西秦岭北缘上新统木梯寺砾岩成因——兼论青藏高原东北缘隆升  

Genesis of the Pliocene Muti Temple Conglomerates in the Northern Margin of West Qinling Mountains:Implication for the uplift of the northeastern margin of the Qinghai-Tibet Plateau

作　　者：沈迪 郭进京 于美娜 宫恩麟 常西玲 常璐璐 SHEN Di;GUO JinJing;YU MeiNa;GONG EnLin;CHANG XiLing;CHANG LuLu(School of Geology and Geomatics,Tianjin Chengjian University,Tianjin 300384,China)

机构地区：[1]天津城建大学地质与测绘学院,天津300384

出　　处：《沉积学报》2023年第2期409-424,共16页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41772215)。

摘　　要：青藏高原东北缘是何时卷入现今青藏高原动力学系统而隆升成为高原的组成部分一直存在争议。高原周缘上新世—第四纪广泛出现的粗砾岩多被认为是高原隆升的重要地质标志。西秦岭北缘构造带北侧出露的上新世积石山砾岩、甘家砾岩、韩家沟砾岩等都被认为是青藏高原东北缘快速隆升的地质依据,但这些砾岩由于第四纪以来隆升—侵蚀,多呈孤立块体分布在山顶。西秦岭北缘武山县新寺镇与高楼镇之间卧龙里—大坪一带山顶出露的一套粗砾岩(木梯寺砾岩)具有与漳县北出露的上新统砾岩相同或相似的特征,但却分布在西秦岭北缘断层之南,其研究对于西秦岭上新世隆升及构造边界确定具有重要的地质约束。通过对木梯寺砾岩的地貌特征、沉积旋回、岩性分段、砾石大小、分选性、磨圆度、砾石成分和古流向等较详细的研究,主要取得了如下认识:1)木梯寺砾岩是一套厚度约380 m,粒度粗且变化大、分选差、磨圆度低、旋回性清晰的洪积扇相和扇上季节性河道相互层的粗砾岩,高耸陡峭的山体地貌形态区别于下伏白垩系红色砂砾岩、砂岩的相对平坦地貌;2)扇上河道相砾岩中砾石叠瓦排列指示了自南向北的古流向,砾石成分以石灰岩、砂岩为主,含有少量花岗闪长岩、花岗岩砾石,指示了其物源区主要为西秦岭印支期造山带地层和侵入体;3)该套砾岩近水平的产状、特征性的地貌、典型的冲洪积扇组合,指示了其应该为山前近源、快速堆积体,这与漳县地区上新统韩家沟砾岩具有惊人的相似性,因此,认为这套砾岩与韩家沟砾岩是同时代、同成因的地层,即这套砾岩时代应该为上新世;4)木梯寺砾岩虽然与漳县上新统韩家沟砾岩相似,代表了西秦岭北缘上新世以来的挤压背景下的类前陆盆地沉积,指示了青藏高原东北缘(西秦岭地块)一次快速隆升,但其分布�It is controversial when the northeastern margin of the Qinghai-Tibet Plateau was involved in the present dynamic system of the present Qinghai-Tibet Plateau and uplifted into a part of the plateau.Pliocene-Quaternary coarse conglomerates are widely distributed around the plateau margins,which are considered as important geological indicators for the uplift of the plateau.The Pliocene Jishishan conglomerate,Ganjia conglomerate,and Hanjiagou conglomerate,outcropped on the north side of the northern margin of the West Qinling Mountains,are considered as the geological evidence for the rapid uplift of the northeastern margin of the Qinghai-Tibet Plateau.However,due to the uplift erosion that has occurred since the Quaternary,these conglomerates are mostly distributed in isolated blocks on the top of the mountain.In the Wolongli-Daping area between Xinsi town and Gaolou town,Wushan coun⁃ty,the northern margin of the West Qinling Mountains,a set of coarse conglomerates(Muti Temple conglomerates,abbreviated as MTC)outcropped on the top of the mountain have the same or similar characteristics with the Pliocene Hanjiagou conglomerates outcropped in northern Zhangxian county,but they are distributed south of the northern margin fault of the West Qinling Mountains.Based on the detailed study of the geomorphic features,sedimentary cy⁃cles,lithologic segmentation,gravel size,sorting,roundness,gravel composition,and paleocurrent direction of the MTC,the following understandings are obtained:(1)the MTC is a set of conglomerates with coarse grain size and large variation,poor sorting,bad roundness,and clear cyclicity;interbeded coarse conglomerates with alluvial fan facies,seasonal channel facies on the fan,and its high and steep mountain landform are different from the relatively flat landforms of the underlying Cretaceous red conglomerate,glutenite,and sandstone;(2)The gravel imbricate ar⁃rangement in the channel facies on the fan conglomerate indicates a paleocurrent direction from south to north,and the gravel composi

关 键 词：西秦岭北缘 上新世 木梯寺砾岩 砾石特征 冲洪积扇 

分 类 号：P534.62[天文地球—古生物学与地层学]