Geochronology and Geochemistry of Late Devonian I- and A-Type Granites from the Xing'an Block, NE China: Implications for Slab Break-off during Subduction of the Hegenshan-Heihe Ocean

We present detailed geochronological, geochemical, and zircon Hf isotopic data for Late Paleozoic granitic rocks from Handagai and Zhonghe plutons in the Xing'an Block, NE China, aiming to provide constraints on their origin and tectonic implications. New zircon U-Pb ages indicate they were formed in the Late Devonian (ca. 379 Ma) immediately after a striking 50 Ma magmatic lull (ca. 430-380 Ma) in the Xing'an Block. Petrological and geochemical features suggest that the Handagai monzogranites and Zhonghe alkali-feldspar granites are I- and A-type granites, respectively, although both of them have high-K calc-alkaline features and positive zircon epsilon(Hf)(t) values (+3.47 to +10.77). We infer that the Handagai monzogranites were produced by partial melting of juvenile basaltic crustal materials under a pressure of <8-10 kbar, whereas the Zhonghe alkali-feldspar granites were generated by partial melting of juvenile felsic crustal materials at shallower depths (P <= 4 kbar). Our results, together with published regional data, indicate their generation involves a subduction-related extensional setting. Slab break-off of the Hegenshan-Heihe oceanic plate may account for the subduction-related extensional setting, as well as the transformation of arc magmatism from the Early-Middle Devonian lull to the Late Devonian-Early Carboniferous flare-up in the Xing'an Block.