Structure and Petrology of a Cumulus Norite Boulder Sampled by Apollo 17 in Taurus-Littrow Valley, the Moon

EVERETT D. JACKSON U.S. Geological Survey, Menlo Park, California 94025 ROBERT L. SUTTON U.S. Geological Survey, Flagstaff, Arizona 86001 HOWARD G. WILSHIRE U.S. Geological Survey, Menlo Park, California 94025

ABSTRACT grammatic nomenclature of Streckeisen and gabbroic composition. As yet, no system- others (Geotimes, 1973), and the cumulus atic study has been made of fragments of A glass-coated half-meter-size boulder nomenclature of Jackson (1967)1 will be rocks that have survived crushing, and in was sampled by the Apollo 17 crew at sta- used throughout. which original textures are at least partially tion 8 near the foot of the Sculptured Hills. Jackson (1971) had previously noted ex- preserved. The rock proved to be a coarse-grained amples of cumulates from among the lunar Of these, sample 15415, a thermally (0.5-cm) plagioclase-orthopyroxene cumu- rocks returned by the Apollo 11 and Apollo metamorphosed and partly shattered anor- late, and the samples are the only true nor- 12 missions (portions from samples 10084 thosite composed of more than 98 percent ites returned from the lunar surface. and 12057, respectively). The origin of the calcic plagioclase (Wilshire and others, Photographs of the boulder showed it to fine-grained Apollo 11 rock, which was 1972), was collected as a fragment in a contain at least nine structural surfaces and called a plagioclase-olivine cumulate (mi- breccia from the Apennine Mountain front. four glass veins. Orientation and inspection crogabbro) in Jackson's (1967) double This rock has an average grain size of about of three of the returned samples resulted in nomenclature systems, is not understood, 0.5 cm, and the maximum dimension of the identification of six surfaces and one although it texturally resembles a rock some plagioclase crystals is as much as 1.8 vein. One of the structural surfaces visible formed by crystal settling. The Apollo 12 cm. The texture of 15415, as viewed in in the boulder was identified as primary sample was a coarse-grained olivine- randomly cut thin sections, is neither cumulus planar lamination, which was pigeonite cumulate (olivine-gabbro) that clearly cumulus or noncumulus, in part be- folded through an angle of at least 35° be- appearedto be related to the main popula- cause of the lack of postcumulus phases tween two oriented samples, whereas frac- tion of Apollo 12 olivine and pigeonite other than plagioclase (Vernon, 1970). In ture sets representing the other surfaces phyric basalts. hand sample, the rock appeared to us to were coincident. The boulder is believed to Wilshire and Jackson (1972) pointed out have a planar lamination, but oriented slabs be a sample of the deeper highlands or that rocks called "dunites," "pyroxenites," of the sample were not cut for thin sections. submare lunar crust, derived from a depth and "anorthosites" by a number of authors A small relict of a clast in Apollo 16 sample of 8 to 30 km and somewhat shock- (Wood and others, 1970; Marvin, 1973) in 67435, with an average grain size of about metamorphosed during at least two excava- the Apollo 14 samples were simply single 0.1 cm (Prinz and others, 1973a) may also tion events. The chemical composition of recrystallized mineral grains, disaggregated be a cumulate with original textures pre- the norites, when determined, should be of from rocks that were dominantly served, and indeed, some similar rocks ap- special interest in view of the large amount feldspathic and whose grain size ranged up pear to be included among the Apollo 16 of literature concerning glass, cataclasite, to more than 1 cm. rake samples (Keil and others, 1972), espe- hornfels, and "basalt" of noritic composi- In retrospect, it would seem that no true cially some of the fragments from the LM tion returned by other Apollo missions. anorthosite (defined as a phanerocrystalline area and station 5 of that mission. At least However, the cumulus texture of the boul- rock in the sense of Holmes), no true norite, two examples of phanerocrystalline rocks der precludes its being representative of any and only one coarse-grained cumulate that appear to retain their original textures magmatic liquid composition, suggests that (olivine-gabbro, sample 12057, 20[9]) were collected by the Apollo 17 crew. Sam- the lunar crust is heterogeneously layered, closely associated with mare basalt (and ple 76535 is probably a deformed partially and that plagioclase sank, not floated, in almost undoubtedly composed of a packed recrystallized plagioclase-olivine cumulate magmatic liquids that formed the lunar collection of 0.3- to 0.4-cm-sized phenocryst with a small amount of postcumulus crust. Key words: Moon, cumulate, norite, minerals containing postcumulus plagio- clinopyroxene (Gooley and others, 1974; igneous, lunar crust, anorthosite, Apollo clase) had been returned from the moon be- Brown and others, 1974; Haskin and 17. fore the Apollo 15 mission. others, 1974; Wilshire, 1974). The rock has With the advent of Apollo 15, visits to an average grain size of about 0.5 cm and INTRODUCTION lunar highland scarps yielded an abundance would be classed as either a troctolite or an of coarse-grained rocks, metamorphosed in olivine gabbro by Streckeisen and others In the extended discussions of rocks that some degree, and most with anorthositic or (Geotimes, 1973). The rock appeared might represent samples of the primordial among the fragments of a rake sample from the North Massif (station 6), but there was lunar crust, the terms "anorthosite," "nor- 1 In this nomenclature, a cumulus crystal is a crystal ite," "cumulate," and other like words (mineral) that came into existence outside of and prior no description of the individual fragment have been used in widely different ways by to the magmatic sediment of which it now forms a part. when it was collected on the lunar surface. Postcumulus material is primary material that formed in Another relatively undamaged phanero- different authors. In this paper, the rock the places it now occupies in the magmatic sediment, as definitions of Holmes (1928), the dia- a "cement" between cumulus grains. crystalline rock was collected by the Apollo

