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

Petit-spot是在早白垩世（~ 130 Ma）西北太平洋板块上发现的一个年轻的火山岩区（<1 Ma）。火山属于小斑点，是深海平面（水深约6000米）上的非常小的山丘，喷发出强到中等碱性玄武岩，通常包括深源捕虏体。火山区距离日本海沟、任何扩张中心和任何热点都有600公里远。因此，火山活动并不适合地球上任何现存的火山模型。为了了解这个小地方的火山活动，我们进行了多学科的调查。包括使用JAMSTEC R/V YOKOSUKA和KAIREI的巡航在内的三年研究的主要结果（YK 05 -06、KR 05 -10、KR 06 -03、KR 07 -06、KR 07 -07和YK 07 -15）和岸基研究如下所列。另外两个小圆丘被发现作为小斑点火山与SHINKAI 6500潜水器，碱性玄武岩样品采集的小圆丘。用单道拖缆（SCS）对小斑点丘和西北太平洋地区进行了几次声学勘探。在火山区周围部署和回收了五个海底电磁仪。2006年，在小斑火山区及周边地区进行了多矢波束测深和海底声学勘探; 2007年，在火山区部署了3台宽带海底地震仪和3台OBEM，观测了板内地震活动和上地幔熔融补给过程。在SHINKAI 6500次潜水中采集了几个地幔捕虏体，包括小斑点碱性玄武岩。除此之外，在日本海沟附近的外部隆起上还发现了另一个小点火山区。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发表。

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.