Evolution of Chitradurga Shear Zone; Some insights to the current interpretations in the tectonic context of Dharwar Craton, South India

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月30日（金） 統計数理研究所 ３階セミナー

ヒガシ ドロンイングモードランド セール・ロンダーネ サンチ チガク チョウサタイ ホウコク 2009–2010(JARE-51)

セール・ロンダーネ山地は,東南極・東ドロンイングモードランドに位置している.第51 次日本南極地域観測隊(JARE-51)夏隊の一部は2009-2010年の夏期に,セール・ロンダーネ山地においてベルギー南極観測隊(BELARE)との国際共同により地質,地形,隕石探査の地学野外調査を実施した.地質隊と地形隊はドロンイングモードランド航空ネットワーク(DROMLAN)によりセール・ロンダーネ山地に赴き,隕石探査隊は日本の新南極観測船「しらせ」の処女航海として南極に到着した.地質隊は山地東部を含むセール・ロンダーネ山地のほぼ全域をカバーし,地形隊は山地の西部および中央部で調査を行った.隕石探査隊は山地東部で調査を行った.野外活動は安全かつ成功裏に終了した.地質隊の一部はDROMLAN により帰国し,他のメンバーはセール・ロンダーネ山地からDROMLAN により昭和基地へ離脱したのち,「しらせ」により帰国した.本稿では設営,気象を含めた野外行動全般について報告する.Earth science-related field activities, involving geology, geomorphology and meteorite searches, were carried out in the Sør Rondane Mountains, Eastern Dronning Maud Land, during the 2009-2010 summer season as a part of the 51st Japanese Antarctic Research Expedition (JARE-51), in collaboration with the Belgian Antarctic Research Expedition (BELARE). Geology and geomorphology parties accessed the Sør Rondane Mountains using the Dronning Maud Land Air Network (DROMLAN), and the meteoritesearch party to Antarctica on the maiden voyage by the new Japanese icebreaker Shirase. The geology party covered the entire area of the Sør Rondane Mountains, although with an emphasis on the eastern part. The geomorphology party carried out fieldwork in western and central parts of the mountains, and the meteorite search party performed a survey in the eastern part. All field activities were succes fully carried out. Some of the geology members returned to Japan by DROMLAN, while others flew to Syowa Station from the Sør Rondane Mountains by DROMLAN, and then returned to Japan on board Shirase. This report provides a summary of the field operations, including logistics and weather records

Infiltration of Meteoric and Sea Water into Deep Fault Zones during Episodes of Coseismic Events : A Case Study of the Nojima Fault, Japan

Fluid infiltration into active faults and shear zones is usually studied in the middle to upper crustal environment. Circulating fluids deposit clay and carbonate material into cracks within the fault zone. Such crack-fill clay, calcite veins, and oxidized/weathered open cracks are well observed in the drill cores, from near-surface to a depth of 1,800 m, in the Nojima fault zone, Japan, which triggered the 1995 M7.2 Kobe earthquake. Powder X-ray diffraction analysis indicates that the crack-fill clay veins are mainly composed of siderite, calcite, laumontate, and fine-grained clasts of granitic rock. Isotopic analyses of carbonate material within the clay and calcite veins reveal variable δ18O (SMOW) values ranging from 20.1‰ to 27.7‰, and δ13C (PDB) values of -4.3‰ to -18.5‰, which are comparable to those of typical meteoric and sea water. 14C dates of 10 clay and calcite vein samples range from 35.0 kyr B.P. to 58.4 kyr B.P. Geological, petrological, stable isotopic, and 14C data suggest that these crack-fill clay and calcite veins and brown-colored open cracks developed due to the repeated infiltration of O2- and CO2-bearing meteoric and sea water downward into the deep Nojima fault zone during the last 35- 60 kyr. We propose a seismic fault suction pumping model to interpret the infiltration of subsurface waters being carried down into the deep fault zone by a rapid potential change during episodes of seismic faulting

Carbon isotope anatomy of a single graphite crystal in a metapelitic migmatite revealed by high-spatial resolution SIMS analysis

