77215 Cataclastic Norite 846.4 G; Largest Piece Is 6.5 X 4.5 X 2.5 Cm (41 Or More Pieces)

SAMPLE 77215 - 283 77215 Cataclastic Norite 846.4 g; largest piece is 6.5 x 4.5 x 2.5 cm (41 or more pieces) INTRODUCTION and stretched or smeared out to form PETROGRAPHY schlieren, so that the relict host rock Sample 77215 was sampled from the types are only represented by very Sample 77215 is a pristine norite large white clast in the Station 7 small clasts (Chao et al., 1976). This that has been shocked and crushed Boulder (see the section on the made consortium work very difficult in place. It contains lithic Station 7 Boulder, page 235). It was to coordinate because samples fragments of "norite" and apparent quite friable and broke up into many representative of the major lithic "anorthosite" set in a porous mass pieces on the way back from the clasts in 77215 were generally too of fine mineral fragments and thin Moon (Fig. 1). One of the pieces small for allocation to all consortium glass veins (Fig. 5). The modal (,19, now 80,81 and 82) contains the members (Minkin et al., 1978). mineralogy is approximately 41% dark dike similar to 77075 (Fig. 2) Selected subsamples were therefore orthopyroxene and 54% and other pieces contain black assigned to individual consortium plagioclase with trace amounts of dikelets (similar to 77077). Some participants for analysis on the basis troilite, ilmenite, clinopyroxene, pieces have small areas of of suitability for their experiments, spine], silica, K-feldspar, unbrecciated norite with primary and the resulting data cannot now be zirconolite, whitlockite, and Fe-Co igneous texture (Fig. 3). The large exactly correlated for this sample as metal (Table 1). The fragments of cataclastic -"norite" sample may a whole (as is sometimes done). In "anorthosite" may be plagioclase- itself contain other clasts of similar general, the whole sample seems to rich regions within the original igneous material (Fig. 4). Most of be one material, but care should be norite (Chao et al., 1976). the lithic clasts in 77215 have been exercised because of the cataclastic crushed and fractured, and some nature of the sample. have been intensely granulated Figure 1: Tray full of 77215. Note that some pieces have "off-white" patina. S73-17778. SAMPLE 77215-284 Figure 2: Photograph of sawn surfaces of slab and butt ends of 77215,19. Cube is I cm. S75-21992. Figure 3: Photograph of 77215,16, showing igneous textures of some regions in the rock. Cube is 1 cm. S83-34595. SAMPLE 77215-285 Figure 4: Photograph of saw cut through 77215,92. 575-21980. Scale bar is in cm. Figure 5: Photomicrograph of thin section 77215,12. Field of view is 4 x 5 mm. According to Chao et al. (1976), has a narrow compositional range also has a narrow compositional the original uncrushed norite is (An 88-92 Ab11-7 Or1), mostly range (Wo3-5En63-68Fs29-32), The medium-to coarse-grained (up to 3 An90-91. Plagioclase grains orthopyroxene in 77215 is notable mm, with an average of about 1 frequently contain small inclusions for having well-developed, yet nun) and has a holocrystalline of K-feldspar (An2 Ab1 Or 97), texturally diverse, augite blebs and igneous texture. Its principal silica, and granitic glass. The lamellae (Wo41-43En44-47Fs12-13). assemblage consists of plagioclase is not chemically Huebner et al. (1975) distinguish idiomorphic greenish-yellow zoned and has not been converted these blebs as "worms, planes, orthopyroxene and clear to milky to maskelynite by the shock hachures, and septa." Within a white calcie plagioclase. The pressure. The orthopyroxene plagioclase SAMPLE 77215-286 single orthopyroxene, all augite is in Lindsley (1982) have carefully 77215. The plagioclase and pyrox- the same optical orientation, but this calculated the equilibrium temper- ene are uniform in composition does not seem to be crystallo- ature of the pyroxene pairs in 77215. (Fig. 7). graphically controlled. Augite lamellae are 5-10µm thick, rarely 30 The anorthite, orthopyroxene, and Winzer et al. (1977) report pm thick. The host and exsolved minor augite account for 97.35% of analyses of orthopyroxene and pyroxenes are optically and chemi- the norite. The rest, 2.7%, consists plagioclase mineral separates for cally homogeneous (Fig. 6). of mesostasis, with a variety of the white noritic portion of 77215 accessory minerals, that occurs in (Fig. 8). Papike et al. (1994) have Pyroxenes in 77215 show some of the interstitial areas between the also used the ion probe to the features of "inverted pigeonites." anorthite and orthopyroxene. K- determine the REE in Huebner et al. (1975) explain that feldspar with a fine network of thin orthopyroxene from 77215,203. the misoriented nature of the augite, silica lamellae is a common relative to the host orthopyroxene, is accessory mineral in these interstitial WHOLE-ROCK CHEMISTRY