昆秦接合部志留-泥盆纪侵入岩及其构造环境

通过详细的地质填图和年代学研究,确定昆秦接合部存在志留-泥盆纪岩浆活动,采用单颗粒锆石U-Pb定年方法测定侵入岩的形成时代为382~423Ma,即志留-泥盆纪.岩体以小岩株、岩脉及构造岩片产出,普遍受后期构造作用,多数以构造片岩卷入海西期苦海-赛什塘构造混杂岩带内.岩性有石英闪长岩、英云闪长岩、花岗闪长岩及二长花岗岩4种,属于典型的钙碱性系列.常量和微量元素特征及构造环境判别显示,其形成于岛弧或陆缘弧及同碰撞构造环境,反映了原特提斯洋壳俯冲消减及随后的陆壳碰撞过程.该阶段侵入岩在侵入时代和形成的构造环境上,与东昆仑早古生代岩浆活动一致,因此,昆秦接合部发育的志留-泥盆纪岩浆弧向西可与东昆仑早古生代岩浆岩带相接.志留-泥盆纪侵入岩产出的地质特征及其形成的构造环境进一步说明,昆秦接合部地区古特提斯多岛小洋盒形成于弧后扩张作用,与原特提斯洋的关闭紧密相关. 

Silurian-Devonian Intrusive Rocks and Tectonic Environment in Copulae of Kunlun-Qinling Mountains

Silurian-Devonian magmatic activity was discovered in the copulae of the Kunlun-Qinling mountains by detailed mapping and chronology analysis. Single grain zircon U-Pb dating yielded formation dates of 382-423 Ma in the intrusive rocks, which is Silurian-Devonian. The intrusive bodies are output in stocks, dikes and tectonic slices, which were suffered from later tectonism and evolved in the Kuhai-Saishitang Hercynian mélange belt as tectonic slices. The rock types are quartz-diorite, tonalite, granodiorite and monzonite granite, belonging to typical calc-alkali rocks. The characteristics of trace elements, main elements and tectonic environment discrimination reveal that the rocks were formed in an island arc tectonic environment or a continental margin arc tectonic environment. Some were also formed in a syncollisional tectonic environment, which reflects the stages of the prototethys ocean subduction and later continental crust collision. In that period intrusive rocks are in accordance with the East Kunlun Early Paleozoic magmatic activity zone, so it is suggested that a Silurian-Devonian magmatic arc developed in the copulae between the Kunlun-Qinling mountains, which joins the East Kunlun Early Paleozoic magmatic rock zone to the west. The geological characteristics and tectonic environment of the Silurian-Devonian intrusive rock in the copulae between Kunlun-Qinling Mountains indicated that the Paleotethys archipelagic ocean was formed in back-arc expandation, which was closely related to the close of the prototethys ocean.