Jadeite-bearing meta-basalt occur within a greenstone complex at the southern margin of the Mikabu greenstones in the Shimonita area, northern Kanto Mountains, Central Japan. The greenstone complex shows a block-in-matrix structure consisting of small, sporadically occurring greenstone blocks (jadeite-bearing meta-basaltic lavas, jadeite-free pargasite rocks, and jadeite-free garnet-epidote rocks) embedded within a matrix of actinolite rocks. The complex has been interpreted as a tectonic meá lange composed of allochthonous metamorphic blocks within the Mikabu greenstones. However, both the greenstone blocks and actinolite rocks preserve original igneous or pyroclastic textures without the deformation structures commonly seen in tectonic melanges. The concentrations of high field strength (HFS) elements within the jadeite-bearing lavas indicate that these rocks are alkali basalts derived from oceanic island basalt (OIB). The composition of these lavas is similar to that of OIB blocks in the Mikabu greenstones in Shikoku, western Japan. The whole-rock chemical composition of the lavas reveals higher Na2O concentrations (max. 10.1 wt%) than in unmetamorphosed Hawaiian OIB alkali basalts. The actinolite rocks of the matrix show a pyroclastic texture and contain relic Ca-pyroxenes. The concentrations of HFS elements and pyroxene chemistry of the actinolite rocks indicate an origin from tholeiitic MORB, similar in composition to typical Mikabu greenstones in the Kanto Mountains and Shikoku. These observations strongly suggest that the greenstone complex is not a tectonic melange comprising allochthonous meta-morphic rocks within a matrix of Mikabu greenstones, but that the entire complex consists of Mikabu greenstones. Therefore, the complex was subjected to Sanbagawa metamorphism after a Na-enrichment event
jadeite grew in Na-rich blocks during the metamorphism. © 2011, Japan Association of Mineralogical Sciences. All rights reserved.

A means for estimating pressures in natural samples based on both the coupled substitution (Na+)([1+]) + Si-[VI]([4+]) = (M)([2+]) (Al + Cr)([3+]), and the classic pyroxene-stoichiometry majorite-substitution into garnet at high-pressure, is derived for garnets with majoritic chemistry. The technique is based on a compilation of experimental data for different bulk compositions. It is compositionally and thermally robust and can be used to estimate pressures experienced by natural materials during formation of majoritic garnet. In addition, it can be used either retrospectively, or in new experimental studies to establish the pressures of crystallization of reaction products, and determine if disequilibrium is recorded by the chemistries of majoritic garnets. Pressures are calculated based on majoritic chemistries in chondritic meteorites and diamond inclusions. Majoritic garnets associated with Mg perovskite in shocked L chondrites (n = 4) yield uniform pressures of 23.8 +/- 0.2 GPa that are slightly higher than pressures recorded by majoritic garnet in shock-derived melt veins in L chondrites (22.4 +/- 0.6 GPa; n = 5). Similar pressures are also exhibited by shock-derived majoritic garnets in H chondrites (22.2 +/- 1.1 GPa; n = 3). Diamond inclusions with eclogitic and peridotitic majoritic garnet chemistries exhibit mean pressures of 10.7 +/- 2.7 GPa (n = 30) and 8.3 +/- 1.6 GPa (n = 15) respectively, consistent with a sub-lithospheric origin. However, pressures defined by majoritic diamond inclusions from Jagersfontein (22.3 +/- 0.8 GPa and 16.9 +/- 1 GPa), Monastery (15.7 +/- 7 GPa) and Kankan (15.5 +/- 0.2 GPa) show that these inclusions originated from the mantle transition zone. Thus, this new single-phase method for pressure estimation has unmatched potential to map the depth of formation of garnets with majoritic chemistries that occur as diamond inclusions in all parageneses except those that include Ca silicate perovskite. The derived pressures confirm the sub-lithospheric origin of eclogitic majoritic diamond inclusions, and thus provide a more comprehensive picture of the important role of storage of oceanic lithosphere in the transition zone. (C) 2010 Elsevier Ltd. All rights reserved.