Geological Society of America Bulletin, v. 86, p. 433-442, 10 figs., April 1975, Doc. no. 50401.

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17 crew at station 8, at the base of the tinued, "This looks like maskelynite or at boulder, it was again photographed, this Sculptured Hills (ALGIT,2 1973a, 1973b). least blue-grey plagioclase, and a very — time by Astronaut Cernan (see Figs. 1A and It was also identified and described by the let's say light yellow-tan mineral, probably 2). Four chips were collected from the top crew, and it is the subject of this paper. orthopyroxene. It's fairly coarsely crystal- side of the norite boulder. These were as- line" (ALGIT, 1973a, p. 293). As labora- signed the LRL numbers 78235 through GEOLOGIC SETTING OF tory examination showed later, this was a 78238; however, during sample orientation THE BOULDER very accurate field description! studies (see Appendix), two of the frag- Sampling of the boulder proceeded as fol- ments were fitted together, thus eliminating Station 8, visited during the Apollo 17 lows: after climbing uphill to the rock, lo- number 78237 and changing it to 78235,2. third EVA, was located about 4 km north- cated on a 10° slope east-northeast from the The original 78235 became 78235,0. Sam- east of the LM, at the base of the Sculptured Rover, Schmitt first described the rock and ple 78238, although not fitted successfully Hills. Although the steeper (25° ±), upper then photographed it in place (NASA to 78235,0 or to 78235,2, is believed to reaches of the Sculptured Hills are among the highlands surrounding Taurus-Littrow valley, they differ from the North and South Massifs in that they appear to be more heav- ily pocked by craters, more hummocky, and more markedly lineated; they also appear to be less rocky and are a shade of gray in- termediate between the dark mantle and the massifs. Station 8 was only about 20 m above the valley floor and within the zone mapped as dark mantle in detailed pre- mission maps (Wolfe and Freeman, 1972; Lucchitta, 1972). Small cohesive clods and coherent rock fragments were common in the station area, but larger rocks and boulders were rare. With the exception of the one glass-coated norite boulder, all other rocks larger than about 20 cm examined by the crew resem- bled subfloor basalt (ALGIT, 1973a, 1973b). The crew's attention was immediately at- tracted to the norite boulder, even though it lay 50 m uphill from the Rover, because the boulder was perched on the surface, in con- trast to all other rocks larger than about 10 to 20 cm in the immediate area, which were partially buried. The fact that it was perched was interpreted by Astronaut Schmitt to mean that the rock had arrived there quite recently. In addition, the absence of a boulder track and the presence of a glass coating suggested to Schmitt that the rock was probably exotic, having been thrown into the area by impact. However, the relationship of the rock to the higher part of the Sculptured Hills is not known. The morphology and color of the Sculp- tured Hills certainly suggest that the underlying rock type may be different from the North and South Massifs, where breccias were sampled. The norite boulder was described by Figure 1A. Station 8 norite boulder before sampling. The entire boulder is coated by 1 mm to 2 cm Schmitt, before he rolled and sampled it, as of black vesicular glass. NASA photograph AS17-146-22369. "a big chunk of shattered, but still visible, bluish-grey anorthosite . . . glass coated, photographs AS17-142-21698-21703). come from an adjacent part of the boulder and it actually looks vesicular." (from the He then rolled the boulder, measuring 30 x (see Figs. 2 and 3). Sample 78236 was taken NASA Apollo 17 Technical Air-to-Ground 55 x 55 cm, downslope. The tabular rock from the south edge of the boulder's top Voice Transcription, NASA Informal Rept. made four complete (360°) flips, stopping side (Figs. 1 through 3). The post-sampling No. MSC-07629, in ALGIT, 1973 a, p. with the original top side up. The size of the photograph is shown in Figure 3. 291). After he sampled it, Schmitt con- boulder and the angle of the slope on which Another sample, comprising two pieces it rested were determined by Raymond Jor- fitted together as 78255 (see Apollo 17 dan, U.S. Geological Survey, using an Lunar Sample Information Catalog; origi- 2 ALGIT is the acronym for the Apollo Lunar Geol- ogy Investigation Team, of which all three authors were OMI/AP/C analytical plotter. nally these were numbered 78255 and members. Before samples were chipped from the 78256), was taken from the underside of

