U–Pb zircon geochronology of basal granite by LA-ICP-MS in Yitong Basin, Northeast China: Implications for origin of limestone
U–Pb zircon geochronology of basal granite by LA-ICP-MS in Yitong Basin, Northeast China: Implications for origin of limestone
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DOI：
10.1016/j.marpetgeo.2014.08.001
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发表时间：
2015-12
影响因子：
4.2
通讯作者：
Weiming Wang;Jijun Li;Shuxia Zhang;G. Wang;Xuelu Yan;Weichao Tian
中科院分区：
文献类型：
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作者：
Weiming Wang;Jijun Li;Shuxia Zhang;G. Wang;Xuelu Yan;Weichao Tian
中国东北伊通盆地基岩中的钻井首次发现大量石灰岩沉积物。然后采用 LA-ICP-MS 锆石 U-Pb 定年分析确定矿床的地质年龄，并分析后期岩浆侵入对矿床生烃和保存环境的影响。对6个灰岩花岗岩样品的分析表明，伊通盆地基底含有大量岩浆成因锆石，这些锆石在CL图像上表现为颜色浅、振荡分带清晰、晶型完整，稀土元素含量及其分布规律表现为Eu流失轻微、Th/U比值较高、分布曲线左倾。基于 61 个岩浆成因锆石 U-Pb 测年的 Concordia 图显示数据点集中在 Concordia 线上，表明没有明显的 Pb 损失。 6 个花岗岩样品的结晶年龄分别为 220 Ma、192 Ma、261 Ma、185 Ma、270 Ma 和 273 Ma。据此推测，埋藏于盆地二叠纪地层中的沉积成因灰岩是在二叠纪沉积过程中形成的。侏罗纪时期岩浆活动最为活跃。岩浆侵入被认为起源于二叠纪地层以下更深的母岩。它从下往上切开二叠纪石灰岩，并释放出大量的热量来烘烤石灰岩。这加速了石灰岩中碳氢化合物的生成，并将其 KTG（干酪根与天然气）比率在 190 Ma 和 185 Ma 期间提高到 0.9 或更高。生烃早和保存差是石灰岩与生烃相关的两个特征。从储层岩性来看，石灰岩在岩浆活动的热量和挥发成分的作用下发生了热接触变质作用。还观察到，在岩浆喷发点附近，石灰岩的接触变质作用最为活跃。
Massive deposits of limestone were encountered for the first time by wells drilled into the bedrocks of Yitong Basin, Northeast China. U–Pb zircon dating analyses with LA-ICP-MS were then employed to determine the geological ages of the deposits and analyze the impact of a later magmatic intrusion upon the hydrocarbon generation and preservation environment in the deposits. Analyses of 6 granite samples taking from the limestone shows that the basement of the Yitong Basin contains numerous zircons of magmatic origin and these zircons are characterized in CL images as light color, clear oscillatory zoning and intact crystalline form, In terms of REE (rare earth elements) content and its distributive pattern, the zircons are shown with mild loss of Eu, high Th/U ratio and left-slanting distributive curves. Concordia plots based on U–Pb dating of 61 zircons of magmatic origin showed concentrated data points along the Concordia line, indicating no obvious Pb loss. The crystallization ages of 6 granite samples were dated as 220 Ma, 192 Ma, 261 Ma, 185 Ma, 270 Ma and 273 Ma, respectively. Based on the understanding, we inferred that the limestone of sedimentary genesis imbedded with the Permian formations of the basin was formed during deposition in the Permian era. The magma activity was the most active during the Jurassic. Magmatic intrusion was thought to be originated from deeper parent rocks below the Permian layers. It cut through the Permian limestone from the bottom up and released great amount of heat to bake the limestone. This accelerated hydrocarbon generation in the limestone and increased its KTG (kerogen to gas) rate to 0.9 or more during 190 Ma and 185 Ma. Early hydrocarbon generation and poor preservation are the two hydrocarbon-related features of the limestone. In terms of reservoir lithology, the limestone went through thermal contact metamorphism with the heat and volatile components from magmatic activities. It is also observed that contact metamorphism of the limestone was the most active near the eruption points of magma.