Variety and genesis of the pyroxene-bearing S- and I-type granitoids from the Hidaka Metamorphic Belt, Hokkaido, northern Japan

Author(s):  
Toshiaki Shimura ◽  
Masaaki Owada ◽  
Yasuhito Osanai ◽  
Masayuki Komatsu ◽  
Hiroo Kagami

ABSTRACTThe high-dT/dP-type Hidaka Metamorphic Belt in Hokkaido, northern Japan, represents a tilted crustal section of a magmatic arc of Tertiary age. The highest metamorphic grades reached are granulite facies, and the syn-metamorphic granitic rocks are widely distributed in this metamorphic terrane. The granitic rocks are mainly tonalitic and granodioritic in composition, and are classified into peraluminous (S-type) and metaluminous (I-type) granitoids. A large amount of pyroxene-bearing S-type tonalites (garnet-orthopyroxene tonalite) is distributed in the Niikappu river region in the northern part of the Hidaka Metamorphic Belt. Pyroxene-bearing I-type tonalite (two-pyroxene hornblende tonalite) bodies are also distributed in this area.The pyroxene-bearing tonalites are classified into several sub-types on the basis of their field occurrence, texture, mineral assemblage and geochemical features. Homogeneous IH- and SH-type tonalite are thought to represent original magmas, i.e. those which have been generated by partial melting of mafic metamorphic rocks and pelitic-psammitic metamorphic rocks, respectively. Model calculations assuming batch partial melting indicate that possible restites are garnet-two-pyroxene mafic granulite for IH-type and garnet-orthopyroxene aluminous granulite for SH-type. The unexposed lowermost crust of the ‘Hidaka crust’ is thought to be composed of garnet-two-pyroxene mafic granulite, garnet-orthopyroxene aluminous granulite and metagabbros.


2006 ◽  
Vol 112 (11) ◽  
pp. 623-638 ◽  
Author(s):  
Yasuhito Osanai ◽  
Masaaki Owada ◽  
Toshiaki Shimura ◽  
Nobuhiko Nakano ◽  
Seishi Kawanami ◽  
...  


Author(s):  
T. Shimura ◽  
M. Komatsu ◽  
J. T. Iiyama

ABSTRACTThe 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% H2O, respectively. The results show that the primary S-type tonalite magma was at a temperature above 900°C and contained 3-4 wt% H2O 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 KAlSi3O8 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.



1970 ◽  
Vol 7 (6) ◽  
pp. 1383-1401 ◽  
Author(s):  
K. Shibata ◽  
T. Nozawa ◽  
R. K. Wanless

Rb–Sr whole-rock and mineral isochron ages have been determined for metamorphic and granitic rocks of the Hida metamorphic belt. The results indicate that an extensive metamorphic event together with plutonic activity took place within the belt during the latest Paleozoic – early Mesozoic period. The older ages of 220–250 m.y. represent an earlier phase of the metamorphism, whereas the younger ages of 170–180 m.y. represent a later phase. The Funatsu granitic rocks yielded a whole-rock isochron age of 176 m.y. with an initial 87Sr/86Sr ratio of 0.7056. This age is believed to indicate the time of original emplacement, and the rocks are considered to represent late-kinematic intrusion in the Hida belt.Some information on the middle Paleozoic metamorphism in the Hida Mountains was obtained from the isochron study. The whole-rock isochron age of 412 m.y. for the metamorphic rocks of the Fujibashi area may be considered, although not confirmed, to indicate the time of older metamorphism. The Omi Schist of the Circum–Hida crystalline schist belt, which belongs to the glaucophanitic type of metamorphism, gave a mineral isochron age of 350 m.y. thereby providing evidence of mid-Paleozoic metamorphism.The initial 87Sr/88Sr ratios for the whole-rock samples of the Hida metamorphic belt are found to be generally low, i.e. 0.705–0.708. This is especially so for the metamorphic rocks from the northern part of the belt where the lowest values were found.



2013 ◽  
Author(s):  
Daniel Tavares Gradim ◽  
Gláucia Nascimento Queiroga ◽  
Tiago Amâncio Novo ◽  
Carlos Maurício Noce ◽  
Antônio Carlos Pedrosa-Soares ◽  
...  