An anisotropy of magnetic susceptibility (AMS) analysis was conducted for a typical S-C mylonite in a small-scale ductile shear zone derived from Late Cretaceous magnetite-free granite in the Ryoke Belt, Teshima Island, southwest Japan. In such mylonites, paramagnetic minerals such as biotite and hornblende, which define foliations, are assumed to control the AMS. Accordingly, we attempted to measure the orientations of both minerals to correlate the S-C-C' fabric to the AMS using techniques of microscopic and back-scattered electron (BSE) image analyses. A measured magnetic fabric of the S-C mylonite that is expressed by a K(min) normal plane (K(max)-K(int) plane) approximated S foliation, K(max) orientation coincided well with the orientations of mean resultant vectors for long axes of biotite and minor hornblende, whereas K(max) did not coincide well with those of the mean resultant vectors for long axes of the brighter domain (aggregates of biotite and minor hornblende) from the binary BSE image. These results show that the magnetic fabric fairly reflects the shape preferred orientation of individual grains of paramagnetic monoclinic minerals, especially biotite, which forms the S-C-C fabric. (C) 2009 Elsevier Ltd. All rights reserved.

The exhumation of high-P/T metamorphic rocks plays a key role in the rearrangement of the geotectonic framework in arc-trench systems. The deposition of clasts of exhumed rocks constrains the timing of exhumation and the denudation history. We obtained the K-Ar ages of clasts from the Miocene Aoiwa Conglomerate, Hiki Hills, eastern Kanto Mountains. The Aoiwa Conglomerate is an unsorted breccia (maximum clast diameter up to ca. 3 m) composed of clasts of high-P/T metamorphic rocks (greenstones and crystalline schists), granitic rocks, low-P/T metamorphic rocks (mafic to felsic plutono-metamorphic rocks), and sedimentary rocks.The clasts of high-P/T metamorphic rocks were previously considered to have been derived from the Sanbagawa metamorphic rocks, which have been exposed nearby since the Miocene. However, schist clasts yield K-Ar phengite ages of 127.2-121.0 and 98.4-80.7 Ma, significantly older than ages obtained for the Sanbagawa metamorphic rocks in the Kanto Mountains, although the mineral assemblage and metamorphic grade of clasts are similar.Clasts of granitic rocks and low-P/T metamorphic rocks yield K-Ar hornblende ages of 131.5-114.0 Ma and phengite ages of 97.8-88.9 Ma, significantly older than ages obtained for Ryoke granites in the Kanto Mountains. In addition, a tonalite mylonite clast yields a lower 87Sr/86Sr initial ratio (0.70510-0.70520 or 0.70498-0.70505) than that of the Ryoke granites.Based on the results of K-Ar dating and a detailed petrologic study of the clasts, we conclude that the schist clasts were derived from an older unit within the Sanbagawa metamorphic rocks and that granitic and mafic metamorphic clasts were derived from the paleo-Ryoke terrane, which previously overlaid the Sanbagawa metamorphic rocks and today occurs only as sporadic allochthonous rocks. The Aoiwa Conglomerate was probably deposited in association with denudation of the paleo-Ryoke and uppermost Sanbagawa terranes. Deposition was accelerated during exhumation of Sanbagawa metamorphic rocks during the Middle Miocene.

Geological information is of little value in the absence of location data regarding the site where the observation was made. Topographic maps have traditionally been used for this purpose; however, this role has now been taken over by GPS receivers. The past decade has seen the development of compact and inexpensive GPS receivers, the so-called GPS loggers, which sequentially record positional data every 1–15 seconds. Such data can be linked with, for example, image files taken by a digital camera, using common time-stamp data. The geographic coordinates (latitude and longitude) of the site where the image was taken are embedded within the image file as metadata (i.e., a geotag). This paper introduces a geotagging system designed for use with a GPS logger and digital camera, and examines the accuracy and precision of positioning by GPS logger, as well as its application in geological surveys.

Understanding the exhumation process of deep-seated material within subduction zones is important in comprehending the tectonic evolution of active margins. The deformation and slip history of superficial nappe pile emplaced upon high-P/T type metamorphic rocks can reveal the intimate relationship between deformation and transitions in paleo-stress that most likely arose from changes in the direction of plate convergence and exhumation of the metamorphic terrane. The Kinshozan-Atokura nappe pile emplaced upon the high-P/T type Sanbagawa (=Sambagawa) metamorphic rocks is the remnant of a pre-existing terrane located between paired metamorphic terranes along the Median Tectonic Line (MTL) of central Japan. Intra- and inter-nappe structures record the state of paleo-stress during metamorphism and exhumation of the Sanbagawa terrane. The following tectonic evolution of the nappes is inferred from a combined structural analysis of the basal fault of the nappes and their internal structures. The relative slip direction along the hanging wall rotated clockwise by 180 degrees, from S to N, in association with a series of major tectonic changes from MTL-normal contraction to MTL-parallel strike-slip and finally MTL-normal extension. This clockwise rotation of the slip direction can be attributed to changes in the plate-induced regional stress state and associated exhumation of the deep-seated Sanbagawa terrane from the Late Cretaceous (Coniacian) to the Middle Miocene. (C) 2007 International Association for Gondwana Research. Published by Elsevier B.V All rights reserved.

Chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering. However, the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock. To overcome this limitation, the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis (PCA) of a large dataset derived from unweathered igneous rocks and their weathering profiles. The PCA analysis yields two principal components (PC1 and PC2), which capture 39.23% and 35.17% of total variability, respectively. The extent of weathering is reflected by variation along PC1, primarily due to the loss of Na2O and CaO during weathering. In contrast, PC2 is the direction along which the projections of unweathered felsic, intermediate and mafic igneous rocks appear to be best discriminated; therefore, PC1 and PC2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock. Subsequently, PC1 and PC2 were then mapped onto a ternary diagram (MFW diagram). The M and F vertices characterize mafic and felsic rock source, respectively, while the W vertex identifies the degree of weathering of these sources, independent of the chemistry of the unweathered parent rock.
The W index has a number of significant properties that are not found in conventional weathering indices. First, the W index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides, whereas most conventional indices are defined by between two and four oxides. Second, the W index provides robust results even for highly weathered sesquioxide-rich samples. Third, the W index is applicable to a wide range of felsic, intermediate and mafic igneous rock types. Finally, the MFW diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock. (C) 2007 Elsevier B.V. All rights reserved.

Compositional data, represented as percent or parts per million, are subject to the constant-sum constraint that precludes compositional data from much of statistical analysis. Despite this constraint, a theory for statistically rigorous treatment of compositional data is currently under intense development. This paper reviews the utility of two main procedures for compositional data analysis, which will be termed "logratio analysis" and "simplicial analysis". Logratio analysis is a way to map compositional data from a simplex space to a Euclidean real space by transforming compositional data into logarithms of component ratios. This bijectional mapping allows the transformed data to be analyzed by many traditional statistical methods available in real space. On the other hand, simplicial analysis introduces proper classes of parametric distribution, translation operation, scalar multiplication operation, identity unit and metric function within the simplex space. These definitions permit the simplex space to be reviewed as a metric space and compositional data as an Abelian group. Moreover, simplicial analysis provides statistical methodologies for compositional data, which are analogous to those for data sets associated with real space. A brief overview of the constant-sum constraint is followed by mathematical descriptions of logratio and simplicial analyses. Practical analyses of real data sets based on logratio and simplicial analyses are provided to illustrate their potential and to encourage their use.

The Woronow-Love-Schedl method is a logratio-based statistical assessment for detecting immobile variables in compositional data. The method was designed in order to address the constant-sum constraint. This method is effective, but difficult to apply without special statistical software. A computer program to process the method for open source statistical environment 'R' was developed. This program enables a user to assess the immobile variables in given data set. Care must be taken, however, because the program just gives some statistical information about the candidates for immobile variables. Hence, additional geological evidence is necessary for a definite decision about immobility.

In the field of geology, compositional data, such as petrochemical compositions, faunal compositions and modal compositions of sandstones, are common. This type of data contains an awkward mathematical problem known as constant-sum constraint. To resolve this problem, logratio and simplicial analyses have been developed in the last two decades. However, zero and missing values are common in practical compositional data, which are troublesome for logratio or simplicial analysis because neither logarithm nor geometric mean can take zeros. In this context, many authors have suggested nonparametric replacement methods of zero and missing values to overcome this problem. We review these nonparametric methods, additive replacement and multiplicative replacement, with their merits and limitations, after showing types and nature of zeros: rounded zeros stemmed from a detection limit of apparatus and essential (or true) zeros designating nothing. Zero replacement, however, may create outliers of data vectors and would lead us to erroneous conclusions. For this reason, we also review how to assess the outlier: by atypicality indices of data vectors and by confidence regions of a population. To disseminate statistically rigorous replacement and outlier detection, computer programs for open source statistical environment 'R', which replace zeros in a given data set and calculate atypicality indices, were developed.

