Formation of Distinct Granitic Magma Batches by Partial Melting of Hybrid Lower Crust in the Izu Arc Collision Zone, Central Japan
Formation of Distinct Granitic Magma Batches by Partial Melting of Hybrid Lower Crust in the Izu Arc Collision Zone, Central Japan
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DOI：
10.1093/petrology/egm037
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发表时间：
2007-09
影响因子：
3.9
通讯作者：
S. Saito;M. Arima;T. Nakajima;K. Misawa;J. Kimura
中科院分区：
文献类型：
--
作者：
S. Saito;M. Arima;T. Nakajima;K. Misawa;J. Kimura
中新世甲府花岗质杂岩（KGC）产于伊豆碰撞带中，自中新世中期以来，伊豆、小笠原、马里亚纳（IBM）岛弧与本州岛弧发生了碰撞。（Shosenkyo和Mizugaki岩体），含角闪石、黑云母的花岗闪长岩、英云闪长岩、石英闪长岩和花岗岩（盐平、三浦、广濑和佐佐子岩体），到含角闪石英云闪长岩和奥长花岗岩（足川-Tonogi岩体），表明它是由具有不同整体化学性质的多个岩浆侵入体构成的。锶同位素组成校正敏感的高分辨率离子探针（SHRIMP）锆石年龄（SrI）表明，每个岩体的原生岩浆形成的混合下地壳源，涉及年轻的玄武岩的IBM弧和本州岛弧Shimanto沉积岩。原生岩浆形成后，个别岩体演化的晶体分馏过程中没有显着的地壳同化或额外的地幔贡献。KGC中锆石SHRIMP U^Pb年龄为16 8 ~ 10 6 Ma，与IBM弧和本州弧的岩浆活动恢复相重叠。17 Ma和IBM弧与本州弧碰撞的起始时间为c.花岗岩体的形成时代与弧岩浆活动的幕式活动密切相关，底侵幔源弧岩浆侵入诱发下地壳深熔作用，可形成不同的花岗质岩浆批次。根据角铝压力计测定的压力，KGC岩浆侵入中地壳。因此，KGC可以代表整个IBM弧的中地壳层的一个例子，其地震速度为6 0^6 5 km/s。这一花岗质中地壳层在IBM弧与本州弧碰撞过程中起了强烈的作用，导致IBMarc中地壳向本州弧的浮积。
The Miocene Kofu Granitic Complex (KGC) occurs in the Izu Collision Zone where the Izu^Bonin^Mariana (IBM) arc has been colliding with the Honshu arc since the middle Miocene.The KGC includes rocks ranging in compositions from biotite-bearing granite (the Shosenkyo and Mizugaki plutons), and hornblende^biotitebearing granodiorite, tonalite, quartz-diorite, and granite (the Shiodaira, Sanpo, Hirose and Sasago plutons), to hornblende-bearing tonalite and trondhjemite (the Ashigawa^Tonogi pluton), indicating that it was constructed from multiple intrusions of magma with different bulk chemistry. The Sr-isotopic compositions corrected to sensitive high-resolution ion microprobe (SHRIMP) zircon ages (SrI) suggest that the primary magmas of each pluton were formed by anatexis of mixed lower crustal sources involving both juvenile basalt of the IBM arc and Shimanto sedimentary rocks of the Honshu arc. After the primary magmas had formed, the individual plutons evolved by crystal fractionation processes without significant crustal assimilation or additional mantle contribution. SHRIMP zircon U^Pb ages in the KGC range from 16 8 to 10 6Ma and overlap the resumption of magmatic activity in the IBMand Honshu arcs at c. 17Ma and the onset of IBM arc^Honshu arc collision at c. 15Ma.The age of the granite plutons is closely related to the episodic activity of arc magmatism and distinct granitic magma batches could be formed by lower crustal anatexis induced by intrusion of underplated mantle-derived arc magmas. Based on pressures determined with the Al-in-hornblende geobarometer, the KGC magmas intruded into the middle crust. Thus, the KGC could represent an example of the middle-crust layer indicated throughout the IBM arc by 6 0^6 5 km/s seismic velocities. This granitic middle-crust layer acted buoyantly during the IBM arc^Honshu arc collision, leading to accretion of buoyant IBMarc middle crust to the Honshu arc.