The third group of volcanic rocks ( VTG-III ) consists of highly depleted MORB-type lavas, and is believed to have been generated by partial melting of the depleted mantle wedge in an inter-arc basin. 第三组火山岩形成于弧间盆地,由亏损的地幔楔高度部分熔融形成比N-MORB亏损的的火山岩(异常MORB)。