K-Ar ages of biotites and hornblendes from granitoids in central area of the Tamba Belt, Southwest Japan.

Kiji, Michio; Ohira, Takeshi; Itaya, Tetsumaru

doi:10.5575/geosoc.101.462

Cited by 11 publications

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“…1). These are composed of several small plutons of quartz diorite to tonalite, whose K–Ar ages are 101–107 Ma (hornblende ages: 101.5 ± 5.2 Ma, 106.5 ± 5.5 Ma; biotite ages: 103.1 ± 5.1 Ma, 103.9 ± 2.3 Ma) (Kiji et al . 1995).…”

Section: Discussionmentioning

confidence: 99%

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Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan

2005

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Small-volume plutons of Early to Late Cretaceous ages are widely distributed in the Yamizo Mountains, central Japan. These plutons consist predominantly of granitoids, classified into hornblende gabbro, quartz diorite, hornblende-biotite granodiorite and coarse-grained biotite granite. The quartz diorite (52-64 wt% of SiO 2 ) is characterized by a high Sr content (606-769 p.p.m.) associated with a low Y (13-27 p.p.m.) and heavy rare earth element content (Yb content of 1.19-2.13 p.p.m.). On the Sr/Y versus Y diagram, this rock type mainly plots in the adakite and Archean high-Al tonalite, trondhjemite and granodiorite (TTG) field. Together with its initial Sr isotopic ratios, which range from 0.7038 to 0.7046, these data suggest that quartz diorite originated as slab melts. However, geochemical calculations assuming either eclogite or garnet amphibolite as the source material do not support this suggestion. Instead, the chemical compositions of quartz diorite are better explained by the fractional crystallization of hornblende, plagioclase and biotite from a primitive, basaltic melt in a magma chamber. In this case, the formation of the associated hornblende gabbro can also be explained by the accumulation of hornblende and plagioclase. Adakitic rocks of Early Cretaceous ages have also been reported in the Tamba Belt of the inner zone of southwest Japan, located ca 500 km west of the Yamizo Mountains. These rocks can be correlated to the adakitic rocks in the Yamizo Mountains based on the geology, petrography, geochemistry and radiometric ages. Therefore, we propose the possibility that the Early Cretaceous adakitic rocks in the inner zone of southwest Japan were produced by fractional crystallization from basaltic arc magmas generated by a partial melting of metasomatized wedge mantle peridotite.

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Section: Discussionmentioning

confidence: 99%

“…Recently, Early Cretaceous ( ca 105 Ma) adakitic granitoids were reported in the Tamba Belt, in the inner zone of southwest Japan (Kiji et al . 1995, 2000) (Fig.…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan

2005

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“…() reported U–Pb ages of 107.9 ± 3 Ma for accidental zircons in the Kusandong Tuff that was erupted at 97 Ma in the Gyeonsang Basin, and suggested that Cretaceous magmatism in and around the Gyeonsang Basin began at approximately 110 Ma. In the western part of SW Japan, Lower Cretaceous andesites, lamprophyres and granitoids have been reported from the Kinki district (109–99 Ma: Matsuura and Yoshikawa, ; Kiji et al ., ; Imaoka et al ., ), and andesites have been also reported from the Chugoku district (107–103 Ma: Imaoka et al ., ; Matsuura, ); it follows, therefore, that magmatism in these districts commenced in the Albian. Taking all these data into consideration, we conclude that Cretaceous magmatism commenced at progressively later dates across the area extending from the Liaodong Peninsula–eastern Jilin Province to SW Japan, i.e.…”

Section: Across‐arc Temporal Variations Of Jurassic–cretaceous Magmatmentioning

confidence: 95%

Spatiotemporal variations of Jurassic–Cretaceous magmatism in easternAsia (Tan‐Lu Fault toSW Japan): evidence for flat‐slab subduction and slab rollback

2013

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Here, we examine spatiotemporal variations of Jurassic-Cretaceous magmatism along a c. 1000-km transect across eastern Asia, including SW Japan, the Korean, Jiaodong and Liaodong peninsulas, and eastern Jilin Province. Integration of tectonic regime data with age data from igneous rocks in eastern Asia (from the Tan-Lu Fault to SW Japan) suggests a shallowing of the subduction angle and subsequent flat-slab subduction during the Jurassic, and slab rollback during the Early Cretaceous. The combination of a subducting plateau and rootenhanced suction provides the best explanation for the flatslab subduction. In the final stage (Albian) of slab rollback, the geotectonic setting changed from subduction-accretion to a continental arc in the area close to the ancient trench (i.e. the Inner Zone of SW Japan).

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“…It is important that the problem of why such older magmatisms or younger ones as three outliers have occurred in Southwest Japan is solved, because the ages of the outliers themselves seem to be correct, no matter how few there are. Recently, some papers reported older ages as the outliers in Southwest Japan (Kiji et al 1995; Yuhara & Kagami 1995). However, those are also minor magmatic activities.…”

Section: Construction Of a Migration Model Of Magmatismmentioning

confidence: 99%

A migration model of magmatism explaining a ridge subduction, and its details on a statistical analysis of the granite ages in Cretaceous Southwest Japan

Katoh

1999

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A migration model of magmatism based on the granite ages in Southwest Japan is proposed to explain the ridge subduction beneath the Eurasia continent as the cause of the along‐arc and across‐arc youngings of the granite ages and the very high activity of the magmatism in the Cretaceous. For the construction of the magmatic model, the localities of the granite age samples are denoted by the cartesian coordinates X and Y, which are measured along and normal to the Median Tectonic Line (MTL), respectively, and their ages are set corresponding to the coordinate Z vertical to the X–Y plane. The age trend is then formulated by a regression plane of Z on X and Y, which inclines in both directions along and normal to the MTL, and approximates the ages with the very high multiple correlation coefficient 0.91. Evaluating the magmatic trend by such a method, various characteristics of the activities can be taken easily; for example, the isochronous line of the magmatism, which is an intersection of the regression plane and an arbitrary horizontal plane, is found to extend landward obliquely across the continental margin. The migrating rate of the isochronous line along the MTL is also taken to be 2.8 cm/year as a reciprocal of the inclination of the along‐arc younging. The isochronous line is speculated to be the out‐cropped manifestation of the subcrustal linear heat source. Such a migrating linear heat source is probably due to the subduction of an active ridge, the Kula (or Izanagi)–Pacific ridge in the Cretaceous. The migration model of magmatism harmonizes very well with the plates and the ridge motions in the East Asia area during the late Mesozoic. The ridge subduction is one of the important phenomena that explain the unusually active arc magmatism and the migrating slab window; it is important to grasp dynamically the geological messages issued from the system.

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K-Ar ages of biotites and hornblendes from granitoids in central area of the Tamba Belt, Southwest Japan.

Cited by 11 publications

References 0 publications

Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan

Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan

Spatiotemporal variations of Jurassic–Cretaceous magmatism in easternAsia (Tan‐Lu Fault toSW Japan): evidence for flat‐slab subduction and slab rollback

A migration model of magmatism explaining a ridge subduction, and its details on a statistical analysis of the granite ages in Cretaceous Southwest Japan

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