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the boulder after overturning it again. This hoped that by mapping the surfaces we nearly at right angles to structural surfaces. sample, however, is not included in our could identify them by orientation of the re- For example, the pole of V3 lies at almost study, because it was not located or turned samples. To this end, we estimated 90° to S3. The pole of VI lies at 90° to S7. oriented with respect to its place of origin the distance from the camera lens to the The poles of V2 and V4 lie not only at on the boulder. boulder at 1 to 1.5 m and used a perspec- nearly 90° to one another, but also to the tive grid and a protractor to estimate strikes structural surface complex Sla-Slb. This STRUCTURES IN THE BOULDER and dips of the structural surfaces to the relationship between sheeting and tensile nearest 5 degrees. fractures has been noted in materials Stereoscopic examination of the boulder The most pronounced feature of the shocked during terrestrial impact events photographs revealed at least nine struc- boulder is the closely spaced sheeting (SIa, (see Fig. 5). tural surfaces of unknown origin and at Sib) that strikes northeast and dips north- least four double-walled vesicular, some- west. In following this structure across the TEXTURES AND STRUCTURES what branching glass veins (see Figs. 1A boulder, we found it strongly bent in a few IN THE SAMPLES and IB).3 A number of these structures places, possibly by S9 (see Figs. 1A and IB), could also be observed in the photograph but also variable. As a result, we plotted Inasmuch as only three samples [78235,0; 78235,2 (combined); and 78236] were successfully oriented on the boulder from which they were taken, our attention was directed to them. However, all of the boulder samples were carefully studied by us in the Lunar Receiving Laboratory. In addition to the NASA or- thogonal and stereoscopic photographs of the samples, we photographed the samples in various orientations, including their lunar orientation under simulated lunar lighting conditions (see Appendix 1).

Petrographic Descriptions of the Samples

Hand-specimen examination of all the samples (78235,0; 78235,2; 78236; and 78238) from the top of the boulder, and sample 78255 from the bottom of the boulder, showed them to be plagioclase- orthopyroxene cumulates (norites). Most of the postcumulus material also consists of plagioclase and orthopyroxene, but a small amount of bright-green postcumulus clinopyroxene can be seen in most samples. Cumulus orthopyroxene is tabular, and generally ranges in size from 0.2 cm by 0.3 cm to 0.5 by 0.7 cm, and averages about 0.3 by 0.4 cm in the a-c or b-c crystallo- graphy planes. Cumulus plagioclase tends to be a little larger, ranging from 0.3 by 0.4 cm to 0.7 by 1.0 cm and averaging about 0.4 by 0.5 cm in the a-c or b-c planes. In both minerals, a-b sections seem nearly Figure IB. Overlay sketch of Figure 1A. Figure shows gnomon, gnomon shadow, and true lunar equidimensional. Both minerals were found north. SI through S9 are surfaces observed in the boulder through its glass coating. VI through V4 are to be partially shattered, and much of the glass veins. These features are described in the text. Positions from which samples 78235,0; 78235,2; plagioclase was glassy and obviously con- and 78236 were later removed are also shown. verted to maskelynite. Our estimates of the relative proportions of orthopyroxene and taken after sampling (see Fig. 3). None Sla as its most northerly striking and shal- plagioclase ranged between 60 percent or- of the nine structural surfaces could be lowest dipping variant, and Sib as its more thopyroxene to 40 percent plagioclase and interpreted with confidence as either lam- easterly and more steeply dipping variant. 60 percent plagioclase to 40 percent or- ination, foliation, sheeting, or fracture The structural surfaces and glass veins, as thopyroxene, but averaged about 50-50. planes through the glass coating, and we we identified them, are shown in Figures IB Green clinopyroxene is invariably rare, and and 3, tabulated in Table 1, and plotted in opaque minerals, one type occurring within the orthopyroxene and the other a post- 3 stereographic projections (Fig. 4), as great The structurai surfaces were numbered SI through cumulus phase, form less than 0.1 percent S9 in the order in which they came to our attention dur- circles rather than as poles. ing the boulder mapping; they were not renumbered in The S structural surfaces appear, for the of the rocks. All samples are partially order of age sequences to avoid introducing errors into most part, to be conjugate fracture systems coated with vesicular black glass which, in the simultaneously made maps and nets. Our opinion of one sample (78235,0), connects directly the relative ages of the surfaces is given in the text of a type well known in subcrater shocked below. The same is true of the veins, which were num- rocks (Moore, 1969). It is interesting to with glass that veins the rock (Fig. 6). In bered VI through V4. note also that the identifiable veins are some rocks, vein glass could be observed in-

