Elucidation of basaltic magmatism in extra back-arc province: An example of worldwide forth magmagenesis

阿根廷巴塔哥尼亚Somuncura-Canquel省是世界上一个典型的弧外弧后地区，我们以该地区为研究对象，对其进行了产状调查，采集了玄武岩样品，测定了其主量元素、微量元素组成和K-Ar年龄。研究结果表明：28 ~ 20 Ma期间，由于Farallon-Nasca板块的板块旋转作用，该地区最上部的“湿”地幔过渡带可能发生了上翘，并产生了含水熔体，使上翘部分的含水华德士来石转变为橄榄石。

As a typical “extra back-arc” province in the world, we focused on the Somuncura-Canquel province, Patagonia, Argentina, and investigated their occurrence, collected the basaltic rocks and determined both their major & trace element compositions and K-Ar ages. Our results suggest the following scenario of its magmatism; uppermost “wet” mantle transition zone beneath the region might be up-warped triggered by the slab rotation of the Farallon-Nasca plate between 28 and 20 Ma, and a hydrous melt might beproduced to change hydrous wadsleyite to olivine in the up-warped parts.