Fingerprints of the Kerguelen Mantle Plume in Southern Tibet: Evidence from Early Cretaceous Magmatism in the Tethyan Himalaya

Abstract

Early Cretaceous magmatism suggested to be related with the Kerguelen mantle plume has been reported in both eastern and western Tethyan Himalaya (TH). Coeval magmatism has been recently discovered in the central TH. This magmatism is recorded by an intrusion next to the Xiongma township. This intrusion is composed of gabbro and dolerites. The Xiongma gabbros are characterized by significant enrichment of light rare earth elements and prominent Na-Ta depletion in the primitive mantle–normalized spider diagrams. The εNd(t) ratios of the gabbros are between −4.33 and −2.20, and initial 87Sr/86Sr ratios are 0.707807–0.708557. Lead isotopes 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb of the gabbros range from 39.042 to 39.630, 15.646 to 15.709, and 18.455 to 18.833, respectively. Zircons from the gabbros and dolerites yielded three U-Pb ages of 138.5±1.6, 133.6±2.5, and 136.4±2.2 Ma, respectively. The magmatic zircons are exclusively characterized by negative εHf(t) values. Through geochemical modeling, we concluded that the Xiongma magmatic rocks have experienced combined crustal assimilation (10%–15% for the gabbros and 28%–32% for the dolerites) and fractional crystallization processes. The gabbros are derived from an Sp+Grt facies (Grt>Sp) enriched mantle source. The Xiongma magmatism is geochemically and geochronologically comparable with those in the western and eastern TH. Through comparison study between oceanic island basalt–like rocks in both the Yarlung Zangbo Suture Zone and TH, we propose a possibility that these geochemically and geochronologically comparable magmatic rocks may be genetically related with the Kerguelen mantle plume, and thus represent the dispersed fingerprints of the Kerguelen plume preserved in southern Tibet, China.