This paper reviews recent progress on the geotectonic evolution of exotic Paleozoic terranes in Southwest Japan, namely the Paleo-Ryoke and Kurosegawa terranes. The Paleo-Ryoke Terrane is composed mainly of Permian granitic rocks with hornfels, mid-Cretaceous high-grade metamorphic rocks associated with granitic rocks, and Upper Cretaceous sedimentary cover. They form nappe structures on the Sambagawa metamorphic rocks. The Permian granitic rocks are correlative with granitic clasts in Permian conglomerates in the South Kitakami Terrane, whereas the mid-Cretaceous rocks are correlative with those in the Abukuma Terrane. This correlation suggests that the elements of Northeast Japan to the northeast of the Tanakura Tectonic Line were connected in between the paired metamorphic belt along the Median Tectonic Line, Southwest Japan. The Kurosegawa Terrane is composed of various Paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the Jurassic Chichibu Terrane accretionary complex. It is correlated with the South Kitakami Terrane in Northeast Japan. The constituents of both terranes are considered to have been originally distributed more closely and overlay the Jurassic accretionary terrane as nappes. The current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike-slip faults. The constituents of both exotic terranes, especially the Ordovician granite in the Kurosegawa-South Kitakami Terrane and the Permian granite in the Paleo-Ryoke Terrane provide a significant key to reconstructing these exotic terranes by correlating them with Paleozoic granitoids in the eastern Asia continent.

En-echelon veins hosted by sandstone and mudstone of the Atokura Formation were examined to clarify the paleostress field in that formation which constitutes the Atokura Nappe in a northern part of the Kanto Mountains. The veins are morphologically classified into two groups:1) a similar fold type with smoothly curved limbs, the vein tips pinch out and are not linked to any other fractures (type A) and, 2) a chevron fold type, the vein tips linked to joints formed before the vein opening (type B). The two types show a different texture and assemblage of infilling minerals. The type A consists mostly of fibrous to polygonal quartz and chlorite with lesser amounts of calcite and albite, whereas the type B of polygonal to prismatic calcite and quartz with lesser amounts of plagioclase and chlorite. Regardless of the vein type, morphology of the en-echelon sigmoidal veins is represented by a similar fold, but that of bridges is close to a parallel fold. The presence of undulatory extinction and subgrains in the fibrous quartz and pressure-solution cleavage in the bridges, which are considered to have simultaneously formed, indicates that the en-echelon veins were formed in a brittle-ductile shear zone. According to the paleostress analysis with conjugate sets of type-A vein arrays, the maximum (σ_1) principal stress axis is inferred to have been oriented in the NW-SE to NNE-SSW direction and horizontal, intermediate (σ_2) principal stress axis vertical, and minimum (σ_3) principal stress axis in the NE-SW to WNW-ESE direction and horizontal. The veining could have occurred during the formation of E-W trending open upright folds of the Upper Cretaceous Atokura Formation.

The Upper Cretaceous Atokura Formation constitutes the Atokura Nappe overlying the Mikabu Unit of the Sambagawa Belt. Framework mode of sandstones, modal composition of heavy minerals, and chemical composition of detrital garnets from the Atokura Formation were investigated. Detritus in the Atokura Formation are characterized by fragments of granitic rocks, hornfels, acidic to intermediate volcanic rocks, while those derived from rocks of accretionary complex such as chert, limestone, and greenstones are rather rare. Sandstone compositions plotted on a Qm-F-Lt diagram show dominant provenance types of the basement uplift, and subsidiary of dissected arc and transitional continental. Composition of heavy minerals is characterized by epidote, biotite, titanite, garnet, and muscovite. The chemistry of detrital garnets implies that low to intermediate P/T metamorphic rocks, plutonic rocks and calcareous metamorphic rocks were present in the provenance, while high P/T metamorphic rocks such as the Sambagawa metamorphic rocks was not exposed. Detrital high-Mg garnets whose source rocks have not been found in present Japanese Island are contained in sandstones, and might have been derived from Precambrian basement of the Asian Continent. Most of detritus in the Atokura Formation probably originated from Permian and mid-Cretaceous plutono-metamorphic complex of the Atokura and Kinshozan Nappes. Correlatives of the Lower Cretaceous in the Kitakami Mountains and the Siluro-Devonian in the Kurosegawa Belt are possible sources of acidic to intermediate volcanic clasts. The Paleo-Ryoke Terrane has been constructed of the source of these detritus.