Engineering topics

Shirley, D. N.

Publications and source records attributed to Shirley, D. N..

5 records

NASA NTRS1986

A potpourri of pristine moon rocks, including a VHK mare basalt and a unique, augite-rich Apollo 17 anorthosite

The anorthosite fragment, 76504,18, the first of the Apollo 17's pristine anorthosites, was found to have: (1) a higher ratio of high-Ca pyroxine to low-Ca pyroxene, (2) higher Na in its plagioclase, (3) higher contents of incompatible elements, and (4) a higher Eu/Al ratio in comparison to ferroan anorthosites. With a parent melt having a negative Eu anomaly, 76504,18 closely resembles a typical mare basalt. This anorthosite was among the latest to be formed by plagioclase flotation above a primordial magmasphere; typical mare basalt regions accumulated at about the same time or even earlier. Another fragment 14181c, a very high potassium basalt, was studied and found to be similar to typical Apollo 14 mare basalt though it has a K/La ratio of 1050. It is suggested that this lithology formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderphile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination.

Warren, P. H.↗

NASA NTRS1983

Seventh Foray - Whitlockite-rich lithologies, a diopside-bearing troctolitic anorthosite, ferroan anorthosites, and KREEP

Seventeen nonmare samples, most of them pristine, are characterized, and implications of the new data are discussed. Five pristine samples are from Apollo 14, near the center of the KREEP-rich zone in the moon's western hemisphere. Three of them are alkali anorthosites rich in Ca-phosphate (whitlockite), which apparently crystallized from magmas with REE contents roughly 6 x those of high-K KREEP. The alkali anorthosites probably formed from Mg-rich magmas that assimilated large amounts of urKREEP, but some might have formed by metasomatism of ferroan anorthosite by urKREEP. The gabbronorite/norite classification scheme is not well suited to western hemisphere lithologies, probably due mainly to the overriding effects of longitude-petrochemistry correlations. A diopside-bearing Mg-rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic (high-Ca pyroxene-rich) Mg-rich magmas, and suggests that some source regions of Mg-rich magmas were relatively Ca-rich. Several pristine KREEP fragments from Apollo 15 station 2 are texturally and compositionally much like other pristine KREEP, and thus reinforce the evidence that KREEP is highly uniform. The pristine anorthosites, on the other hand, demonstrate further that lunar anorthosites are diverse.

Warren, P. H.↗

NASA NTRS1983

Petrology and chemistry of two 'large' granite clasts from the moon

Pristine granite clasts in Apollo-14 breccias 14321 and 14303 have estimated masses of 1.8 and 0.17 g, respectively. The 14321 clast is about 60 percent K-feldspar and 40 percent quartz, with traces of extremely Mg-poor mafic silicates and ilmenite. The 14303 clast is roughly 33 percent plagioclase, 32 percent K-feldspar, 23 percent quartz, 11 percent pyroxene, and 1 percent ilmenite; pyroxene and ilmenite are moderately Mg-rich; plagioclase and pyroxene are strongly zoned. Both clasts are severely brecciated, but monomict (pristine). Both have abundant graphic integrowths of K-feldspar with quartz. Unlike the majority of similar earth rocks, both clasts are devoid of hydrous phases. The bulk composition of the 14321 clast is similar to those of several other lunar granitic samples, but the 14303 clast is unique: it bears as close a resemblance to KREEP as it does to other lunar granites. Silicate liquid immiscibility may explain why the granites are low in REE relative to KREEP.

Warren, P. H.↗

NASA NTRS1983

A partially molten magma ocean model

Under the assumption that the outer 300-400 km of the moon was at first only partially, rather than fully molten, an explanation of the properties of the lunar crust and upper mantle is obtained according to which nuclei of anorthositic crust formed over localized bodies of magma segregated from the partial melt, and then grew peripherally until fully covering the moon. Over most of its growth period, the anorthosite crust floated on a layer of magma whose thickness was regulated by the opposing forces of (1) loss of material by fractional crystallization, and (2) addition of magma from the partial melt below. The clustering of Eu, Sr and Mg values found among pristine ferroan anorthosites are predicted by this model.

Shirley, D. N.↗

NASA NTRS1982

Mechanism for the extrusion of KREEP

The evolution of the final residue of the magma ocean from the time it entered the anorthositic crust until it was extruded is modeled. The magma density first increased as anorthite and orthopyroxene crystallized, but once ilmenite precipitation began the density dropped. The KREEPy magma collected beneath the thinnest parts of the anorthitic crust, and intruded the crust when the density dropped below that of the adjacent crustal materials. The nearly constant degree of incompatible element fractionation moon-wide was maintained because the rapid drop in density during ilmenite crystallization occurred after about the same degree of crystallization at all locations. The high viscosity of the final residue of the magma ocean and its low density contrast with the crust initially resulted in very slow migration through the crust.

Shirley, D. N.↗