Green Tuff metamorphism of the Miocene basaltic rocks in the northern part of Northeast Japan.

开展该项目是为了更好地了解“绿色凝灰岩蚀变”期间具有玄武质至安山质成分的中新世海底熔岩和火山碎屑岩的次生矿化。为此目的，在日本东北部的北方选择了秋田县的花冈地区和Aosoll县的Okiura、Hakamagoshi-dake和Kanita地区。钻探证实，在花冈和冲浦地区发育的中新世玄武岩堆至少有700米厚。其他地区的厚度估计超过几百米。这4个地区的变质基性岩较好地保留了原始结构和单斜辉石、斜长石等原生相，但在低温下发生了不同程度的重结晶，形成了多种次生矿物。而深部岩芯中除钠长石和石英外，还含有钠长石+绿帘石+葡萄石+阳起石。在地表暴露的样品中，仅在静脉和杏仁核中出现了锌离子。Ca-沸石在花冈地区是浊沸石和汤原沸石，在Okiura地区是怀拉石、浊沸石和汤原沸石。在Hakamagoshi-dake和Kanita地区，斜长石之后的基质和假晶中有绿帘石、绿帘石、葡萄石和pumpellyite。阳起石在Kanita地区的残留单斜辉石晶体上很少以过度生长的形式出现。这两个地区的钙沸石以浊沸石、辉沸石和片沸石为特征，它们在脉和杏仁体中广泛地经历了“绿色凝灰岩”热液变质作用。据估计，这四个地区的化石地温梯度超过100摄氏度/公里。

This project was undertaken in order to understand better the secondary mineralization of the Miocene submarine lavas and pyroclastic rocks with basaltic to andesiiic compositions during the "Green Tuff alteration". The Hanaoka area of the Akita Prefecture, and the Okiura, Hakamagoshi-dake and Kanita areas of the Aosorl Prefecture were selected for this purpose in the northern part of the Northeast Japan. Drilling has confirmed that the Miocene basaltic piles developed in the Hanaoka and Okiura areas are at least 700 meters thick. Their thickness in the other areas are estimated to be more than a few hundred meters. The metabastes in these four areas well preserved their original textures and primary phases such as clinopyroxene and plagioclase, but they have been recrystallized to varying degrees at low temperatures, resulting in the formation of various secondary minerals.In the Hanaoka and Okiura areas, the metabastes are characterized by the assemblage of chlorite + epidote + pumpellyite + prehnite at the surface exposures, but chlorite + epidote + prehnite + actinolite in the deep drill core, in addition to albite and quartz. Zeolites occur only in veins and amygudules of the samples from the surface exposures. Ca-zeolites are laumontite and yugawaralite in the Hanaoka area and wairakite, laumontite and yugawaralite in the Okiura area. In the Hakamagoshi-dake and Kanita areas, chlorite, epidote, prehnite, and pumpellyite in the matrices and in pseudomorphs after plagioclase. Actinolite rarely occurs as overgrowth on relict clinopyroxene crystal in the Kanita area. Characteristic Ca-zeolites are laumontite, stilbite and heulandite in veins and amygudules in both areas.These Miocene rocks have been extensively subjected to the "Green Tuff" hydrothermal metamorphism. Their fossil geothermal gradients of more than 100ﾟC/km would be estimated in these four areas.