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A discussion of isotopic systematics and mineral zoning in the shergottites; evidence for a 180 m.y. igneous crystallization age


, : A discussion of isotopic systematics and mineral zoning in the shergottites; evidence for a 180 m.y. igneous crystallization age. Geochimica et Cosmochimica Acta: , Pages 969-977. 1986.

Proposed igneous and metamorphic ages of the shergottites, a suite of achondritic basaltic meteorites, are examined in terms of the shergottites' petrography and mineral chemistry. No metamorphic or hydrothermal event appears capable of resetting the refractory Sr and Nd isotopic systems of the shergottites since the time of their igneous crystallization. The approximately concordant Rb-Sr (180 ± 20 m.y.) and U-Th-Pb (190 ± 30 m.y.) internal “isochrons” are thus interpreted as representing the time of igneous crystallization. The Sm-Nd internal “isochrons” which yield older apparent ages also show large scatter and are regarded as artifacts of the shergottites' complex igneous history. Rubidium-Sr, Sm-Nd and Pb-Pb wholerock “isochrons” are interpreted as mixing lines and are reasonably attributed to igneous processes such as wall-rock assimilation and magma mixing. If the shergottites are indeed less than 200 m.y. old, they represent the youngest known extraterrestrial basalts. This conclusion is supportive of the hypothesis that the SNC meteorites are samples of the planet Mars.

US$19.90

DOI: 10.1016/0016-7037(86)90377-7


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