Daniel Dunkley

Recent research cruises surveying forearc slopes of Izu-Bonin-Mariana (IBM) arc have discovered outcrops representing the deep crustal section of the early IBM arc. Ongoing geochemcial, petrological, and geochronological studies of recovered rocks are providing new insights into the magmatism and development of arc crust during the inception of an intra-oceanic subduction system. ROV traverses, conducted at the northern Izu-Bonin forearc,

In bothpalaeoenvironmentalandpalaeogeographicalstudies,Antarctica plays a unique roleinourunderstandingofthehistoryoftheEarth.Ithasmaintainedauniquegeographicalposition at the South Pole for long periods. As the only unpopulated continent, the absence of political barriers or short-term economic interests has allowed international collaborative science to flour- ish. Although 98% of its area is covered by ice, the coastal Antarctic region is one of the well- studied regions in the world. The integrity

The chemical Th–U total Pb isochron method (CHIME) of dating was carried out on accessory minerals in samples from the Okcheon metamorphic belt in Korea. Dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the Hwanggangri Formation, metamorphic allanite in garnet-bearing muscovite–chlorite schist of the Munjuri Formation, and polycrase and monazite in post-tectonic granite

The Higo Complex of west-central Kyushu, western Japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south, where granitoids are emplaced along the southern margin. The timing of granulite metamorphism has been extensively investigated and debated. Previously published Sm–Nd mineral isochrons for garnet-bearing

The Izu Peninsula, central Japan, is situated in a zone where the active intra-oceanic Izu–Bonin arc has been colliding end-on with the mainland Honshu arc for the past 15million years. As a result of this arc–arc collision, parts of the submarine Izu–Bonin upper crustal sequences have been accreted and uplifted to form the Izu Peninsula, exposing seafloor volcaniclastic deposits, associated

抄録 The Kamimura River, an upper tributary of the Yahagi River, flows through steep valleys in the mountainous Kamiyahagi area of Gifu Prefecture. The Tokai Gou flood of September 11-12, 2000 destroyed embankments along the river, and exposed ...

... Western Australia (eg Jacobs et al. 1998; Fitzsimons 2000; Grantham 2003; Jacobs & Thomas 2004; Bisnath et al. 2006; Mikhalsky et al. 2006; Meert & Lieberman 2007). Boger et al. (2001) proposed an early Palaeozoic orogenic ...

Trends in whole-rock and mineral chemistry are seen along a 95 km traverse of lower Archean granitic orthogneissic crust, in the Eastern Dharwar Craton, Tamil Nadu, south India (Hansen and Harlov 2007 J Petrol 48, 1641). Going from north (amphibolite ...

Serpentinization does not generally produce minerals suitable for direct isotopic dating. Therefore the age of serpentinization is usually estimated on the basis of age of other rocks associated with serpentinites. In this study, we report the ion probe dating of zircon in metasomatic lithologies such as rodingite veins and zoisite- rich rocks, which are considered to have formed at the same time as serpentinization. Zoisitites and rodingites from the Nagasaki Metamorphic Rocks, western Japan, are high-pressure-low-temperature metasomatic rocks that occur as tectonic inclusions in a serpentinite-matrix melange. The reaction zone is present between rodingite and serpentinite, with sharp contacts. The serpentinite mainly consists of antigorite with minor chrysotile, diopside, spinel, pyrrhotite, and chlorite. Chrysotile occurs near the reaction zone and also occurs as veins in serpentinite. Zoisitite occurs as blocks several meters across, consisting of granular clinozoisite, diopside, chlorite, apatite, titanite, and zircon. Rodingite occurs as veins in serpentinite. A large number of rodingite dykes intrude the serpentinite. The rodingite veins are centimeters to tens of centimeters wide and several meters in length. Rodingite is pinkish, mostly consisting of garnet, vesuvianite, diopside, apatite, titanite, and zircon. On the basis of the field observation and petrology, we infer that zoisitite, rodingite and antigorite-serpentinite formed at the same time. The reaction zone formed during the latter period of serpentinization when the chrysotile was produced. To characterize mass transfer during the serpentinization, major and trace element bulk analysis was performed. The zoisitite and rodingite have similar geochemical characteristics. We infer that elements released by serpentinization are Fe, Ni, Zn, V, Cr, Mg, Sc, Co, and Cu. On the other hand, Ca, Al, Mn, Ti, Sr, Zr, Nb, LREE, Bi, Th, and U were enriched in serpentinite by the fluid. Zircon grains are found in the zoisitite, rodingite, and the reaction zone. Two types of zircon were found in these rocks. Zircons 10-160 microns long are characterized by irregular margins and magmatic cores. Other grains <10 microns across are anhedral, mostly with homogeneous, high cathodoluminescence, although some grains have complex textures. The zircon grains are interpreted as follows: 1. zircon with magmatic features, such as oscillatory zoning, formed in protoliths, probably gabbroic; 2. zircon with patches and crack-fillings of high-CL were modified from magmatic zircon during the early stages of serpentinization and rodingite - zoisitite formation, by partial dissolution and recrystallization; 3. new sub-10 micron grains, together with overgrowths of homogeneous high-CL zircon, grew along fractures from hydrous fluids. Few magmatic grains with recrystallized areas and high-CL overgrowths could be dated by SHRIMP at NIPR. The weighted mean of common-Pb corrected U-Pb ages from 3 grains in zoisitite is 109.2±2.2Ma, with no resolvable age difference between magmatic cores and high-CL overgrowths. Age data from 4 grains in rodingite are scattered between 107 and 97Ma, with younger ages from spots overlapping porous annealed cracks. Age data are tentative but suggest that serpentinization occurred only shortly after crystallization of the gabbroic protolith.