SCIENCE GOALS AND OBJECTIVES THE ANCIENT CRUST OF MARS RECORDS REMARKABLE CHANGES IN CONVECTION PATTERN AND VOLCANISM IN TIME. THIS INCLUDES: (1) PLUMES AND VOLCANISM RELATED TO THE FORMATION OF THE CRUSTAL DICHOTOMY AND ITS AFTERMATH (2) PLUME MIGRATION IN THE NOACHIAN AND HESPERIAN AND (3) THE DEVELOPMENT OF LONG-LIVED VOLCANIC CENTERS SUCH AS THARSIS AND ELYSIUM WHICH HAVE REMAINED STABLE FOR BILLIONS OF YEARS. OVER THE PAST 4.5 BILLION YEARS BOTH THE INTRUSION AND ERUPTION OF MARTIAN MAGMAS HAVE LIKELY RESULTED IN PROFOUND IMPACTS ON THE CRUSTAL STRUCTURE LONG-WAVELENGTH TOPOGRAPHY AND CLIMATE OF MARS. WE HYPOTHESIZE THAT THE PATTERN AND MIGRATION OF MARTIAN PLUMES AND VOLCANISM CAN BE EXPLAINED BY A COMBINATION OF (1) THE INFLUENCE OF MANTLE STRUCTURE PERHAPS AS A CONSEQUENCE OF MAGMA OCEAN INITIAL CONDITIONS ON MANTLE THERMAL EVOLUTION AND MELT PRODUCTION AND (2) THE INFLUENCE OF EVOLVING COMPOSITIONAL AND MECHANICAL PROPERTIES OF THE MARTIAN CRUST AND LITHOSPHERE PERHAPS AS A CONSEQUENCE OF CRUSTAL PRODUCTION AND/OR EXCAVATION BY IMPACTS. TO TEST OUR HYPOTHESES WE PROPOSE TO PURSUE THE FOLLOWING SCIENTIFIC OBJECTIVES: OBJECTIVE 1: EXAMINE HOW CHANGING PROPERTIES OF THE MARTIAN CRUST LITHOSPHERE AND MANTLE CAN INFLUENCE PLUME FORMATION AND MIGRATION. THIS INCLUDES UNDERSTANDING HOW CONVECTION PATTERNS CAN BE CONTROLLED BY MANTLE PROPERTIES (SUCH AS A COMPOSITIONALLY LAYERED MANTLE) AND SURFACE EVOLUTION (SUCH AS CRUST PRODUCTION AND EXCAVATION). OBJECTIVE 2: UNDERSTAND HOW THE PUTATIVE THARSIS AND ELYSIUM PLUMES MAY HAVE REMAINED SPATIALLY STABLE IN SPACE FOR BILLIONS OF YEARS. OBJECTIVE 3: RECONCILE OBSERVED RATES OF MARTIAN SURFACE VOLCANISM WITH THERMAL EVOLUTION OF THE MANTLE AND MELT PRODUCTION AND QUANTIFY EXPECTED MELT AND VOLATILE PRODUCTION ON MARS OVER TIME. PROPOSED METHODOLOGY WE WILL USE THREE-DIMENSIONAL SIMULATIONS OF MARTIAN MANTLE CONVECTION TO STUDY HOW CONVECTION PATTERNS EVOLVE WITH VARIOUS MANTLE PROPERTIES AND ARE AFFECTED BY CHANGES IN LITHOSPHERIC STRUCTURE AND EVOLUTION. MANTLE CONVECTION SIMULATIONS WILL BE CONDUCTED WITH THE FULLY BENCHMARKED AND OPERATIONAL CITCOMS CODE. WE WILL USE A MELTING MODEL IN CITCOMS TO TRACK MELT PRODUCTION OVER TIME AND DETERMINE ITS INFLUENCE ON PLUME MIGRATION. WE WILL COMPARE OUR MODEL PREDICTIONS FOR A RANGE OF SCENARIOS TO PUBLISHED ACCOUNTS OF THE TIME EVOLUTION OF MARTIAN MAGMATISM DERIVED FROM CRATER-COUNTING AND TO RECENT SPECTRAL OBSERVATIONS OF SURFACE MINERALOGY. RELEVANCE TO SOLAR SYSTEM WORKINGS THE PROPOSED RESEARCH DIRECTLY ADDRESSES SEVERAL KEY TOPICS OF RESEARCH WITHIN THE SOLAR SYSTEM WORKINGS PROGRAM IN THE CONTEXT OF MARS: VOLCANISM THE STRUCTURE OF THE MARTIAN INTERIOR AND THE THERMAL EVOLUTION OF THE MARTIAN MANTLE VOLCANIC PERTURBATIONS TO THE COMPOSITION OF THE MARTIAN ATMOSPHERE AND THE RESULTANT CLIMATE CHANGE. THIS PROPOSAL FOCUSES ON PROCESSES THAT POST-DATE PLANETARY DIFFERENTIATION AND THAT SPAN THE PERIOD FROM THE NOACHIAN TO THE RECENT GEOLOGIC PAST. OUR RESULTS WILL BE RELEVANT TO BOTH THE UPCOMING INSIGHT AND CURRENT MAVEN MISSIONS WHICH EXAMINE THE MARTIAN INTERIOR AND ATMOSPHERIC LOSS RESPECTIVELY.