Mixing of Enriched Lithospheric Mantle‐Derived and Crustal Magmas: Evidence from the Habo Cenozoic Porphyry in Western Yunnan

Abstract

AbstractNew zircon U–Pb ages, whole‐rock geochemistry and zircon Hf isotopes from the Habo porphyry Western Yunnan, China, were determined to provide constraints on the timing of uplift of the Eastern Tibetan Plateau. The intrusive rocks consist of shoshonitic porphyry (syenite porphyry and monzonite porphyry). Zircon laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) U–Pb dating indicates coeval emplacement ages of ~35 Ma. The porphyries have alkaline affinities, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) (e.g., Rb, Th, U, Pb), with depletion of high field strength elements (HFSEs) (e.g., Nb, Ti, Ta) and weak Eu anomalies. They display uniform Lu–Hf isotopic compositions with negative zircon εHf(t) values ranging from ‐3.9 to ‐0.6. The chemical characteristics of the syenite porphyries indicated that they most likely originated from the lower crust, with mantle‐derived material involved in their generation. Geochemically, the monzonite porphyries are similar to the syenite porphyries; however, the lower MgO contents suggest that they were produced by different degrees of partial melting of the same lower crust source. Combined with the geochemical and isotopic data in this paper, imply that the alkali‐rich porphyries of the Habo polymetallic deposit were derived from the partial melting of lower crust, enriched by mantle magma, formed in a conversion stage from stress extrusion (a strike‐slip shear process) to local stress relaxation (a strike‐slip pull‐apart process) at the Ailaoshao tectonic zone.