THARSIS SUPERPLUME (2): EARTHLIKE EVOLUTION OF THE THARSIS MAGMATIC COMPLEX

High-resolution topography, imagery, and geophysical data reveal an active and varied Martian geological history. Whereas Earth has protracted periods of high erosion rates and well-documented plate tectonism, Mars comprises geologic terrains that archive substantial stratigraphic, magmatic, paleotectonic, and paeloerosional information potentially further back than 4 GA. Similar to Earth, however, magmatic-driven processes, including plume-driven tectonism, dominate the dynamic geologic history. This is best exemplified at Tharsis and surroundings, where five major pulses of activity [Planet. & Space Sci., 1999, v. 47, p. 411-431] are observed in the geologic record from Early/Middle Noachian through the Amazonian. The sporadic activity formed a magmatic complex that exhibits topography, structure, geomorphic expression, and geophysical traits similar to superplumes of Earth [Journal of the Geological Society of Japan, 1994, v. 100, p. 4-23 and p. 24-49]. Some of the more distinctive traits of the proposed Tharsis superplume include: (1) early basin formation during [JGR-Planets, in press], (2) distinct episodes of intensive early magmatic/tectonic activity that declines with time, including development of local and regional centers of tectonic activity of varying age, size, and duration of formation [Lunar & Planet. Sci. XXIX, 1998, p. 1881-1882], interpreted to be the sites of plume-related activity, including uplift, tectonism, dike emplacement, volcanism, and hydrothermal activity, (3) early explosive activity transiting into more concentrated, volcano and fissure-fed eruptions, (4) a suite of landforms, including volcanic constructs of diverse sizes and shapes and extensive lava flow fields, large igneous plateaus, putative ash-flow and air-fall deposits, circumferential systems of wrinkle ridges and fold belts [J. Geophys. Res., 1994, V. 99, p.8371-8385], and catastrophic outflow channels, and (5) fault and rift systems of varying extent and relative age of formation, including vast canyon systems of Valles Marianeris, interpreted to be the site of a lithospheric zone of weakness, vertical uplift related to plume manifestation [Astron. & Geophys., 1998, v. 39, p. 3.20-3.22], and rotation of the Thaumasia crustal block (also see Maruyama et al. and Baker et al., this volume).