Genesis of the lower crustal garnet–orthopyroxene tonalites (S-type) of the Hidaka Metamorphic Belt, northern Japan

Abstract

The Hidaka Metamorphic Belt (HMB) in Hokkaido, northern Japan, consists of tilted metamorphic layers of an island-arc type crust from lower (granulite facies) to upper (very low-grade metasedimentary) horizons. Abundant granitic rocks, mainly S-type tonalites of crustal origin, intrude various metamorphic layers and are classified into four depth types, namely upper, middle, lower and basal. The basal orthopyroxene-garnet (S-type) tonalities were intruded into granulite facies country rocks. Textural and compositional evidence from minerals in the basal tonalite indicates that the crystallisation sequence is Grt-Pl-Opx-Bt-Qtz-Crd-Kfs, and that crystallisation took place at about 600 MPa and 900°C-700°C.Some crystallisation experiments were carried out in an internally heated pressure vessel, using the basal tonalite, under the conditions of 300 and 600 MPa, 700-900°C, and with 0-20 wt% H 2 0, respectively. The results show that the primary S-type tonalite magma was at a temperature above 900°C and contained 3-4 wt% H 2 0 at the beginning of crystallisation. In order to study the influence of normative orthoclase content on orthopyroxene crystallisation, some starting materials also included 15, 20 and 25% normative orthoclase, by adding KAlSi,0 8 gel to the rock powder. Normative orthoclase content has an influence on the subliquidus crystallisation limit of orthopyroxene.The changes in P-T conditions and chemical composition of the magma during ascent would generate the sequence from the basal to upper S-type granite. Opx-free S-type granitic magma can be generated from lower crustal Grt-Opx S-type granitic magma, by differentiation with falling magmatic temperature.

Timing of Okhotsk Sea Plate Collision With Eurasia Plate: Zircon U‐Pb Age Constraints From the Sakhalin Island, Russian Far East

“…Coeval S‐type granites have been widely reported from the Hidaka metamorphic belt in the Hokkaido Island, which is considered as the southern extension of the ESAC (e.g., Shimura et al, ). These S‐type granites are characterized by aluminous‐rich minerals such as garnet, cordierite, and biotite and intrude into granulite facies country rocks (Shimura et al, ).…”

“…Coeval S‐type granites have been widely reported from the Hidaka metamorphic belt in the Hokkaido Island, which is considered as the southern extension of the ESAC (e.g., Shimura et al, ). These S‐type granites are characterized by aluminous‐rich minerals such as garnet, cordierite, and biotite and intrude into granulite facies country rocks (Shimura et al, ). The generation of these S‐type granites is considered to have been derived through crustal anatexis of pelitic metamorphic rocks (garnet‐cordierite‐biotite granulite) in the lower crust after tectonic thickening of accreted terrigenous sedimentary and oceanic crustal rocks (Osanai et al, ; Owada & Osanai, ).…”

Relationship Between Solidification Depth of Granitic Rocks and Formation of Hydrothermal Ore Deposits

“…3 ), the solidification pressures of the Inada coarse granite and the granitic rocks genetically related to the Kiwada and Fijigadani mining districts are estimated as 2.1 and 1.4 -2.2 kb, respectively (data from Takahashi, 1993 ). In addition, the solidifi cation pressure of the granitic rocks in the Tsukuba area except for the Inada coarse granite is estimated as 3 -4.5 kb based on the mineral assemblages of the surrounding metamorphic rocks ( Shiba, 1982 ) and that of the middle tonalite in the main zone of the Hidaka metamorphic belt is estimated to be 4 kb ( Shimura et al , 1992 ). Fig.…”

Plutonic and metamorphic rocks in the southern Hidaka metamorphic belt, Hokkaido

“…, , , Komatsu et al, 1983;, 198619801990, 1986Osanai et al, 1991Osanai et al, , 1992Shimura et al, 1992;Komatsu et al, 1994 S Rb-Sr 56 Ma Owada et al, 199155 Ma , 1992 I Rb-Sr 51 Ma Owada et al, 1997 55 Ma Owada et al, 1991Owada et al, , 1997Osanai et al, 1992;, 19922000Owada et al, 2003;U-Pb Usuki et al, 2006Kemp and Shimura, 2006;Kemp et al, 2007Usuki et al 2006 Kemp et al, 200719 Ma Kimura, 1986Usuki et al, 2006;Kemp et al, 2007Kemp et al 20072 I 37 Ma 2 2 , 2015, 40 30 Ma , 1995, 2002;, 20171 , 2015, 1992, 1992 Whitney and Evance 2010 Ueda, 2016-, 1992Kimura, 1996 140 km 20 km -, 1986;Komatsu et al, 1989Komatsu et al, 2 , 1985, 1986;Osanai et al, 1991…”