Geochemical Characteristics and Geodynamic Significance of Cenozoic Basalts from Maguan and Pingbian, Southeastern Yunnan Province
详细信息
- 责任者：Huang Xingkai (China Non-Ferrous Metals Resources Geological Survey ; Beijing 100012 ; China) ; Mo Xuanxue
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(4)
- 关键词：玄武岩 ; basalts ; 云南 ; Yunnan Province
- 页码：p.1325-1337
- 图表：illus., 3 tables, 59 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Cenozoic basaltic magmatism in Maguan and Pingbian area, southeastern Yunnan Province, is an important component of post-collisional magamatism of eastern Tibetan Plateau. Whole-rock 39Ar/40Ar dating results reveal two pulses of magma eruption occured in Maguan area, in 12.9±0.2Ma and 21.2±1.2Ma, respectively. Basalts in Pingbian area are very young products of lately erupted magma, with age less than 1.7Ma, which is well synchronous to the magmatism distributed in Tengchong, Vietnam, Hainan and South China Sea area. According to CIPW normalization and whole-rock chemistry, basalts from Maguan can be classified into olivine tholeiite, alkaline olivine basalts and basanite, which originate from depths of 57～73km, 82km and 67.5～87km, respectively. Basalts from Pingbian are exclusively basanite, with segregation depth ranging from 79km to 88km. Basalts show OIB-like geochemical characteristic, with enrichment in light rare earth elements, large ion lithophlie elements and high field strength elements (Nb, Ta), high Nb/U ratios and without Eu anomaly. Relatively high initial 143Nd/144Nd and low 87Sr/86Sr ratios and positive εNd collectively ascribe the source region of basalts to a hybrid of depleted asthenospheric mantle and EMⅠ (and/or EMⅡ) type enriched mantle, which is akin to those of basalts from northern Vietnam and South China Sea area. Simulation results and Re-Os isotopic characteristics illustrate that the source region of basalts situates at the transition zone of spinel and garnet, and the basaltic melt is a mixture of partial melt of garnet-facies lherzolite and spinel-facies lherzolite, with melt degree of 1% and 2%～5%,respectively. As a response to the huge collision between India and Eurasian plate onset around 65Ma, significant block rotation, extrusion or escape took place along Jinshajiang-Ailao Shan-Red River strike-slip fault belt, which resulted in the migration of deep material beneath Tibetan Plateau toward surrounding area. The suction of Western Pacific subduction zone stimulates the flow and upwelling of asthenospheric mantle to migrate along southeast direction, and subsequently bring forth the Cenozoic magamatism in southeastern Yunnan Province. As a result, volcanism in this area is also a response to the collision between Indian and Asian plate, and exceptionally records the lateral extrusion of asthenospheric material beneath Tibetan Plateau and accompanying migration along the Ailao Shan-Red River strike-slip belt.