Origin and Implication of the Paoma Granite in the Western Yangtze Block, South China Craton

The Meso- to Neoproterozoic magmatic rocks cropping out in the western Yangtze Block are pivotal to comprehending the tectonic-magmatic revolutionary processes of the South China Craton during the breakup and assembly of Rodinia. A combined study including a detailed geological survey, systemic measurement of the geological section, petrographic observations, geochronology, and elemental geochemistry was carried out on the southern margin of the Paoma granitic pluton in SW China. The obtained data of major elements, along with the mineralogy that includes aluminosilicate minerals, indicate that the studied 825.7 ± 6.0 Ma Paoma granites are peraluminous, which is consistent with an affinity with S-type granites. They show seagull-shaped chondrite-normalized REE patterns with strongly negative Eu anomalies. They are enriched in LRREs and Large Ion Lithophile Elements but are depleted in High Field Strength Elements, with strongly negative Nb, Sr, P, and Ti anomalies. We conclude that the Paoma granite magma originated from the partial melting of clay-rich mudstone from the upper crust. The geochemical data of Paoma granite, integrated with the regional geological context, are consistent with a tectonic setting involving a fossil ridge subduction. The 825.7 Ma Paoma granite, along with the 830 Ma Guandaoshan gabbros showing N-MORB geochemical signatures, defines an east-west trending Neoproterozoic “slab window” in the WYB.