Engineering topics

Mcsween, Harry Y., Jr.

Publications and source records attributed to Mcsween, Harry Y., Jr..

24 records · Page 2

NASA NTRS1989

Antarctic carbonaceous chondrites - New opportunities for research

An account is given of the types of carbonaceous meteorites available in the Antarctic collections of the U.S. and Japan. In the case of the collection for Victoria Land and Queen Maud Land, all known classes for meteorites except C1 are present; available pairing data, though limited, are indicative of the presence of many different falls. Thus far, attention has been focused on the largest meteorites. Most samples, however, are small.

Mcsween, Harry Y., Jr.↗

NASA NTRS1988

Origin of petrofabrics and magnetic anisotropy in ordinary chondrites

Three-dimensional finite strain and magnetic susceptibility anisotropy have been determined for 15 ordinary chondrites. The axes of strain and magnetic ellipsoids roughly correlate in both magnitude and orientation. The shapes of these ellipsoids are generally oblate spheroids that define a dominant foliation and a weak lineation. These characteristics suggest deformation involving uniaxial compaction. The degree of uniaxial deformation correlates with intensity of shock, as indicated by optical, TEM and chemical criteria. These data, plus the lack of a relationship between foliation and metamorphic history, indicate that dynamic processes, i.e., impacts, produced planar deformation fabrics in chondrites.

Sneyd, Deana S.↗

NASA NTRS1988

Comparison of Archean and Phanerozoic granulites: Southern India and North American Appalachians

Archean granulites at the southern end of the Dharwar craton of India and Phanerozoic granulites in the southern Appalachians of North America share an important characteristic: both show continuous transitions from amphibolite facies rocks to higher grade. This property is highly unusual for granulite terranes, which commonly are bounded by major shears or thrusts. These two terranes thus offer an ideal opportunity to compare petrogenetic models for deep crustal rocks formed in different time periods, which conventional wisdom suggests may have had different thermal profiles. The salient features of the Archean amphibolite-to-granulite transition in southern India have been recently summarized. The observed metamorphic progression reflects increasing temperature and pressure. Conditions for the Phanerozoic amphibolite-to-granulite transition in the southern Appalachians were documented. The following sequence of prograde reactions was observed: kyanite = sillimanite, muscovite = sillimanite + K-feldspar, partial melting of pelites, and hornblende = orthopyroxene + clinopyroxene + garnet. The mineral compositions of low-variance assemblages in mafic and intermediate rocks are almost identical for the two granulite facies assemblages. In light of their different fluid regimes and possible mechanisms for heat flow augmentation, it seems surprising that these Archean and Phanerozoic granulite terranes were apparently metamorphosed under such similar conditions of pressure and temperature. Comparison with other terrains containing continuous amphibolite-to-granulite facies transitions will be necessary before this problem can be addressed.

Mcsween, Harry Y., Jr.↗

NASA NTRS1988

Thermal metamorphism

Most chondrites have experienced thermal metamorphism, resulting in changes in texture, mineralogy and possibly chemical composition. The physical conditions for metamorphism range from approximately 400 to 1000 C at low lithostatic pressure. Metamorphism may have resulted from decay of short-lived radionuclides, electromagnetic induction or accretion of hot materials. Several thermal models for chondrite parent bodies have been proposed. The least metamorphosed type-3 chondrites probably carry the most information about the early solar system, but even these have been affected to some degree by thermal processing.

Mcsween, Harry Y., Jr.↗

NASA NTRS1988

Aqueous alteration

In previous considerations of the effects that postaccretional heating can have on the record of nebular processes contained in meteorites, heat was not the only agent of alteration; of even greater importance in the evolution of some of the most compositionally primitive meteorites was the chemical reactivity of water at relatively low temperatures. Present knowledge of the nature of aqueous-alteration products in meteorites has improved to the point where the course of such alteration processes can be modeled. Isotopic studies show that at least some of this alteration took place very early in solar-system history.

Zolensky, Michael↗

NASA NTRS1987

Aqueous alteration in carbonaceous chondrites - Mass balance constraints on matrix mineralogy

Bulk chemical compositions of matrix material were determined in eleven Antarctic CM chondrites and five non-Antarctic CM and CI chondrites, using microprobe defocused-beam technique. The results, along with previously published data, are used to provide mass balance constraints on the relative proportions of intergrown and intermixed phyllosilicate phases in carbonaceous chondrite matrices. In terms of Fe, Si, and Mg, the CM matrix bulk compositions plot within a triangle defined by the compositions of PCP (a mixture of 25 percent tochilinite and 75 percent cronstedtite), Mg-rich serpentine, and Fe-rich serpentine. Results indicate differing amounts of PCP and serpentines in individual CM matrices. The discrepancies found between predicted and measured S and Ni values require additional sulfide phases. CI matrices were found to contain little, if any, PCP; they consist mostly of serpentine and montmorillonite.

Mcsween, Harry Y., Jr.↗