Tharsis is the most prominent volcanic province on Mars,yet the compositions of lava flows and how composition relates to the development of Tharsis are poorly known.Most of Tharsis is covered with air-fall dust,which inhibits spectroscopic determination of lava mineralogy.The Syria-Thaumasia Block(STB)is a complex tectono-volcanic province closely related to the Tharsis bulge.The lava plains of STB have different emplacement ages,which provide an opportunity to examine whether magma composition changed with the evolution of Tharsis.In this study,we assessed the lava plains using Thermal Emission Spectrometer(TES)data.Using derived physical properties,we targeted dust-free regions from four different-aged geological units'surfaces and determined the mineralogical composition by modeling the average TES surface spectrum from each of the four surfaces.All units have similar mineralogy but the younger two units have elevated abundance of high-SiO2phases.The spatial distribution of wrinkle ridges indicates lava plains of unit HNr(older ridged plains material)and Hr(younger ridged plains material)were emplaced before the rise of Tharsis,whereas Hsl(flows of lower member)and Hsu(upper member)were emplaced after Tharsis uplift was initiated.We show that the magma composition differed in the lava plains of STB after the uplift of Tharsis.This study further characterizes early martian magma composition and evolution.
We present topographic, geomorphologic and compositional characteristics of a l°×l° （-660 km2） region centered near the landing site of Chang＇E-3 using the highest spatial resolution data available. We analyze the topography and slope using Digi- tal Terrain Model （DTM） generated from Terrain Camera （TC） images. The exploration region is overall relatively flat and the elevation difference is less than 300 m, and the slopes of 80% area are less than 5~. Impact craters in the exploration region are classified into four types based on their degradation states. We investigate the wrinkle ridges visible in the exploration region in detail using TC and Lunar Reconnaissance Orbiter （LRO） Narrow Angle Camera （NAC） images. We calculate FeO and TiO2 abundances using Multispectral Imager （MI） data, and confirm two basaltic units： the northern part belongs to Imbrian low-Ti/very-low-Ti mare basalts, and the southern part is Eratosthenian low-Ti/high-Ti mare basalts. Finally, we produce a ge- ological map and propose the geologic evolution of the exploration region. We also suggest several rover traverses to explore interesting targets and maximize the potential scientific output.
ZHAO JianNanHUANG JunQIAO LeXIAO ZhiYongHUANG QianWANG JiangHE QiXIAO Long
