北大巴山凤凰山岩体锆石U-Pb LA-ICP-MS年龄及其构造意义

Zircon U-Pb LA-ICP-MS Dating of Fenghuangshan Pluton in Northern Daba Mountains and Its Implications to Tectonic Settings

北大巴山凤凰山岩体是扬子陆块北缘典型的新元古代侵入岩群,对采自岩体的6个花岗岩(闪长岩)样品进行了LA-ICP-MS锆石U-Pb同位素定年分析。定年数据显示,岩浆活动可分为早期(797±6Ma)、中期(770±6Ma、774±5Ma)、晚期(755±6Ma、750±13Ma和743±6Ma)三个阶段,证实凤凰山岩体为多期岩浆侵入形成。这几期岩浆活动在扬子陆块具同步性和普遍性,广泛被记录在黄陵、汉南等其它新元古代杂岩中。凤凰山花岗岩完整记录了扬子陆块北缘南华纪初期的区域拉张—裂陷事件,其形成可能与导致Rodinia超大陆裂解作用的幕式地幔柱活动有关。本次研究对认识扬子陆块新元古代地壳生长与再造过程及Rodinia超大陆裂解机制具有重要意义。

The Fenghuangshan Pluton in the north edge of the Daba Mountains, is a Neoproterozic intrusive rock unit in the northern margin of the Yangtze Block. This paper reports the LA-ICP-MS zircon U-Pb dating of this pluton. The dating results can be divided into three phases： early phase （797 6Ma）, middle phase （770 6Ma, 774 5Ma）, late phase （755 6Ma, 750 13Ma and 743 6Ma）, indicating multi-phase magmatic activity in the Fenghuangshan Pluton. These magmatic activities were also widely recorded in the other Neoproterozoic complex rocks in the Yangtze Block, such as the Hannan and Huangling complex. The Fenghuangshan Massif recorded the regional extension-rifting in the northern margin of the Yangtze Block during early Nanhuan Period, formation of which may be associated with the activities of mantle plume that lead to the breakup of the Rodinia supercontinent. This research has important significance in understanding the growth and reconstruction process of continental crust of the Yangtze Block and the breakup mechanism of Rodinia supercontinent.