摘要
晚古生代在后加里东华南新地台的滇黔桂交界区发育一系列裂谷及与峨眉山玄武岩有关的基性岩浆活动.高温玄武岩浆在研究区地壳深部的停留使地壳多处熔融出中酸性岩浆(以此解释裂谷双模式岩浆成因)并使地壳整体塑性增强.伸展变薄,最终导致完整的中三叠世滇黔桂深海盆的形成.论述了海盆北缘的内聚性碎屑流及相带分布.研究认为中三叠世该海盆的北侧陆缘属被动陆缘,其陆坡为北侧的陆壳与南侧次洋壳的过渡带.
Middle-Triassic Dian-Qian-Gui deep basin is situated in the southern Guizhou, the northern Guangxi and the southeast Yunnan province. This basin covers an area about 90000 km2. The length of northern boundary (from Kaiyuan to Fuquan) is about 500 km.
1 .Tectonic setting of the basin
Dian-Qian-Gui deep basin is situated on the boundary between Yangzi platform in north and the Caledonian fold belt in south. Many deep faults intersected at there. A few narrow rifts were developed in D2-P12. The deposits in these rifts consist of black mudstone or limestone , siliceous shele and is characterized by plankton and nekton. There are some intermediate-basic volcanic rocks in D2-P1deposits in west part of basin . In P2- T intermediate- acid volcanic rocks were widespread. By Middle Trias a integrated Dian-Qian-Gui deep basin had been formed.
2.Packs belts in northern margin of Middle Triassic Dian-Qian-Gui deep basin
Based on the rock texture , sedimentary structure and biological assemblages there are some facies belts (from north to south) as following: l.open platform facies belt; 2.lagoon facies belt; 3.biohermal (shoal) fades belt; 4.marginal siope facies belt and abyssal basin facies belt.
3.Debris flow sediments of northern margin of Middle Triassk Dian-Qian-Gui deep basin
Debris flow sedimments were developed mainly in the marginal slope facies belt in Early-Middle Trias. There are seven rock suites of debris flow sediments. There arc change of characters and thickness of debris flow sediments from north to south: l.the thickness of rock suite: thin-thick-thin; 2.autochthonous debris: less-more; 3.the persentage of debris: less-more; 4.sediments support: grain supportmatrix support. These debris flow deposits belong to cohesive debris flow deposits.
4. The comparision between the northern continental slope off the Eastern U.S.
The two of them are similar in many aspects:
1.The. stability of situation of slope is a general character of former (T1- T22) and the latter (J, K); 2.Facies groups:
The facies groups of the J, K continental slope off the Eastern U.S.were (from west to east): lagoon facies , biohermal facies, marginal, marginal slope facies and so did the northern margin of Triassic Dian-Qian-Gui deep basin;
3.The continental slope of both were steep and narrow.
So we conclude that the northern margin of Middle-Triassic Dian-Qian-Gui deep basin was a passive continental margin and its continental slope is a transitional zone between continental crust in north (under abyssal sea basin) as the J, K continental slope off the Eastern U.S. was (the latter is a transitional zone between continental crust and oceanic crust).
出处
《沉积学报》
CAS
CSCD
北大核心
1989年第2期63-69,共7页
Acta Sedimentologica Sinica
