ALBERT

Description: The Indus Suture Zone is defined as the plate boundary between India and Eurasia. Here we document geochronological data that suggest that Indian rocks outcrop to the north of this suture zone. The inherited age spectrum of zircons from mylonitic gneiss collected in the southern part of the Karakorum Batholith is similar to those obtained from the Himalayan Terrane, the Pamir and is apparently Gondwanan in its affinity. These data are taken to indicate that the Karakorum Terrane was once a component of Gondwana, or at least derived from the erosion of Gondwanan material. Several continental ribbons (including the Karakorum Terrane) were rifted from the northern margin of Gondwana and accreted to Eurasia prior to India-Eurasia collision. Many therefore consider the Karakorum Terrane is the southern margin of Eurasia. However, we do not know if rifting led to the creation of a new microplate(s) or simply attenuated crust between Gondwana and these continental ribbons. Thus there is a problem using inherited and detrital age data to distinguish what is “Indian” and what is “Eurasian” crust. These findings have implications for other detrital/inherited zircon studies where these data are used to draw inferences about the tectonic history of various terranes around the world.

Description: A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ebihara, M -- Sekimoto, S -- Shirai, N -- Hamajima, Y -- Yamamoto, M -- Kumagai, K -- Oura, Y -- Ireland, T R -- Kitajima, F -- Nagao, K -- Nakamura, T -- Naraoka, H -- Noguchi, T -- Okazaki, R -- Tsuchiyama, A -- Uesugi, M -- Yurimoto, H -- Zolensky, M E -- Abe, M -- Fujimura, A -- Mukai, T -- Yada, Y -- New York, N.Y. -- Science. 2011 Aug 26;333(6046):1119-21. doi: 10.1126/science.1207865.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan. ebihara-mitsuru@tmu.ac.jp〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21868669" target="_blank"〉PubMed〈/a〉

Description: Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tsuchiyama, Akira -- Uesugi, Masayuki -- Matsushima, Takashi -- Michikami, Tatsuhiro -- Kadono, Toshihiko -- Nakamura, Tomoki -- Uesugi, Kentaro -- Nakano, Tsukasa -- Sandford, Scott A -- Noguchi, Ryo -- Matsumoto, Toru -- Matsuno, Junya -- Nagano, Takashi -- Imai, Yuta -- Takeuchi, Akihisa -- Suzuki, Yoshio -- Ogami, Toshihiro -- Katagiri, Jun -- Ebihara, Mitsuru -- Ireland, Trevor R -- Kitajima, Fumio -- Nagao, Keisuke -- Naraoka, Hiroshi -- Noguchi, Takaaki -- Okazaki, Ryuji -- Yurimoto, Hisayoshi -- Zolensky, Michael E -- Mukai, Toshifumi -- Abe, Masanao -- Yada, Toru -- Fujimura, Akio -- Yoshikawa, Makoto -- Kawaguchi, Junichiro -- New York, N.Y. -- Science. 2011 Aug 26;333(6046):1125-8. doi: 10.1126/science.1207807.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Space Science, Osaka University, Toyonaka, 560-0043, Japan. akira@ess.sci.osaka-u.ac.jp〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21868671" target="_blank"〉PubMed〈/a〉

Description: Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yurimoto, Hisayoshi -- Abe, Ken-ichi -- Abe, Masanao -- Ebihara, Mitsuru -- Fujimura, Akio -- Hashiguchi, Minako -- Hashizume, Ko -- Ireland, Trevor R -- Itoh, Shoichi -- Katayama, Juri -- Kato, Chizu -- Kawaguchi, Junichiro -- Kawasaki, Noriyuki -- Kitajima, Fumio -- Kobayashi, Sachio -- Meike, Tatsuji -- Mukai, Toshifumi -- Nagao, Keisuke -- Nakamura, Tomoki -- Naraoka, Hiroshi -- Noguchi, Takaaki -- Okazaki, Ryuji -- Park, Changkun -- Sakamoto, Naoya -- Seto, Yusuke -- Takei, Masashi -- Tsuchiyama, Akira -- Uesugi, Masayuki -- Wakaki, Shigeyuki -- Yada, Toru -- Yamamoto, Kosuke -- Yoshikawa, Makoto -- Zolensky, Michael E -- New York, N.Y. -- Science. 2011 Aug 26;333(6046):1116-9. doi: 10.1126/science.1207776.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan. yuri@ep.sci.hokudai.ac.jp〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21868668" target="_blank"〉PubMed〈/a〉

