Zircon U-Pb geochronological and Hf isotopic constraints on petrogenesis of Late Mesozoic intrusions in the southeast Hubei Province, Middle-Lower Yangtze River belt (MLYRB), East China

During the Late Mesozoic. extensive magmatism and associated ore deposits were developed in the southeast Hubei Province, Middle-Lower Yangtze River metallogenic belt (MLYRB), East China. To understand the petrogenesis of the intrusions in the area, we performed in situ zircon U-Pb and Hf isotopic analyses on 14 samples from the Fengshangdong stock, and from the Echeng, Tieshan, Wangbaoshan-Jinshandian and Yangxin batholiths. Three major suites of intrusive rocks are recognized in the southeast Hubei Province: (1) 141-146 Ma granodiorite and granite porphyries (associated with 143-144 Ma porphyry-skarn Cu-Mo deposits) have enriched radiogenic Hf isotopic compositions (epsilon Hf (t) = -9.5 to -1.6), comparable to those of Cretaceous pyroxene diorites. trachyandesites, and basalts (epsilon Hf (t) = -8.9 to -1.3) in the MLYRB, which were derived from an enriched lithospheric mantle. (2) Voluminous 136-143 Ma gabbros, diorites, and quartz diorites (associated with 137-144 Ma skarn Cu-Fe. Fe-Cu. and Au-Cu deposits) have variable Hf isotopic compositions (epsilon Hf (t) = -19.1 to -5.4). indicating an origin via the hybridization of enriched mantle-derived mafic magma and variable amounts of ancient lower-crustal components. (3) 127-133 Ma diorites, quartz diorites, and granites (associated with 132-133 Ma skarn Fe deposits) characterized by a wide range of epsilon Hf (t) values (-28.2 to -6.4), suggest the assimilation of various ancient lower-crustal materials by enriched mantle-derived basaltic magma. The intrusions of Suites 1 and 2 are characterized by high Sr contents (329-2087 ppm), and high Sr/Yb (36-1710) and (La/Yb)(N) ratios(17.6-172). but low Yb contents (0.45-1.82 ppm) and do not show negative Eu anomalies (delta Eu = 0.74-1.4). The intrusions have radiogenic Sr-Nd isotopic compositions (epsilon Nd(t) = -10.0 to -3.4 and (Sr-87/Sr-86)(i) = 0.7054-0.7084). Compared with the intrusions of Suites 1 and 2, rocks of Suite 3 have relatively low Sr contents (60.5-327 ppm), and low Sr/Yb (33.0-315) and (La/Yb)(N) ratios (2.28-30.0), but relatively high Yb contents (1.04-5.17 ppm) and significant negative Eu anomalies (delta Eu = 0.22-0.73). The rocks of Suite 3 are characterized by a wide range of radiogenic Sr-Nd isotopes with epsilon Nd (t) values of -12.5 to -4.9 and (Sr-87/Sr-86)(i) = 0.7057-0.7085. The proposed magma sources, combined with the geochemical and Sr-Nd isotopic differences between these three suites of intrusive rocks, indicate that Late Mesozoic magmatic activity in the southeast Hubei Province, MLYRB was associated with lithospheric thinning induced by asthenospheric upwelling at that time. (C) 2011 Elsevier B.V. All rights reserved.