Distribution and Classification of Volcano - Tectonic Features of Venus

Introduction: Venus as a probable single-plate planet [1] has a unique set of volcano-tectonic features. The enigmatic circular structures, coronae are of great interest in particular. The corona definition does also include other concentric features known as the “arachnoids” [2], but it does not elaborate on the details of the concentric volcano-tectonic structures. In several cases, coronae and arachnoids are mixed resulting in several controversial catalogues of the features [3,4]. Alongside with hundreds of coronae and large number of arachnoids, there are large volcanoes and smaller structures with prominent radial features. The term “nova” is used to describe this special group of Venusian volcano-tectonic structures with a stellate fracture pattern [5,6] centered on a central summit or fracture. Coronae and novae display some interesting associations due to the fact that half of the novae are located in the interior part of the coronae [7]. Futhermore, the novae have been interpreted to represent the initial stage of the corona evolution [5,3,8] and therefore are hypothesized to predate the corona rim structure [9,10]. However, this presumption is in contrast to the recent studies. Majority of the novae which are located in the inner part of the coronae seem to postdate the corona formation. It is displayed that a nova can form within different stages of corona development, which also reflects the nova characteristics [11]. These corona structures with nova inside them have been called as “corona-novae”. Novae, which in many cases exist within coronae, are never associated similarly with arachnoids [11]. In this study we try to elaborate and analyse the characteristics of these volcano-tectonic structures which seem to share to some extent similar origin and evolution phases. We also present a classification based on their locations in different geological environments which seem to control their volcanic as well as topographic properties and morphology. Distribution of the features: Our study begun as a separate studies on arachnoids and novae, two groups of clearly identifiable features that had been both associated with coronae, either as a subtype, part of coronae formation process or belonging to the same class of corona-like features [3,12,13,14]. The inconsistencies in several previous studies of these features and in coronae studies [3,4] led to independent catalogue of arachnoids, novae and coronae and corona-novae as well [15]. In all, we have found 349 coronae, 96 arachnoids and 74 novae on the Cytherean surface. We also have 34 corona-nova joint structures. All groups have very different global distrbutions (Figs 1-4). Studying these distributions and correlating them to the differencies in local geology is bound to have major impact on the understanding of formation and evolution processes of these features [7,16] as well as unveiling the geological history of the lithosphere in general.