苏北地区牛蹄山新元古代辉绿岩锆石U-Pb年龄、Hf同位素特征及其地质意义

    Zircon U-Pb age and Hf isotopic characterization of the Niutishan dolerite sills in the Northern Jiangsu Region and their geological implication

    • 摘要: 苏北地区位于华北克拉通东南缘,该区域内的新元古代沉积岩中广泛分布着辉绿岩床(墙)群,这些辉绿岩的年代学研究尚处于初步阶段,且现有成岩年龄记录与确定的震旦纪地层年龄存在不一致。本研究对牛蹄山中岩床状侵入到倪园组薄层灰岩(Zn)中的辉绿岩开展了高精度的锆石U-Pb定年和微区原位Hf同位素特征研究。锆石LA-ICP-MS U-Pb定年结果表明这些辉绿岩的形成年龄为962.3±8.5 Ma,暗示该区域内存在新元古代的岩浆活动。这些锆石的εHf(t)值介于8.48和11.92之间,表现出一致的正值;其一阶段Hf模型年龄(tDM1)和二阶段Hf模型年龄(tDM2)分别为1220~1063 Ma和1301~1095 Ma;这些数据共同指示其原始岩浆可能是直接从岩石圈地幔上升至地表的,并可能来源于中元古代的过渡型地幔。根据苏北地区牛蹄山辉绿岩的年代学和锆石Hf同位素特征,结合对Rodinia超大陆的研究进展,可以推断华北克拉通东南缘在新元古代早期很可能发生了与Rodinia超大陆分裂相关的岩浆作用。

       

      Abstract: The northern Jiangsu region is located in the southeast margin of the North China Craton, and the Neoproterozoic sedimentary rocks in this region are widely distributed with dolerite sill swarms. The chronology of these dolerite is still in the preliminary stage, and the existing diagenetic ages are inconsistent with the Sinian strata. Zircon U-Pb dating and in situ Hf isotope characterization were studied on the dolerite from the Niutishan region, which intrude into the Niyuan Formation in midsill-shaped. Zircon LA-ICP-MS U-Pb dating results indicate that the formation age of these dolerite is 962.3±8.5 Ma, suggesting the existence of Neoproterozoic magmatic activity in this area. The εHf(t) values of these zircons range from 8.48 to 11.92, showing consistent positive values. The first-stage Hf model age (tDM1) and the second-stage Hf model age (tDM2) were 1220~1063 Ma and 1301~1095 Ma, respectively. Together, these data indicate that the primordial magma may have risen directly from the lithospheric mantle to the surface and may have originated from a Mesoproterozoic transitional mantle. Based on the chronology of Niutishan dolerite and Hf isotopic characteristics of zircon, combined with the research progress of the Rodinia supercontinent, it can be inferred that magmatic processes related to the breakup of the Rodinia supercontinent may have occurred in the southeast margin of the North China Craton in the early Neoproterozoic.

       

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