Geochronological and geochemical constraints on the petrogenesis of the Ailaoshan granitic and migmatite rocks and its implications on Neoproterozoic subduction along the SW Yangtze Block

摘要: Abstract The Neoproterozoic tectonic pattern of the South China Block (SCB) is considered to be a key element in Rodinia reconstruction and subsequent Gondwana assembly. Numerous studies have been done on igneous rocks along SE NW Yangtze SCB, but contemporaneous SW has poorly known so far. This paper documents comprehensive set U–Pb geochronological, elemental Sr–Nd–Hf isotopic data for granitic gneiss migmatite from Ailaoshan zone basis field investigations. These are mainly granodiorite, monzogranite quartz diorite spatially associated with synchronous mafic dioritic rocks. On A/CNK values CIPW-normative corundum contents, these samples subdivided into Group 1 A/CNK > 1.1 1.5–6.5 vol.% 2 A/CNK = 0.87–1.09 corundum = 0–1.5 vol.%, generally similar S- I-type rocks, respectively. representative give weighted mean ages 810–785 Ma 790–764 Ma, respectively, interpreted as crystallization ages. They show strong Nb–Ta P–Ti negative anomalies variable Eu/Eu∗ (0.10–0.92). eNd(t) eHf(t) ranges −6.5 ∼ −4.2 −3.8 ∼ +3.1 −6.2 ∼ +1.8 −6.3 ∼ +5.7 2, might originate hybridization source metagreywacke proportionally “ancient” component abundant juvenile mafic-derived 2. Our data, available geological observations, demonstrate extensive occurrence (761–833 Ma) zone. previously-mapped Yaoshan groups Complexes including Neoproterozoic, Triassic Cenozoic A persistent long-lived (∼830–760 Ma) subduction southwestern northwestern margins Panxi then Hannan proposed. locate at periphery during early Neoproterozoic.