北秦岭晋宁期主要地质事件及其构造背景探讨

北秦岭主要发育元古宙构造岩石地层单位，包括古元古代秦岭杂岩、中元古代峡河岩群、宽坪岩群和武关岩群、中元古代晚期松树沟蛇绿岩构造岩片、新元古代丹凤岩群和二郎坪岩群的下部地层单位等。北秦岭广泛存在晋宁期的强烈构造－岩浆－变质地质事件，且是新元古代主体形成的古老造山带。晋宁期的地质事件可能并不代表扬子地块和华北地块之间的直接碰撞拼合，而是具扬子地块基底特征的“中秦岭微地块 与北秦岭微地块或华北地块之间的俯冲碰撞拼台 震旦纪之后又逐渐开始发生大陆裂解，进入显生宙的构造演化阶段。新元古代晋宁期(1000-800Ma)发生的主要地质事件和有限的俯冲－碰撞拼台及震旦纪之后又逐渐开始发生裂解与国外一些地质学家提出的新元古代时期Rodinia超大陆的形成和700～570 Ma期间Rodinia超大陆的裂解不谋而台

MAJOR GEOLOGICAL EVENTS OF JINNING PERIODAND THEIR TECTONIC SETTINGS IN THE NORTH QINLING

The Proterozoic tectono-lithostratigraphic units in the North Qinling orogenic belt mainly include the QinLing complex of Paleo-Proterozoic，the Xiaba Group, Kuanping Group and Wuguan Group of the Mesoproterozoic, Songshugou ophiolite tectonic slice of the Late Mesoproterozoic, the Danfeng Group and lower part lithostratigraphic units of the Neoproterozoic Erlangping Group. The Qinling complex belongs to metamorphic crystalline basement(2 226～1 984Ma) of the North Qinling orogenic belt. The Xiahe Group(1 605 Ma), Kuanping Group(1 827～1 142Ma) and Wuguan Group(1 382Ma)were respectively formed in the tectonic settings of the active continent margin, back-arc small ocean basin and continent rift in the Mesoproterozoic. The Songshugou ophiolite was formed in small ocean-basin of the late Mesoproterozoic. The Danfeng Group(973～825Ma)and lower part of the Erlangping Group(948～708Ma)were formed respectively in the tectonic settings of the island-arc and back are-basin in the Neoproterozoic. Strong tectono-magmatic-metamorphic geological events of the Jinning period (1 000～800Ma) occurred widely in the North Qinling, which include island-arc-type basic-intermediate basic and granitic magmatism, collision type granitic magmatism, tectonic emplacement of the Songshugou ophiolite, regional and high-pressure metamorphism of the meta-geological bodies during main metamorphic stage (996～ 744Ma), strong structural deformation and tectonic superimposition, as we1l as intensive crust accretion. These geological events indicate that main body of the North Qinling was an ancient orogenic belt formed during the Neoproterozoic. Although these events may not suggest a direct subduction-collision integrating between the Yangtze block and North China block, they are evidences for a subduction-collision integrating between “the Middle Qinling micro-blocks” with characteristics of the Yangtze block basement and the North Qinling micro-block or the North China block. The continent breakup happened after the Sinian period in the Qinling region, which marked the beginning of the Pbanerozoic tectonic evolution stages. The major geological events of Jinning period(1 000～800Ma)and the tectonic history after the Sinian period in the Qinling orogenic belt ale coincidence with the formation of the Rodinia supercontincnt during the Neopmterozoic and breakup of the Rodinia supercontinent during 700～570Ma as suggested by some geologists.