作　　者： ; ; ; ; ;

机构地区： 中国地质科学院地质研究所

出　　处： 《地质学报》 2005年第2期220-231,i004,共13页

摘　　要： 已有的研究表明,主要形成于显生宙的秦岭造山带发生过新元古代碰撞造山作用,但确切的碰撞时间尚需研究。综合物质组成、S→I→A型花岗岩演化、强烈的变形改造、区域变质作用和地质演化等多方面的证据,进一步论证了秦岭造山带核部以牛角山岩体为代表的片麻状过铝质S型花岗岩体为同碰撞岩体;其中,牛角山岩体可能为同碰撞早期岩体。该岩体的15个锆石SHRIMP测年点给出2 0 6 Pb/ 2 38U加权平均年龄为95 5±13Ma。该年龄可代表陆壳下冲深埋、碰撞增厚的时间。在同一地点侵入于岩体中的弱变形花岗岩脉的锆石SHRIMP年龄为92 9±2 5 Ma,从而证明,该片麻状花岗岩体记录的同碰撞变形主要发生于95 5～92 9Ma。这为确定新元古代同碰撞造山作用及其时代提供了有利证据。该碰撞时间滞后于全球格林威尔碰撞造山的时间(130 0～10 0 0 Ma) ,与华南陆块汇聚时间大致相同。根据花岗岩演化特点推测,该事件可能是华北南缘或扬子地块北缘的一次小陆块汇聚增生。 Previous studies have revealed that the Neoproterozoic continental collision took place in the core of the Qinling orogen. The timing, however, remains questionable. This paper, based on mineral compositions, geochemistry, isotopic compositions, S→I→A-type granitic evolution, strong deformation, regional metamorphism and geological evolution, proves that the peraluminous S-type gneissic granites are syn-collisional granites with the Niujiaoshan pluton being the oldest and representative one. 15 Zircon-SHRIMP data yields a 206Pb/ 238U age of 955±13 Ma, consistent with the zircon age we previously determined by the TIMS method. This is the oldest age of the plutons in the core of the Qinling orogen, which may reflect the timing of the collisional thickening. Additionally, zircon SHRIMP dating of a weakly deformed granitic veins intruded into the Niujiaoshan pluton gives an age of 929±25 Ma. This, combined with strain partitioning, suggests that the syn-collisional deformation recorded by the plutons occurred mainly between 955 and 929 Ma, providing strong evidence for the Neoproterozoic collisional orogeny and continental-block collision. Therefore, the Neoproterozoic collision and continental-bock assemblages in the Qinling are appear to be later than the Grenville orogeny (1300～1000 Ma), but consistent with the collision and continental-bock assemblages of the South China block. The evolution feature of the granitic magmatism further suggests that this event might be an accretion collision along the south margin of the North China block, or the north margin of the South China block.

关 键 词： 秦岭地区 造山带 新元古代 花岗岩 变形时间

领　　域： [天文地球] [天文地球] [天文地球] [天文地球]