Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

Abstract

The Hidaka metamorphic belt consists of an island-arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, Dors, D,, D,rs, and D,, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (Do) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D, is the stage of prograde metamorphism with increasing temperatures a t a constant pressure during an early phase, and with a slight decrease of pressure a t the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite-granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S-type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D, stage, mafic and intermediate magmas supplied and transported heat to form the arc-type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D, stage is characterized by subhorizontal top-to-the-south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (dkollement) and duplex structures associated with intrusions of S-type tonalite. Deformation structures and textures of high-temperature mylonites formed along the dkcollement, as well as the duplex structures, show that the D, stage movement occurred under a N-S trending compressional tectonic regime. The depth of intra-crustal dkcollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal dhcollement, however, might have extended to the crust-mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral-reverse-slip (dextral transpression) movement accompanied by low-temperature mylonitization with retrograde metamorphism, the stage defined as D,. The crustal rocks from the basal dkcollement to the upper were tilted eastward on the N-S axis and exhumed during the D, stage. During D, and D, stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime.

Characteristics of the Lithology, Fault-Related Rocks and Fault Zone Structures in TCDP Hole-A

“…It is interpreted as large fossil remnants from paleoseismic events, usually with a magnitude larger than 6.0 (Sibson 1975;Magloughlin and Spray 1992;Toyoshima et al 1994;Lin et al 2001;Theunissen et al 2002). In TCDP Hole-A, pseudotachylyte can only be observed under a transmitted electron microscope (TEM) at a depth of 1111.29 m (Kuo and Song 2005).…”

Crystal bending, subgrain boundary development, and recrystallization in orthopyroxene during granulite-facies deformation

“…The mylonite studied here is located in the western border of the Hidaka Main Zone, a unit within Hidaka Metamorphic Belt interpreted as continental gabbros exhumed from the middle crust (Arita, et al 1978;Jolivet and Miyashita 1985;Miyashita and Maeda 1978;Toyoshima, et al 1994). The mylonite, constituted principally of elongated (up to a few mm) orthopyroxene (opx) grains embedded in a matrix of small (~50μm) plagioclase grains (details of the microstructure in Raimbourg, Toyoshima, Harima and Kimura (2008)), is characterized by a strong dextral deformation at granulite-facies conditions (T~800 − 900℃ and P~6.1 − 7.2 kbar) (Osanai, et al 1991;Toyoshima, et al 2000), which was completely preserved from lower-grade retrogression described in Kanagawa, et al (2008).…”

Occurrence of mylonite zones and pseudotachylyte veins around the base of the upper crust: An example from the southern Hidaka metamorphic belt, Samani area, Hokkaido, Japan

“…The Hidaka metamorphic belt (HMB) is an exhumed crustal section of an island arc formed during early Paleocene to Miocene (e.g., Komatsu et al, 1994;Owada et al, 1997), where relatively fresh fault zones formed within the deep crust are exposed (e.g., Toyoshima et al, 1994). A huge volume of S-type tonalite was intruded along largescale shear zones in preexisting metamorphic rocks subsequent to peak metamorphism (e.g., Toyoshima, 1991;Shimura, 1992;Toyoshima et al, 1994). This paper describes the occurrences and the meso-to microstructures of mylonites and pseudotachylytes in these tonalitic rocks.…”