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and reconstructed modes were made of both sections (Table 2). Surprisingly, the plagioclase/plagioclase-plus-orthopyroxene (X100) ratios of both rocks were in the range 67 to 70, considerably higher than visual estimates in all the hand samples. It is not known whether the thin sections are representative of the rock as a whole, whether the visual estimates were biased toward the darker mineral, or whether the boulder is modally heterogeneous.

Structures in Oriented Samples

We are able to recognize five structural surfaces in oriented samples 78235,0 and 78235,2 and three surfaces in sample 78236. For example, in 78235,0 and 78235,2 (combined), the prominent vein VI could be seen plainly both on the after sampling photograph (Fig. 3) and on the samples as fitted together (see Fig. 6 for a part of this vein). Sla and Sib proved to be a closely spaced set of fractures, somewhat variable in both strike and dip. S4 and S7 are conjugate fracture sets. S5, however, proved to be the planar lamination typical of cumulates with non-equidimensional minerals (Jackson, 1961). Planar lamination was best developed in sample 78236, and its attitude corresponded to S8 on the boulder. Table 3 shows the attitudes of all structural surfaces in the three oriented samples from the top of the boulder. The planar attitudes are plotted as great circles on Figure Figure 2. Locations and orientations of samples 78235,0; 78235,2; 78236; and probable location 9. The poles to the structural surfaces of of 78238, chipped from top of station 8 boulder. Fluted surface is glass coated, and some fragments both the boulder and of the returned and broke along glass veins. NASA photograph AS17-146-22370; inset photographs are, top to bottom: oriented samples are shown in Figure 10. S-73-17816, S-73-17962, and S-73-17814. Modified from ALGIT, 1973b, p. 88. It is apparent from inspection of Figure 10 that the surfaces of the samples match those in the boulder within the limits of our trading fracture sets, indicating that at least which, unfortunately, is not one of the error (±5° for both the boulder and the some fracturing predated veining. The oriented samples but is one of which the samples). The surprising feature of the composition of the glass has not yet been presence of planar lamination can be clearly diagram is that is suggests that the planar determined, and therefore we are not able seen. Figures 7A and 8A are mosaics of lamination, which is ordinarily in cumu- to say whether the norite boulder was par- plane-light photomicrographs of thin sec- lates a horizontal, gravity-controlled fea- tially melted or the glass injected from an tions 78238,7 and 78238,9 with overlays ture, has been rotated at least 30° between external source. Figure 6 shows a vein (VI) (Figs. 7B and 8B) showing their morphol- two of the sampled localities. A recheck of intruding a prominent set of fractures in ogy and identity of their included minerals. the boulder photograph and map (Figs. 1A sample 78235,0. On the other hand, some Unfortunately, a vein of crushed material and IB) suggests that this is indeed the case. fracture sets appear to postdate the glass bonded by tan glass cuts both sections. Inasmuch as the poles of the fractures and veins. Zap pits, reflecting micrometeorite Nevertheless, the cumulus texture of the vein coincide, it is apparent that the planar impacts and averaging about 0.5 mm in rock is preserved on either side of the vein. lamination was folded before the shock diameter, are present on the glassy surface Cumulus and postcuniulus phases are event (or events) that is recorded by the of all samples, and their abundance (5 to 25 identified on the overlays where they are mapped fracture surfaces and the veins. 2 per cm ) is about equal on samples collected clearly distinguishable, but it is of course To our knowledge, we did not see surface from both top and bottom of the boulder, realized that both cumulus plagioclase and S2, S6, or S9 in any of the oriented samples. indicating that the rock had been rotated at orthopyroxene contain some postcumulus However, it appears reasonable that S6 is least once, and that the top and bottom had overgrowth material on their outer rims coincident with S8, which is the planar been exposed for about equal lengths of that cannot be identified in thin sections lamination in sample 78236. time. Keith and others (1974) give exposure due to lack of zoning. Although we were ages for the boulder of about .75 m.y. unable to orient sample 78238 on the boul- PETROLOGY At the time of writing, only two thin sec- der with assurance, the thin sections were tions of these rocks have been examined by cut parallel to side B, of the sample, and The formation of ultramafic and gab- us. The sections are sequential cuts from a what appears to be the trace of a planar broic rocks by the gravitative accumulation 1-gram chip removed from sample 78238, lamination occurs in both sections. Modes of early liquidus precipitates from magmas

