摘要
安徽沿江地区中三叠统角砾岩极其发育,岩性、形态、岩石组合类型多样,但成因尚无定论,多被解释为膏溶角砾岩。通过对多地若干条剖面调查,发现用简单的膏溶角砾岩来解释这套复杂的砾岩有所不妥。根据岩石特征及组合辨识出5类不同成因机制的角砾岩:滨岸缓坡砾屑岩、膏溶角砾岩、岩溶角砾岩、冲积扇砾岩和构造角砾岩。滨岸缓坡砾屑岩和冲积扇砾岩均发育于同生期,前者与所处的滨岸缓坡位置密切相关;后者与构造隆升区的各类岩石受物理和化学风化作用有关,在突发性事件的诱导下,母岩剥离而形成的沉积物随雨水坡面流冲刷、搬运作用由山顶和斜坡向山谷快递移动,快速沉积形成,代表了印支运动早幕活动的加强期,指示了印支运动早幕是以抬升运动为主、褶皱运动为辅。膏溶角砾岩、岩溶角砾岩与印支运动早幕无明显的关联性,可能与印支运动晚幕—燕山运动的构造活动及淡水淋浴作用的结果。前者砾石成分相对单一,发育于干旱蒸发的高水位体系域内,可能为原先含膏白云岩、白云岩与石膏互层,后由于构造抬升,石膏层受到淡水的作用溶蚀,造成了岩层空疏—垮塌,在原地堆积形成;后者砾石成分较为复杂,其形成与构造存在着较为密切的关系,前期的构造破碎为后期渗流水和潜流水提供了岩溶作用空间。构造角砾岩应为构造活动的产物,应与印支运动早幕无关,而为北西、北东向张性断裂破坏的结果,其成因可能与印支运动晚幕或燕山运动有较为密切的关系。
Middle Triassic breccias are well developed along the Yangtze River in Anhui Province. However, their origin is poorly understood. Some geologists interpret these as gypsum karst breccias. This paper review the characteristics of five different kinds of breccias, including platform margin-slope rudstone, gypsum karst breccia, karst breccia, alluvial fan conglomerate and tectonic breaccia. Shore slope rudstone and alluvial fan conglomerate are sedimentary breccias and they have a close relationship with the Indosinian Movement. The former is controlled by depositional environment in continental margin and slope during the early stage of the Indosinian Movement. Alluvial fan conglomerate represents the main phase of the Indosinian Movement. Allu-vial fan conglomerate is controlled by erosional processes that are in turn related to tectonic uplift and physical and chemical weathering processes. Gypsum karst breccia and karst breccia are not closely related to the early phase of the Indosinian Movement. They may be related to tectonic activities in the late Indosinian - Yansha- nian movement and hydrological processes. Gravel composition is relatively simple in gypsum karst breccias, which are typically developed in arid evaporitic environment of the highstand systems tract. The original lithologies may contain gypsum dolomite, dolomite and gypsum interbeds, and gypsum layers. Duing tectonic uplift, gypsum layers are dissolved by fresh water, resulting in collapse and breccia formation. Gravel composi- tion can be complex in karst breccias, whose formation is closely related with structures. Tectonic breccias are products of tectonic activities that are unrelated to the early phase of the Indosinian Movement. They are the result of the northwest- and northeast-trending faults. The causes may be closely related with the late phase of the Indosinian Movement or the Yanshan movement.
作者
徐锦龙
储东如
夏军
王朝
XU Jin-long;CHU Dong-ru;XIA Jun;WANG Chao(Anhui Institute of Geological Survey,Hefei 230001)
出处
《地层学杂志》
CSCD
北大核心
2018年第3期267-277,共11页
Journal of Stratigraphy
基金
安徽省公益性地质(科技)工作项目(编号:2010-g-18)
中国地质调查局大调查项目(编号:12120113069200)资助
关键词
角砾岩
成因机制
中三叠统
安徽沿江地区
breccia
genesis mechanism
Middle Triassic Series
along the Yangtze River in Anhui Province
