Volcanism on Mars

摘要: More than 15 years of planetary exploration Mars have given insight into the geologic processes that shaped its surface. The newly acquired Viking data shown volcanism is one most important operating on throughout history. In situ chemical analyses Martian soil by lander spacecraft indicate mafic to ultramafic source rocks. This consistent both with available remote sensing data, which presence minerals such as pyroxene and olivine, petrologic modeling, based geophysical suggest lavas are probably iron rich ultramafic. These strongly basaltic widespread Mars, much photogeological may be studied in this context. Photogeological analysis surface has two main types volcanic morphologies: first type central volcanoes, landforms developed continued prolonged eruption from a point vent. category includes (1) shields, classic low-profile mountains Olympus Mons spectacular example, (2) domes, steep-sided constructs, Tharsis Tholus, represent lower rates shields or, possibly, more silicic lava compositions, (3) highland patera, radially textured volcanoes occur cratered terrain interpreted ash (4) Alba Patera, an apparently unique landform consisting vast center over 1500 km across flank slopes less tenth degree, (5) various small features cinder cones. second major plains, units recognized several criteria, mare ridges flow lobes useful. Volcanic plains subdivided four groups: simple flows, broad, smooth rolling contain numerous mare-type but no lobes, being composed thick, single-cooling units, complex displaying multiple overlapping indicative thin, multiple-cooling undifierentiated typically lack any morphologic identifying feature considered partly basis their association large centers, questionable volcanic(?) heavily modified other (erosion, tectonism, etc.) so origins uncertain. When these categories morphologies combined relative age provided crater statistics, history for can derived follows: Early heavy bombardment was accompanied followed small-scale fluvial channeling, extensive flood (the plateau plains), shield terrain. Shortly after time, resurface planet during formation northern/southern hemisphere dichotomy. Central became prominent development Patera well older domes northern (early Elysium regions). uplifts triggered release large-scale catastrophic floods, producing channels. Continued uplift lithospheric thinning concentrated activity region, plains. Both vent been active history, volumes extrusion gradually decreased time. moonlike thermal involving lithosphere increasing thickness ‘turning off’ volcanism. Although many questions remain regarding volcanism, remarkable, detailed overview probable nature Mars.