Linked Life Data

11543074

Source:http://linkedlifedata.com/resource/pubmed/id/11543074

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
2000-6-15
pubmed:abstractText
The geologic history of Martian meteorite Allan Hills (ALH) 84001 is more complex than previously recognized, with evidence for four or five crater-forming impacts onto Mars. This history of repeated deformation and shock metamorphism appears to weaken some arguments that have been offered for and against the hypothesis of ancient Martian life in ALH 84001. Allan Hills 84001 formed originally from basaltic magma. Its first impact event (I1) is inferred from the deformation (D1) that produced the granular-textured bands ("crush zones") that transect the original igneous fabric. Deformation D1 is characterized by intense shear and may represent excavation or rebound flow of rock beneath a large impact crater. An intense thermal metamorphism followed D1 and may be related to it. The next impact (I2) produced fractures, (Fr2) in which carbonate "pancakes" were deposited and produced feldspathic glass from some of the igneous feldspars and silica. After I2, carbonate pancakes and globules were deposited in Fr2 fractures and replaced feldspathic glass and possibly crystalline silicates. Next, feldspars, feldspathic glass, and possibly some carbonates were mobilized and melted in the third impact (I3). Microfaulting, intense fracturing, and shear are also associated with I3. In the fourth impact (I4), the rock was fractured and deformed without significant heating, which permitted remnant magnetization directions to vary across fracture surfaces. Finally, ALH 84001 was ejected from Mars in event I5, which could be identical to I4. This history of multiple impacts is consistent with the photogeology of the Martian highlands and may help resolve some apparent contradictions among recent results on ALH 84001. For example, the submicron rounded magnetite grains in the carbonate globules could be contemporaneous with carbonate deposition, whereas the elongate magnetite grains, epitaxial on carbonates, could be ascribed to vapor-phase deposition during I3.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
S
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
1086-9379
pubmed:author
pubmed:issnType
Print
pubmed:volume
33
pubmed:owner
NASA
pubmed:authorsComplete
Y
pubmed:pagination
753-64
pubmed:dateRevised
2008-11-21
pubmed:meshHeading
pubmed:year
1998
pubmed:articleTitle
The history of Allan Hills 84001 revised: multiple shock events.
pubmed:affiliation
Lunar and Planetary Institute, Houston, Texas 77058-1113, USA. treiman@lpi.jsc.nasa.gov
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S.