| 扬子地台北缘中段震旦纪早期地层沉积类型及构造古地理演化 |
| |
| 引用本文： | 梁传茂.扬子地台北缘中段震旦纪早期地层沉积类型及构造古地理演化[J].现代地质,1988,2(2):137. |
| |
| 作者姓名： | 梁传茂 |
| |
| 摘 要： | 本文主要通过对湖北省西北部及其邻区早震旦世地层沉积类型的分析,再造其构造古地理演化。 本区早震且世地层分为下部姚营寨组和上部耀岭河群,两者呈过渡关系。 姚营寨组由一套由陆相到海相的火山—沉积组合组成,属火山复陆屑建造大类。主要包括冲积扇相、网状河流相、滨—浅海相及半深海相。其火山岩主要为偏碱的酸性岩类,少量基性岩。该组地层类型的综合特征表明,其形成的构造古地理背景属于拉张型的边缘断陷裂谷盆地。 耀岭河群可分为以海底基性火山岩为主,夹半深海、深海相钙、硅、泥质沉积组合的沉积序列和以凝灰质细粒陆源浊积岩及深海相泥质岩组合为主的两种组合类型。该群下部普遍发育冰水沉积物。该群火山岩类属典型的拉斑玄武岩系列,稀土配分表现为轻微富集型。其细粒浊积岩及钙、硅、泥质岩组合与现代远洋沉积层序相似。这些特征说明,耀岭河时期已经发育成为扬子地台北缘具一定规模的边缘小洋盆。 本区早震旦世经历了边缘断陷裂谷和陆缘小洋盆两个构造演化阶段。
|
| 关 键 词： | 鄂西北 早震旦世 地层类型 边缘裂谷 小洋盆 |
SEDIMENTARY TYPES OF STRATA AND TECTONO-PALEOGEOGRAPHIC EVOLUTION OF EARLY SINIAN PERIOD IN THE MIDDLE PART OF THE NORTHERN BORDER REGION OF THE YANGZI PLATFORM |
| |
| Liang Chuanmao.SEDIMENTARY TYPES OF STRATA AND TECTONO-PALEOGEOGRAPHIC EVOLUTION OF EARLY SINIAN PERIOD IN THE MIDDLE PART OF THE NORTHERN BORDER REGION OF THE YANGZI PLATFORM[J].Geoscience——Journal of Graduate School,China University of Geosciences,1988,2(2):137. |
| |
| Authors: | Liang Chuanmao |
| |
| Institution: | China Univertity of Gcosciencces |
| |
| Abstract: | The range of studied area is roughly the same as that of the Yunyang region of northwestern Hubei and the neighbouring parts of Henan and shaanxi where occurs chiefly the Sinian System. This paper, from the view point of mobilism, attempts to reconstruct the paleogeographic and tectonic evolution of early Sinian period in this area on the basis of analysis of lithostratigraphic types with the method of historical geotectonics.
The lower sinian, in the area, include two stratigraphic unites. Yaoying-zhai Formation, and Yaolinghe Group, Which are continuous and transitional in sedimentary facies.Their geological time and their correlation with the other regions have been studied by author in a previous article.
1. The Yaoyingzhai Formation
It is a volcano-sedimentary association from land to marine facies and can be divided into four facies types:
(1) Alluvial fan facies, which occurs at the base of the Formation and was built up in both the southern and the northern sides, probably marking the borders of basin at that time.
(2) Braided river facies, in the lower part of the Formation, consists chiefly of conglomerates and sandstones, which shows many fining-upwardcycles. The conglomerates are clast-supported with well-rounded pebbles. The sandstones, medium-bedded arid coarse to medium-grained, mostly belong to feldspathic sandstones and small amount feldspathic quartzite.
(3) Coastal-shallow marine facies, which comprises tuffaceous sandstone, siltstone and" mudstone, can be subdivided into two types,of sedimentary successions, tidal flat and shallow marine.
(4) Semi-deep sea facies, only at the top of the Formation, is mainly composed of fine sandstone, siltstone and mudstone. Occasionally graded bedding may be found in the facies.
The volcanic rocks are common in the Yaoyingzhai Formation and the alkali-acidic rocks are much more than the basic rocks in. volume.
The sedimentary facies associations mentioned above and the data from paleo-current and chemical composition of sandstories indicate that the sedimentary framework of early Yaoyingzhai period was NEE trend a marginal taphrobasin, the alluvial fan deposits derived from the south and the north developed on both sides of the basin, and a braided river flowing from the east to the west. In late period, the taphrobasin was connected with an . open sea due to the continuous extension and depression, and this area became a marine environment.
2. Yaolinghe Group
The Group can be divided into two types of sedimentary sequences. One of them consists mainly of marine basic lava and semi-sea to deep sea cal-cilutite, silicolites, and pelite. Another mainly finegrained tuffaceous turbidi-tes assemblage with small amount basic volcanic rocks. Dropstone are common in silty argillite succession of the lower parts of both sequences of the Yaolinghe Group.
The volcanic rocks of the Group belong to typical tholeiitic series with the Peacock Index 51.1, and most of Rittmamn Indices are more than 3.5. The Chondrite-normalized LREE shows an enrichment pattern. The tuffaceous turbidites, occurs mostly in the east of the studied area near Danjiangkou, consist of fine-grained graded sandstone, siltstone and shales with certain volcanic ash,which may be comparable with the succession of distal turbidi-te.The calcilutite,and silicolite pelite, as a intercalated beds in the section of Yaolinghe Group, shows similarities to modern pelagic sedimentary successions.
The Sequences and lithofacies of the Yaolinghe Group represent that the Taphrobasin during Yaoyingzhai period had became a small marginal oceanic basin which lain the north to the Yangzi Platform in this time.
The Jinningian Movement (I ) ended the history of the island arcs in the region, A complex tectonic evolution is characterized by marginal protero-zoic. Two stages of evolution may be discetned during the early Sinian p riod:
(1) Marginal rift stage, (2) Smill epicontinental initial oceanic basin. |
| |
| Keywords: | : northwestern Hubei early Sinian epoch stratigraphic types marginal rift initial oceanic basin |
| 本文献已被 CNKI 等数据库收录！ |
| 点击此处可从《现代地质》浏览原始摘要信息 |
| 点击此处可从《现代地质》下载免费的PDF全文 |
|
