Understanding of the new type volcanism on the 130 m. y. -old Cretaceous Pacific Plate

Petit-spot是在太平洋板块西北部早白垩世（~ 130 Ma）发现的一个年轻的火山场（<1 Ma）。火山属于小点（petit-spot），是深海平面（~ 6000 m水深）上的非常小的小丘，喷发出强至中等碱性玄武岩，一般包括深部捕虏体。火山场距离日本海沟、任何扩散中心和热点都有600公里远。因此，火山活动不足以形成地球上任何现存的火山模型。为了了解这个小的斑点火山活动，我们一直在进行多学科调查。三年研究的主要结果包括使用JAMSTEC R/V YOKOSUKA和KAIREI（YK05-06, KR05-10, KR06-03, KR07-06， KR07-07和YK07-15）的巡航和岸上研究。2005年度：利用新海6500潜水器发现了另外两个小丘为小点火山，并采集了碱性玄武岩样品。用单通道拖缆（SCS）对小点丘和西北太平洋海域的几种声学探测。在火山场周围部署并回收了5台海底电磁计（obem）。地壳热流测量采用小型化温度记录仪进行。2006财年：在小点火山场及周边地区进行了多箭头波束测深和南海声波勘探。2007年度：在火山场部署了3台宽带海底地震仪（bobss）和3台海底地震仪（obms），观测上地幔板内地震活动和熔融供应过程。在新海6500潜水中采集了包括小斑点碱性玄武岩在内的几种地幔捕虏体。除此之外，在日本海沟附近的外隆起处发现了另一个小点火山场。这些结果发表在国际和国内期刊上，并在科学会议和新闻发布会上提出。

Petit-spot is a young volcanic field(<1 Ma) discovered on the Early Cretaceous(〜130 Ma) northwestern Pacific Plate. The volcanoes belong to petit-spot are very small knolls on the abyssal plane(〜6000 m water depth) and erupted strong to moderate alkaline basalt, generally including deep-seated xenoliths. The volcanic field is far 600 km away from the Japan Trench, any spreading centers and any hotspots. Therefore, the volcanic activity is not adequate for any existence volcanic models on Earth. In order to understand this petit spot volcanism, we've been taking multidisciplinary surveys. The main results for three years' research including the cruises using JAMSTEC R/V YOKOSUKA and KAIREI(YK05-06, KR05-10, KR06-03, KR07-06, KR07-07 and YK07-15) and shore-based research were listed below.FY2005 : Two other small knolls were discovered as the petit-spot volcanoes with SHINKAI 6500 submersible, and alkaline basalt samples were collected from the knolls. Several acoustic explorations on the petit-spot knolls and NW Pacific area with a single channel streamer(SCS). Five Ocean Bottom Electro-Magnetometers(OBEMs) were deployed and recovered around the volcanic field. The crustal heat flow measurements were taken using with Miniaturized temperature data loggers.FY2006 : Multinarrow-beam bathymetry mapping and SCS acoustic explorations were taken in the petit-spot volcanic field and surrounding area.FY2007 : Three broad band ocean bottom seismometers(BBOBSs) and three OBEMs were deployed in the volcanic field to observe the intraplate seismicity and the melt supply process in the upper mantle. Several mantle xenoliths included petit-spot alkaline basalts were sampled during SHINKAI 6500 dives. In addition to this, another petit-spot volcanic field was discovered on the outer rise near the Japan Trench.These results were published on both international and domestic journals, presented at scientific meetings and press releases.