Origin and early evolution of the Lhasa Terrane, South Tibet: Constraints from the Bomi Gneiss Complex

Abstract

The Precambrian history of the Lhasa Terrane provides important context for understanding the India–Asia continental collision and formation and evolution of the Tibetan Plateau. However, it has not yet been well constrained, due to the scarcity of Precambrian outcrops. In this study, we present geochronological, geochemical, and Lu–Hf isotopic data for granitoid gneisses from the Bomi Complex in the eastern Lhasa Terrane. Our new data, together with those from the literature, reveal three episodes of magmatic activity at ca. 1866–1782 Ma, ca. 1343–1250 Ma, and ca. 824 Ma, and two metamorphic events at ca. 1117 Ma and ca. 625–600 Ma. While the Mesoproterozoic gneiss complexes suggest a transition from early rift-related to late arc signatures, the other two episodes of gneiss formation have arc signatures. We suggest that during the Paleoproterozoic and Middle Neoproterozoic, the Bomi Complex had an affinity with the Lesser and Greater Himalaya terranes along the northern margin of India, respectively. During the Mesoproterozoic and late Neoproterozoic, the Bomi Complex might be correlated with the contact zone between the Indian Archean cratons and the Eastern Ghats Belt in southeastern India. These magmatic and metamorphic events indicate that the Lhasa Terrane was located along the northern margin of the Indian continent during its early evolution. We propose the Precambrian evolution of the Lhasa Terrane was as follows: (1) the Lhasa Terrane and Lesser Himalayan sequence represent a Paleoproterozoic continental arc along the northern margin of the Indian continent; (2) the eastern Lhasa Terrane was affected by the Grenvillian-age Eastern Ghats orogeny during the Mesoproterozoic; (3) the Lhasa Terrane and Greater Himalayan Crystalline Complex formed a middle Neoproterozoic Andean-type orogen along the margin of the Rodinia supercontinent; and (4) the Lhasa Terrane experienced the Pan-African Orogeny, which might have marked the initial assembly of East Gondwana.