Contrasting Sr-Nd-Hf isotope systematics in Early Jurassic magmatic rocks from the Lhasa terrane: Implications for the lithospheric architecture of the Lhasa terrane

Early Jurassic plutonic rocks from the Central Lhasa block that range from gabbro to granite yield similar Pb-206/U-238 ages ranging from 187.6 Ma to 196.0 Ma. Gabbros and diorites are characterized by similar radiogenic Sr-87/Sr-86(t) ratios that range from 0.7053 to 0.7060, unradiogenic epsilon(Nd)(t) values ranging from -4.2 to -2.5 and epsilon Hf(t) values ranging from -8.8 to -2.8. Compared with the intermediate to mafic rocks, the granites have much higher Sr-87/Sr-86(t) ratios, from 0.7102 to 0.7127, and lower epsilon(Nd)(t) values, from -8.7 to -7.5, and epsilon(Hf)(t) values from -11.9 to -7.5. Elemental and isotopic data suggest that the gabbros were derived from a melt-modified subarc mantle, diorites represent derivatives produced by hornblende fractional crystallization of gabbros, and granites were generated by the melting of ancient crustal basement rocks. Combined with literature data, these results suggest that the Central Lhasa block, as well as parts of the Southern and Northern Lhasa blocks, also contains ancient crystalline basement rocks. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The Early Jurassic plutonic rocks from the Central Lhasa block have similar Pb-206/U-238 ages, with diverse rock sources including a melt-modified subarc mantle for gabbros, derivatives produced by hornblende fractional crystallization of gabbros for diorites, and granites generated by the melting of ancient crustal basement rocks.