TABLE 1. ATTITUDES OF STRUCTURAL SURFACES AND VEINS ON THE BOULDER AT STATION 8

Strike Dip

Sla N. 20° E. 40° NW. Sib N. 30° E. 50° NW. S2 N. 75° E. 55° SM. S3 N. 50° E. 15° SE. S4 N. 60° W. vertical S5 N. 50° E. 80° SE. SG N. 70° E. 40° SE. S7 N. 40° W. 40° NE. S8 N. 70° E. 55° SE. S9 N. 35° E. 70° NW. VI N. 70° W. 65° SW. V 2 N. 20° U. 60° NE. V3 N.-S. vertical V4 N. 70° E. 60° SE.

* 1—i-J .. 8

Figure 4. Stereographic projection of surfaces (SI through S9) and glass veins (V1-V4) mea- sured on stereographic surface photographs of the station 8 boulder in its final resting position after rolling. Surfaces shown as solid lines, veins as dashed lines. Hachured area shows variation in the SI structural surface. Wulff projection, lower hemisphere.

that occur in stable shields, such as the Figure 3 A. Station 8 norite boulder after sampling. Dust now covers much of its surface. Gnomon Stillwater, Bushveld, and Great Dyke; (3) and scoop are visible in the photograph. Scoop indicates location of removed sample 78236. Note scar those associated with ophiolite complexes; left after removal of 78235,0; 78235,2; 78238; and two stray chips (not returned). NASA photograph AS17-147—22371. Overlay sketch shows scoop, gnomon, gnomon shadow, and true lunar north. and (4) those formed in the magma cham- SI, S5, and S7 are surfaces observed on the boulder and recognized on the oriented samples 78235,0 bers of certain individual volcanoes. Jack- and 78235,2 (combined). VI is a glass vein 1 to 2 mm thick used for identity in relating samples to son (1971) and Jackson and Thayer (1972) boulder surfaces. See text for further details. The probable location of removed sample 78238 is also presented evidence that cumulus processes shown, although sample orientation is not known. Two stray chips flew off during hammering and were important in the formation of the ear- were not retrieved. Sketch constructed from NASA photograph AS17-146—22371. liest terrestrial continental crust, and at the present time cumulates constitue a consid- erable proportion of the oceanic crust. is now one of the better understood proc- graphic position and composition corre- The depth of formation of the lunar esses in petrology. The order of appearance spond very closely to liquidus mineral se- cumulates are most likely comparable to of cumulus minerals, their chemical compo- quences and compositions determined ex- those of the Stillwater and Bushveld Com- sition, and the way in which their composi- perimentally in basaltic systems. At the plexes, which have projected thicknesses of tion changes with time reflect igneous proc- same time, the stratiform character of the about 8 km (Hess, 1960; Jackson, 1961); esses ultimately controlled by the composi- layers in the great layered intrusions, and this would certainly be a minimum depth tion and depth of crystallization of their the packing density, shape, sorting, and for the formation of the norite boulder. parent magmas. The texture and structure orientation of the cumulus crystals that Gooley and others (1974) contend that of the cumulus pile that is built as liquidus make up the layers correspond to the sample 76535, discussed above, cooled at crystallization proceeds, on the other hand, dynamic behavior expected of particles depths between 10 and 30 km beneath the reflect sedimentary processes ultimately suspended and deposited in moderately vis- lunar surface. controlled by gravity, hydraulic parameters cous magmas in a gravity field. Inasmuch as the Moon is not a dynamic of the magmas, and the presence or absence Jackson and Thayer (1972) divided ter- planet, and volcanic landforms other than of currents. The ultramafic parts of the restrial stratiform rocks with cumulus tex- lava flows, though much discussed, were great stratiform layered intrusions of the tures into four types: (1) those that occur in not found during the Apollo missions, ter- Earth contain cumulus phases whose strati- Archean terranes; (2) those large complexes restrial analogs for the primordial lunar

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Figure 5. Sheared and compressed target material with grooves and striations on surface. Note open tension fractures intersecting shear surfaces at right angles. Target was gypsiferous alluvium at White Sands, New Mex- ico. Photograph by H. J. Moore.

