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1 引 言 最近,对诸如大陆溢流玄武岩和海台火山作用等大范围的火成活动引起了兴趣,因它们对了解地球内部活动和对地球环境变化的可能灾难性影响具有意义(Coffin等,1991;Du-ncan等,1991)。这些火成活动的周期性亦已从地质史中获得启示(Larson,1991a,b)。 在太平洋中部至南部有数个活动的热点,该区下的地球体正剩余异常和下地幔的低Vp速度,意味着存在有一个广阔的上涌热地幔。利用热点踪迹和重建板块运动可追溯该上涌作用至中生代。通过对翁通爪哇、赫斯海隆等巨型海台的研究,证实了该区的白垩纪地幔柱上涌作用。白垩纪之前的古老太平洋(原始超级大洋)的地幔柱活动是不清楚的,因为仅保存了很少的侏罗纪板块部分。为了弄清白垩纪前的地幔柱活动,唯一的途径是通过对环太平洋造山带内增生大洋物质作地质分析。
1 INTRODUCTION Recently, a wide range of enthalpic activities such as continental overburden basalts and the Hai Dui volcano have attracted interest because of their significance in understanding the possible catastrophic effects of intra-Earth activities and changes in the Earth’s environment (Coffin et al., 1991 ; Du-ncan et al., 1991). The cyclical nature of these igneous events has also gained enlightenment from geological history (Larson, 1991a, b). There are several hotspots of activity in the central and southern Pacific Ocean where the positive residual anomalies of the Earth and the low Vp velocities of the lower mantle mean that there is a vast upwelling-hot mantle. The upwelling effect can be traced back to the Mesozoic using hot spot traces and reconstructed plate motions. A study of the giant seawalls such as Wengtong Java and Hersheyon confirmed the upwelling of the Cretaceous mantle plume in this area. The mantle plume activity of the ancient Pacific (pristine super oceanic) before the Cretaceous was unclear because only a few parts of the Jurassic plate were preserved. In order to understand the pre-Cretaceous mantle plume activity, the only way is through geological analysis of the Pacific Ocean orogenic oceanic material.