RELATIONSHIP BETWEEN GEOLOGY AND GEOCHEMISTRY IN THE UNDARUM/ SPUMANS REGION, P.E. Clark, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, and B.R. Hawke, Hawaii Institute of Geophysics, University of Hawaii, Honolulu, HI, 96882.

INTRODUCTION. This paper represents a portion of the on-going work in the geochemical classification of the 1unar high1 ands (1,2,3,4). We continue to explore the relationship between photogeologically-defined units, petro- logical information, and a1 l avail able orbital geochemical data including A1/Si and Mg/Si ratios (4,5), Fe, Ti, and Th concentrations (6,7) as previ- ously done in the Hadley Apennine region (1,2). The Undarum/Spumans region has been selected for study as an example of a typical eastern limb terrain (8) for comparison with other more "anomalous" areas. Additionally, no in- depth geochemical studies have yet been pub1 ished for this area. The results of this study provide more insight into the relationship between geochemical and photogeological variations in the highlands. UNIT DEFINITION. The Undarum/Spumans region presents good correspon- dence between photogeological ly defined (8) and geochemical units. A few major types of units are apparent, as described below, and as seen in the Figure. Mare Units. Portions of Mare Crisium and Mare Fecunditatis are included in the study area, as well the mare deposits intermixed with highland terrain in the areas labeled and Mare Undarum. All of the mare areas show ranges of concentrations of A1 , Mg, Fey Ti and Th which indicate the presence of maria basal ts (1,Z). Spumans has the low aluminum concen- tration characteristic of typical maria . Undarum is somewhat more aluminous and somewhat less mafic probably indicating a greater proportion of intermixed ANT suite material. Smaller pockets of maria material throughout these approach the limit of spatial resolution of the XRF data in size; in the case of , Kastner G, and some craters of the Maclaurin series, these pockets have markedly mafic characteristics. Gilbert is also relatively high in Th (7). Plains Units. In most cases, these areas are equally evident on the geologic map used for this study (8) and, even though relatively small in size, in XRF data unit maps. A1 and Mg concentrations are typically low to moderate, and correlated. While concentrations of these two elements are indicative of Fra Mauro basalt (1,2), Th concentrations (7) are not dis- tinctively high, indicating that this material is not abundant.

Larger Craters. These include and La Perouse. Both are mapped as crater materials. These units are low in magnesium, wi-th marked variations in aluminum and are probably a mixture of rock types.

Partially Mantled Terra Units. The remainder of the region shows typical highland compositions (2,9), particularly in the northeastern portion of the region, where there is the least amount of mare contamination. The orbital geochemistry and photogeological data for this region are consistent with the presence of AN.T suite material in the highland terrain, and mare material, contaminated in some instances with highland debris, in

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P.E. Clark and B.R. Hawke

basins and ponds. While the moderate to low A1 and Mg values associated with some plains could be due to Fra Mauro basalt, the relatively low Th values suggest that Fra Mauro basalt is not abundant in the region.

This work was partially supported under NASA contract NAS 7-1000 at the Jet Propulsion Laboratory. The work was performed both at the University of Hawaii, and at the Jet Propulsion Laboratory.

REFERENCES Clark 3 P.E. and Hawke, B.R. (1981) Lunar and Planetary Science -XII, 155. Clark 3 P.E. and Hawke, B.R. (1981) Proc tun Plan Sci Conf 12th(in press). Hawke 9 B.R. et a1 . (1982) Lunar and Planetary Science XI11 (this volume) Clark y P.E. and Hawke, B .R. (1982) EOS (in press). Clark , P.E. et al. (1978) ~rdc~un Plan'sci' conf'gth, 3029, Davis P.A. (1980) JGR 85, 3209. Hai ne s E. e t a1 . (m8r~rocLun Plan Sci Conf 9th, 2985. Wi 1he lms, D .E. and El-Baz, F. (1977) U.S.G.S. 1-948. Andre , C.G. (1981) Proc Lun Plan Sci Conf 12A, 125.

GEOLOGICAL UNITS IN THE UNDARUM/SPUMANS REGION MARE 2 CRlSlUM

UNIT FEATURE MAJOR ROCK

F.M. BASALT CRATERS F.M. BASALTlANT 4 TERRA ANT

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