Figure 6. View of broken face of sample 78235,0, showing vesicular vein connecting with surface glass coating, and intruding one prominent fracture set.

crust should be sought among Jackson and At this time, we prefer the hypothesis ing excavation or possibly during the same Thayer's (1972) groups one and two. that these few coarse-grained rocks repre- event as 4, producing the other conjugate It was proposed a number of years ago sent highland or submare crust of the type fracture sets, the glass veins, more maskely- that mare basins might be underlain by envisaged by Prinz and others (1973b), nite, and the glass coating. In any event, Sla layered intrusions which would be expected Brett (1973), and Walker and others and Sib appear to be offset or bent by S9. to have cumulus textures (Lowman, 1963; (1973), which has been reported to have a 6. At rest at an unknown location for Shoemaker and others, 1968). More re- seismic velocity in the range of 6.3 to 7.0 about .75 m.y., with its bottom up, receiv- cently, Biggar and others (1972) have km/sec (Nakamura and others, 1973), and ing micrometeorite impacts into its glass amplified their opinion on the kinds of that, if they have terrestrial analogs, these coating. layered rocks that might be found in the rocks have been found among the rocks of 7. Movement to its discovery site at sta- lower parts of mare lava lakes. Jackson and Thayer's groups one or two — tion 8, where it has rested, with its top side In the absence of whole-rock chemical among the most ancient rocks on Earth. up, for an amount of time approximately compositions, or even mineral chemical equal to that at its former site. compositions of samples from the norite A SUGGESTED HISTORY OF THE 8. Rolling and sampling by the Apollo boulder, it is difficult to discuss the possibil- NORITE BOULDER 17 crew. ity that such rocks could be cumulates from the lower part of the mare basins. If they The history of the station 8 boulder, as DISCUSSION AND CONCLUSIONS are, exceedingly complicated fractionation best we know it, is as follows: schemes are required; for no mare basalt, 1. Crystallization from a magma, with The source of the station 8 norite boulder from any Apollo mission, has contained both plagioclase and orthopyroxene on the remains a problem. Its glass veins, glass plagioclase feldspar phenocrysts or shown liquidus. The grain size and texture argue coating, and striations indicate that it was other evidence of having plagioclase on the that the depth of crystallization was at least ejected in a manner analogous to that pro- liquidus. Indeed, if the plagioclase- 8 km, and perhaps as much as 30 km. duced experimentally by Shoemaker and orthopyroxene cumulates were formed 2. Settling of the plagioclase and or- others (1963), and that the boulder itself from a basaltic liquid chemically like the thopyroxene crystals onto a floored was, at one time, a projectile. On the other lower chilled margin of the Stillwater Com- chamber under the influence of lunar grav- hand, its setting, when found, suggests that plex (Jackson, 1971), subtraction calcula- ity. its last movement was not a hypervelocity tions indicate that the AI203 content of the 3. Folding of the planar lamination by impact and that its former site was not far liquid, originally 15.8 percent, rose to more an unknown process, possibly an irregular distant. It seems unlikely that it is a clast than 17.5 percent before plagioclase ap- magma chamber floor. from the breccias sampled at the North and peared with orthopyroxene in the liquidus. 4. Shock metamorphism, producing South Massifs; not only is it larger than No mare basalt is known that contains this maskelynite and fracture sets Sla and Sib. most clasts observed there, but there is no amount of A1203. 5. Shock metamorphism, possibly dur- trace of matrix adhering to the boulder.

Figure 7A. Mosaic photomicrograph of thin section 78238,7. Plane light. A zone of partially vitrified crushed material runs vertically through section, roughly parallel to the planar lamination. Very dark material is Figure 7B. Overlay of Figure 7A. Hachured area labeled V is partially glass. Dark material is orthopyroxene. Light material is plagioclase, about vitrified crushed material, cp = cumulus plagioclase; co = cumulus or- 80 percent converted to maskelynite. Light gray areas in light material con- thopyroxene; po = postcumulus orthopyroxene; pp = postcumulus sist of unaltered plagioclase, very white material is maskelynite. Note that plagioclase. Vertical line shows the probable trace of planar lamination. For maskelynite is concentrated near vein. mode of thin section, see Table 2.

