Age and generation of Fogang granite batholith and Wushi diorite-hornblende gabbro body

Abstract

Fogang granitic batholith, the largest Late Mesozoic batholith in the Nanling region, has an exposure area of ca. 6000 km2. Wushi diorite-homblende gabbro body is situated at the northeast part of the batholith. Both the granitic batholith main body and the diorite-homblende gabbro body belong to high-K calc alkaline series. Compared with the granitic main body, the Wushi body has lower Si (49%–55%), higher Fe, Mg, Ca, lower REE, less depletion of Eu, Ba, P, Ti, and obvious depletion of Zr, Hf. Zircon LA-ICP-MS dating and the mineral-whole rock isochron dating reveal that Fogang granitic main body and Wushi body were generated simultaneously at ca. 160 Ma. The Fogang granitic main body has high (87Sr/86Sr)i ratios (0.70871–0.71570) and low ɛNd(t) values (−5.11–−8.93), suggesting the origins of the granitic rocks from crustal materials. Their Nd two-stage model ages range from 1.37–1.68 Ga. The Sr and Nd isotopic compositions and the Nd model ages of the granitic rocks may suggest that the giant Fogang granitic main body was generated from a heterogeneous source, with participation of mantle component. Wushi diorite-homblende gabbro is an unusual intermediate-basic magmatic rock series, with high (87Sr/86Sr)i ratios (0.71256–0.71318) and low ɛNd(t) values (−7.32–−7.92), which was possibly formed through mixing between the mantle-derived juvenile basaltic magma and the magma produced by the dehydration melting of lower crustal basaltic rocks.