Description: Noble gas isotopes were measured in three rocky grains from asteroid Itokawa to elucidate a history of irradiation from cosmic rays and solar wind on its surface. Large amounts of solar helium (He), neon (Ne), and argon (Ar) trapped in various depths in the grains were observed, which can be explained by multiple implantations of solar wind particles into the grains, combined with preferential He loss caused by frictional wear of space-weathered rims on the grains. Short residence time of less than 8 million years was implied for the grains by an estimate on cosmic-ray-produced (21)Ne. Our results suggest that Itokawa is continuously losing its surface materials into space at a rate of tens of centimeters per million years. The lifetime of Itokawa should be much shorter than the age of our solar system.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Nagao, Keisuke -- Okazaki, Ryuji -- Nakamura, Tomoki -- Miura, Yayoi N -- Osawa, Takahito -- Bajo, Ken-ichi -- Matsuda, Shintaro -- Ebihara, Mitsuru -- Ireland, Trevor R -- Kitajima, Fumio -- Naraoka, Hiroshi -- Noguchi, Takaaki -- Tsuchiyama, Akira -- Yurimoto, Hisayoshi -- Zolensky, Michael E -- Uesugi, Masayuki -- Shirai, Kei -- Abe, Masanao -- Yada, Toru -- Ishibashi, Yukihiro -- Fujimura, Akio -- Mukai, Toshifumi -- Ueno, Munetaka -- Okada, Tatsuaki -- Yoshikawa, Makoto -- Kawaguchi, Junichiro -- New York, N.Y. -- Science. 2011 Aug 26;333(6046):1128-31. doi: 10.1126/science.1207785.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geochemical Research Center, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan. nagao@eqchem.s.u-tokyo.ac.jp〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21868672" target="_blank"〉PubMed〈/a〉

Description: We present the results of long-baseline optical interferometry observations using the Precision Astronomical Visual Observations (PAVO) beam combiner at the Center for High Angular Resolution Astronomy (CHARA) Array to measure the angular sizes of three bright Kepler stars: Cygni, and both components of the binary system 16 Cygni. Supporting infrared observations were made with the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the CHARA Array. We find limb-darkened angular diameters of 0.753 ± 0.009 mas for Cyg, 0.539 ± 0.007 mas for 16 Cyg A and 0.490 ± 0.006 mas for 16 Cyg B. The Kepler Mission has observed these stars with outstanding photometric precision, revealing the presence of solar-like oscillations. Due to the brightness of these stars the oscillations have exceptional signal-to-noise, allowing for detailed study through asteroseismology, and are well constrained by other observations. We have combined our interferometric diameters with Hipparcos parallaxes, spectrophotometric bolometric fluxes and the asteroseismic large frequency separation to measure linear radii ( Cyg: 1.48 ± 0.02 R , 16 Cyg A: 1.22 ± 0.02 R , 16 Cyg B: 1.12 ± 0.02 R ), effective temperatures ( Cyg: 6749 ± 44 K, 16 Cyg A: 5839 ± 42 K, 16 Cyg B: 5809 ± 39 K) and masses ( Cyg: 1.37 ± 0.04 M , 16 Cyg A: 1.07 ± 0.05 M , 16 Cyg B: 1.05 ± 0.04 M ) for each star with very little model dependence. The measurements presented here will provide strong constraints for future stellar modelling efforts.

Description: Meteorites originating from asteroids are the oldest-known rocks in the Solar System, and many predate formation of the planets. Refractory inclusions in primitive chondrites are the oldest-known materials, and chondrules are generally a few million years younger. Igneous achondrites and iron meteorites also formed in the first five million years of the protoplanetary disk and escaped accretion into planets. Isotopic dates from these meteorites serve as time markers for the Solar System's earliest history. Because of the unique environments in the protoplanetary disk, dating the earliest meteorites has its own opportunities and challenges, different from those of terrestrial geochronology.

Description: New zircon U–Th model-age and trace element datasets are presented from Taupo volcano (New Zealand), which are used to investigate the timescales and broad-scale magmatic processes involving zircon crystallization after the caldera-forming 25·4 ka Oruanui supereruption. Detailed 14 C-based chronologies and controls on vent locations allow the timing and location of post-caldera eruptions to be spatially and temporally constrained to an extent not possible for any other supervolcano. After ~5 kyr of post-Oruanui quiescence, Taupo erupted three dacitic units, followed by another ~5 kyr break, and then a sequence of rhyolitic units in three subgroups (SG1–SG3) from 12 ka onwards. Despite overlapping vent sites and crustal source domains between the Oruanui and post-Oruanui eruptions, U–Th zircon model ages in Taupo SG1 rhyolites (erupted from 12 to 10 ka) indicate only minor inheritance of crystals from the Oruanui magma source. Post-Oruanui model-age spectra are instead typically centred close to eruption ages with subordinate older pre-300 ka equiline grains in some units. U–Pb dating of these older grains shows that both 300–450 ka plutonic-derived and pre-100 Ma greywacke basement-derived zircons are present. The former largely coincide in age with zircons from the 350 ka Whakamaru eruption products, and are dominant over greywacke in young units that were vented within the outline of the Whakamaru caldera. Despite multiple ages and vent sites, trace element compositions are broadly similar in zircons, regardless of their ages. However, a small subset of zircons analysed from SG1 rhyolite (Units B and C) have notably high concentrations of U, Th, P, Y + (REE) 3+ and Nb but with only minor variations in Hf and Ti. SG2 zircons typically have higher Sc contents, reflecting large-scale changes in melt chemistry and crystallizing mineral phases with time. The age spectra indicate that most Oruanui zircons were removed by thermally induced dissolution immediately following the supereruption. U–Th ages from single post-Oruanui eruptions show consistent inheritance of post-Oruanui grains with model ages that centre between the temporally separated but geographically overlapping eruption groups, generating model-age modes. Within the statistical limitations of the isotopic measurements, we interpret these repeated modes to be significant, resulting from incorporation of crystal populations from cyclic post-Oruanui periods of magmatic cooling and crystallization, acting within a crustal protolith chemically independent of that which was dominant in the Oruanui system. These periods of cooling and crystallization alternate with times of rejuvenation and eruption, sometimes demonstrably accompanying syn-eruptive regional rifting and mafic magma injection. Not only were the processes that developed the supersized Oruanui magma body rapid, but this huge magma system was effectively reset and rebuilt on a comparably short timescale.

