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

IODP第334号和第344号考察队在哥斯达黎加近海发现了大量的海洋火山岩沉积物，一直到中新世中期。在过去的16个月里，与前DSDP和ODP中美洲近海巡航的海洋火山岩以及来自陆地的相关新近纪火山岩一起，获得了大量的主要和部分微量元素数据集（995个海洋火山岩，282个野外火山岩）。这促进了钻柱、位置和孔以及陆上火山岩之间的首次关联。资料整理表明，新近纪以来，中美洲火山弧（CAVA）沿线海陆火山岩的时空变化沿着，Cocos海岭俯冲至少发生在1.8Ma之前，并可能伴随着北哥斯达黎加类加拉帕戈斯地壳的俯冲，影响了该段的弧火山活动。此外，确实有一个显着的贡献，从加拉帕戈斯热点内的中新世海洋沉积物的科科斯岭的爆发阶段。利用我们的数据集，我们还能够发现沿CAVA沿着隐藏的火山中心，现有火山复合体的寿命可能远远超过我们的实际知识。根据我们的分析数据，也有合理的证据表明，在CAVA周期丰富的爆发性火山活动。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，将导致一个完整的火山灰年代地层框架的新第三纪爆发火山作用的中美洲和突出俯冲输入和弧输出之间的成分和时间关系沿着整个新第三纪中美洲火山弧。

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.