阿武隈山地東縁の石炭紀および白亜紀アダカイト質花崗岩類とその地質学的意義

Abstract

The Wariyama Sheared Granodiorite occurs along the east side of the Futaba Fault with the Wariyama uplift zone, Miyagi, Japan. Rocks from the WariyamaSheared Granodiorite can be geochemically classified as typical adakite, and further subdivided into medium-grained and K O-and Sr-poorer rocks, and coarse-grained and K O-and Sr-richer rocks. Zircons from the former yield U-Pb ages of and Ma, whereas zircons from the latter have ages of and Ma. On the basis of these results, the Wariyama Sheared Granodiorite can be redefined. The late Carboniferous granite is renamed the Wariyama Granite as in the past, but we use the term granite in a broad sense as describing the rock type. The Early Cretaceous granite is newly defined as the Takase Granite. The Takase Granite crops out on the eastern side of the central region of the Wariyama Granite with faulted contact. The Takase Granite is divided into the SiO -poor Takase Granite A and the SiO -rich Takase Granite B. The U-Pb zircon age of Ma obtained here corresponds to an interval of five major granitic events, and the timing of the onset of Permian granitic magmatism ( Ma) may actually be ca.Ma. Typical adakites are considered to be the product of slab melting, which occurred in response to unusual tectonic conditions, such as subduction of young lithosphere and/or an active ridge at ca. Ma.

Zircon growth in a granitic pluton with specific mechanisms, crystallization temperatures and U–Pb ages: Implication to the ‘spatiotemporal’ formation process of the Toki granite, central Japan

“…The closure temperature of the zircon U-Pb age will be in excess of 900°C based on diffusion characteristics of Pb determined in natural and synthetic zircons under a temperature range between 1000 to 1500°C and 0.1 MPa (1 atm) to 1000 MPa pressure (Cherniak and Watson, 2001). In previous studies, the zircon UPb age of a granitic body was therefore interpreted as either the emplacement age of the magma chamber (e.g., Tsuchiya et al, 2014) or as the crystallization age of the granitic pluton (e.g., Hassanzadeh et al, 2008;Kon and Takagi, 2012) because the closure temperature given by Cherniak and Watson (2001) is significantly higher than that of dating systems based on other minerals (e.g., closure temperature of the hornblende K-Ar system: 510 ± 25°C; Dodson and McClelland-Brown, 1985). However, such high temperature conditions (>900°C) are consistent with the melting (magmatic) condition in most granitic systems (e.g., Tuttle and Bowen, 1958).…”

Cretaceous granitoids and their zircon U–Pb ages across the south‐central part of the Abukuma Highland, Japan

“…Toward the north, Tsuchiya et al . () also reported SHRIMP zircon age of 303–308 Ma on the K 2 O and Sr‐poor Wariyama sheared granodiorite, which occurs along the eastern side of the Futaba fault.…”

“…Tsuchiya et al . () added supporting evidence of 117–118 Ma zircon in the Takase adakitic granite exposed at east of the Futaba Fault.…”

“…; Tsuchiya et al . ), there occur plutonic rocks composed mostly of quartz diorite to granite in composition, along with small amounts of gabbroids (Fig. ).…”

SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains, Japan: Implications for late Paleozoic granitic activity in Japanese Islands

“…One of the interval is 350–280 Ma, though granitic rocks with zircon U–Pb ages of this time interval have been found recently in several locations (e.g., Tsuchiya et al . ), suggesting further studies will be necessary to evaluate the timing of late Paleozoic granitic magmatism. U–Pb ages of detrital zircons from sedimentary rocks of Japan have been examined by Nakama et al .…”