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Herrin J.S.,NASA | Herrin J.S.,ESCG Astromaterials Research Group | Zolensky M.E.,NASA | Ito M.,NASA | And 8 more authors.
Meteoritics and Planetary Science | Year: 2010

The Almahata Sitta fall event provides a unique opportunity to gain insight into the nature of ureilitic objects in space and the delivery of ureilite meteorites to Earth. From thermal events recorded in the mineralogy, petrology, and chemistry of ureilites recovered from the fall area, we reconstruct a timeline of events that led to their genesis. This history is similar to that of other known ureilites and supportive of a disrupted ureilite parent body hypothesis. Temperatures of final mantle equilibrium were 1200-1300-°C, but this high-temperature history was abruptly terminated by rapid cooling and reduction associated with pressure loss. The onset of late reduction reactions and onset of rapid cooling must have been essentially simultaneous, most likely engendered by the same event. Cooling rates of 0.05-2-°C-h -1 determined from reversely zoned olivines and pyroxenes in Almahata Sitta imply rapid disassembly into fragments tens meters in size or smaller. This phenomenon seems to have affected all known portions of the ureilite parent body mantle, implying an event of global significance rather than localized unroofing. Reaccretion of one or more daughter asteroids occurred only after significant heat loss at minimum time scales of weeks to months, during which time the debris cloud surrounding the disrupted parent was inefficient at retaining heat. Fragments initially dislodged from the ureilite parent body mantle underwent subsequent size reduction and mixed with various chondritic bodies, giving rise to polylithologic ggregate objects such as asteroid 2008 TC 3. © The Meteoritical Society, 2010. Source

Joy K.H.,University College London | Joy K.H.,Natural History Museum in London | Joy K.H.,Lunar and Planetary Institute USRA | Joy K.H.,NASA | And 4 more authors.
Meteoritics and Planetary Science | Year: 2010

Dar al Gani (DaG) 400, Meteorite Hills (MET) 01210, Pecora Escarpment (PCA) 02007, and MacAlpine Hills (MAC) 88104/88105 are lunar regolith breccia meteorites that provide sampling of the lunar surface from regions of the Moon that were not visited by the US Apollo or Soviet Luna sample return missions. They contain a heterogeneous clast population from a range of typical lunar lithologies. DaG 400, PCA 02007, and MAC 88104/88105 are primarily feldspathic in nature, and MET 01210 is composed of mare basalt material mixed with a lesser amount of feldspathic material. Here we present a compositional study of the impact melt and impact melt breccia clast population (i.e., clasts that were generated in impact cratering melting processes) within these meteorites using in situ electron microprobe and LA-ICP-MS techniques. Results show that all of the meteorites are dominated by impact lithologies that are relatively ferroan (Mg#<70), have high Sc/Sm ratios (typically >10), and have low incompatible trace element (ITE) concentrations (i.e., typically <3.2 ppm Sm, <1.5 ppm Th). Feldspathic impact melt in DaG 400, PCA 02007, and MAC 88104/05 are similar in composition to that estimated composition for upper feldspathic lunar crust (Korotev et al. 2003). However, these melt types are more mafic (i.e., less Eu, less Sr, more Sc) than feldspathic impact melts returned by the Apollo 16 mission (e.g., the group 3 and 4 varieties). Mafic impact melt clasts are common in MET 01210 and less common in PCA 02007 and MAC 88104/05. We show that unlike the Apollo mafic impact melt groups (Jolliff 1998), these meteorite impact melts were not formed from melting large amounts of KREEP-rich (typically >10 ppm Sm), High Magnesium Suite (typically >70 Mg#) or High Alkali Suite (high ITEs, Sc/Sm ratios <2) target rocks. Instead the meteorite mafic melts are more ferroan, KREEP-poor and Sc-rich, and represent mixing between feldspathic lithologies and low-Ti or very low-Ti (VLT) basalts. As PCA 02007 and MAC 88104/05 were likely sourced from the Outer-Feldspathic Highlands Terrane our findings suggest that these predominantly feldspathic regions commonly contain a VLT to low-Ti basalt contribution. © 2010 The Meteoritical Society. Source

Galgana G.A.,Indiana University Bloomington | Galgana G.A.,Lunar and Planetary Institute USRA | Newman A.V.,Georgia Institute of Technology | Hamburger M.W.,Indiana University Bloomington | Solidum R.U.,Institute of Volcanology and Seismology
Journal of Volcanology and Geothermal Research | Year: 2014

We investigate active crustal deformation patterns associated with magmatic activity at Taal Volcano, an active tholeiitic volcano located in southwestern Luzon, Philippines. We present comparisons of elastic and combined elastic-viscoelastic modeling results with deformation observed by continuous GPS measurements on and near the volcano. Continuous dual-frequency and single-frequency (L1) GPS data between 1998 and 2005 provide evidence for smoothly transitioning periods of inflation and deflation centered under the volcano. Within deformation phases that typically last 3-9months (with rates exceeding 200mmyr-1), prominent inflationary phases were observed in February-November 2000 and June 2004-March 2005. The 2000 period of inflation was characterized by up to 145mmyr-1 surface extension and 220mmyr-1 of uplift of the center of Volcano Island relative to the northern caldera rim, while the 2005 inflation was characterized by as much as 116mmyr-1 horizontal extension of the volcanic edifice and 180mmyr-1 uplift. Inversions of observed surface deformation to determine the source location points to a relatively stable spherical source, situated under Volcano Island's central crater, at depths of ~5km (based on the preferred Mogi model). Using this source geometry, we develop axisymmetric finite element models with annuli of concentric shells around the magma reservoir, embedded within a multi-layered elastic lithosphere. Using simply varying pressure histories as input, a variety of forward models are fit to the time history of continuously observed deformation for GPS stations located on Volcano Island. Though the inferred source geometry, volume and near-source rheological properties are non-unique, they represent more physically appropriate material properties than those assumed in simple elastic half-space models. The sources inferred using viscoelastic shell models suggest simpler pressure histories and reduced overall pressure changes, relative to equivalent elastic half-space models. © 2013 Elsevier B.V. Source

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