辽西地区中生代义县旋回火山活动特征分析

STUDY ON VOLCANIC ACTIVITIES OF MESOZOICYIXIAN CYCLE, WESTERN LIAONING

辽西地区广泛发育中生代火山岩，其中以义县旋回火山岩最为发育。本文在对辽西地区义县旋回火山岩微量元素地球化学特征研究的基础上，认为义县旋回火山岩具有同源性质，由壳幔混溶物质作用于统一的火山活动过程中产生。火山活动总体逐渐减弱，前期以部分熔融作用为主，后期发生了结晶分异作用。所建立的详细的微量元素变化剖面很好地反映了本旋回火山活动具有脉动性的特点。火山活动形成于与俯冲作用有关的远离大陆活动边缘的板内环境，处在由区域的挤压应力场向拉伸应力场转变期之后，这种转变可能与岩石圈的拆沉作用有关。

Mesozoic volcanic rocks are widely distributed in western Liaoning Province. They can be mainly divided into three eruption cycles,i.e. the Xinglonggou, the Lanqi and the Yixian cycles, among which the Yixian cycle is most importantly developed. Based on a high precision sampling on Yixian cycle, this paper made a particular study on the geochemical characteristics of trace elements in volcanic rocks of Yixian cycle. We found that all volcanic rocks in Yixian cycle were derived from a common source, which seems to be an admixture of crust and mantle materials. All of them were formed through several eruption pulses in a prolonged geodynamic process. Each eruption cycle had pulsation character and the volcanic activity weakened gradually. The variation of trace element parameters shows a quite coincidence with the lithology and eruption cycle subdivision,and provides a sensitive indicator on volcanic activities. This paper also discusses the structure background of Yixian volcanic cycle, which should be affected by the lithosphere delamination at K 3-J 1 in this area.