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 mélange 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 mélanges. 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 mélange comprising allochthonous metamorphic 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.

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.

関東山地東縁部比企丘陵には，結晶片岩角礫を多量に含む淘汰不良の中新統青岩礫岩が分布する．今回，礫の岩石学的・年代学的検討を行い，その起源を明らかにした．K-Ar年代測定によると，結晶片岩のフェンジャイト年代は石英片岩で127.2～121.0 Ma，泥質片岩で98.4～80.7 Maで，これまでに報告された関東山地三波川変成岩類の年代よりも有意に古い．一方花崗岩類は，角閃石年代で131.5～114.0 Ma，フェンジャイト年代で97.8～89.9 Maを示す．トーナル岩マイロナイト試料のSr同位体比初生値は0.705であり，領家花崗岩類よりも古い年代・低い初生値を示す．したがって結晶片岩礫は現在露出している三波川変成岩類の上位に存在したより古いユニット，花崗岩類礫は古領家帯構成要素（寄居複合岩体）に対比される．青岩礫岩は，中期中新世に三波川帯が急激に上昇し，その上位の古領家帯と共に削剥され，そのごく近傍に堆積したものと考えられる．

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.

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.

岩石・鉱物の化学組成,砕屑物の粒度組成やモード組成,生物の群集組成などで利用される組成データは変数の総量が一定であるために定数和制約を受ける.このような形式のデータを対象とした統計学的推定,検定の方法論は最近まで確立されていなかった.しかし,近年,組成データの厳密な統計学的解析方法が急激に進歩した.本論では,このような手法の1つである対数比解析と単体解析を実例を交えて紹介する.対数比解析は,組成データを単体空間から実空間に写像する方法である.単体解析は,単体空間に属する組成データに対して,新たに統計量や解析方法を開発する試みである.今後はこのような解析方法を用いて,より適切な論理的基盤から地質学的諸現象を解析することが重要となるであろう.

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.

変数の総和が一定となる組成データには定数和制約と呼ばれる数学的制約が存在し,通常の手法を用いたデータ解析を行うことができない.この間題を回避するための方法として,対数比変換を行いデータを実空間に写像する対数比解析法と,単体空間に留まって解析する単体解析法が考案されている.しかしいずれの方法においても,組成データに0値や欠損値が含まれると,数学的な問題から解析を実行できないという問題がある.このため,これまでにいくつかの0値および欠損値置換法が考案されてきた.本論では,組成データにおける0値の種類を明確にした上で,これらの0値置換方法と,その長所および短所について詳しく言及した.また,0値置換の問題点にも触れ,外れ値の検定法についても解説した.また,代表的な0値置換法と,外れ値を検定するための不適合度を計算するためのフリー統計環境R用プログラムを作成した.

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.

関東山地北縁部,跡倉ナップを構成する上部白亜系跡倉層には共役雁行脈が発達する.これを用い,跡倉層中の古応力場を解析した.雁行脈はその形態的特徴により,個々の脈が相似褶曲の形態を呈し,尖端が他の機械的異方面に連続しないもの(Aタイプ)と,Aタイプに比べて規模が大きく,個々の脈がシェブロン褶曲の形態を呈し,尖端が節理に連続するもの(Bタイプ)の2つに区分される.共役雁行脈はAタイプにのみ認められる.Aタイプは主に石英および緑泥石からなり,脆性-延性剪断帯で形成された.Bタイプは方解石および石英を主とし,節理形成後の開口で形成された.共役雁行脈から求めた古応力場は,最大圧縮主応力軸:北西-南東〜北北東-南南西方向,水平,中間圧縮主応力軸:ほぼ鉛直,最小圧縮主応力軸:北東-南西〜西北西-東南東方向,水平である.これらは跡倉層の重複褶曲構造のうち,正立褶曲群形成時後期に形成された.

関東山地跡倉層の後背地を, 砂岩モード組成, 重鉱物組成, 砕屑性ザクロ石の化学組成から推定した.跡倉層の砂岩は, Qm-F-Lt図上で主にbasement uplift, 一部はdissected arcおよびtransitional continentalのprovenance typeを示す.岩片は花崗岩類, 酸〜中性火山岩類を主体とする.重鉱物は緑簾石, 黒雲母, 白雲母, チタン石, ザクロ石で特徴づけられる.砕屑性ザクロ石の化学組成から, その源岩として低〜中P/T変成岩および石灰質変成岩が推定される.これらの特徴から, 跡倉層の主な堆積物供給源岩は跡倉層を除く跡倉ナップおよび金勝山ナップ構成要素であったと推察される.また, 酸〜中性火山岩類岩片の供給源岩は, 北上山地の前期白亜紀火山岩類や黒瀬川帯のシルル-デボン系に対比される可能性がある.これらの供給源岩は古領家帯を構成し, それが跡倉層の後背地であったと考えられる.