THE DISTRIBUTION OF NA ON MARS IS IMPORTANT FOR CHARACTERIZING THE IGNEOUS PROCESSES THAT FORMED THE CRUST AND THE AQUEOUS PROCESSES THAT SUBSEQUENTLY ALTERED IT IN SOME LOCATIONS. IGNEOUS PROCESSES ARE FREQUENTLY EXPLORED USING THE ABUNDANCES OF TOTAL ALKALIS (NA+K) AND SILICA. THE RELATIVE PROPORTIONS OF THESE ELEMENTS ARE TIED TO ABUNDANCES OF COMMON IGNEOUS MAFIC AND FELSIC MINERALS. THUS A TOTAL ALKALIS VS. SILICA (TAS) DIAGRAM CAN GUIDE EFFORTS TO CONSTRAIN THE IGNEOUS EVOLUTION OF UNALTERED CRUSTAL MATERIALS [1]. GLOBALLY TAS DIAGRAMS REVEAL A SURFACE COMPOSED DOMINANTLY OF THOLEIITIC BASALTS PRODUCED VIA PARTIAL MELTING [1]. LOCAL (ROCK-BY-ROCK; [2-4]) DATA ACQUIRED BY MARS ROVERS REVEAL A DIVERSITY OF ROCK TYPES THAT REQUIRE A VARIETY OF FORMATION PROCESSES [5 6] INCLUDING AQUEOUS ALTERATION. GLOBAL TAS DATA COME FROM THE MARS ODYSSEY (MO) GAMMA-RAY SPECTROMETER (GRS). MO/GRS DATA PROVIDED ABSOLUTE CONCENTRATIONS OF SOME ELEMENTS ON MARS' SURFACE [7] BUT NOT NA. MO/GRS-DERIVED TAS DATA INCLUDED NA INFERRED FROM K MEASUREMENTS (VIA THE GUSEV AVERAGE NA2O/K2O RATIO OF 8.9 [1]). YET IN-SITU ANALYSES OF ROCKS YIELD A WIDE RANGE OF VALUES INDICATING THAT THIS MEAN VALUE IS NOT ADEQUATE. NA2O/K2O = 2.92-4.32 IN MERIDIANI PLANUM [2] 3.9-9.39 IN GUSEV CRATER [3] AND 0.74-5.55 IN GALE CRATER; [4]. MESSENGER GRS DATA RECENTLY YIELDED NA VALUES FOR MERCURY [8 9] PROVIDING A PATH FOR DERIVING NA ON MARS. A PILOT STUDY IDENTIFIED THE NA PEAK IN MO/GRS DATA (440 KEV GAMMA RAYS) AND SHOWED IT IS COMPOSED OF TWO DISTINCT COMPONENTS: A SURFACE ORIGINATING CONTRIBUTION (NA ON MARS' SURFACE) AND A LOCAL SPACECRAFT BACKGROUND. WE PROPOSE TO USE THE MO/GRS DATA TO PRODUCE A MAP OF NA CONTENT ACROSS MARS' SURFACE. SPECIFIC PROJECT TASKS INCLUDE: 1. USE MO/GRS DATA TO MAP NA COUNT RATES ACROSS MARS' SURFACE 2. CORRECT THE DATA FOR SYSTEMATIC VARIABILITY ARISING FROM VARIATIONS IN ATMOSPHERE THICKNESS GALACTIC COSMIC RAY FLUX AND BACKGROUND SIGNALS. 3. USE RADIATION TRANSPORT MODELS TO CONVERT NA COUNT RATE MAPS TO NA ABUNDANCE MAPS. 4. IN REGIONS WITHOUT EVIDENCE FOR AQUEOUS ALTERATION PRODUCE A NEW TAS DIAGRAM FOR MARS USING MO/GRS-MEASURED NA K AND SI ABUNDANCES AND CLASSIFY THE IGNEOUS ROCK TYPES OBSERVED AT MARS' SURFACE. 5. IN REGIONS WITH EVIDENCE FOR AQUEOUS ALTERATION MAP NA VS. K AND COMPARED TO PREDICTED VALUES FOR VARYING AQUEOUS ALTERATION PROCESSES. OUR NA MAP WILL BE DELIVERED TO THE NASA PLANETARY DATA SYSTEM AND ALL RESULTS WILL BE PUBLISHED IN OPEN-ACCESS PEER-REVIEWED LITERATURE. REFERENCES [1] MCSWEEN H.Y. ET AL. (2009) SCIENCE 324 736-739. [2] RIEDER R. ET AL. (2004) SCIENCE 306.5702 1746-1749. [3] MCSWEEN H. Y. ET AL. (2006) JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS 111.E9. [4] SCHMIDT M. E. ET AL. (2014) JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS 119.1 64-81. [5] SAUTTER V. ET AL. (2016) LITHOS 254-255 PG. 36-52. [6] SAUTTER V. ET AL. (2015) NAT. GEOSCI. 8 605-609. [7] BOYNTON W. V. ET AL. (2007) JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS 112.E12 (2007). [8] EVANS L.G. ET AL. (2012) JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS 117.E12. [9] PEPLOWSKI P.N. ET AL. (2014) ICARUS 228 86-95.