昆仑造山带早-中泥盆世沉积特征及盆地性质探讨

昆仑造山带基本构造—地层格架奠基于古生代，是早古生代和晚古生代洋陆转换、碰撞造山的结果。早古生代末的加里东碰撞造山运动，使早古生代洋盆闭合，昆仑地区整体抬升为陆，作为造山运动的沉积响应，在结合带的山前地区形成早—中泥盆世前陆盆地沉积。东昆仑下—中泥盆统分布于昆中、昆南区，北部为深海、次深海盆地沉积和浅海陆棚及海陆过渡相沉积，南部为滨浅海沉积，沉积物在三维空间上具有北厚南薄的楔状体特点。时间序列上表现为深海、次深海—浅海陆棚—海陆交互相特征，反映沉积盆地向上变浅的规律。物源主要来源于北部北昆仑早古生代造山带，南部为次要物源区。由于其发育于志留纪末祁漫塔格洋盆闭合后的俯冲陆块之上，反映其具有周缘前陆盆地沉积的总体特征。西昆仑只在昆北区发育中泥盆统，西南部主要为深海、次深海盆地沉积，上部发育滨浅海沉积，北部及塔里木南部边缘为滨浅海沉积，沉积物在三维空间上具有西南厚东北薄的楔状体特点。时间序列上表现为深海、半深海—浅海—海陆交互—陆相沉积特点，亦表现为沉积盆地向上变浅的规律。物源主要来源于西南造山带，东北部塔里木古陆为次要物源区。结合该套地层发育于奥陶纪末库地洋盆闭合后的中昆仑岩浆弧后的昆北地区，反映其具有弧后前陆盆地沉积的总体特征。

Discussion on Depositional Characteristics and Basin Quality in Kunlun Orogenic Belt During Early-Middle Devonian

The basic tectono-stratum pattern of Kunlun Orogenic Belt, which was the product of ocean-continent transformation and collisional orogeny during Early Paleozoic and Late Paleozoic, was developed on the basis of Paleozoic. The Caledonian collisional orogeny, at the end of Early Paleozoic, made the Early Paleozoic ocean basin close and the whole Kulun area was uplifted to be land. As a sedimentary response to orogeny, the sediments of Early-Middle Devonian foreland basin formed at the piedmont area within the suture zone. The Early-Middle Devonian of East Kunlun mainly distributes in Middle Kunlun and Southern Kunlun. The northern part has sediments formed in the environment of abyssal-bathyal basin, shallow sea shelf and sea-land transition facies while the southern part is littoral-neritic. The sediments are characterised by wedge shape which becomes thinner from north to south in 3-D space. They display characteristics that the environment once changed from abyssal-bathyal to shallow sea shelf finally to sea-land alternation facies in temporal sequence, which reflect that the basin became shallower upward. The material sources were mainly from the northern part, namely the Early Paleozoic Orogenic Belt of Northern Kunlun, the southern part was secondary source area. Because the sediments developed on the subduction landmass, at the end of Silurian when Qimantage ocean basin had closed, they reflect that they have peripheral foreland basin sedimentary characteristics. In West Kunlun, the Middle Devonian only developed in the northern part, while the southwest was mainly abyssal-bathyal basin sediments and the upper developed littoral-neritic sediments, the northern part and the southern margin of Tarim basin developed littoral-neritic sediments. These sediments are wedge-shaped in 3-D space becoming thinner from southwest to northeast. In temporal sequence, their sedimentary environment changed from abyssal-bathyal to shallow sea to sea-land alternation finally to land facies. They also reflect that the basin became shallower upward. The material sources were mainly from southwest orogenic belt, while the Tarim ancient land in the northeast was secondary source area. Considered that the strata developed in the northern part of Middle Kunlun magmatic back-arc, at the end of Ordovician when Kudi ocean basin had closed, it can be concluded that the sedimentary environment is back-arc foreland.