山东蓬莱玄武岩地质与地球化学特征对鲁东地块地幔演化的指示意义

Indicating significance of geological and geochemical characteristics of Penglai basalt to mantle evolution of Ludong block

受断裂带的影响,蓬莱玄武岩集中在蓬莱北部,呈NE向至NNE向分布。火山活动分为四个阶段:前寒武纪时近EW向基底构造的形成、中生代NE--NNE向断裂构造的发育、中生代末期地幔柱强烈上涌和新生代火山活动的末期等4个构造阶段。玄武岩喷发主要集中于新生代,以气孔玄武岩、苦橄玢岩和辉橄岩为主。常量元素分析显示,蓬莱玄武岩与世界玄武岩平均成分有差异,表现为低Al2O3、CaO和MnO,高K2O、MgO和Na2O;与中国玄武岩平均成分相比,Al2O3、K2O和Na2O低,CaO、P2O5和MgO高。微量元素分析显示蓬莱玄武岩具有大陆玄武岩典型的右倾稀土元素配分模式,具有中度负铕异常。鲁东地块经历两期地幔交代过程,分别为寒武纪时期和中生代末至新生代时期。

Being influenced by the faults, Penglai basalts were mainly centralized at the north of Penglai are- a, distributing as NE to NNE trend. Volcanic activities are divided into four stages： the nearly EW basement tec- tonic formation of Precambrian ; the development of NE-NNE fault structure in Mesozoic ; the mantle plume intense upwelling at Late Mesozoic, and the end phase of volcanic activity in Cenozoic. The basalt eruption was mainly fo- cused on the Cenozoic, and the lithologics were primarily as vesicular basalt, picrite-porphyrite and augite perido- tite. The analysis of constant elements indicated that the elements of Penglai basalt were different from the average elements of basalt of world in lower contents of AlzO3, CaO and MnO and higher contents of K20, MgO and Na20; while compared with Chinese basalt, in lower contents of A1203, K20 and Na20 and higher content of CaO, PzO5 and MgO. The analysis of microelement indicated that Penglai basalt had the typical rightward rare earth element distribution patterns of the continental basalt with moderately abnormal negative europium. There were two mantle metasomatism processes in Penglai area in the Cambrian and in the Late Mesozoic to Cenozoic.