RESUMO: A característica fundamental da região de Jequeri-Viçosa, situada no extremo sul do Orógeno Araçuaí, é a abundância de rochas metamórficas, ortoderivadas e paraderivadas, de fácies anfibolito alto e granulito. O embasamento paleoproterozóico é representado, a oeste, por ortognaisses tonalíticos a graníticos do Complexo Mantiqueira e, a leste, por ortognaisses charno-enderbíticos do Complexo Juiz de Fora. Ambos os complexos incluem anfibolitos e exibem intensidades variáveis de migmatização. O contato entre eles é marcado pela zona de cisalhamento transpressiva destral de Abre Campo, interpretada como uma sutura paleoproterozóica reativada no Neoproterozóico. O Anfibolito Santo Antônio do Grama e rochas meta-ultramáficas associadas (Córrego do Pimenta) representam restos ofiolíticos ediacaranos, colocados ao longo da Zona de Cisalhamento de Abre Campo. Assentada sobre o embasamento, na parte oeste da área, ocorre uma associação metavulcano-sedimentar neoproterozóica do Grupo Dom Silvério, composta por xistos diversos e quartzito. Na porção leste da área mapeada, a cobertura metassedimentar neoproterozóica é atribuída ao Grupo Andrelândia que inclui paragnaisse migmatítico e raro quartzito. Corpos de hidrotermalito quartzoso, indiscriminadamente associados às unidades do embasamento e da cobertura neoproterozóica, ocorrem ao longo de zonas de cisalhamento. Hidrotermalitos ferruginosos associam-se ao Complexo Mantiqueira na Zona de Cisalhamento de Ponte Nova. O granito foliado a milonitizado da Serra dos Vieiras parece ser um produto de fusão parcial do paragnaisse Andrelândia. Completam o quadro geológico os pegmatitos da Suíte Paula Cândico e diques de diabásio mesozóicos.Palavras-chave: Paleoproterozóico, Neoproterozóico, Orógeno AraçuaíABSTRACT: GEOLOGY OF THE JEQUERI-VIÇOSA REGION, MINAS GERAIS STATE, SOUTHERN ARAÇUAÍ OROGEN. This paper focuses on the southwestern sector of the Araçuaí orogen in a region located close to the boundary with the northern Ribeira orogen. This region is rich in ortho- and para-derived metamorphic rocks of the high amphibolite and granulite facies. The Paleoproterozoic basement includes, to the west, tonalitic to granitic orthogneisses of the Mantiqueira Complex and, to the east, enderbitic to charnockitic orthogneisses of the Juiz de Fora Complex. Both complexes also include amphibolite enclaves and show several rates of partial melting. The contact between them is marked by the dextral transpressional Abre Campo shear zone, considered to be a Paleoproterozoic suture reactivated during the Neoproterozoic Era. The Santo Antônio do Grama Amphibolite and associated meta-ultramafic rocks (Córrego do Pimenta) are Ediacaran ophiolite slivers emplaced along the Abre Campo shear zone. In the western part of the region, the Paleoproterozoic basement is locally covered by a metavolcano-sedimentary assemblage composed of amphibolite facies schist and quartzite of the Neoproterozoic Dom Silvério Group. To the east, the Neoproterozoic cover comprises the migmatized paragneiss and rare quartzite of the Andrelândia Group. The Serra dos Vieiras foliated to mylonitic granite seems to be formed from the partial melting of the Andrelândia paragneiss. Pegmatites of the Paula Cândido Suite and Mesosozic diabase dikes complete the geologic framework of the mapped area.Keywords: Paleoproterozoic, Neoproterozoic, Araçuaí Orogen



2010 ◽  
Vol 32 (2) ◽  
Author(s):  
Ricardo Varela ◽  
Miguel A.S. Basei ◽  
Carlos A. Cingolani ◽  
Oswaldo Siga Jr. ◽  
Claudia R. Passarelli

Isotopic data are presented for rocks of the Andean crystalline basement at 40°S, in Neuquén and Río Negro provinces. The methods used were U-Pb in zircon (crystallization ages of plutonic rocks), K-Ar in micas and U-Pb in titanite (metamorphism and cooling ages) and Sm-Nd in whole rock (crustal evolution). No Proterozoic ages were obtained as suggested by previous Rb-Sr and K-Ar data, and two different igneous-metamorphic events were identified. The older one is Devonian and exposed in San Martín de los Andes region, according to 420-380 Ma zircon ages and 375-310 Ma ages in micas of deformed tonalitic and granitic rocks. The younger one, in rocks cropping out to the south of Limay River region, is revealed by Early Permian zircon ages (about 280 Ma) and Late Permian cooling ages (260-250 Ma) of metaigneous rocks. The rocks of both sets were assigned to a magmatic arc environment and correlated respectively with the Chanic orogeny (Devonian; Upper Famatinian Cycle) and Gondwanic Cycle (Upper Paleozoic-Triassic). The Sm-Nd TDM model ages, ca.1907-1165 Ma, eNd for the crystallization age of the rocks ca. -3,0 and -8,4 and eNd(0) ca. -6,9-11,9 suggest reworking of continental proterozoic crust with minor addition of juvenile magmas from the mantle during the Paleozoic.







Island Arc ◽  
2021 ◽  
Author(s):  
Yutaka Takahashi ◽  
Masumi Mikoshiba ◽  
Toshiaki Shimura ◽  
Mitsuhiro Nagata ◽  
Hideki Iwano ◽  
...  


1993 ◽  
Vol 5 (2) ◽  
pp. 193-206 ◽  
Author(s):  
P. D. Kinny ◽  
L. P. Black ◽  
J. W. Sheraton

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.



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