Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11c1605l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11C-1605
Physics
[1115] Geochronology / Radioisotope Geochronology, [6205] Planetary Sciences: Solar System Objects / Asteroids
Scientific paper
The CM carbonaceous chondrites contain abundant evidence for low temperature aqueous alteration in the form of minerals including calcium, magnesium, iron and manganese bearing carbonates and magnesium-iron phyllosilicates. The chronology of carbonate mineralization can be determined using the Mn-Cr system and results reveal crystallization ages ranging from ~4569 to 4565 Ma [1]. A problem with using these data to explore the chronology of aqueous processing of the CM parent body is that it is unclear when in the alteration sequence the carbonates formed. If they all crystallized early and remained unchanged, then the Mn-Cr ages date the onset of aqueous alteration and show that it initiated at different times within or between parent bodies. Conversely, carbonates could have recrystallized continuously during aqueous alteration so that the Mn-Cr data may record any point in this alteration sequence. Petrographic evidence from CM2 carbonaceous chondrites, including Murchison, Pollen and QUE 93005, shows that carbonates have been extensively replaced by phyllosilicates. Thus, the carbonates formed relatively early. To determine the longevity of the aqueous system, it would therefore be desirable to also determine the crystallization ages of phyllosilicates in the meteorite matrices. Here we report the first results of dating phyllosilicates in the Murchison meteorite using the Ar-Ar system. [1] de Leuw, S., Rubin, A.E., Schmidt, A.K. and Wasson, J.T. (2009) 53Mn-53Cr systematics of carbonates in CM chondrites: Implications for the timing and duration of aqueous alteration. Geochimica et Cosmochimica Acta 73, 7433-7442
Alexander Clark
Lee Minchul
Lindgren Paula
Mark Darren Francis
Sofe M. R.
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