川北上三叠统须家河组砾岩物源的多源性探讨:来自阴极发光的约束

DISCUSSION ON THE MULTIPLE SOURCE OF THE PROVENANCE OF SILICEOUS CONGLOMERATE FORM UPPER TRIASSIC XUJIAHE FORMATION,NORTHERN SICHUAN:CONSTRAINTS FROM CATHODOLUMINESCENCE ANALYSIS

针对四川盆地北部上三叠统须家河组硅质砾岩外表单调的物理特性和物源难以明确区分的问题,利用阴极发光技术对米仓山—大巴山前缘9条须家河组砾岩剖面中采集的砂砾岩和胶结物共计36块样品,127片薄片进行砾石和砂级碎屑组分详细的对比分析。结果表明须家河组硅质砾岩中石英质砾石主要有两种阴极发光类型：1以紫光、蓝光为主,变化于蓝-紫、红-紫之间,占40.2%-84.5%,平均为67.97%,其中紫色光占3.2%-13.04%,红色光占3.8%-13%,蓝色光占16.7%-33.3%,蓝紫色光占8.7%-37.5%,紫红色光占17.5%-22.6%,主要来自于岩浆岩（1%-15%）,变质岩（40%-80%）,主要分布于万源-南江一带;2不发光,占15.49%-59.79%,平均为32.03%,主要来自于沉积-成岩成因的石英（燧石）,主要分布于旺苍-金溪,呈现出由东到西递减的趋势。揭示须家河组硅质砾石尽管成分单一,但其硅质来源具有明显的差异,来源于岩浆岩、变质岩、沉积岩等不同的母源。综合分析认为四川盆地北部须家河组砾岩沉积时期存在三大源岩体系,具有明显的多源性。秦岭造山带是川北地区须家河组的主要物源供给区。研究结果亦证明,阴极发光分析方法可作为沉积岩物源分析的一种有效手段。

The conglomerate from the Xujiahe Formation in the northern Sichuan is characterized by the monotonous appearance of physical characteristics with uncertain provenance.36 samples,127thin sections are analyzed by cathodoluminescence and it reveals that the quartz in the siliceous conglomerate shows two types of cathodoluminescence features.First,the quartz shows violet and blue colors,varying from blue-violet to red-purple,accounting for 40.2% -84.5%,with average of 67.97%.Of the colors,purple accounts for 3.2%-13.04%,red for 3.8%-13%,blue for 16.7%-33.3%,violet for 8.7%-37.5% prunosus for 17.5%-22.6%.These conglomerates mainly originated from metamorphic（40%-80%）and magmatic rocks（1%-15%）in the host rock.Second,cathodoluminescence analysis shows non-luminance,accounts for 15.49% -59.79%,average 32.03%,mainly due to depositional quartzes.Microscopic characteristics of quartzes in the conglomerate suggest that the conglomerate of Xujiahe Formation in the north Sichuan displays a single composition of silica,they come from different sources,ranging from volcanic rock,metamorphic rock to sedimentary rocks.It is considered that the Qinling orogenic belt is the main source supplying area for the conglomerates of Xujiahe Formation.Therefore,cathodoluminescence analysis can be used as an effective means of sedimentary provenance analysis.