The rock may be exotic to the area, as the 76255) in the South and North Massif 15415) appear to have undergone thermal Apollo 17 crew suggested, but we must still breccias could be cataclasite formed from metamorphism of a type that differs from entertain the possibility that it came from, rocks associated with the same suite as the that produced by ejection from craters and may be representative of, material of norite boulder. Third, the norite boulder (Wilshire and others, 1972, 1973). The Sculptured Hills. There are several reasons provides the only large example of nonmare primary cumulus planar lamination of the for believing in this possibility. First, the material recognized by the crew at station Apollo 17 norite boulder appears to have morphology of the Sculptured Hills sug- 8. No boulder track was visible, but the been folded prior to shock metamorphism. gests an underlying rock type that is rela- boulder could have come from above by a Hence, these rocks are likely to be samples of tively soft or friable compared to breccias series of bounces. the deeper lunar crust exposed as a result of of the North and South Massifs. Second, The coarse grain size and cumulus nature a major, basin-forming event. If this is so, the rock type is not entirely foreign to the of the norite boulder, as well as the handful and if these rocks formed as cumulates, ter- area. The plagioclase-olivine cumulate of other coarse-grained gabbroic rocks restrial experience leads us to expect ex- (76535) found in the station 6 rake sample found on Apollo 15, 16, and 17 missions, treme heterogeneity in bulk rock composi- indicates a community of origin, and a are rocks which no doubt formed at some tions of individual layers. number of clasts (for example, 72415 or depth in the lunar crust. Some (for example, The exceedingly confusing use of terms

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I cm Figure 8A. Mosaic photomicrograph of thin section 78238,9. Plane I light. A zone of partially vitrified crushed material runs vertically through section, roughly parallel to the planar lamination. Very dark material is Figure 8B. Overlay of Figure 8A. Hachured area labeled V is partially glass. Dark material is orthopyroxene. Light material is plagioclase, about vitrified crushed material, cp = cumulus plagioclase; co = cumulus or- 80 percent converted to maskelynite. Light gray areas in light material con- thopyroxene; po = postcumulus orthopyroxene; pp = postcumulus sist of unaltered plagioclase; very white material is maskelynite. Note that plagioclase. Vertical line shows the probable trace of planar lamination. For maskelynite is concentrated near vein. mode of thin section, see Table 2.

TABLE 3. ATTITUDES OF STRUCTURAL SURFACES IN ORIENTED SAMPLES TABLE 2. MODES OF THIN SECTIONS* COLLECTED FROM THE NORITE BOULDER

Modest Reconstructed modes Description Identified Attitude of surface Divergence from of surface surface In oriented sample boulder map 78238,7 78238,9 78233,7 78238,9 orientation W M (*) .(*>

co = cumulus orthopyroxene 18.1 18.0 23.1 25.0 Samples ?8335,0 and 78225,2 cp = cumulus plagioclase 50.7 44.8 64.4 62.2 Irregular, closely Sia* N. 10° E. 35° NW. 6° po = postcumulus orthopyroxene 5.7 6.0 7.3 8.4 spaced fractures Sib* N. 30° E. 40° NW. 9° pp = postcumulus plagioclase 4.1 3.2 5.2 4.4 Fracture set S4* N. 55° H. 80° SW. 10° 0.7 0.8 g = glass Planar lamination S5* N. 40° E. vertical 12° v = crushed orthopyroxene Fracture set S7* N. 35° M. 40° NE. 4° plagioclase and tan glass 20.7 27.2

opaque minerals <1.1 <0.1 •0.1 <0.1 Sample 78236

postcumulus cllnopyroxene <0.1 <0.1 <0.1 Irregular, closely spaced fractures Slb+ N. 40° E. 50° NW. 8° Total 100.0 100.0 100.0 100.0 Fracture set S7+ N. 45° W. 45° NE. 6° Ratio of plagloclase/plagioclase + orthopyroxene (x 100) 69.6 66.6 Planar lamination S8+ N. 70° E. 50° SE. 4°

* See Figures 7B and 8B. * Surfaces Identified In sample 78235,0 and 78235,2 (combined),

t Total counts 78238,7 = 9,500; 78238,9 = 6,275. t Surfaces identified 1n sample 78236.

