Early Cretaceous High Mg~# and High Sr/Y Clinopyroxene-Bearingdiorite in the Southeast Gangdese Batholith, Southern Tibet
详细信息
- 责任者：Wang Li (State Key Laboratory of Continental Tectonics and Dynamics ; Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Zeng Lingsen
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(6)
- 关键词：辉石闪长岩 ; pyroxene diorite ; 冈底斯山 ; Gangdise Range
- 页码：p.1977-1994
- 图表：illus., 7 tables, 67 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Field investigations and SHRIMP zircon U-Pb dating indicate that a suite diorite that intruded into gneisses of granodioritic composition north of Langxian of the southern Gangdese belt,formed at 121. 8 ± 1. 5Ma. This Early Cretaceous suite contains magmatic epidote and clinopyroxene. Whole rock geochemical data and zircon Hf isotopedata of this suite ofdiorite show the following characteristics: ( 1) low SiO2 ( 54. 9%～55.4%) ,high Al203 ( 17. 7%～17. 9%) and high Mg # ( 65.3～66. 1) ; (2) relatively high Na20/K20 ( >2. 5) ,indicating that they were of granite rich in sodium; (3) enriched in LREE,depleted in HREE, nearly flat distribution patterns for elements from Ho to Yb with ( Ho/Yb) N = 0. 93～1. 07,and weak negative Eu anomalies with Eu/Eu * = 0. 88～0. 91; (4) relatively high Sr (488 × 10 - 6～500 × 10 - 6 ) and Ba ( 176 × 10 - 6～181 × 10 - 6 ) ,high Sr/Y (37. 5 ～41. 7) and low La/Yb ( 7. 6～9. 8) ; ( 5) relatively high zircon ε Hf ( t) values ( +3.4～+6. 9) ; and ( 6)depleted in the HFSE,but relatively enriched in garnet compatible elements ( Sc,Y and HREE) aswell as mantle compatible elements ( Cr,Ni and Co) . These geochemical features and mineral assemblages indicate that they were hydrous magmaderived from the partial melting of fluid metasomatised mantle wedge during the northward subduction of the Neo-Tethyan slab. Emplace depths for the Early Cretaceous diorite as well as the Early Carboniferous granodiorite estimated by Al-in-hornblende geobarometer indicate that they were emplaced at～13km and ～21km,respectively,which in turn yields a long term exhumation rate of～0. 04mm/yr.
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