鄂尔多斯盆地西南部早白垩世岩浆事件及其地质意义OA

Cretaceous magmatic events in the Ordos Basin are crucial for unraveling the regional tectonic dynamic evolution mechanisms of the Early Cretaceous and exploring the spatiotemporal coupling relationships between magmatism,hydrocarbon accumulation,and sandstone-type uranium mineralization.This study identified,for the first time,Early Cretaceous intrusive rocks within the Lower Cretaceous Huanhe-Huachi Formation in the southwestern part of the Ordos Basin.Integrated petrological,zircon U-Pb geochronological,and Hf isotopic analyses were conducted.A melanocratic porphyry intrusive body is identified in the Huanhe-Huachi Formation,yielding a zircon U-Pb weighted mean age of(126.5±0.9)Ma(MSWD=1.6),indicating the middle Early Cretaceous magmatism.Zircon εHf(t)values of-12.32--4.70,and TDM2 model ages of 1 960-1 501 Ma indicate that this region records the Early Cretaceous magmatic activity of the westernmost North China Craton.The magmatic ages decrease eastward and westward from the Taihang-Lüliang tectonic belt,reflecting an extensional setting jointly controlled by the westward subduction of the Paleo-Pacific Plate and the northeastward subduction of the Bangong-Nujiang Ocean.Asthenospheric upwelling triggered lithospheric thinning and the partial melting of the ancient crust,forming a mantle heat-driven magmatic system.Magmatic thermal effects promoted hydrocarbon generation and expulsion in deep-source rocks.The released reducing agents participated in redox interface regulation for shallow sandstone type uranium mineralization,although magmatic-hydrothermal fluids did not directly contribute to uranium ore-forming processes.