演化过程,又有助于揭示昌都地区煤炭资源的赋存规律。
In order to reconstruct the original coal accumulation,this paper analyzed the geochemical characteristics of Machala Formation. The results show that the source rocks of Machala Formation include sedimentary rock from passive continental margin and granite, alkali basalt from island arc（La/Yb=10.04~15.62 μg/g; La/Th= 1.33~3.17 μg/g; Hf=4.58~13.90 μg/g）. The site of samples in Zr-Th, La-Th-Sc, Th-Co-Zr/10 tectonic setting discrimination diagrams also show that Machala Formation sediments were deposited in the active continental margin, which is near the continental island arc, with the characteristics of both active continental margin and continental island arc（∑REE=193.96 μg/g, LREE/HREE=6.29; δEu=0.61; La/Yb=13.17;（La/Yb）N=8.55）. Machala Formation was deposited in continent margin with shallow sea and continental-oceanic environment. The coal seams were developed in TST, and are characterized by numerous thin layers, poor continuity, and coal-accumulating centre dispersion. By the analysis on sequence stratigraphy and provenance, when Machala Formation was deposited, Lancangjiang ocean basin had subducted. Coal accumulation pattern in Machala Formation was coal-forming in garc-island basin in active continental margin. The results can both detail the evolution of Tethysintheeraly Carboniferous and reveal the occurrence regularity of coal in Qamdo.
出处
《煤田地质与勘探》
CAS
CSCD
北大核心
2018年第1期13-19,共7页
Coal Geology & Exploration
基金
中国地质调查局地质调查项目(DD20160187)~~
关键词
马查拉组
构造地球化学
构造背景
聚煤模式
青藏高原
昌都地区
the Machala Formation
tectonogeochemistry
tectonic setting
coal accumulation patterns
Qinghai-Tibet Plateau
Qamdo area
