Timing and conditions of metamorphism and melt crystallization in Greater Himalayan rocks, eastern and central Bhutan: insight from U–Pb zircon and monazite geochronology and trace-element analyses

• DOI: 10.1007/s00410-015-1143-6
• Publication Date: 2015-04-27T10:25:23Z
• Authors: K. Zeiger; S. M. Gordon; S. P. Long; A. R. C. Kylander...; K. Agustsson; M. Penfold
• Keywords: Main Central Thrust; Geochronology; Migmatite

Within the eastern Himalaya in central and eastern Bhutan, Greater Himalayan (GH) rocks are inter- preted to have been thickened by the Kakhtang thrust (KT). In order to understand the metamorphic and exhumation history of the GH and to evaluate the structural significance of the KT, zircon and monazite from twenty samples were analyzed by laser-ablation split-stream ICPMS. In eastern Bhutan, zircon and monazite from samples collected in the KT hanging wall revealed ca. 36-28 Ma metamorphism. Subsequently, the initiation of melt crystallization shows a trend with structural distance above the KT, with early melt crystallization (ca. 27 Ma) in the structurally highest samples and younger melt crystallization (ca. 16 Ma) for leucosomes within the KT zone. Melt crystallization was protracted and continued until ca. 14-13 Ma in both the KT hanging wall and the footwall. In comparison, in central Bhutan, two leucosomes revealed extended melt crystal- lization from ca. 31 to 19 Ma. The youngest zircon dates from samples exposed structurally above and below the KT are similar, indicating that the KT was not as significant of