Geochemistry and origin of Late Cretaceous (~90Ma) ore-bearing porphyry of Balazha in mid-northern Lhasa terrane, Tibet
拉萨地块中北部晚白垩世(约90Ma)拔拉扎含矿斑岩地球化学特征及其成因

The ore-bearing porphyry of Balazha in mid-northern Lhasa terrane, with a forming age of 90~88Ma, shows some typical geochemical characteristics of an adakite, such as high SiO2 (>69%), Al2O3(15.89% in average), Sr (354×10-6 in average), but low Y (12.97×10-6 in average), Yb (0.95×10-6 in average) contents, and strongly fractionation between LREE and HREE ((La/Yb)N=19.8 in average). Meanwhile, it is of relatively higher Mg# (65 in average), Cr (107×10-6 in average) and Ni (13×10-6 in average). These geochemical features, combined with other characteristics of Late Cretaceous lavas in mid-northern Lhasa terrane, indicate that they did not result from melting of young oceanic crust, assimilation and fractional crystallization, or from either underplated or thickened continental crust. Instead, they were possibly derived from partial melting of delaminated lower continental crust. On the other hand, they are also likely to the result of partial melting of crust-mantle material, triggered by slab break-off of south-dipping subduction of Slainajap ocean or Bangong Co-Nujiang ocean.