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Dating clasts in polymict breccias

Posted on by Daikora Posted in Correspondence 4 Comments ⇩

The fragmental nature of the breccia clasts is more obvious in cross-polarized light. This is an unusual plagioclase fragment that appears to have undergone considerable shock deformation. This sample was collected by the Apollo 14 mission to the Fra Mauro crater, on the northeastern margin of Mare Nubium. In this article we review the basic differences between the bulk composition of Mars and the Earth and the manner in which this plays into our understanding of the timing and mechanisms of accretion and core formation. Field width is 0. Field width is 4 mm. Chronology and Evolution of Mars: The unusual texture is indicative to me of shock-induced deformation twinning. Field width is 1. The heating event that melted and permitted crystallization of the matrix also permitted partial assimilation of some of the clasts, making their margins fuzzy. The low density is partially explicable if there is a greater proportion of more volatile elements. The two clasts on the left are quite feldspathic. Polymict breccia, lunar thin section This is an impact breccia that incorporates fragments from several different lithologies. Many of the fragments are themselves breccias. Fundamental differences between the composition of Mars and that of other terrestrial planets are apparent from the planet's slightly lower density and from the compositions of Martian meteorites.

Dating clasts in polymict breccias


It consists of a very fine-grained crystalline matrix and fragments ranging from highlands anorthosite to mare basalt. This sample was collected by the Apollo 14 mission to the Fra Mauro crater, on the northeastern margin of Mare Nubium. The fur ther growth of the Earth was sustained by major collisions with planetesimals and planets such as that which resulted in the formation ofthe Earth's moon Hartmann and Davis, ; Cameron and Ward, ; Wetherill, ; Cameron and Benz, It may contain fragments of only a few plagioclase and pyroxene crystals in the original coarse-grained rock. The fragmental nature of the breccia clasts is more obvious in cross-polarized light. Much of the matrix of this whole breccia looks like the finer-grained matrix of this fragment. This low-magnification view shows a dark matrix in which are set a variety of crystal and lithic fragments, including breccias. Polymict breccia, lunar thin section This is an impact breccia that incorporates fragments from several different lithologies. Notice how the edges are not sharp. Quenched glass fragment with lath-shaped dark-gray plagioclase, lighter gray pyroxene, bright white specks of iron, and tiny light brown crystals of ilmenite. Chronology and Evolution of Mars: This late accretionary history, which lasted more than 50 Myr in the case of the Earth Halliday, a, b , appears to have been shorter and less catastrophic in the case of Mars Harper et ai. The large light-colored fragment on the right is shocked anorthosite. Kallenbach, Johannes Geiss, W. The heating event that melted and permitted crystallization of the matrix also permitted partial assimilation of some of the clasts, making their margins fuzzy. The two clasts on the left are quite feldspathic. Fundamental differences between the composition of Mars and that of other terrestrial planets are apparent from the planet's slightly lower density and from the compositions of Martian meteorites. We highlight some of the evidence for early cessation of major collisional growth on Mars. Field width is 4 mm. In cross-polarized light the fragmental nature of this fragment is obvious. This is an unusual plagioclase fragment that appears to have undergone considerable shock deformation. Finally, we reevaluate the isotopic evidence that Mars differentiated quickly. Field width is 8 mm. The low density is partially explicable if there is a greater proportion of more volatile elements. Many of the fragments are themselves breccias. Field width is 0. The two grains at the very top of this basalt clast are colorless and have high birefringence, and are probably olivine.

Dating clasts in polymict breccias


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