a common feature of pyroxenes that areas. Clusters of accessory minerals originally crystallized as homoge- occur in the norite clast and in the Winzer et al. (1974 and 1977) neous pigeonite crystals at high brecciated matrix. Fe-Co metal, report analyses of various portions temperatures. According to Huebner troilite, ilmenite, chromite, of the 77215 sample, including et al., coarse pyroxene exsolution plagioclase (An ), orthopyroxene 91-92 dikes, glass, and the white noritic lamellae can form in geologically (Wo En Fs ), silica, rare 4 64-72 24-32 material short periods of time (<30,000 yr.) at augite, whitiockite, zirconolite, and (Table 2 and Fig. 9). The grey elevated temperatures (>300 ° C. rare armalcolite occur in these glass appears to be melted norite, Huebner et al. argue that such condi- clusters. All these accessory phases while the black glass has been tions could have been met in the are thought to be from the parent injected from the surrounding upper levels of the lunar crust during norite (Chao et al., 1976). matrix. Wolf et al. (1979) report early lunar history as a consequence the trace siderophile and volatile of the cooling of anorthositic crustal MINERAL CHEMISTRY elements (Table 3). This rock is a material. According to Huebner et pristine norite. James (1994) has al., the exsolved pyroxenes do not Chao et al. (1974), Huebner et al. also reviewed the siderophile and necessarily suggest the deep-seated (1975), and Chao et al. (1976) report volatile element composition. origin as originally proposed by the compositions of the minerals in Chao et al. (1974). Anderson and Figure 6: Pyroxene composition for 77215 norite. From Huebner et al. (1975). SAMPLE 77215-287 Figure 7: Plagioclase and pyroxene composition of 77215. Fields from James and Flohr (1983). Figure 8: Normalized rare earth element diagram for whole rock and minerals in the noritic portion of 77215. Data from Winzer et al. (1977). SAMPLE 77215-288 Figure 9: Normalized rare earth element data for portions of 77215. Data from Winzer et al. (1977). The orthopyroxene within the clast 4.42 ± 0.04 b.y. and 4.37 ± 0.07 SIGNIFICANT CLASTS contains the exsolved augite. This b.y. respectively, for the bulk norite clast is probably a small sample 77215,37 (Figs. 12 and Chao et at. (1976) describe two sample of the source material for 13). This is one of the few pristine clasts (1 and 2) of least-shocked the breccia-a relict that escaped samples of the original crust that norite that they separated from granulation. have been dated! fragment 77215,22 and distributed for age dating. A thermal event must have heated RADIOGENIC ISOTOPES the noritic breccia at 3.98 Ky. Chao et al. (1976), Huebner et al. without disturbing the Rb-Sr and (1975), and Minkin et al. (1978) Stettler et al. (1978) separated Sm-Nd isotopic systems. This describe a region (or "clast") feldspar from clast 2 (sample,151) could have been the event that within 77215 that has highly from fragment 77215,22 and intruded the dike material and magnesian olivine grains (Fo ) obtained a well-defined 39Ar-4OAr 83-97 enclosed the norite clast in the and calcic plagioclase (An ). plateau age of 3.98 ± 0.03 to.y. 90-91 melt sheet represented by the (Fig. 10). This confirms the ages boulder matrix (samples 77115 Huebner et al. (1975) briefly of 3.96 to 4.05 b.y. (Fig. 11) and 77135), or it could have been describe a small clast in thin reported earlier based on mild heating throughout the time section 77215,13 that consists intetmediate temperature plateau span 3.9 to 4.4 b.y. entirely of orthopyroxene and from samples of crushed matrix plagioclase in equal proportions material (Stettler et al., 1974). Nunes et al. (1974) have also with a subophitic texture. The reported U-Th-Pb data for 77215 composition of the pyroxene and Nakamura et al. (1976) obtained (Table 6). This system has been plagioclase is the same as for the Rb-Sr and Sm-Nd data (Tables 4 disturbed. isolated grains and grain and 5) and internal isochrons of fragments observed elsewhere in the sample. SAMPLE 77215-289 Chao et al. (1976). Detailed COSMOGENIC PROCESSING description of the splits is given in RADIOISOTOPES AND open-file report 78-511. EXPOSURE AGES The initial processing and distribution of 77215 are outlined The largest pieces of 77215 that Stettler et al. (1974) determined an in Butler and Dealing (1974). It remain unprocessed are: ,18 (103 exposure age of 27.2 m.y. was studied by the international g); ,17 (101 g); ,21 (69 g); and ,22 consortium led by E.C.T. Chao (60 g). Twenty-five thin sections (see final report by Minkin et al., have been prepared. 1978). Some notes on the distribution of 77215 are given in the appendix to Figure 10: 39Ar-40Ar temperature release pattern for plagioclase from a norite clast in 77215.

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