龙门山北段辉绿岩墙地球化学特征及其成因

In order to discuss the petrogenesis and formative environment of the northern section of Longmenshan tectonic belt, which locate at the northwest margin of Yangtze Block, this article tested major element contents and trace element abundances of the diabases. The result showed that the diabases are characterized by relatively high Ti，Fe and Al,，but low Mg. Most samples have alkaline-subalkline basalt features. The rare earth elements(REE) abaundances are higher，and the chondrite normalized REE pattern slightly tilt to the right，with unobviously differentiation of LREE and HREE, and week negative Eu anomaly or no Eu anomaly, they show the geochemical characteristics of within plate alkali basalt. The spider diagram of trace element reveal are similar to typical continental rift basalt. We believed that the diabases have high-Ti basalt features and probably resulted from relatively low-degree partial melts of protomagma with fractional crystallization. Magma were from the mantle lithosphere and formed in the continental within-plates environment. They were products of extensional background in the early-middle Jurassic after late Triassic intracontinental subduction orogeny.