Geochemical and Sr–Nd–Pb isotopic compositions of Cretaceous granitoids: constraints on tectonic framework and crustal structure of the Dabieshan ultrahigh-pressure metamorphic belt, China

摘要: Abstract The Dabie orogenic belt can be divided into four tectonic and lithological units. They are, from north to south, the North Huaiyang (NHY) unit, Northern complex (NDC) ultrahigh-pressure (UHP) metamorphic high-pressure (HP) unit. Cretaceous granitoids units, irrespective of unit lithology, show surprisingly similar major trace element particularly Sr–Nd–Pb isotopic compositions, indicating a crustal source for their magma genesis. have initial ( 87 Sr/ 86 Sr) t values 0.7068–0.7091 Nd-depleted mantle model ages 1.6–2.4 Ga e Nd ) at time emplacement (120 Ma) ranging −13 −26. Their present-day Pb compositions are 206 Pb/ 204 Pb=15.62–17.06, 207 Pb=15.21–15.44, 208 Pb=36.59–37.81. With comparison basement rocks in belt, indicate that is but distinct This strongly suggests exposed extends deep crust southward beneath UHP/HP units northward best interpreted as core dome within belt. only thin-skinned slab confined shallower levels over complex. Present framework terrain was formed by extensional tectonics post metamorphism. has an affinity Yangtze craton. also suture between China cratons marked Xiaotian–Mozitang Fault separating rather than previously thought Wuhe–Shuiko Fault, which separates UHP