U-Pb ages of granitoids around the Kofu basin: Implications for the Neogene geotectonic evolution of the South Fossa Magna region, central Japan
U-Pb ages of granitoids around the Kofu basin: Implications for the Neogene geotectonic evolution of the South Fossa Magna region, central Japan
复制标题
甲府盆地周围花岗岩的 U-Pb 年龄：对日本中部南马格纳地区新近纪大地构造演化的启示
DOI：
10.1111/iar.12361
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发表时间：
2020
期刊：
影响因子：
1.5
通讯作者：
Hirata Takafumi
中科院分区：
文献类型：
--
作者：
Sawaki Yusuke;Asanuma Hisashi;Abe Mariko;Hirata Takafumi
日本群岛在新近纪经历了两次弧弧碰撞。西南本州弧与伊豆-博宁-马里亚纳弧碰撞，东北本州弧与千岛弧碰撞。伊祖-博宁-马里亚纳弧与本州岛西南弧之间的碰撞导致了南大福萨岛地区复杂的地质结构。了解这一构造活动区的大地构造演化对于圈定日本群岛的新近纪构造至关重要。在南大窝区科福盆地周围分布着许多侵入花岗岩类。虽然这些花岗岩类的火成岩年龄主要是通过黑云母和角闪石K-Ar定年来估计的，但为了更准确地确定火成岩年龄，我们在这里进行了锆石U-Pb定年。在大多数情况下，锆石U-Pb系统上的次生岩浆后叠加作用很小。根据我们的结果，我们确定了四组U-Pb年龄：Ca15.5 Ma、Ca13 Ma、Ca10.5 Ma和Ca4 Ma。Tsubai岩体属于第一类，其年龄表明伊豆-博宁-马里亚纳弧内的花岗岩形成至少可追溯到15.5 Ma。第二类花岗岩类侵入本州弧与古伊豆-博宁-马里亚纳弧的边界，表明弧-弧碰撞始于约13 Ma。与Kaikomagatake岩体的情况一样，Chino岩体很可能对应于与第三类其他花岗闪长岩平行的弧后环境中形成的花岗闪长岩。属于第四类的Kogarasu岩体的U-Pb值与坦塔泽英云闪长岩的U-Pb值一致。这可能支持了南大窝区同碰撞快速花岗岩浆形成。
The Japanese archipelago underwent two arc–arc collisions during the Neogene. Southwest Honshu arc collided with the Izu‐Bonin‐Mariana arc and the northeast Honshu arc collided with the Chishima arc. The complicated geological structure of the South Fossa Magna region has been attributed to the collision between the Izu‐Bonin‐Mariana arc and the southwest Honshu arc. Understanding the geotectonic evolution of this tectonically active region is crucial for delineating the Neogene tectonics of the Japanese archipelago. Many intrusive granitoids occur around the Kofu basin, in the South Fossa Magna region. Although the igneous ages of these granitoids have been mainly estimated through biotite and hornblende K–Ar dating, here, we perform U–Pb dating of zircon to determine the igneous ages more precisely. In most cases, the secondary post‐magmatic overprint on the zircon U–Pb system was minor. Based on our results, we identify four groups of U–Pb ages:ca15.5 Ma,ca13 Ma,ca10.5 Ma, andca4 Ma. The Tsuburai pluton belongs to the first group, and its age suggests that the granite formation within the Izu‐Bonin‐Mariana arc dates back to at least 15.5 Ma. The granitoids of the second group intruded into the boundary between the Honshu arc and the ancient Izu‐Bonin‐Mariana arc, suggesting that the arc–arc collision started byca13 Ma. As in the case of the Kaikomagatake pluton, the Chino pluton likely corresponds to a granodiorite formed in a rear‐arc setting in parallel with the other granodiorites of the third group. The U–Pb age of the Kogarasu pluton, which belongs to the fourth group, is the same as those of the Tanzawa tonalitic plutons. This might support a syncollisional rapid granitic magma formation in the South Fossa Magna region.