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Geologic Map of the Ganiki Planitia Quadrangle (V-14), Venus

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Geologic Map of the Ganiki Planitia Quadrangle (V-14), Venus Prepared for the National Aeronautics and Space Administration Geologic Map of the Ganiki Planitia Quadrangle (V–14), Venus By Eric B. Grosfils, Sylvan M. Long, Elizabeth M. Venechuk, Debra M. Hurwitz, Joseph W. Richards, Brian Kastl, Dorothy E. Drury, and Johanna Hardin Pamphlet to accompany Scientific Investigations Map 3121 75° 75° V–1 V–3 V–6 50° 50° V–4 V–5 V–11 V–16 V–12 V–15 V–13 V–14 25° 25° V–23 V–28 V–24 V–27 V–25 V–26 90° 120° 150° 180° 210° 240° 270° 0° 0° V–37 V–38 V–36 V–39 V–35 V–40 –25° –25° V–49 V–50 V–48 V–51 V–47 V–52 V–58 V–59 –50° –50° V–57 V–60 2011 V–62 –75° –75° U.S. Department of the Interior U.S. Geological Survey Contents The Magellan Mission ..................................................................................................................................1 Magellan Radar Data ..........................................................................................................................1 Ganiki Planitia Quadrangle ...........................................................................................................................1 Introduction ...........................................................................................................................................1 Mapping Techniques ...........................................................................................................................2 Unit Physical Properties .....................................................................................................................3 Unit Robustness ...................................................................................................................................3 Qualitative Evaluation ................................................................................................................4 Quantitative Evaluation ..............................................................................................................4 Map Units ..............................................................................................................................................5 Heavily Deformed Units .............................................................................................................5 Local Plains Units ........................................................................................................................6 Regional Plains Units .................................................................................................................8 Edifice and Corona Units ...........................................................................................................9 Impact Units .................................................................................................................................9 Discrete Landforms Within V–14 .......................................................................................................9 Canali ..........................................................................................................................................9 Major Volcanic Edifices ...........................................................................................................10 Smaller Volcanic Features ......................................................................................................12 Coronae ......................................................................................................................................13 Impact Craters ...........................................................................................................................14 Structural Deformation .....................................................................................................................15 Contractional Deformation ......................................................................................................16 Extensional Deformation .........................................................................................................16 Geologic History .................................................................................................................................17 Precursor ....................................................................................................................................17 Period 1 .......................................................................................................................................17 Period 2 .......................................................................................................................................18 Period 3 .......................................................................................................................................18 Cratering .....................................................................................................................................18 Discussion ....................................................................................................................................................18 Acknowledgments ......................................................................................................................................21 References ...................................................................................................................................................21 Tables 1. Summary of map unit properties within Ganiki Planitia (V–14) quadrangle, Venus ...................25 2. Individual map unit properties and names for every geographically distinct example of each unit, arranged alphabetically by map symbol and then by increasing area. ..........26 i The Magellan Mission above which high dielectric minerals or coatings are thermody- namically stable. This effect leads to very bright SAR echoes from virtually all areas above that critical elevation. The Magellan spacecraft orbited Venus from August 10, The measurements of passive thermal emission from 1990, until it plunged into the Venusian atmosphere on October Venus, though of much lower spatial resolution than the SAR 12, 1994. Magellan Mission objectives included (1) improving data, are more sensitive to changes in the dielectric constant the knowledge of the geological processes, surface properties, of the surface than to roughness. As such, they can be used to and geologic history of Venus by analysis of surface radar char- discriminate between roughness and reflectivity effects. Obser- acteristics, topography, and morphology and (2) improving the vations of the near-nadir backscatter power, collected using a knowledge of the geophysics of Venus by analysis of Venusian separate smaller antenna on the spacecraft, were modeled using gravity. the Hagfors expressions for echoes from gently undulating sur- The Magellan spacecraft carried a 12.6-cm radar system to faces to yield estimates of planetary radius, Fresnel reflectivity, map the surface of Venus. The transmitter and receiver systems and root-mean-square (RMS) slope. The topography data pro- were used to collect three data sets: (1) synthetic aperture radar duced by this technique have horizontal footprint sizes of about (SAR) images of the surface, (2) passive microwave thermal 10 km near periapsis and a vertical resolution of approximately emission observations, and (3) measurements of the backscat- 100 m. The Fresnel reflectivity data provide a comparison to the tered power at small angles of incidence, which were processed emissivity maps, and rms slope parameter is an indicator of the to yield altimetric data. Radar imaging and altimetric and radio- surface tilts, which contribute to the quasi-specular component. metric mapping of the Venusian surface were accomplished in mission cycles 1, 2, and 3 from September 1990 until Septem- ber 1992. Ninety-eight percent of the surface was mapped with radar resolution on the order of 120 m. The SAR observations Ganiki Planitia Quadrangle were projected to a 75-m nominal horizontal resolution, and these full-resolution data compose the image base used in Introduction geologic mapping. The primary polarization mode was hori- zontal-transmit, horizontal-receive (HH), but additional data for The Ganiki Planitia (V–14) quadrangle on Venus, which selected areas were collected for the vertical polarization sense. extends from 25° N. to 50° N. and from 180° E. to 210° E., Incidence angles varied between about 20° and 45°. derives its name from the extensive suite of plains that domi- High-resolution Doppler tracking of the spacecraft took nates the geology of the northern part of the region. With a place from September 1992 through October 1994 (mission surface area of nearly 6.5 x 106 km2 (roughly two-thirds that cycles 4, 5, 6). Approximately 950 orbits of high-resolution of the United States), the quadrangle is located northwest gravity observations were obtained between September 1992 of the Beta-Atla-Themis volcanic zone and southeast of the and May 1993 while Magellan was in an elliptical orbit with a Atalanta Planitia lowlands, areas proposed to be the result of periapsis near 175 km and an apoapsis near 8,000 km. An addi- large scale mantle upwelling and downwelling, respectively tional 1,500 orbits were obtained following orbit-circularization (see Bindschadler and others, 1992; Crumpler and others, 1993; in mid-1993. These data exist as a 75° by 75° harmonic field. Phillips and Hansen, 1998). The region immediately south of Ganiki Planitia is dominated by Atla Regio, a major volcanic Magellan Radar Data rise beneath
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