Geochemical secular variation of magma source during Early to Middle Miocene time in the Niigata area, NE Japan: Asthenospheric mantle upwelling during back-arc basin opening
Geochemical secular variation of magma source during Early to Middle Miocene time in the Niigata area, NE Japan: Asthenospheric mantle upwelling during back-arc basin opening
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DOI：
10.1016/j.lithos.2005.06.001
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发表时间：
2006
期刊：
影响因子：
3.5
通讯作者：
K. Shuto;H. Ishimoto;Y. Hirahara;M. Sato;Koji Matsui;N. Fujibayashi;E. Takazawa;Kaori Yabuki
中科院分区：
文献类型：
--
作者：
K. Shuto;H. Ishimoto;Y. Hirahara;M. Sato;Koji Matsui;N. Fujibayashi;E. Takazawa;Kaori Yabuki
在日本东北弧的新泻地区，玄武岩和中长英质火山岩（硅质安山岩、英安岩和流纹岩）在早中新世、中中新世和上新世时期产生，跨越日本海打开前到打开后阶段。早中新世玄武岩具有富Sr和Nd同位素特征（初始87Sr/86Sr（SrI）=0.70557至0.70592和初始143Nd/144Nd（NdI）=0.51255至0.51262），而中中新世和上新世玄武岩比MORB略富集就 SrI (0.70314–0.70416) 和 NdI (0.51286–0.51310) 而言。与中中新世和上新世玄武岩相比，早中新世玄武岩还具有较高的 HFSE 和 LREE 丰度以及较高的 Zr/Y 含量。早中新世玄武岩的地球化学特征几乎与大陆裂谷带（例如里奥格兰德裂谷）中发现的玄武岩相同。早中新世玄武岩的不同地球化学特征可以归因于地幔源区的地球化学差异。除角田地区的安山岩外，新泻地区大部分早中新世中长英质火山岩的 SrI 值（0.70673-0.70773）显着高于早中新世玄武岩，而 NdI 值（0.51234-0.51254）明显高于早中新世玄武岩，表明这些长英质火山岩的地壳起源较低。新泻地区产生早中新世后火山岩的可能构造岩浆模型包括：（1）早中新世（22-20 Ma）；软流圈地幔开始上涌，随后上覆岩石圈地幔部分熔融和地壳裂谷，导致大陆裂谷带型玄武质岩浆的产生，这些岩浆要么在地表喷发，要么引发下地壳部分熔融，产生更多的长英质岩浆，以及（2）在中中新世（15 Ma之后）；由于日本海的开放，上覆岩石圈变薄。这与软流圈上涌随后软流圈部分熔化产生广泛的玄武岩岩浆有关。这些岩浆要么喷发，要么熔化下地壳，产生更多的长英质岩浆。这种构造岩浆过程也可能适用于日本东北弧弧后边缘的许多其他部分的早至中中新世玄武岩到长英质火山岩的生成。
In the Niigata region of the NE Japan arc, basaltic and intermediate to felsic volcanic rocks (silicic andesite, dacite and rhyolite) have been produced during the Early Miocene, Middle Miocene and Pliocene ages, spanning the pre-Japan Sea opening to post-opening stages. Early Miocene basaltic rocks are characterized by enriched Sr and Nd isotopic signatures (initial87Sr/86Sr (SrI)=0.70557 to 0.70592 and initial143Nd/144Nd (NdI)=0.51255 to 0.51262), whereas Middle Miocene and Pliocene basaltic rocks are slightly enriched than MORB in terms of SrI (0.70314–0.70416) and NdI (0.51286–0.51310). Early Miocene basaltic rocks are also characterized by higher abundances of HFSE and LREE, and higher Zr/Y compared to Middle Miocene and Pliocene basaltic rocks. The geochemical features of Early Miocene basaltic rocks are almost identical to those of basaltic rocks found in continental rift zones, such as the Rio Grande rift. The different geochemical signatures of Early and Middle Miocene basaltic rocks can be ascribed to the geochemical differences in the mantle source. Apart from andesitic rocks of the Kakuda area, most of Early and Middle Miocene intermediate to felsic volcanic rocks from the Niigata region show significantly higher SrI values (0.70673–0.70773) and lower NdI values (0.51234–0.51254) than Early Miocene basaltic rocks, indicating a lower crustal origin for these more felsic volcanic rocks. A possible tectono-magmatic model for the production of post-Early Miocene volcanic rocks from the Niigata region includes: (1) at the Early Miocene (22–20 Ma); commencement of asthenospheric mantle upwelling followed by both partial melting of the overlying lithospheric mantle and crustal rifting, resulting in the production of continental rift zone-type basaltic magmas which have either erupted on the surface or initiated partial melting of the lower crust to produce more felsic magmas, and (2) at the Middle Miocene (after 15 Ma); thinning of the overlying lithosphere due to the opening of the Japan Sea. This was associated with asthenospheric upwelling followed by partial melting of the asthenosphere to generate extensive basaltic magmas. These were either erupted or melted the lower crust to generate more felsic magmas. Such tectono-magmatic processes may also be applicable to the generation of Early to Middle Miocene basaltic to felsic volcanic rocks in many other parts of the back-arc margin of the NE Japan arc.