High-spatial resolution carbon isotope analyses of natural graphite using secondary ion mass spectrometry (SIMS), together with conventional mass spectrometry techniques, demonstrate isotopic heterogeneity within single graphite crystals precipitated from a partially melted metamorphic rock. SIMS (13)C/(12)C measurements were calibrated using an internal graphite standard previously analyzed by conventional isotope ratio mass spectrometry, which gave a reproducibility of 0.3aEuro degrees (1 sigma) at a spatial resolution of 2-3 mu m. This resolution helped to identify an unusual carbon isotope distribution in a single graphite crystal from a metapelitic leucosome, showing remarkable core to rim variations with sharp delta(13)C steps up to 10aEuro degrees. The results suggest that the graphite crystal grew from one edge to other forming layers perpendicular to the c-axis. The sharp isotopic steps indicate the presence of disequilibrium carbon isotope zoning in graphite and points to the possible existence of carbon isotope sector zoning. Intra-crystalline carbon isotope disequilibrium in graphite is believed to have resulted from the difference in diffusivity between (12)C and (13)C in the growth medium to the interface of graphite precipitation in different growth sectors

Petrogenesis of Cr-rich calc-silicate rocks from the Bandihalli supracrustal belt, Archean Dharwar Craton, India

Chromium-rich calc-silicate rocks in the Archaean Bandihalli supracrustal belt in the Dharwar Craton, India, show a characteristic mineral assemblage that includes euhedral and anhedral (resorbed) green garnet associated with chromite, in addition to diopside, quartz, clinozoisite and calcite. Two distinct types of green garnets and a brown variety were identified in the calc-silicate rocks. These garnets show complex chemical compositional variations that range between the endmembers of uvarovite, grossular, and spessartine. Chromite grains in the matrix are euhedral or subhedral, whereas inclusions in garnet are rounded or amoeboid in shape. The two textural varieties of chromite from Bandihalli are separated by a compositional gap. Furthermore, chromites from the study area have high Cr# (0.80–0.97) and low Mg# (0.01–0.04), which is similar to the chromite in serpentinites and are in contrast with chromite compositions reported from igneous rocks. Therefore, the chromite in the calcsilicate rocks may have been derived from serpentinized ultramafic rocks. Textural and compositional data presented here provide evidence for chemical changes of the primary chromite with increasing metamorphic grade, presumably associated with primary hydrothermal alteration that resulted in serpentinization and carbonation of the ultramafic protolith. Therefore, Cr-rich calcsilicate rocks can be considered as products of metamorphosed carbonated and serpentinized mafic or ultramafic igneous rocks

深部断層帯に地震イベントに伴う地表水の流入 : 野島断層を例に

Fluid infiltration into active faults and shear zones is usually studied in the middle to upper crustal environment. Circulating fluids deposit clay and carbonate material into cracks within the fault zone. Such crack-fill clay, calcite veins, and oxidized/weathered open cracks are well observed in the drill cores, from near-surface to a depth of 1,800 m, in the Nojima fault zone, Japan, which triggered the 1995 M7.2 Kobe earthquake. Powder X-ray diffraction analysis indicates that the crack-fill clay veins are mainly composed of siderite, calcite, laumontate, and fine-grained clasts of granitic rock. Isotopic analyses of carbonate material within the clay and calcite veins reveal variable δ18O (SMOW) values ranging from 20.1‰ to 27.7‰, and δ13C (PDB) values of -4.3‰ to -18.5‰, which are comparable to those of typical meteoric and sea water. 14C dates of 10 clay and calcite vein samples range from 35.0 kyr B.P. to 58.4 kyr B.P. Geological, petrological, stable isotopic, and 14C data suggest that these crack-fill clay and calcite veins and brown-colored open cracks developed due to the repeated infiltration of O2- and CO2-bearing meteoric and sea water downward into the deep Nojima fault zone during the last 35- 60 kyr. We propose a seismic fault suction pumping model to interpret the infiltration of subsurface waters being carried down into the deep fault zone by a rapid potential change during episodes of seismic faulting