Kinematic Interpretation of the Quartz Fabric of Triclinic Tectonites from Besshi, Central Shikoku, Japan

Three examples showing successive changes in quartz fabric pattern have been selected from triclinic tectonites from Besshi for geometrical and kinematic analyses of rock structure. After geometrical considerations, three sets of schistosity or cleavage surfaces have been discriminated, i.e., the axial-plane-schistosity, the first and the second transversal-schistosities, the latter two consisting of conjugate sets of s-surfaces. Quartz fabric patterns of these tectonites show an unmistakable triclinic character with respect to the situation of principal maximum, and their girdle patterns show a tendency to lie on certain small circles. Types of quartz pattern of these examples have been interpreted successfully in terms of orienting movements along the analysed s-surfaces after a working hypothesis about the rule of quartz orientation proposed in the preceding paper (G. KOJIMA and T. SUZUKI, 1958). It has been revealed that the quartz pattern represents mainly the last phase of orienting movement, that is, the phase of the second transversal-schistosity. Geometrical and kinematic relations between several types of quartz pattern have been discussed. The tectonites in question belong to the category of B⊥B'-tectonites. Geological conditions and kinematic character of deformation of successive phases of development of these s-surfaces have been considered. The result emphasizes the necessity of phase analysis of metamorphism

On New Occurrence of Aegirine Augite-Amphibole-Quartz-Schists in the Sambagawa Crystalline Schists of the Besshi-Shirataki District, with Special Reference to the Preferred Orientation of Aegirine Augite and Amphibole

The present authors have collected in the Besshi-Shirataki district, Shikoku, three samples of aegirine augite-bearing quartz-schists, which have not been known from the Sambagawa metamorphic zone proper. Geological setting and petrographical properties of these rocks are described. They have been found in the spotted terrain characterized by the forming of porphyroblastic albite petrographically, and by the presence of recumbent type of folding and syntectonic intrusion of ultramafic rocks tectonically. The quartz-schists consist of aegirine augite, alkalic amphibole (especially of glaucophane-crossite series), garnet, muscovite, quartz, albite, and accessory minerals such as apatite, hematite, pyrite, sphale-rite, and titanite. Petrofabric analyses have been carried out on aegirine augite, amphibole, muscovite, and quartz. Prisms of amphibole are oriented with the plane (100) parallel to the bedding-schistosity plane (ab), and with the crystallographic axis: c parallel to the b-lineation. In the quartz-schist at Shira-taki the axis: c is parallel both to the tectonic axis: b and to a. Grains of aegirine augite are oriented with the plaine (010) parallel to the bedding-schistosity plane (ab), and with the crystallographic axis: c parallel to the tectonic axis : b. Quartz diagrams show the common pattern, which is not distinguishable from that of the other quartz-schists in the district. These petrofabric characteristics suggest that the quartz-schists in question have experienced the same history of deformation and crystallization as the normal quartz-schists in the district, and that the possible effect of metasomatism from serpentinites locally in-truded late- or post-tectonically may be excluded

Orientation of an Epidote with a Unique Crystal Habit in a Quartz-Schist from Besshi

Epidote crystals characterized by the development of the crystallographic plane (102) have been found in a quartz-schist from Besshi, Ehime Pref. The crystallographic axis b of the epidote coincides with fabric axis b of the rock, and the plane (102) is oriented parallel to the fabric plane (ab).今村外治教授退官記念特集

Nappe Boundary Migration during the Subcretion: Exhumation Processes of the Sambagawa Schists

The Sambagawa schists consist of some successively subcreted units as nappes, Saruta unit as Saruta nappe II and Saruta nappe I, Fuyunose unit (Fuyunose nappe) and Sogauchu unit (ST subunit, KAT subunit and NOM subunit) etc. in descending order of structural level. The coupling of the Saruta nappe II and the Saruta nappe I occurred accompanying the underplating of the Fuyunose unit schists. When the underplating of the Sogauchi unit occurred accompanying the exhumation of the previously subcreted units, the latter was highly deformed, accompanying the formation of large—scale recumbent folds such as Shirataki II fold and Suryo fold and the nappe boundary migration from the Saruta I —II boundary and Saruta I — Fuyunose boundary to the Kuwanokawa thrust

Discontinuously Zoned Garnet in Sambagawa Schist from Central Shikoku, Japan

The garnets in the Sambagawa siliceous pelitic schist from Tomisato, Central Shikoku,Japan, which have been described in this paper, belong to the type of reverse-zoned garnet. From zoning profiles for MnO and FeO and electron beam scanning images, individual garnet grains appear to be divided into four zones, core, intermediate zone, mantle and reverse zone in the rim. And the chemical composition changes discontinuously by about 9% for MnO between the outer part of the core (=ca. 32% for MnO) and the inner part of the intermediate zone and by about 7.2-16.5% for MnO between the outer part of the intermediate zone (=ca. 19.5-10.1% for MnO) and the inner part of the mantle. The garnets in the present specimen, therefore, will be newly designated as discontinuously zoned garnet

