浙江沿海晚中生代拉斑玄武岩浆侵位深度的讨论

浙江沿海晚中生代复合岩流中拉斑玄武岩高度富集大离子亲石元素，反映除了源区富集作用外还有地壳混染的贡献，Rb、Nb的丰度特征指示玄武岩浆主要与中、上地壳岩石发生了相互作用。用岩石化学成分计算的这种拉斑玄武岩浆熔体的平均密度为ρm = 2.678 g/cm3 , 根据岩浆与周围地壳的压力平衡关系，推算得来自地幔的玄武岩浆一直侵位到距地表约16.3km左右的中地壳时才滞留下来，并被相应的地壳物质所混染。

On the Depth of Emplacement of Late Mesozoic Tholeiitic Magma from Coastal Area of Zhejiang Province

The early Cretaceous mafic-acidic igneous rocks from the coastal area of Zhejiang Province constitute the typical composite lavas flow and dikes. The basalts and diabases in the early Cretaceous composite lavas flow and dikes are highly enriched in large-ion lithophile elements (LILE). The working of source enrichment alone could not result in such high abundance of LILE and related variation, and the contribution of crustal contamination should be considered. Relationship between ratios of Rb/Y and Nb/Y (with Rb/Nb ratios varying from 0.4 to 9.1) indicates that the tholeiitic magma might interact with the rocks of mid-upper crust. Calculated average melt density of the tholeiitic magma by its chemical composition is 2.678g/cm3 . This is approximately corresponding with density of the mid-upper crust of the coastal area of Zhejiang Province. Assuming that the rising of magma was driven mainly by float force resulted from density difference between magma and surrounding rocks of crust; it would stagnate at the level of neutral float. According to the hydrostatic pressure equilibrium between magma and surrounding crystal rocks, it is estimated that the tholeiitic magma from the mantle source would continue to rise till it was trapped by mid-crust at the depth about 16.3 km below the surface. Meanwhile the magma was contaminated by the crustal materials.