Contribution of slab melting and slab dehydration to magmatism in the NE Japan arc for the last 25 Myr: Constraints from geochemistry
Contribution of slab melting and slab dehydration to magmatism in the NE Japan arc for the last 25 Myr: Constraints from geochemistry
复制标题
DOI：
10.1029/2005gc001220
复制
发表时间：
2006-08-02
影响因子：
3.5
通讯作者：
Yoshida, Takeyoshi
中科院分区：
文献类型：
--
作者：
Hanyu, Takeshi;Tatsumi, Yoshiyuki;Yoshida, Takeyoshi
[ 1]日本东北弧中新世-第四纪火山岩的Hf同位素组成、Pb-Sr-Nd同位素组成和微量元素组成记录了弧后开启（23 - 14 Ma）岩浆源区成分的地球化学演化。Hf同位素比值的时间变化明显，从中新世早期的最低Hf（+ 9）到中新世晚期和第四纪的最高Hf（+ 14），而Sr和Nd同位素组成变化不大。Hf同位素比值与某些微量元素比值明显相关。所观察到的时间变化是由于来自俯冲板，这可能是由冷却的地幔楔在同步和弧后开口后阶段的交代剂的变化。在弧后开启的早期阶段，当热的软流圈地幔的注入导致地幔楔中的高温条件时，板片熔融导致火山岩中的低Hf（Hf）、低eNd、相对低的La/Nb和高Th/Yb。另一方面，晚期火山作用以高Hf、Hf和N（N）d的解耦、La/Nb和Ba/La比值高且变化大为特征，其最好的解释是来自俯冲沉积物和洋壳的流体加入地幔楔中。
[ 1] Hf isotope compositions, coupled with Pb-Sr-Nd isotopes and trace element compositions, for the Miocene to the Quaternary volcanic rocks from the NE Japan arc have documented the geochemical evolution in the magma source compositions in association with back-arc opening ( 23 - 14 Ma). Clear temporal variation in Hf isotope ratios is demonstrated, from the lowest epsilon(Hf) (+ 9) in the early Miocene to the highest epsilon(Hf) (+ 14) in the late Miocene and the Quaternary, whereas there are little changes in Sr and Nd isotope composition. Hf isotope ratios are clearly correlated with some trace elemental ratios. The observed temporal variation is attributed to a change in metasomatic agents derived from the subducted slab, which could have been caused by cooling of the mantle wedge during the syn and post stages of the back-arc opening. In the early stage of the back-arc opening, when injection of hot asthenospheric mantle induced high-temperature conditions in the mantle wedge, slab melting contributed to low epsilon(Hf) coupled with low e Nd, relatively low La/Nb, and high Th/Yb in volcanic rocks. On the other hand, the later stage volcanism, characterized by high epsilon(Hf), decoupling of epsilon(Hf) and epsilon(N)d, high and variable La/Nb and Ba/La, is best explained by addition of fluids from subducted sediments and oceanic crust to the mantle wedge.