The Baric Structures and Exhumation Processes of the Sogauchi Unit in the Sambagawa Belt

The Sogauchi unit is developed as the Sogauchi nappe as a member of primary structure and as the Omogiyama nappe, Terano—Isozu nappe and Saredani—Kabayama—Izushi nappe as members of secondary structure. The baric structures of these nappes have been analyzed on the basis of chemical composition of amphibole in hematite—bearing basic schist. The Sogauchi nappe consists of three subunits as nappes, showing increase of pressure from the lower nappe to the upper nappe and northward increase of pressure for each nappe. The assumed isobaric lines appear to be running in WNW—ESE trend, which is slightly oblique to the general trend of mineral lineation (Lm), and the lower pressure part of each nappe appears to be placed on the western side on the line along Lm. The displacement of the nappes during their subcretion— exhumation appears to have been of westward sense judging from quartz microtextures. The Omogiyama nappe and Saredani—Kabayama —Izushi nappe have been assumed to have been derived as nappes from the northwestern extension (higher pressure parts) of the Sogauchi nappe. However, an alternative model has also been shown for the root of the Saredani — Kabayama —Izushi nappe

The Weakly Metamorphosed Paleozoic Formations near Ibara City, Western Okayama Prefecture

The weakly metamorphosed Paleozoic rocks distributed in the vicinity of Ibara City, Okayama Prefecture, Southwest Japan, are classified lithostratigraphically as follows. Komachi formation Main part (Km, 1000～4500 m. in approximate thickness): Composed mainly of pelitic rock and basic volcanic and pyroclastic rocks, with subordinate acid pyroclastics. Thin layers of psammitic rock and siliceous rock are intercalated and small lenses of limestone are also included. Upper part (Ku, 400～500 m. thick): Composed almost exclusively of pelitic and psammitic rocks. They are often alternated rhythmically, showing a graded bedding. A conglomerate occurs locally. Sabara formation Main part (Sm, 2000～3000 m. in approximate thickness): Similar in lithofacies to the main part of the Komachi formation, but there is no lens of limestone. Upper part (Su, 700～800 m. thick): Similar to the upper part of the Komachi formation, but the psammitic rock is less developed. From the occurrence of Yabeina shiraiwensis OZAWA the upper part of the Sabara formation can be correlated to the Upper Permian. The main part may possibly range from the Middle to the Lower Permian, though no fossil has yet been found. It is questionable whether the Komachi formation is contemporaneous with or older than the Sabara. Metagabbro-metadiabase and mylonitic granite-felsite, which have been grouped under the name of the Yakuno complex, occur closely associated with basic volcanic and acid volcanic rocks, respectively. These volcano-plutonic associations are considered to be a product of the geosynclinal igneous activity preceding the deposition of flysch facies, and are traceable along the boundary between the Central non-metamorphic zone and the Sangun metamorphic zone. Based on the distribution of metamorphic minerals in basic rocks, the surveyed area is divided into three zones, I, II and III. The zone I is characterized by the assemblage of prehnite-pumpellyite, and is represented by rocks of the Sabara formation. Schistosity is scarcely observed and recrystallization is weak. The zone II is characterized by the assemblage of pumpellyite-actinolite, and is represented by rocks of the Komachi formation. Schistosity and lineation are in general well developed and recrystallization is more advanced. These two zones are probably correlative with the weakly metamorphosed upper part of the Sangun complex. As for the zone III, the assemblage of actinolite-epidote is common, and furthermore, hornblende appears in some cases. This zone occupies the limited areas adjacent to the Cretaceous granite and granodiorite, and therefore is undoubtedly related to the later contact metamorphism. Both the Komachi and Sabara formations take a general strike of E-W direction and dip usually to the north with low to moderate angle. The structure is, however, by no means simple. The Komachi formation exposed in the northern part of the surveyed area is, as a whole, overturned, and is in contact by a tectonic slide with the gently folded Sabara formation on the south

Sinistral En Echelon Folding of the Sambagawa Schists and Its Tectonic Implication

