May 2021 LIP of the Month

The Derceto Large Igneous Province (LIP), Astkhik Planum, Venus

Lauren MacLellan (1), Richard Ernst (1,2), Hafida El Bilali (1), Richard Ghail (3), Erin Bethell (1)

1 Department of Earth Sciences, Carleton University, Ottawa, ON, Canada

2 Faculty of Geology and Geography, Tomsk State University, Tomsk, Russia

3 Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX,

United Kingdom

Emails: laurenmaclellan@cmail.carleton.ca (Lauren MacLellan); Richard.Ernst@ErnstGeosciences.com (Richard Ernst)

Extracted and modified from:

MacLellan, L.M., Ernst, R.E., El Bilali, H., Ghail, R.C., Bethell, E. (2021a).  Volcanic history of the Derceto large igneous province, Astkhik Planum, Venus.   Earth Science Reviews, 103619, https://doi.org/10.1016/j.earscirev.2021.103619

Large Igneous Provinces (LIPs) on Earth are voluminous (> 0.1 Mkm³); frequently above 1 Mkm³), mainly mafic(ultramafic) magmatic events of intraplate affinity (based on tectonic setting and/or geochemistry) that occur in both continental and oceanic settings, are often linked with mantle plumes, and are typically emplaced over a short time period ( < 5 myr; often < 2 myr) or in multiple short pulses with a maximum duration of a few tens of myr (e.g., Coffin and Eldholm, 1994; Courtillot and Renne, 2003; Bryan and Ernst, 2008; Bryan and Ferrari, 2013; Ernst, 2014; Ernst et al. 2021). LIPs consist of volcanic packages (flood basalts) and a plumbing system of regional dyke swarms (linear, radiating, and a recently identified circumferential type), sill complexes, layered mafic-ultramafic (M-UM) intrusions, and crustal magmatic underplates (Ernst et al. 2019; Buchan and Ernst, 2021). Continental LIPs can also be associated with major silicic magmatic events termed Silicic LIPs (SLIPs), as well as carbonatites and kimberlites. LIPs and SLIPs are associated with regional uplift, attempted continental breakup, various classes of ore deposits, and dramatic climate change, including mass extinctions.

Given an absence of plate tectonics, the voluminous basaltic magmatism that covers most of Venus is intraplate and the largest volume events represent LIP analogues (e.g. Head and Coffin, 1997; Hansen 2007; Ernst et al. 2007; Ernst, 2014, Buchan and Ernst 2021). Another important difference from Earth is the hyper-warm (450^oC) dense CO₂-dominated atmosphere associated with global loss of water and no significant surface erosion. [However, it has recently been suggested that Earth-like conditions with potential fluvial erosion may have existed for most of Venus’s history up into the time of the tesserae, the complexly deformed and stratigraphically oldest units (Way et al. 2016; Way and Del Genio, 2020, Khawja et al. 2020, Byrne et al. 2021).]

As a consequence, Venus (at least post-tesserae time) preserves the surface record of LIP volcanism, but the characteristics of the LIP plumbing system are inferred only indirectly (e.g. Buchan and Ernst, 2021). This contrasts with the Earth where erosion has removed the volcanic component (particularly for pre-Mesozoic continental LIPs) but has exposed parts of the LIP plumbing system. Thus, the combined and integrated analysis of the LIP records on Venus and Earth has the potential to produce a more comprehensive understanding of LIPs (including their emplacement history, plumbing systems, and influence on climate) (e.g. Ernst and Buchan 2021).

Herein we report on our detailed mapping at 1:500,000 scale of the Derceto Corona (DC) LIP event located in southern Astkhik Planum, Venus (our map area: 1,920,000 km²) using full resolution (100-200 m/pixel) Magellan synthetic aperture radar (SAR images) (Figure 1; see MacLellan et al. 2021a for full details).  This mapping builds on earlier reconnaissance scale mapping (1:5,000,000 scale) in parts of Venus quadrangles V-44, V-45, and V-56 (Bridges and McGill, 2002; Hansen and Tharalson, 2014, and Kumar and Head (2013), respectively), and also on reconnaissance mapping by Lancaster et al. (1995).

The map (Fig. 1) includes a total of thirty-seven distinct lava flow units which were grouped into eight main and multiple minor volcanic stages, along with six regional graben systems (marking underlying dyke swarms). The distribution of the main flow stages are illustrated in Figure 3, and are briefly described here (full details in MacLellan et al. 2021a). On the east side of DC (Fig. 3a), the Eastern Stage flows (fES) which extend for 750 km, are fed from NNW-NW-trending grabens (overlying dykes) and from more local (small shield) sources. The Kallistos-Ubastet Stage (fKUS) (Fig. 3b) consists of the 1200 km long Kallistos Vallis and its overflow Ubastet Fluctus, all fed from an irregular 30 x 10 km depression (interpreted to represent roof collapse above a magma chamber) on the south side of DC. Lavas of both the Eastern Stage and the Kallistos-Ubastet Stage flowed over a section of Vaidilute Rupes and spread out on its eastern side. A Western Stage flow field (fWS-3) (>1000 km long) (Fig. 3c) was sourced from the elliptical graben system (overlying dykes) of DC; after flowing downslope to the north it swings almost 180 degrees to follow a pre-existing rift, Hanghepiwi Chasma (Fig. 2). At its distal end, fWS-3 is locally superimposed with radar-bright flows interpreted to be derived from east trending grabens (overlying dykes) belonging to Sarpanitum Corona. On the north side of DC, (Fig. 3d) a laterally propagating NE-trending graben system (overlying dykes) produces a 90 km “Great Dyke” that itself feeds a flow field; additional grabens of this swarm also spawned smaller flows.

As a final aspect we have attempted to link these various major flow stages (Fig. 3) and their relative ages (Fig. 4) with evolution of the DC magmatic centre (Fig. 5). Two flow stages, Western Stage-3 (Fig. 3c) and the Great Dyke/NE-trending dyke swarms (Fig. 3d) are inferred to be fed via dykes from elliptical-shaped down-sag caldera collapse of DC (Fig. 5). Such down-sag collapse associated with coronae has been noticed elsewhere on Venus (e.g., Sacajawea, Head et al. 1991, 1992) and has terrestrial analogues (e.g. Iceland; Gudmundsson et al. 2016). The Eastern Stage flows (Fig. 3a) are fed mostly from a region to the east of the corona, and the rest of the flows are fed via an older (pre-Derceto) regional NW-trending graben system that was reused for transport of magma from a magmatic underplate or fed laterally from the collapse of the central chamber of DC. The total areal extent of flows is 534,650 km² with an inferred volume of 26,730 km³ (assuming an average flow thickness of 50 m; thickness constraints detailed in MacLellan et al. 2021a), corresponding to LIP-scale in terms of area, and likely LIP-scale volume if the expected underlying plumbing system were catalogued.  

Similar detailed (1:500,000 scale) mapping is in progress on other Venusian magmatic centres to further improve understanding of the LIP records of Venus and Earth (Antropova et al. 2021; Braga et al. 2021; El Bilali et al. 2021; Ernst and Buchan, 2021; MacLellan et al. 2021b; Sanchez et al. 2021) and on the recently completed Quadrangle V-32 mapped at 1:2,500,000 scale (Bethell et al. 2019).

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