新疆塔县达布达尔地区二叠系神仙湾组杂砂岩沉积构造背景分析

Tectonic setting of the greywackes from the Permian Shenxianwan Formation in the Daftar area, Taxkorgan, Xinjiang

关键词:  达布达尔地区  神仙湾组  杂砂岩  地球化学  构造背景

Key words:  Daftar area  Shenxianwan Formation  greywacke  geochemistry  tectonic setting

摘要:

新疆塔县达布达尔地区二叠系神仙湾组位于塔阿西构造混杂岩带南侧,总体为一套深海复理石建造,主要以杂砂岩为主。源区岩石没有经过充分的搬运、分选,成熟度比较低。杂砂岩的稀土元素特征表现为轻稀土元素富集和Eu亏损明显的特征,与典型的后太古宙页岩和上地壳非常相似。微量元素含量也接近于大陆上地壳值,说明杂砂岩中的物源来自上地壳。沉积环境分析表明,杂砂岩母岩原岩为大量长英质火成物质和少量沉积物,其形成于深海厌氧环境。大地构造背景分析表明,杂砂岩物源区的构造背景以大陆岛弧为主,兼具活动大陆边缘的性质。结合区域地质构造背景,认为下-中二叠统神仙湾组为裂陷盆地沉积。

Abstract:

The Permian Shenxianwan Formation as the abyssal flysch deposits in the Daftar area, Taxkorgan, Xinjiang is located in the southern part of the Ta' axi tectonic mélange zone. The clastic sedimentary rocks primarily consist of greywacke. The source rocks are poorly transported and sorted, and thus have low maturity. The REE distribution patterns for the greywackes display the LREE enrichment and markedly negative Eu anomalies, indicating the close similarity to those of typical post-Archean shales and the upper continental crust. The trace element contents in the greywackes also approach those in the upper continental crust, suggesting that the greywackes are derived from the upper continental crust. The presence of abundant felsic rocks and minor amount of sedimentary rocks shows that the parent rocks of the greywackes were formed in the deep-sea anaerobic environments. The tectonic settings of the provenances of the greywackes are dominantly composed of the continental island arcs, with subordinately the active continental margins. The Lower to Middle Permian Shenxianwan Formation is interpreted as the rift basin deposits.