The folds of the Sambagawa schists, which were produced during the last phase (Hijikawa—Oboke phase = Dh phase) of their folding history, are developed as a series of sinistral en echelon upright folds with half wavelength of less than 20 Km (Hara et al.,1977,1992). The Dh phase folds in Shikoku are accompanied with two culminations, Oboke culmination and Nakashichiban culmination, placed near the MTL. Their movement picture during the formation process of such the Dh phase folds has been analyzed on the basis of orientation pattern of parasitic folds and quartz microtextures. It has been clarified that the Dh phase folds were produced by left—lateral shear under N —S compression, being accompanied by the southward tectonic emplacement of two rigid bodies which gave rise to the Oboke and Nakshichiban culminations. These bodies can be assumed to be granitic and/or high—temperature metamorphic rocks tectonically derived from the Kurosegawa—Koryoke continent, as judged from the seismic refraction data in the Oboke district after Ichikawa (1968)

Tectonic Evolution of the Sambagawa Schists and its Implications in Convergent Margin Processes

The Sambagawa schists as high P /T metamorphic rocks are a member of Mesozoic accretionary complexes developed in the southern front of the Kurosegawa-Koryoke continent of Southwest Japan. The Mesozoic accretionary complexes are divided into four megaunits developed as nappes, Chichibu megaunit II, Sambagawa megaunit, Chichibu megaunit I and Shimanto megaunit in descending order of structural level. The Chichibu megaunit II consists of three accretionary units developed as nappes, late early Jurassic unit, late middle Jurassic unit and latest Jurassic unit (Mikabu unit) in descending order of structural level. The Chichibu megaunit I consists of five accretionary units developed as nappes, late middle Jurassic unit (Niyodo unit), late Jurassic unit, Valanginian unit, Barremian unit and Albian unit in descending order of structural level. The Shimanto megaunit, which just underlies the Chichibu megaunit I, is Cenomanian-Turonian accretionary unit and Coniacian-Campanian accretionary unit. The schists, which underlie the Chichibu megaunit II, all have been so far called the Sambagawa schists. These are divided into six units, Saruta unit, Fuyunose unit, Sogauchi unit, Sakamoto unit, Oboke unit and Tatsuyama unit in descending order of structural level, which show different tectono-metamorphic history and different radiometric ages from each other. The Sakamoto unit, Oboke unit and Tatsuyama unit have been assumed with reference to their radiometric ages and structural relations to belong to the late middle Jurassic accretionary unit of the Chichibu megaunit I (high pressure equivalent of the Niyodo unit), the Cenomanian-Turonian accretionary unit of the Shimanto megaunit and the Coniacian-Campanian accretionary unit of the Shimanto megaunit respectively in this paper. The upper member of the Sambagawa schists, Saruta unit, Fuyunose unit and Sogauchi unit, is therefore called the Sambagawa megaunit in this paper. The northern half and the southern half of the Sambagawa megaunit are intercalated as nappes between the Chichibu megaunit II and the Oboke unit and between the Chichibu megaunit II and the Sakamoto unit respectively. The constituent units of the Chichibu megaunit II, Sambagawa megaunit and Shimanto megaunit clearly show a downward younging age polarity, as compared with each other with reference to the oldest one of radiometric ages ( = metamorphic ages) of each unit. The Chichibu megaunit II and the Chichibu megaunit I show the same radiometric ages as compared between them with the same fossil age. The Saruta unit, Fuyunose unit and Sogauchi unit have therefore been assumed to be high pressure equivalent of Valanginian unit, that of Barremian unit and that of Albian unit of the Chichibu megaunit I respectively. These high pressure units were exhumed, separating the Chichibu supermegaunit into the Chichibu megaunit II and the Chichibu megaunit I and thrusting up onto the Chichibu megaunit I. On the basis of the growth history of amphibole in hematite-bearing basic schists of the Sambagawa megaunit, it has been assumed that the highest temperature metamorphism of the Fuyunose unit occurred, when it had been coupled with the Saruta unit which was exhuming, and that of the Sogauchi unit did through its coupling with the Fuyunose and Saruta units which were exhuming. In the subduction zone which was responsible for the formation of the Sambagawa megaunit, namely, the peak metamorphism of a newly subducted unit appears to have occurred when it had been coupled with previously subcreted units which were exhuming. It has been also clarified that the subduction of a new unit occurred mixing the lower pressure part of the pre-existing subcretion unit as tectonic blocks. There is a distinct difference in the oldest one of radiometric ages between constituent units of the Sambagawa schists, showing a downward younging age polarity. The oldest one of radiometric ages of each unit appears to approximate to the age of the ending of peak metamorphism and to the age (Eh age) of the beginning of its exhumation. Such the tectonics of the Sambagawa megaunit would be explained in term of two-way street model. Because the age (Sub age) of the beginning of the subduction of each unit can be assumed from its fossil age, the average velocity of the subduction and that of the exhumation of the Sambagawa megaunit in Shikoku have roughly been estimated to be ca. 0.9 mm/year and ca. 2.0 