秦岭造山带主要大地构造单元的新划分

根据近年来的地层、沉积、岩浆-火山和构造变形及岩石地球化学等方面研究新进展,结合前人的成果,按照大地构造相单元划分原则,将秦岭造山带分为13个主要构造单元: ①华北南缘陆坡带,包括第一层序的青白口系大庄组、震旦系罗圈组和寒武系,与之对应的豫西栾川群;第二层序的奥陶纪陶湾群;②北秦岭弧后杂岩带,以宽坪群和部分二郎坪群中的基性火山岩与碳酸盐岩的构造块体与变质的古生代深海碎屑岩混杂为特征;③秦岭岛弧杂岩带,由丹凤群不同的古洋隆块体、富水幔源岛弧基性岩浆杂岩、云架山群、斜峪关群和草滩沟群的岛弧钙碱性岩浆岩和火山岩及深海沉积物及秦岭群弧基底杂岩等构成,时间跨度为奥陶纪-石炭纪;④秦岭弧前盆地系,泥盆系及其它晚古生代地层是其主要充填物,同沉积断裂控制了一系列的次级盆地;⑤秦岭增生混杂带,由泥、砂岩组成的基质和基性、超基性岩、火山岩、灰岩、硅质岩等岩块构成,最终形成于二叠纪末-三叠纪初;⑥南秦岭岛弧杂岩带,碧口群的基性-中酸性火山岩和岩浆岩组成,称碧口弧;由三花石群的中基性火山岩以及西乡群的中酸性火山岩共同构成,称西乡弧;由耀岭河群和郧西群中基性熔岩和中酸性火山岩组成,称安康弧;⑦南秦岭弧前盆地系,碧口弧前盆地充填物是以碎屑岩为主的横丹群和关家沟群;西乡弧前沉积主要由三花岩群包括王家坝组砂岩以及由泥岩、砂岩和中酸性火山岩变质而成的片岩、片麻岩和石英岩组成.安康弧前盆地具有明显的深海扇沉积特征梅子垭群和大贵坪组;⑧南秦岭弧后盆地系,包括后龙门山的茂县群和上古生界及三叠系,大巴山的洞河群和部分耀岭河群的火山岩;⑨南秦岭弧后陆坡带,只保留大巴山弧后陆缘,是高川-毛坝以南的下古生界;⑩南秦岭前陆褶冲带,包括龙门山北段、米仓山和大巴山前陆褶冲带.三带形成于印支-燕山期,但构造线不同,且在出现的时间上,由西到东由早到晚;(11)三叠纪残余海盆;(12)中-新生代走滑拉分和断陷盆地;(13)基底断块.

New Division of the Main Tectonic Units of the Qinling Orogenic Belt,Central China

Based on recent research advances in stratigraphy, sedimentary environment, magma-volcanic petrology, structural geology and geochemistry, the Qinling Orogenic Belt can be individed into 13 main tectonic units as follows. ① Slope Sequences in the southern margin of North China block include the lower sequence made up of Later Proterozoic Dazhuang and Luoquan formations and Cambrian , and the upper sequence of the Ordovician Taowan Group. ② Northern Back Arc Complex is constructed of mafic volcanic blocks and meta-fine sandstones in the Kuanping and Erlangping groups. ③ Accretionary Arc Complex in the Northern Qinling is comprised of arc calc-alkalic volcanic rocks in the Paleozoic Yunjiashan, Xieyuguan, Caotangou, Liziyuan and Luohansi groups, different oceanic highs in the Danfeng Group, arc basement in the Qinling Goup, mafic-ultra mafic magma complex in the fore arc at Fushui and meta-abyssal sediments. Its formation duration is from Ordovician to Carboniferous. ④ Northern Fore Arc Basins in the Middle Qinling are characterized by the Divonian fills and other upper Paleozoic sediments, with syndeposition faults controlling a series of secondary basins. ⑤ Accretionary Complex zone in South Qinling is recognized by matrix and blocks. The matrix is mainly composed of mudy and sandy slates containing Permian microfossils. The blocks include Proterozoic to palezoic mafic, ultra-mafic volcanic rocks and limestone blocks. ⑥ Southern Arc Complex, Bikou arc is defined by mafic, intermediate and acidic volcanic rocks of Bikou Group and magmatic rocks; Xixiang Arc by mafic and intermediate volcanic rocks in the Sanhuashi Group and intermediate and acidic volcanic rocks in the Xixiang Group; and Ankang Arc is by volcanic rocks from basic to acidic in the Yunxi and Yaolinghe groups. The three arcs were produced during late Paleozoic. ⑦ Southern Fore arc basins The fillings in the Bikou forearc are sediments of the Hengdan and Guanjiagou groups; Xixiang fore arc sediments contain metamorphic turbidites and acidic volcanic rocks of the Sanhuashi Group; and the strata of the Ankang fore arc are the Meiziya Group and Daguiping Formation with sediments in deep sea fans. ⑧ Southern Back arc complexes consist mainly of Maoxian Group and Upper Paleozoic and Trassic in Longmenshan, and minor basic volcanic complex of the Donghe Group in Dabashan. ⑨ Continental slope of back arc basin retain only Lower Paleozoic in Dabashan. ⑩ Foreland Thrust Fold Belts include Northern Longmenshan, Micangshan and Dabashan belts. The strata formed in Triassic and Jurassic, and structural boundary lines from west to east become newer. (11)Triassic remnant sea basin. (12)Mesozoic and Cenozoic faulted basins and (13)basement bocks.