Geochemical and Boron Isotopic Evidence that Tourmaline Records Country Rock Assimilation of Leucogranites in the Himalayan Orogen

• 作者: HU Guyue GAO Li'e ZENG Lingsen LI Yike
• 来源期刊: 地质学报（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: ORIGINAL ARTICLES
• 页码范围: 123-134
• 页数: 12页
• 语种: 英文

摘要

Tourmaline geochemical and boron (B) isotopic compositions in two-mica granites (TMG),tourmaline-bearing leucogranites (Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite.The schorls in Gyirong leucogranitic plutons show low contents of MgO (0.238％-1.160％) and δ11B values (-12.1‰--11.2‰),while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO (4.815％-6.755％) and δ11B values (-10.7‰--9.3‰).This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome.As a result,three types of tourmaline were identified in the Himalayan orogen:(1) Tou-Ⅰ in the TMG and Tou-LG,which is the most common tourmaline type of schorl;(2) Tou-Ⅱ (dravite and high-Mg schorl) in the Tou-LG and tourmalite at the margins of the leucogranite;and (3) Tou-Ⅲ (mainly dravite,with minor high-Mg schorl) in metapelites of the High Himalayan Crystalline Sequence.The lenses and veins of Tou-LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks,which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.