Neoproterozoic IAT intrusion into Mesoproterozoic MOR Miaowan Ophiolite, Yangtze Craton: Evidence for evolving tectonic settings

摘要: Abstract The Miaowan Complex in the Northern Yangtze Craton consists mainly of layered fine-grained metabasites, pillow lavas, sheeted dikes, gabbros, sepentinized harzburgite, and dunite, with rare metasedimentary rocks metabasite section, was initially regarded as an ophiolite complex. In this study, we divide into two suites including Ophiolite Suite a Late Magmatic Suite, based on differences degree deformation, age geochemical characteristics. (MOS) ductily deformed serpentinized gabbro, basalt, plagiogranite, rocks. All these units were then intruded by (LMS) consisting pegmatitic-isotropic gabbro massive diabase. zircons from MOS yield ca. 1115 Ma, consistent whole-rock Sm-Nd errochron (1135 ± 54 Ma) basalt MOS. Hence, formation is interpreted to be 1115 Ma. Harzburgites are characterized smooth LREE-depleted flat MREE-HREE patterns; whereas dunites display U-shape REE patterns. Deformed slightly LREE enriched patterns, low Th/Yb ratios lack Nb anomalies, showing N-MORB affinities. initial eNd (t) values rock range +6.6 +7.8, indicating that derived strongly depleted mantle source. Accordingly, have formed oceanic spreading center reaction between harzburgites subduction-related boninitic melts when trapped part wedge above subduction zone response initiation intra-oceanic system. Igneous late gabbros LMS weighted mean 207Pb/206Pb ages 973 ± 15 Ma, 999 ± 17 Ma 1002 ± 19 Ma, respectively, suggesting 1000 Ma 970 Ma, their (1007 ± 62 Ma). Pegmatitic-isotropic diabase enriched-LREE patterns high negative Zr setting. +6.0 +7.2. It suggested fore-arc Collectively, magmatic older MORB-type ophiolitic suite younger arc-related suite, recording evolution geodynamic settings Proterozoic ocean. Based previous studies contribution, new tectonic model proposed for Mesoproterozoic-Neoproterozoic northern margin Craton: (1) N-MORB-affinity mafic-ultramafic basin at 1115 Ma; (2) initiated 1100 Ma beneath which Shennongjia arc (north MOS) built; overriding plate harzburgite reacting forming dunite U-shaped (3) subsequent slab roll-back opening basin, forearc-affinity mafic generated 970 Ma; (4) inferred collided MOS + LMS 940–930 Ma.