Geochemistry Research on the Deep Mantle Activity in Baiyun Sag during the Cenozoic from the Volcanic Rocks of Well BY7
详细信息
- 责任者：Que Xiaoming (State Key Laboratory of Marine Geology ; Tongji University ; Shanghai 200092 ; China) ; Li Yuansen
- 刊名：Geology and Mineral Resources of South China
- 出版年：2013
- 卷期：29(2)
- 关键词：火山岩 ; volcanic rocks ; 地球化学 ; geochemistry ; 白云凹陷 ; Baiyun sag
- 页码：p.105-115
- 图表：illus., 1 table, 67 refs.
- 分类号：0801
- issnNo：ISSN1007-3701
- isbnNo：CN42-1417/P
摘要
Baiyun Sag,located in the southwestern Pearl River Mouth Basin,is a transfer zone in Cenozoic.The well BY7,in the vicinity of the boundary fault of Baiyun Sag,records multi-stage magmatism.The basalt-andesitic lavas(sample BY705~BY706) and basalts(sample BY701 ~ BY704) found in well BY7,belong to Enping Formation and Zhujiang Formation,respectively.They record two magmatic activities which took place in pre-opening of South China Sea(SCS) and in the late stage of SCS formation.Geochemically,in the volcanic rocks of Enping Formation,contents of SiO2(53.60% ~ 54.21%) and(Na2O+K2O)(4.63%~5.16%) are different from the volcanic rocks of Zhujiang Formation which are with lower SiO2(47.26% ~ 52.34%) and higher total alkalis(5.93% ~ 6.98%).All volcanic rocks are characterized by low total REE contents(∑REE=153.0 ~ 174.3 ppm) and strong differentiation between LREE and HREE((La/Yb)N=10.1 ~ 13.5).The REE distribution patterns and trace elements spider diagrams of these volcanic rocks are similar to the ocean island basalt(OIB).Evidences of lithospheric involvement are exhibited from the investigation of these volcanic rocks,including enrichment in large ion lithospheric elements(Rb,Ba,Ka),high Pb content and low value of Nb/U.Crustal component,resulted from lithosphere delamination which is induced by crust-mantle interaction during late Cretaceous,involves in magma generation,which is the cause of crustal contamination.Magma is generated in a mantle plume or hotspot environment and originated from enriched mantle source of low-degree partial melting.Volcanic rocks of Enping Formation may be caused by the upwelling of deep mantle with an OIB-MORB type magma,and experience the metasomatism of fluid released from subduction slab and crustal contamination.Volcanic rocks of Zhujiang Formation belonging to intraplate alkaline basalt,consist mainly of an EMI-type OIB end-member mantle source and have crustal contamination,probably are caused by upwelling of Hainan mantle plume.Deep mantle upwelling may play an important role in the incipient period and the following evolution of South China Sea.