云南思茅地区上石炭统沉积特征及其构造背景

Upper Carboniferous sediments in the Simao region, Yunnan and their tectonic settings

关键词:  晚石炭世  火山浊积岩  岛弧  思茅地区

Key words:  Late Carboniferous  volcanic turbidite  island arc  Simao region

摘要:

思茅地区位于东特提斯构造域的东段,晚古生代时期属扬子地台西缘的一部分。晚石炭世具有台-盆相间的沉积格局,形成了三类不同的沉积:滨岸沉积、浅海.台地沉积和深水浊流沉积。其中深水浊流沉积以火山源浊流沉积为特征,是在平缓的碳酸盐台地或陆棚之上通过断陷事件发展起来的,包括了5个沉积旋回,表现出强烈的火山活动期与火山休眠期交递进行的沉积旋回特征。自晚石炭世早期到晚期,火山活动期逐渐增长,休眠期逐渐缩短,反映出盆地性质自稳定向活动的转化过程。火山岩具有岛弧型火山岩特征,说明晚石炭世,思茅地区具有活动型大陆边缘沉积特征。

Abstract:

The Simao region in Yunnan located in the eastern part of the eastern Tethyan tectonic domain was part of the margin of the Yangtze platform during the Late Palaeozoic and displayed the platform-basin sedimentary framework during the Late Carboniferous. Three types of sediments are recognized:littoral clastic sediments, platform carbonate sediments and deep-water volcanic turbidite sediments, the latter of which are characterized by volcanic turbidites and developed on a pre-existing carbonate platform or a continental shelf due to rift faulting. Vertically, these volcanic turbidites represent the alternation of the high-density volcanic turbidites and low-density volcanic turbidites, and may be arranged into five depesitional cycles. The increasing volcanism implies that the regional tectonism became progressively severe from the early stage to late stage of the Late Carboniferous. The volcanic rocks from the volcanic turbidites have the features of island-arc volcanic rocks, indicating that the study area was evolving from the passive margin to the arc-basin system of active margin during the Late Carboniferous.