Planetary Geologic Mappers Meeting 2018 (LPI Contrib. No. 2066) 7024.pdf

GEOLOGIC MAPPING OF IMPACT CRATERS AND THE MAHUEA THOLUS CONSTRUCT: A YEAR THREE PROGRESS REPORT FOR THE MAHUEA THOLUS (V-49) QUADRANGLE, VENUS. N.P. Lang1 , M. Covley1, J. Beltran1, K. Rogers1, and B.J. Thomson2; 1Department of Geology, Mercyhurst University, Erie, PA 16546 ([email protected]), 2Department of Earth and Planetary Sciences, University of Tennessee – Knox- ville, Knoxville, TN 37996 ([email protected]).

Introduction: The Mahuea Tholus quadrangle (V- edifice is ~100 km in diameter (with all flow materials, 49) extends from 25° to 50° S to 150° to 180° E and Mahuea is ~300 km in diameter), ~0.5 km in height encompasses >7×106 km2 of the Venusian surface. with a ~4 km diameter flattish top, and an erupted vol- Moving clockwise from due north, the Mahuea Tholus ume of ~103 km3. Mahuea is located within the center quadrangle is bounded by the Diana Chasma, Thetis of a topographic basin in Zhibek Planitia ~1400 km SE Regio, Artemis Chasma, Henie, Barrymore, Isabella, of the main axis of Diana-Dali Chasma-related rifting. and Stanton quadrangles; together with Stanton, Ma- The volcano resides at the eastern end of Annapurna huea Tholus is one of two remaining quadrangles to be Corona-related fractures (Naguchitsa Fossae) and over- geologically mapped in this part of Venus. Here we lies Annapurna-sourced flow material – material previ- report on our continued mapping of this quadrangle. ously interpreted as possible pyroclastic deposits Specifically, over the past year we have focused on sourced from Mahuea Tholus [3]; Annapurna-sourced mapping and cataloging impact craters located within flows were then subsequently deformed by NE- the quadrangle as well as larger-scale mapping of the trending wrinkle ridges, which was then followed by Mahuea Tholus construct; those efforts are described in formation of Mahuea Tholus. At least four eruptive this contribution. events are recorded at Mahuea Tholus and each event Impact Craters [1]: V-49 contains 13 confirmed is marked by a thick (~100 m), lobate, radar bright impact craters (Table 1). Twelve of the craters occur flow that records numerous pressure ridges and channel entirely within V-49 and one crater, Austen, straddles structures; the earliest recorded flow materials are the the boundary between V-49 and V-37 to the north. In most extensive with the youngest flows being more addition to impact structures, at least four radar dark localized. Based on mapped relations, we interpret that circular splotches that do not host an impact crater oc- fractures within Naguchitsa Fossae facilitated eruption cur within V-49. We interpret these splotches as the of Mahuea Tholus flow material and, therefore, mag- result of air burst events that did not create a crater matism at this volcano is likely related to magmatism at structure; two of these splotches (splotches A and B) Diana-Dali Chasma as a whole. Perhaps the location of are spatially associated with Qarlygha and Kaikilani this volcano off the main axis of rifting caused stalling impact craters and may be tied to their occurrence. of magma ascent, which in turn could have facilitated Impact craters range from 12-100 km in diameter with either a slower effusion rate and/or evolution of magma an average diameter of ~20 km. All craters are associ- chemistry resulting in the eruption of thick lava flows. ated with ejecta blankets and at least three craters – Such a prediction may be testable through continued Howe, Onissya, and Valadon – also host fluidized ejec- regional mapping of intermediate-sized Venusian vol- ta materials. Onissya appears to represent a possible canoes, in situ spectral analyses by Venusian landers, double crater. Located east of Howe, and potentially and further constraints on thickness variations of the associated with its formation, is a radar-bright, Venusian crust. ‘streaky’ patch that could be either ejecta or additional Future Directions: We are now in the final stages fluidized material. Seven craters exhibit radar-dark of mapping V-49. Our current efforts are emphasizing floors. Five craters exhibit a central peak and the oc- cleaning up line work, refining map unit descriptions, currence of a central peak is indeterminate for five cra- creation of a sequence of map units, and writing the ters. Ten craters appear to have occurred after tec- map text. tonism within V-49 and the remaining three craters References: [1] Beltran, J., et al. (2017), GSA Abs w/ have been deformed by wrinkle ridges and fractures Programs; Vol. 49, No. 6 doi: 10.1130/abs/2017AM- meaning they predate at least some tectonic activity in 306199. [2] Covley, M.T., et al. (2017), GSA Abs w/ V-49. Programs, Vol. 49, No. 6 doi: 10.1130/abs/2017AM- Mahuea Tholus Construct [2]: The Mahuea Tho- 306141 [3] Moore, H.J., et al. (1992), JGR, 97, E8, lus construct (37.5° S, 165° E) is a solitary, intermedi- 13,479-13,493. ate-sized volcano located in the center of V-49. The

Planetary Geologic Mappers Meeting 2018 (LPI Contrib. No. 2066) 7024.pdf

Table 1. Impact features of V-49

Crater name Latitude Longitude Diameter Halo Central Peak Deformation

(deg N.) (deg E.) (km)

Austen -25 168.4 45.1 N Y Y

Ayana -29.2 175.5 13.8 Y ? N

Howe -45.7 174.8 38.6 Y Y N

Kaikilani -32.8 163.2 19.9 Y Y N

Onissya -25.6 150.2 8.2 Y N N

Pavlinka -25.5 158.7 7.5 N N Y

Philomena -40.7 151.9 14.8 Y ? N

Qarlygha -33 162.9 9.3 Y N N

Radhika -30.3 166.4 7.9 Y N N

Whitney -30.2 151.3 42.5 N Y Y

Ulpu -35.7 179 7 Y ? N

Valadon -49 167.7 25.2 Y Y N

Yasuko -26.1 169 10.6 Y ? N

Zemfira -46.2 157.7 11.4 Y ? N

Splotch A -33.3 161.9 38.1

Splotch B -33.4 162.8 19.5

Splotch C -36.4 162.5 61.9

Splotch D -41.7 158.2 52.9