东北地区中生代岩石圈减薄时间上限的厘定:来自松辽盆地营城组火山岩年代学约束

The upper age limitation of Mesozoic lithospheric thinning in NE China:Chronology restriction of Yingcheng Formation in Songliao Basin

松辽盆地是我国东北地区一个大型的晚中生代含油气沉积盆地。在盆地发育早期阶段受强烈伸展作用影响形成了大规模的断陷和大量的火山活动。本文以松辽盆地北部徐家围子断陷区火山岩的年代学研究为切入点,通过对徐家围子断陷升深更2井和徐深9-2井营城组(K_1y)火山岩的岩芯样品进行SHRIMP U-Pb定年,获得了营城组火山岩年龄为114～112 Ma,并认为该年龄结果代表了松辽盆地区域晚中生代岩浆作用的上限时间。通过对松辽盆地及邻区的火山年代学的对比发现:中国东北地区晚中生代曾发生过多期的岩浆事件,时间分别为:166～150 Ma;140～130 Ma;130～120 Ma;114～109 Ma。松辽盆地内早白垩世营城组火山岩年龄与我国东北地区中生代最后一期岩浆作用时间一致,指示了东北地区中生代最后一期岩浆事件年龄。松辽盆地营城组火山岩年龄的厘定将为本区中生代岩石圈减薄的上限时间提供进一步可靠的年代学约束。

The Songliao Basin is a large-scale petroliferous extensional sedimentary basin in Late Mesozoic. It is characterized by strong rifting and volcanism in the early stage of the basin evolution. With the SHRIMP U-Pb chronology studies for Yincheng Formation volcanic rocks from Shengshengeng-2 well and Xushen 9-2 well in Xujiaweizhi fault depression, northern part of Songliao Basin,it is indicated that the age of volcanic rock of Yingcheng Formation is about 114 - 112 Ma and it represents the upper age limitation of Mesozoic volcanic event in Songliao Basin. The statistic result of published U-Pb age of Mesozoic volcanic rock in NE China shows that there are four periods of volcanic events,and the age distribution is 166 - 150 Ma, 140 130 Ma, 130 - 120 Ma, 114 - 109 Ma. The age of volcanic rock of Yingcheng Formation in Songliao Basin is the same as the age of the last volcanic event in NE China, and it can represents the last volcanic event of Mesozoic in NE China. Since,the chronological results of this paper can provide strict constraint on the upper limit age of the lithospheric thinning in NE China.