Description: The source of the auriferous fluids that formed Archean greenstone gold deposits remains controversial; metamorphic fluids, fluids derived from felsic magmas, mantle fluids, and meteoric water have all been suggested. We report the results of ion microprobe (sensitive high-resolution ion microprobe stable isotopes) multiple sulfur isotope analyses ( 32 S, 33 S, 34 S) conducted to constrain the source of sulfur in four Archean gold deposits. The analyses are of pyrite samples that are genetically related to the gold mineralization from the Bellerophon, Victory, and Wallaby deposits in the Eastern Goldfield superterrane of the Yilgarn craton, Western Australia, together with sulfide from black shale from the Golden Mile deposit and St. Ives gold camp. Ore-associated pyrite from the Beattie gold deposit of the Abitibi greenstone belt of the Superior craton in Canada was measured to test whether the results obtained from the Yilgarn craton apply to other Archean gold deposits. Sulfur analyses from sulfide from shale show mass-independent fractionation (MIF) with 33 S as high as +1.8, whereas those from the 4 Archean gold deposits are dominated by mass-dependent fractionation, with only a minor contribution of MIF sulfur. In this respect, Archean gold deposits contrast with Archean NiS deposits, which are dominated by MIF sulfur. The absence of MIF in the pyrite from the four Archean gold deposits analyzed in this study is consistent with the auriferous fluid originating from a felsic magma or mantle source, but inconsistent with the metamorphic and meteoritic fluid hypotheses.

Description: We present zircon textural, trace element and U–Pb age data obtained by secondary ion mass spectrometry (SIMS) (SHRIMP-RG: sensitive high-resolution ion microprobe, reverse geometry) from 15 stratigraphically controlled Bishop Tuff samples and two Glass Mountain (GM) lava samples (domes OD and YA). Bishop zircon textures divide into four suites: (a) dominant sector-zoned grains, with (b) subordinate grains showing bright rims [lower U, Th, rare earth elements (REE)] in CL imaging, (c) sparse GM-type grains (texturally similar to zircons from GM dome YA) and (d) sparse Mesozoic xenocrysts from Sierran granitoid country rocks. All Bishop zircons from suites (a)–(c) combined have a weighted mean age of 777·9 ± 2·2 ka (95% confidence) and a tail back to ~845 ka. Our eruption age estimate using the weighted mean of 166 rim ages of 766·6 ± 3·1 ka (95% confidence) is identical within uncertainty to published estimates from isotope-dilution thermal ionization mass spectrometry (ID-TIMS) (767·1 ± 0·9 ka, 2) and 40 Ar/ 39 Ar (767·4 ± 2·2 ka, 2) techniques, the latter using the 28·172 Ma age for the Fish Canyon sanidine standard. We estimate also an eruption age for GM dome YA of 862 ± 23 ka (95% confidence), significantly older than the currently accepted 790 ± 20 ka K–Ar age. The oldest zircon cores from late-erupted Bishop material (including those with GM-type textures) have a weighted mean age of 838·5 ± 8·8 ka (95% confidence), implying that the Bishop Tuff system was active for only ~80 kyr, and had effectively no temporal overlap with the GM system. Trace element variations in Bishop zircons are influenced strongly for many elements by sector zoning, producing up to 3 x concentration differences between sides and tips within the same growth zone. Contrasting trends in molar (Sc + Y + REE 3+ )/P ratios between sides and tips indicate contrasting mechanisms of substitution in different sectors of the same crystal. Concentrations of Ti in tips are double those in the sides of crystals, hindering applicability of the Ti-in-zircon thermometer, in addition to variations inherent to the 0·15–0·67 range in values proposed for aTiO 2 . The bright-rim portions of grains are inferred to have crystallized from the same magma as that which generated the bright rims seen under cathodoluminescence or back-scattered electron imaging on quartz and feldspar, respectively. This less evolved, slightly hotter magma invaded the deeper parts of the chamber represented in the late-erupted northern units possibly up to ~10 kyr prior to eruption, but invaded shallower levels only very shortly before eruption, as shown by our textural information and previously proposed from the sharp delineation of quartz bright rims. By obtaining a large number of analyses from zircon separates that systematically cover the entire Bishop Tuff eruption sequence we can produce an eruption age estimate using SIMS to the same precision and accuracy as ID-TIMS and 40 Ar/ 39 Ar techniques.