西南极乔治王岛菲尔德斯半岛火山岩地质初步研究

西南极乔治王岛菲尔德斯半岛主要由基性熔岩、火山碎屑岩及薄层沉积岩组成,并有次火山岩体及脉岩发育.野外观察及K—Ar,Rb—Sr全岩年龄说明岩石形成于始新一渐新世.主要元素和微量元素地球化学特征说明岩石属低钾高铝钙碱性玄武岩,但具有拉斑玄武岩的某些特征,是岛弧火山活动的产物.岩层呈平缓单斜,发育有近同期及后期走滑正断层,以及由断层活动形成的局部以称褶皱.

GEOLOGY OF VOLCANIC ROCKS ON FILDES PENINSULA, KING GEORGE ISLAND, WEST ANTARCTICA

Fildes Peninsula consists mainly of basaltic, basalt-andesitic lavas, pyroclastic, thin-layered pyroclastic-sedimentary fossil-bearing strata, and subvolcanic intrusions, dykes, corresponding with each effusive periods. The rocks are usually well crystallized, with porphyritic texture. The continental effusive lavas can be subdivided into 3 volcanic cycles. The early eruption centers were relatively concentrated on western coast of the peninsula, and have migrated eastward since the Late Miocene. The strata in the area are structurally marked by gentle monoclines, with NNE dip at angles of 10-15°. A few symmetrical folds are present only in the vicinity of some fracture zones. The strike-slip normal faults are well developed, which have been formed in late period of volcanic activity, and have further intensely activated during the. opening of Bransfield Rift near the end of Tertiary. The nature of volcanic rocks is relatively simple. Based on the features of major, trace elements, and the ralationship between them, these rocks are considered to be the products of island-arc volcanism and represent basically calc - alkaline basalt with some characteristics of island-arc tholeiite. The isochron ages of whole-rock by Rb-Sr and K-Ar methods are 55-25 Ma, which show that the volcanic activity in this re- gion has continued from the Eocene till to Quaternary. Since the Late Mesozoic, the Antarctic Peninsula Igneous-arc migrated westward, with the increase of basic composition of rocks. It means that the composition of continental salic crust diminished westward, and the position of magma chamber has passed through the continental margin and into the oceanic mantle.