豫西崤山早元古代中酸性侵入岩锆石/斜锆石U-Pb测年及其对熊耳火山岩系时限的约束

熊耳火山岩系是华北克拉通早元古代晚期重要的岩浆记录,其火山作用时限的厘定对于揭示华北该时期的构造格局与演化历史有重要意义。对侵入到熊耳火山岩系顶层马家河组的石英闪长岩体中的斜锆石与锆石和花岗斑岩体中的锆石进行了高精度SIMSU-Pb定年。三个样品共58个测点,石英闪长岩体中的斜锆石207Pb/206Pb平均年龄为1789±4Ma,锆石207Pb/206Pb平均年龄1778±12Ma,花岗斑岩体中的锆石207Pb/206Pb平均年龄为1786±8Ma。这些年龄数据表明石英闪长岩体从生成到侵位是一个短暂而连续的过程,这一岩体与花岗斑岩岩体基本同期。同时,由于这两个岩体侵入到了熊耳火山岩系最顶部的马家河组,因此可以限定熊耳火山岩系的上限。结合前人的年代学数据,我们提出熊耳火山岩系的岩浆作用时限在1770～1800Ma之间,峰期为1780Ma。这一研究结果从年代学上支持熊耳火山岩系形成于快速拉张的裂谷环境。

Zircon/baddeleyite U-Pb dating for the Paleo-proterozoic intermediate-acid intrusive rocks in Xiaoshan Mountains, west of Henan Province and their constraints on the age of the Xiong'er Volcanic Province

The Xiong'er Volcanic Province is the most important volcanism event occurring in the North China craton in the Late Paleo-proterozoic. The timing of the volcanism is crucial to understand the tectonic regime and evolutionary history of the North China craton in the Proterozoic. Precise U-Pb ages of zircon/baddeleyite from the quartz diorite and granite-porphyry which intruded the Majiahe Formation of the upper part of the Xiong'er Group were determined by multi-collector SIMS. 58 testing points have been obtained from the three samples. The mean ²⁰⁷Pb/²⁰⁶Pb ages from the quartz diorite are 1789±3.5Ma for baddeleyite and 1778±12Ma for zircon, respectively, while the corresponding mean ²⁰⁷Pb/ ²⁰⁶Pb age is 1786±7.7Ma for zircon from the granite-porphyry. The data implies that it's a transient and continuous process occurred between the generation and emplacement of the quartz diorite, and the quartz diorite and the granite-porphyry were formed almost contemporaneously. Because the two stocks intruded the Majiahe Formation of the upper part of the Xiong'er Group, the data could constrain the upper age limit of the Xiong'er Volcanic Province. It should be proposed that the volcanism age of the Xiong'er Volcanic Province is between 1770Ma and 1800Ma combining with previous chronological data. The peak period is 1780Ma. This result supports that the Xiong'er volcanic rocks should be formed under a rapidly extensional rift environment.