Miocene to Recent tephrostratigraphy offshore Central America: Evolution, Provenance and Cyclicities

哥斯达黎加近海IODP第334和344次探险在中新世中期发现了大量海相冰盖的沉积物。在过去的16个月里，连同中美洲近海的前DSDP和ODP型邮轮的海洋特短语以及相关的陆上新近纪特短语，已经获得了压倒性的主要元素和部分微量元素的数据集(995个海洋特短语，282个野外特短语)。这促进了钻井腿、现场和孔以及陆上短语之间的首次关联。资料汇编表明，海洋和陆地冰盖的时空变化发生在新近纪内的中美洲火山弧(CAVA)上，科科斯山脊俯冲至少发生在1.8 Ma之前，并可能在此之前伴随着北哥斯达黎加类加拉普戈斯地壳的俯冲，影响了这一段的弧火山活动。此外，在科科斯海脊的中新世海洋沉积物中，确实有加拉帕戈斯热点的爆炸相的重大贡献。利用我们的数据集，我们还能够发现洞穴沿线隐藏的火山中心，现有火山复合体的寿命有可能远远超出我们的实际知识。参考我们的分析数据，也有合理的证据表明，火山喷发活动在洞穴中循环丰富。对这些问题的详细阐述，以及剩余的微量元素分析和年龄测定，将导致中美洲新生代火山活动的完整的沉积年代地层格架，并突出整个新近纪中美洲火山弧俯冲输入和弧输出之间的成分和时间关系。

IODP Expeditions 334 and 344 offshore Costa Rica recovered sediments with numerous marine tephras down to the middle Miocene. Together with the marine tephras of former DSDP and ODP cruises offshore Central America as well as correlative Neogene tephras from on-land an overwhelming data set of major and partly trace elements has been acquired in the last 16 months (995 marine tephras, 282 field tephras). This facilitated first correlation between drill Legs, sites and Holes as well as on-shore tephras. Compilation of data showed that temporal and spatial changes in the marine and on-land tephras occur along the Central American Volcanic Arc (CAVA) within the Neogene, that Cocos Ridge subduction took place at least before 1.8 Ma and is probably accompanied by subduction of Galapgos-like crust in N-Costa Rica before, influencing the arc volcanism in this segment. Furthermore, there is indeed a significant contribution of an explosive phase from the Galapagos Hot Spot within the Miocene marine sediments on the Cocos Ridge. Using our data set we are also able to find hidden volcanic centres along the CAVA and there is the possibility that the longevity of existing volcanic complexes exceed our actual knowledge by far. Referring to our analysed data there are also reasonable evidences for cyclic abundance of explosive volcanism at the CAVA. The detailed elaboration on these topics, together with remaining analysis of trace elements and determination of ages, will lead to a complete tephrochronostratigraphic framework for the Neogen explosive volcanism of Central America and highlight the compositional and temporal relationships between subduction input and arc output along the whole Neogene Central American Volcanic Arc.