长江中下游火山岩带东南缘溧阳盆地火山作用的年代学、地球化学及岩浆成因探讨

发布时间：2018-06-24 16:48

本文选题：锆石U-Pb定年 + 钙碱性火山岩　；参考：《地球化学》2016年03期

【摘要】：位于长江中下游晚中生代火山岩带东南缘的溧阳盆地,不同于区内其他火山岩盆地的一个突出特点是出现较大比例的流纹质岩石,该盆地内火山岩/潜火山岩的SiO_2含量总体较高,但Na_2O+K_2O含量却是长江中下游火山岩盆地中最低的,属于高钾钙碱性系列。地球化学上,这些火山岩样品均表现为较强的轻、重稀土元素分馏程度,强烈亏损高场强元素Nb、Ta和Ti的特征。明显的Eu负异常,且δEu值随SiO_2含量的增加总体呈降低趋势,反映斜长石的分离结晶可能对岩浆的演化产生一定的影响。溧阳盆地内火山岩/潜火山岩的ε_(Nd)(t)值在-8.75~-7.44之间,不仅明显低于邻近的宁芜盆地和溧水盆地内的火山岩/潜火山岩,与江南造山带内晚中生代的花岗岩类相比,其ε_(Nd)(t)值也偏低。结合其高的~(87)Sr/~(86)Sr初始比值(~0.7097),指示溧阳盆地内的岩浆可能主要由古老的地壳物质部分熔融形成。本文分别测得溧阳盆地早期龙王山组粗面岩的SHRIMP锆石U-Pb年龄为(140±0.7)Ma,大王山组熔结凝灰岩、闪长玢岩及流纹斑岩的LA-ICPMS锆石U-Pb年龄分别为(129.1±1.1)Ma、(132.5±0.7)Ma和(132.3±0.7)Ma。区域对比表明,溧阳盆地火山活动的起始时间明显早于其他盆地内火山活动(6~10 Ma)。但各盆地内火山活动的峰期时间基本相当,均处于约130 Ma前后。整个火山岩带内的火山活动显示随时间具有从南东侧向北西方向迁移的趋势,并隐约显示火山活动由火山岩带中心区域向周边扩展的趋势。这种双向迁移性可能是太平洋板块与亚洲大陆板块相对运动和晚中生代发生在长江中下游地区的岩石圈减薄两种动力学机制共同作用的结果。
[Abstract]:The Liyang basin, located in the southeastern margin of the late Mesozoic volcanic rock belt in the middle and lower reaches of the Yangtze River, is different from other volcanic basins in the Yangtze River. The content of Sio _ 2 in volcanic rocks / subvolcanic rocks in this basin is relatively high, but the content of Na _ 2O _ K _ 2O is the lowest in the volcanic basins of the middle and lower reaches of the Yangtze River, which belongs to the high-potassium calc-alkaline series. Geochemically, these volcanic samples are characterized by strong fractionation of light and heavy rare earth elements, and strong depletion of high field strength elements, such as NB, Ta and Ti. The obvious negative EU anomaly and the decreasing trend of 未 EU value with the increase of SiO-2 content indicate that the separation and crystallization of plagioclase may have a certain influence on the evolution of magma. The 蔚 _ (ND) (t) value of volcanic rocks / subvolcanic rocks in Liyang basin is between -8.75 and 7.44, which is not only lower than that in adjacent Ningwu basin and Lishui basin, but also lower than that of late Mesozoic granitoids in Jiangnan orogenic belt. Combined with its high initial ratio of ~ (87) Sr / ~ (86) Sr (0.7097), it indicates that the magma in Liyang basin may be mainly formed by partial melting of ancient crustal materials. The shrimp U-Pb zircon U-Pb age of the early Longwangshan formation in Liyang basin is (140 卤0.7) Ma. the LA-ICPMS zircon U-Pb ages of the fused tuff, diorite porphyrite and stream porphyry in the Dawangshan formation are (129.1 卤1.1) Ma, (132.5 卤0.7) Ma and (132.3 卤0.7) Ma, respectively. The regional comparison shows that the onset time of volcanic activity in Liyang basin is obviously earlier than that in other basins (610 Ma). However, the peak time of volcanic activity in each basin is almost the same, which is about 130 Ma. The volcanic activity in the whole volcanic belt shows a trend of migration from east to south to north to west with time, and the trend of volcanic activity extending from the central area of the volcanic rock belt to the periphery. This bidirectional migration may be the result of the relative movement of the Pacific plate and the Asian continental plate and the late Mesozoic lithospheric thinning in the middle and lower reaches of the Yangtze River.
【作者单位】：中国地质科学院地质研究所;
【基金】：中国地质调查局地质调查项目(1212010711814) 地质矿产调查评价专项(1212011121116)
【分类号】：P597.3;P588.1

【相似文献】