广东大湾—港口地震剖面的地质新意义

New Geological Significance of the Seismic Profile between Dawan and Gangkou in Guangdong

以花岗岩原地重熔理论为依据重新解释了广东大湾—港口地震剖面。大湾—港口地震剖面可具体细分为上地幔层(Vp>8.05 km/s)、下地壳层(Vp=6.6-6.8 km/s)、中上地壳的壳内低速层(Vp=5.8 km/s)、基底层(Vp=5.9-6.3 km/s)以及沉积盖层(Vp<5.9 km/s);壳内多次重熔形成多层花岗岩,重熔层上方原始岩石物质组成的差异导致熔融后产生的重熔花岗岩层在横向上由不均一的物质组成,从而使得8 km深度以上的地震界面波动起伏,而在约8 km深度之下,波速界面起伏平缓或近于水平,表明在此深度之下的岩石物质组成在横向上相对均一:壳内重熔过程导致物质成分垂向深度变化是壳内地震波速自上而下增高的原因;壳内低速层的存在表明本区上陆壳重熔层的底部到目前尚未完全固化。地震界面起伏的特点与根据地表地质资料勾画的重熔界面波动形态有极好的吻合性,显示地震资料能够准确地揭示重熔界面位置和形态。

The seismic profile between Dawan and Cangkou in Guangdong is reinterpreted based on the theory of in-situ melting on granite genesis.The results show that the seismic profile can be divided into five layers,the mantle with V_p>8.05km/s,lower crust with V_p=6.6-6.8km/s,a mid-upper crustal lower velocity zone with V_p=5.8km/s,the basement layer with V_p=5.9-6.3km/s and sedimentary cover with V_p<5.9km/s.Multiple crustal remelting formed the multiple granite layers.The difference in substance above the melting interface is the reason of fluctuation of the velocity interfaces above 8km.However,they tend to flat with the reason that the rocks show homogenous below 8km.The seismic velocity increases with the variety of the substance in the depths of the crust caused by the crustal remelting and the low velocity zone below the basement layer to represent the youngest cooling magma layer.The research also displays that fluctuation of the velocity interfaces in the shallow part of the seismic profile is considered to mirror the irregular shapes of the melting interface' s.