38 research outputs found
Hibonite-bearing inclusions from Murchison (CM2) meteorite: A Mg isotopic study using a NanoSIMS.
第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日(木) 国立国語研究所 2階講
Ultra-refractory metal grains in hibonite-bearing inclusions with highly fractionated Mg isotopes.
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月30日(金) 国立国語研究所 2階講
Igneous clasts in the Northwest Africa 801 CR2 chondrite: REE and oxygen isotopic studies.
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月30日(金) 国立国語研究所 2階講
Geology, geochemistry and earthquake history of Lō`ihi Seamount, Hawai`i
Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemie der Erde - Geochemistry 66 (2006): 81-108, doi:10.1016/j.chemer.2005.09.002.A half century of investigations are summarized here on the youngest Hawaiian volcano, Lō`ihi Seamount. It was discovered in 1952 following an earthquake swarm. Surveying in 1954 determined it has an elongate shape, which is the meaning of its Hawaiian name. Lō`ihi was
mostly forgotten until two earthquake swarms in the 1970’s led to a dredging expedition in 1978, which recovered young lavas. This led to numerous expeditions to investigate the geology, geophysics, and geochemistry of this active volcano. Geophysical monitoring, including a realtime
submarine observatory that continuously monitored Lō`ihi’s seismic activity for three
months, captured some of the volcano’s earthquake swarms. The 1996 swarm, the largest
recorded in Hawai`i, was preceded by at least one eruption and accompanied by the formation of
a ~300-m deep pit crater, renewing interest in this submarine volcano. Seismic and petrologic
data indicate that magma was stored in a ~8-9 km deep reservoir prior to the 1996 eruption.
Studies on Lō`ihi have altered conceptual models for the growth of Hawaiian and other
oceanic island volcanoes and led to a refined understanding of mantle plumes. Petrologic and
geochemical studies of Lō`ihi lavas showed that the volcano taps a relatively primitive part of
the Hawaiian plume, producing a wide range of magma compositions. These compositions have
become progressively more silica-saturated with time reflecting higher degrees of partial melting
as the volcano drifts towards the center of the hotspot. Seismic and bathymetric data have
highlighted the importance of landsliding in the early formation of an ocean island volcano.
Lō`ihi’s internal structure and eruptive behavior, however, cannot be fully understood without
installing monitoring equipment directly on the volcano.
The presence of hydrothermal activity at Lō`ihi was initially proposed based on nontronite
deposits on dredged samples that indicated elevated temperatures (31oC), and on the detection of water temperature, methane and 3He anomalies, and clumps of benthic micro-organisms in the
water column over the volcano in 1982. Submersible observations in 1987 confirmed a low
temperature system (15-30oC) prior to the 1996 formation of Pele’s Pit. The sulfide mineral
assemblage (wurtzite, pyrrhotite, and chalcopyrite) deposited after the pit crater collapsed are
consistent with hydrothermal fluids >250oC. Vent temperatures have decreased to ~60oC during
the 2004 dive season indicating the current phase of hydrothermal activity may be waning.This work
was supported by a NSF grant to M. Garcia (OCE 97-29894)
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FeO-rich silicates in the Sahara 97159 (EH3) enstatite chondrite: Mineralogy, oxygen isotopic compositions, and origin
We report the mineralogy and oxygen isotopic compositions of FeO-rich silicates in the Sahara 97159 EH3 chondrite. This component is referred to as FeO-rich because it contains substantially more FeO than the characteristic FeO-poor silicates in the highly reduced enstatite meteorites. These FeO-rich silicates are mostly low-Ca pyroxene (Fs535) and their compositions suggest an origin under more oxidizing conditions, like those for the ordinary chondrites. However, the mafic silicates in ordinary and carbonaceous chondrites are dominantly olivine, and the FeO-rich silicates in the E chondrites are less commonly olivine. The oxygen isotopic compositions of the FeO- rich silicates are indistinguishable from those of FeO-poor silicates in Sahara 97159. These observations suggest that both the FeO-rich silicates and the FeO-poor silicates in EH chondrites formed from the same oxygen reservoir where redox conditions varied widely.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202