Figure 9. Stereographic projection of structural surfaces and vein in re- Figure 10. Stereographic projection of poles of both structural surfaces turned lunar samples 78235,0; 78235,2; and 78236 after orientation in (solid circles) and veins (dashed circles) from the station 8 boulder and the lunar surface positions. Surfaces shown as solid lines, vein as dashed line. oriented samples retrieved from it. One plus following a sample indicates Surfaces with one plus (for example, S5+) from samples 78235,0 and samples 78235,0 and 78235,2. Two plusses indicate sample 78236. Poles 78235,2. Surfaces with two plusses from sample 78236. Wulff projection, believed to be coincident are connected by dashed lines. Numbers in degrees lower hemisphere. indicate angular error. Wulff projection, lower hemisphere.

like highland basalt, high-alumina basalt, samples indicate that plagioclase was more ends is presumably the place from which KREEP basalt, KREEP glass, ANT group, dense than its parental liquid, very much as fragment 78238 was removed, although the PST group, and so on (Hubbard and others, it is known to be in terrestrial cumulates. pieces have not been fitted together in the 1971; Wood, 1972; Meyer, 1972; Prinz laboratory. This interpretation is more re- and others, 1973b; Reid and others, 1973; ACKNOWLEDGMENTS cent and different from the one pictured in Walker and others, 1973; Kushiro and ALGIT (1973b). others, 1973) to refer to a suite of rocks We thank our colleagues Henry J. Moore We have used a small lettered cube (0.3 with widely differing grain size and texture, and George E. Ulrich of the U.S. Geological cm3) in the orientation photographs to and which have in common only a "norit- Survey for critically reviewing this manu- show how the oriented views correlate with ic" composition, has only muddied the script. We also thank M. C. Gilbert of Vir- documentary LRL photographs ("mug- waters of nomenclature. The plagioclase- ginia Polytechnic Institute for his very help- shots") of the same samples using the same orthopyroxene cumulate boulder sampled ful comments. cube. Directions indicated on the cube do at station 8 on the Apollo 17 mission is the not necessarily correspond to lunar direc- first true norite found and sampled on the APPENDIX 1. SAMPLE tions. Shadows do indicate lunar direction, lunar surface. It should, therefore, be ORIENTATIONS however; and at the time that station 8 was analyzed to provide the standard of com- visited, the Sun's azimuth was 108°, thus parison for lunar "noritic" liquid composi- The lunar orientation of samples producing a shadow direction of N. 72°W. tions. Its cumulus texture, on the other 78235,0; 78235,2 (combined); and 78236 hand, precludes the idea that it ever existed on the boulder from which they came was REFERENCES CITED as a liquid and further suggests a hetero- determined by correlating the pre-sampling geneously layered primordial crust, later lunar-surface photographs with shapes and Apollo Lunar Geology Investigation Team, homogenized, in part, by great basin- shadow characteristics of the samples in the 1973a, Documentation and environment of forming events. Lunar Receiving Laboratory under oblique the Apollo 17 samples — A preliminary re- Finally, we wish to emphasize that mod- illumination with nearly collimated light. port: U.S. Geol. Survey Open-File Rept., els of large-scale differentiation of the lunar The light source in the laboratory simulated 332 p. crust (Wood and others, 1970; Smith and the Sun. Figure 2 illustrates our restoration 1973b, Preliminary geologic analysis of the others, 1970; Wood, 1974) in which of samples onto the boulder (after ALGIT, Apollo 17 site: U.S. Geol. Survey Open-File plagioclase is reputedly floated upward to 1973b, p. 88). Comparison of Figure 2 with Rept., 210 p. form the primordial lunar crust receive little the postsampling photograph, Figure 3, Biggar, G. M., O'Hara, M. J., Humphries, D. J., and Peckett, A., 1972, Maria lavas, mas- support from the coarsely crystalline rocks shows that in the fresh scar left by the re- cons, layered complexes, achondrites and moval of 78235,0 and 78235,2 (combined) returned from the Moon. The textures of the lunar mantle, in Runcorn, S. K., and the station 8 boulder and the close associa- the trace of a glass veinlet (VI) shows up Urey, H. C., eds., The Moon: Internat. As- tion of olivine or orthopyroxene with clearly. An extension of the scarred area to tron. Union Symposium No. 47, p. plagioclase in other coarse-grained lunar the right of where the veinlet apparently 129-164.

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Sci., v. 261, p. 668-682. REVISED MANUSCRIPT RECEIVED JULY 24, 1974

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