geological evolution of Atai Mons, Venus: a volcano-corona 'hybrid', The

Abstract:

Atai Mon Venus, is classified as a large volcano at the same time displays characteristics that are typical of coronae. Coronae are widespread volcano-tectonic features that are apparently unique to Venus. Detailed analysis of Atai Mon using photogeological and geophysical techniques illustrates that it has experienced a mingled history and may still be active. We present to view that processes found at one as well as the other coronae and large volcanoes have occurr through every part of the history of Atai Mon with no definite temporal choice It does not have an evolution that can be described simply as the evolution of single feature into another. These flows suggest that large volcanoes and coronae are more intimately linked than previously musing and that detailed mapping and gravity take a view ofs are reliable ways of establishing the evolution of hybrid features.

The Magellan mission to Venus revealed a surface with widespread volcanism and tectonism (Saunders & Pettengill 1991; Saunders el al. 1991 1992; Solomon & Head 1991) Synthetic Aperture Radar (SAR) images of the surface revealed numerous widely distributed large volcanoes and coronae. Large volcanoes are defined as volcanic midmost points with flow apron diameters ?‰? 100 km in diameter, with radial streams and positive topography (Head el al. 1992) Coronae are volcano-tectonic features that are apparently unique to Venus. They have a wide range of morphologies and are thinking to be the surface manifestation of buoyant mantle diapirs (eg Janes et al. 1992; Squyre et ai. 1992; Stofan et al. 1992 1997)

To date, above 140 large volcanoes (McGovern 1996; McGovern & Solomon 1998) and 500 coronae (Stofan et al. 2001b) have been identified. However, a certain quantity of of these features show characteristics typical of the two large volcanoes and coronae. scarcely any of these 'hybrid' features have been investigated previously. Mbokomu Mon has been described as a large volcano because of its distinctive lava stream apron (Head et al. 1992) and radial fractures interpreted as the spring of dyke propagation (Koenig & Pollard 1998) on the contrary also as a radial-concentric corona-like feature because of its concentric fracture annulus (Stofan et al. 1992) Geological mapping adviseed that Anala Mons and Sappho Corona are large volcanoes that have evolv into coronae (McGill 1994 1998) Kunhild and Ereshkigal Coronae were interpreted as a large volcano and corona respectively after photogeological and gravity analyses (Herrick & McGovern 2000) on the contrary both were, and still remain, classified officially as coronae by dint of the US Geological Survey (USGS). A preliminary photogeological investigation of four hybrids revealed no for the use of all evolutionary trend (Grindrod et ai. 2004)

Preliminary analysis refer tos that there may be up to 40 hybrid features upon Venus (e.g. Herrick & Marsh 1997; Dufek & Herrick 2000; Brian et al. 2003) This paper not aways the analysis of a hybrid feature, Atai Mon which although catalogued as the two a large volcano (Grumpier et al. 1997) and a corona (Stofan et al. 1992 2001e) displays characteristics that are indicative of the two

Coronae are approximately circular configurations that range in diameter from 60km to above 1000km (Stofan et al. 2001b) They were originally identified by dint of the presence of a distinctive annulus of closely spaced concentric fractures, which were typically superimposed upon a raised rim (Stofan et al. 1992) However, the identification in stereo images of coronae lacking a significant fracture annulus (Tapper 1997) l to the corona population being almost doubled (Stofan et al. 2001e) impressed sign 1 coronae are defined as having more than 180?° arc of fracturing, impressed sign 2 less than 180?° arc of fracturing (Stofan et al. 2001e) Many coronae have had composite evolutions, and have undergone varying amounts and mode of speechs of volcanism (Copp et al. 1997) Large volcanoes upon Venus have a typical profile of an approximately conical edifice encloseed by an apron with shallow oblique directions (McGovern & Solomon 1997; Stofan et al. 2001a). They are usually identified by the agency of their distinctive radial flow aprons and of frequent occurrence summit calderas (Grumpier et al. 1997) Concentric fractures are rare or absent (McGovern & Solomon 1997 1998) Hybrids are an apparently transitional collection between coronae and large volcanoes as they exhibit a certain quantity of usually many, characteristics typical of the features described above. They are thus an important link between coronae, large volcanoes and heat los mechanisms upon Venus.

An analysis of the evolution of Atai Mon was directioned using Magellan full-resolution SAR images (known as FMAPs), press togethered Once Mosaic Image Data Records (Cl-MIDRs) and synthetic-stereo image pairs. Ancillary data, including the Global Emissivity Data Record (GEDR) Global Reflectivity Data Record (GRDR) Global direction downward Data Record (GSDR) and Global Topographic Data Record (GTDR) were also used in the analysis. Photogeological [i]modus operandi[/i]s were used to determine superposition relationships between different units and tectonic features and thus a geological evolutionary succession for Atai Mons. This was supported by means of geophysical modelling of gravity in the region. This allowed further insight into the apparent intimate relationship between a certain quantity of large volcanoes and coronae upon Venus.