WE PROPOSE TO STUDY THE HYDROLOGICAL SULFUR CYCLE RELATED TO VOLCANIC AND CLIMATIC EVOLUTION OF THE GIANT TERRESTRIAL VOLCANIC SYSTEM OF VALLES CALDERA NEW MEXICO AS A GEOCHEMICAL ANALOGUE FOR SULFATE-MINERAL DEPOSITION ON MARS. VALLES CALDERA IS AN ACTIVE VOLCANIC SYSTEM BUT SEDIMENT CORES FROM COEXISTING CRATER LAKE ALSO PROVIDE A UNIQUE 560 THOUSAND YEAR RECORD OF HISTORICAL CHANGES IN VOLCANIC ACTIVITY AND CLIMATE. SULFATE MINERALS ON THE MARTIAN SURFACE PROVIDE COMPELLING EVIDENCE OF PAST FLUID MOVEMENT CHEMISTRY AND POTENTIAL HABITABILITY. THE GEOLOGICAL AND CHEMICAL PROCESSES LEADING TO THEIR FORMATION ARE THOUGHT TO INCLUDE VOLCANIC DEGASSING HYDROTHERMAL CIRCULATION OXIDATION OF REDUCED SULFUR GASSES AND SULFIDE MINERALS MELTING OF ICE SURFACE WATER FLOW AND EVAPORATION. HOWEVER MANY OF THESE KEY PROCESSES AND THEIR INTERACTIONS ON MARS REMAIN UNCLEAR. FOR EXAMPLE WE ARE UNCERTAIN ABOUT THE RELATIVE INFLUENCE OF CONCURRENT VOLCANIC SULFUR EMISSIONS AQUEOUS SULFIDE WEATHERING AND CLIMATE CONDITIONS ON THE SULFUR CYCLE AND WE POORLY UNDERSTAND THE HYDROLOGICAL CYCLE THAT TRANSPORTED SULFUR ON THE MARTIAN SURFACE. THEREFORE THE GOAL OF OUR RESEARCH IS TO DESCRIBE AND QUANTIFY THE ACTIVE AND HISTORICAL HYDROLOGICAL SULFUR CYCLE IN THE VALLES CALDERA TERRESTRIAL ANALOG SYSTEM AND TO COMPARE THIS TO THE SULFUR CYCLE ON MARS. THE DATA OBTAINED WILL BE COMPARED AND MODELED WITH RESPECT TO CONSTRAINTS SUCH AS THE REPORTED SULFUR CONTENTS IN MARTIAN METEORITES AND MAGMA AND THE QUANTITIES OF SULFUR/SULFATE DEPOSITION IN DIFFERENT EQUATORIAL ENVIRONMENTS ON MARS (E.G. PREVIOUS LANDING SITES OF MERIDIANI PLANUM GUSEV CRATER AND FUTURE LANDING SITE OF THE MARS SCIENCE LABORATORY). THE OBJECTIVES OF OUR STUDY ARE TO: 1) QUANTIFY THE PRESENT SULFUR/SULFATE LOADS ATTRIBUTABLE TO REDUCED VOLCANIC S EMISSION (E.G. H2S GAS) AND SULFIDE WEATHERING (E.G. PYRITE) IN VALLES CALDERA; 2) EVALUATE HOW THESE LOADS CHANGE SPATIALLY AND TEMPORALLY AS A FUNCTION OF CHANGES IN CLIMATE AND THE EVOLUTION OF THE VOLCANIC SYSTEM; AND 3) ASSESS THE DISTANCES OF HYDROLOGICAL TRANSPORT OF ACIDIC VOLCANIC SULFATE-RICH SOLUTIONS (AND THEREFORE THE DEGREE OF WATER-ROCK INTERACTION) THAT OCCURS DURING SURFACE WATER FLOW IN A VOLCANIC SYSTEM. WE WILL ACCOMPLISH OUR OBJECTIVES BY USING HYDROLOGICAL CHEMICAL AND SULFUR ISOTOPE METHODS TO QUANTIFY THE MODERN AND HISTORICAL SULFUR LOADS IN 1) MAJOR STREAMS OF THE VALLES CALDERA THAT CURRENTLY DRAIN THE AREAS OF VOLCANIC SULFUR EMISSIONS AND ARE ADDITIONALLY IMPACTED BY SULFIDE WEATHERING AND IN 2) LACUSTRINE SEDIMENTS OF THE ANCIENT CRATER LAKE OF VALLES CALDERA DEPOSITED DURING TWO MID-PLEISTOCENE GLACIAL CYCLES.THE PROPOSED WORK IS DIRECTLY RELEVANT TO THE MARS FUNDAMENTAL RESEARCH PROGRAM WHICH INCLUDES QUANTITATIVE TERRESTRIAL FIELD EXPERIMENTS THAT IMPROVE UNDERSTANDING OF THE IN-SITU MEASUREMENTS THAT HAVE BEEN MADE BY MARS EXPLORATION ROVERS MARS RECONNAISSANCE ORBITER AND THAT WILL BE MADE BY MARS SCIENCE LABORATORY. OUR WORK IS ALSO RELEVANT TO THE MAJOR GOALS OF THE MARS EXPLORATION PROGRAM THAT FOCUS ON THE 1) LIFE 2) CLIMATE AND 3) GEOLOGY OF MARS IN THAT THE CLIMATE-RELATED HYDROLOGICAL S CYCLE COULD HAVE PROVIDED THE CHEMICAL ENERGY NECESSARY FOR LIFE TO HAVE RISEN. AS A RESULT OF THE PROPOSED WORK WE WILL DEVELOP A MODEL FOR THE MARTIAN SULFUR CYCLE CAPABLE OF DISTINGUISHING THE RELATIVE IMPORTANCE OF VOLCANOGENIC INPUTS AND SULFIDE WEATHERING INPUTS OVER LONG PERIODS OF TIME INFLUENCED BY LARGE CHANGES IN CLIMATE. OUR WORK WILL ALSO PLACE SPATIAL CONSTRAINTS ON THE SURFACE TRANSPORT OF ACIDIC SULFATE-RICH STREAMS ON MARS.