摘要
山西吕梁地区古元古界小两岭组火山岩角度不整合于华北克拉通结晶基底之上,主要由玄武-安山岩、英安-流纹岩组成,SiO_2含量57%～63%的火山岩很少。岩石富集大离子亲石元素(Ba、K等)和轻稀土元素,相对亏损高场强元素(Nb、Ta等)。主、微量元素及Nd同位素地球化学特征表明:玄武-安山岩与英安-流纹岩为同源岩浆产物,成分间隙的产生由分离结晶作用导致;岛弧型火山岩地球化学特征产生的原因主要不是由于地壳的混染,而是继承于受俯冲组分改造的岩石圈富集地幔。对小两岭组顶部流纹岩中的锆石进行激光探针等离子体质谱(LA-ICP-MS)年龄测试,表明火山岩形成于1779±20Ma (^(207)Pb/^(206)Pb)。通过对小两岭组火山岩与熊耳群火山岩的地层层位、岩相学、地球化学和Nd同位素特征的对比,以及年代学方面的证据,表明小两岭组火山岩与熊耳群火山岩相当,是同期岩浆活动在不同空间的产物,都形成于大陆裂谷环境,可能与地幔柱有关。
The volcanic rocks of the Xiaoliangling Formation unconformably ovedy a paleoproterozoic crystalline basement （ L liang Group） in the L liang area. The Xiaoliangling Formation comprises basaltic-andesite and dacite-rhyolite, and display a composition gap of 57% -63%SiO2. The volcanic rocks are enriched in LILE （e. g. Ba and K） and LREE, depleted in HFSE（e. g. Nb and Ta）, similar to the OIB. The distributions of major, trace element and Nd isotope demonstrate that both basaltic-andesite and dacite-rhyolite are from co-magmatism source. Crystal fractionation is the main factor to control the composition gap of the volcanic rocks. The arc geochemical characteristics are the results of an enriched subcontinental lithospheric mantle previously contaminated by a subducted slab, not crustal contamination. This study employed an LA-ICP-MS （laser ablation-inductively coupled plasma mass spectrometry） to analyze rhyolite zircons from the top of Xiaoliangling Formation for U-Pb isotopic chronological age, the age of the rhyolite zircons is 1779 ＋ 20Ma（^207 Tpb/^206pb age）. The stratigraphic, petrographic, geochemical characteristics, Nd isotope and chronology of the volcanic rocks from the Xiaoliangling Formation are consistent with the characteristics of the Xiong＇er Group suggest that the Xiaoliangling Formation is an equivalent of the Xiong＇er Group in the L liang area. The Xiaoliangling Formation and the Xiong＇er Group were formed in an aborted continental rifting setting and probably triggered by mantle plume.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第5期1123-1132,共10页
Acta Petrologica Sinica
基金
国家自然科学基金(40473018
40272041)
中国科学院知识创新工程领域前沿项目(GIGCX-04-03)资助课题
关键词
小两岭组
熊耳群
地球化学
古元古界
华北克拉通
Xiaoliangling Formation, Xiong＇ er Group, geochemical characteristics, Paleoproterozoic, North China Craton
