郯庐断裂带中-南段新生代火山活动与深部过程

CENOZOIC VOLCANIC ACTIVITIES AND DEEP PROCESSES IN THE MIDDLE-SOUTH SECTOR OF THE TAN-LU FAULT ZONE

郯庐断裂带中南段新生代火山活动主要发生在古近纪、中新世和更新世3个阶段,前者出现在断裂带的伸展活动中,后两者出现在挤压活动中。随着时代变新,玄武岩碱性逐渐增强,轻、重稀土元素分离程度及不相容元素富集程度也逐渐增强。Sr、Nd同位素显示,源区地幔具有轻微富集型(EMⅠ)→洋岛型→洋中脊型的演化规律。断裂带所影响的地幔发生了地幔剪切变形及显著的交代作用,两者相互促进。断裂带在新生代演化中切割深度不断加大,火山源区不断加深,现今已切穿了整个岩石圈。断裂带在新生代软流圈上隆的背景下,经过地幔剪切、减压、地幔交代及部分熔融等深部过程,从而出现了大规模的玄武岩喷发。

Three stages of Cenozoic volcanic activities in the middle-southern sector of the Tan-Lu fault zone could be distinguished, namely, in Paleogene, Miocene and Pleistocene respectively. The former occurred in an extensional tectonic setting of the fault zone and the latter two took place in a compressive condition. With the ages becoming younger of the basalts, their alkali, the fractional degree of LREE/HREE and incompatible elements enrichment increased. tire the lithosphere nowadays. Under a background of Cenozoic lithospheric upwelling, the fault zone experienced deep processes of mantle shearing, pressure-reducing, mantle metasomatism and partial melting, at last leading to large-scale basalt eruption.