mm/year respectively. Deformation of quartz, whose style depends strongly upon strain rate, resulted in type I crossed girdle without conentration in Y even in the depth part of more than 10kb of the subduction zone, which was placed under temperature condition of much higher than 500°C, unlike the cases of magma-arcs where quartz c-axis fabrics with maximum concentration in Y are found in gneisses produced under temperature condition of lower than 500°C. Quartz deformation in the depth part of 15-17kb of the subduction zone appears to have occurred as dominant prism slip. The hanging wall of the Kurosegawa-Koryoke continent, which was placed at the depth of ca. 15-17 kb, thrust onto the Saruta unit at the depth of ca. 10-11 kb, accompanying intermingling of constituent rocks of the former and the latter and also mixing of various depth parts of the latter. The highest temperature metamorphism of the Saruta unit, which appears to have occurred under metamorphic condition of lower P /T than under that related to the formation of the general type of high P /T type metamorphic rocks, is ascribed to a contact metamorphism related to the overthrusting of the Kurosegawa-Koryoke continent. The thrusting of the Kurosegawa-Koryoke continent is ascribed to its collision with the Hida continent. The coupling of the previously subcreted Saruta unit with the newly subcreted Fuyunose unit occurred accompanying nearly isobaric cooling of the former. The great exhumation of the Saruta nappe (I + II) and Fuyunose nappe schists with great volume began together with the subcretion of the Sogauchi unit. The beginning age of the exhumation of the Sambagawa schists with great volume appears to coincide with that of the subduction of the Kula-Pacific ridge in Kyushu-Shikoku, which has been assumed by Kiminami et al. (1990). Namely, their great exhumation occurred with the progress of the subduction of the Kula-Pacific ridge with an eastward younging age polarity. The exhumation units, which were developed after the Mikabu unit, clearly show an eastward younging age polarity. Namely, these comparable with the Saruta unit, Fuyunose unit and Sogauchi unit are not found in central Japan and the Kanto Mountains. Rock deformation in the deformation related to the exhumation of the Sambagawa schists and their underlying schists appears to have commonly been of flattened type in mean strain. During the Ozu phase when the Kula-Pacific ridge subducted to the greater depth, the collapse of the Kurosegawa-Koryoke continent took again place, accompanying that of the pile nappe structures of the Sambagawa megaunit, Chichibu megaunit I and Oboke unit, and the thermal gradient along the plate boundary greatly changed, giving rise to medium P/T type metamorphism in the subduction zone (formation of the Tatsuyama nappe schists). The geological structures of the Sambagawa megaunit consist thus of two types of pile nappe structures, pre-Ozu phase pile nappe structures and Ozu phase pile nappe structures. The former is structures related to the coupling of the exhuming units ( = previously subcreted units) with the newly subcreted unit. The latter is structures showing the collapse of the former. The Ozu phase pile nappe structures are further divided into the pile nappe structures formed during the earlier stage (Tsuji stage) of the Ozu phase and these formed during the later stage (Futami stage). The former is disharmonic with reference to movement picture with the latter: The deformation related to the formation of the former, accompanying exhumation of the Oboke nappes, appears to contain a component of northward displacement, while that for the latter does a component of southward displacement. After the Ozu phase deformation the Sambagawa megaunit suffered the Hijikawa-Oboke phase folding, forming a series of sinistral en echelon upright folds. The relationship between the above-mentioned tectonic events of the Sambagawa megaunit and its surroundings and their radiometric ages is summarized as follows: [Original table is skipped. For more details, please refer to the full text.

Large-scale identification and characterization of alternative splicing variants of human gene transcripts using 56 419 completely sequenced and manually annotated full-length cDNAs

We report the first genome-wide identification and characterization of alternative splicing in human gene transcripts based on analysis of the full-length cDNAs. Applying both manual and computational analyses for 56 419 completely sequenced and precisely annotated full-length cDNAs selected for the H-Invitational human transcriptome annotation meetings, we identified 6877 alternative splicing genes with 18 297 different alternative splicing variants. A total of 37 670 exons were involved in these alternative splicing events. The encoded protein sequences were affected in 6005 of the 6877 genes. Notably, alternative splicing affected protein motifs in 3015 genes, subcellular localizations in 2982 genes and transmembrane domains in 1348 genes. We also identified interesting patterns of alternative splicing, in which two distinct genes seemed to be bridged, nested or having overlapping protein coding sequences (CDSs) of different reading frames (multiple CDS). In these cases, completely unrelated proteins are encoded by a single locus. Genome-wide annotations of alternative splicing, relying on full-length cDNAs, should lay firm groundwork for exploring in detail the diversification of protein function, which is mediated by the fast expanding universe of alternative splicing variants