SCIENTIFIC INVESTIGATIONS MAP 2897 U.S. DEPARTMENT OF THE INTERIOR Prepared for the ATLAS OF VENUS: MEAD QUADRANGLE (V–21) U.S. GEOLOGICAL SURVEY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Pamphlet accompanies map 30° 35° 40° 45° 50° 55° 60° 30° 35° 40° 45° 50° 55° 60° 25° 25° 25° 0 Bell Regio t t Vako-nana Bell Regio t na fN3 t t Tesserae pr ld t o-na t –5 fN3 ak fN V 1 hb Tesserae serae Didilia fN Corona 1 Tes pr t AKHTAMAR PLANITIA –10 nitu fN3 Ninmah Mar Corona phB pr 20° sa fc Pavlova t Mead –15 fl Corona fC Didilia itsa Dor fN fM t cu Corona Isong Central volcanoes and localized 1 fD fl fc ae t fP cu Corinna Madina Corona sources cu Ayashe ld Metel –20 Ninmah Kali Corona material fK Mons

Corona IN DECIBELS COEFFICIENT, BACKSCATTER Average backscatter phB Tesser Calakomana cu –25 pr 15° Corona 20 25 30 35 40 45 50 Karo pr t EISTLA Pavlova Corona REGIO pr A INCIDENCE ANGLE, IN DEGREES co Ptesanwi Mons Dzalarhons Manatum 0 Mead Mons Tessera AKHTAMAR PLANITIA Isong Corona A 0 250 KILOMETERS

pr Mamitu ld fl –5

a 10° det Kali ser t Maf cu Mons Tes 20° 20° –10 Sheila phB fc phO Didilia a Calakomana Corona –15 phB ld fc * z Dors Corona s fK

e l l Oju a Ninmah V 50° a Tessera g Corona –20 n ld a Plains material G Pavlova fc Didilia pr Ptesanwi Disani Corona IN DECIBELS COEFFICIENT, BACKSCATTER Average backscatter Mead Mons Corona –25 ld Isong 20 25 30 35 40 45 50 ld t Manatum Tessera Corona Corona B INCIDENCE ANGLE, IN DEGREES Gbadu Dzalarhons Salus Tessera Metelitsa Dorsa Tessera fc Mons 0° A Calakomana 0 Corona Disani hb Ninmah Isong Corona Orczy ld Ninmah Corona Disani Corona Ptesanwi Corona co Pavlova –5 t N Mead Dzalarhons Mons Didilia Corona Mons Manatum Bradstreet Tessera Corona 0° cu Corona 60° B –10 Planetary radius (km) Figure 2. (A) Emissivity map of Mead quadrangle (V–21), Venus. ld 30° 6,055 ld 25° Black corresponds to values less than 0.73, white to values greater than –15 ld Ptesanwi 0.91. Very low emissivity is associated with the summits of shield pr Mons volcanoes and corona topography above ~6,054 km radius; these pr t Rough a’a Amenardes Calakomana ° cu ° 6,052 properties are typical of high-dielectric coatings in the Venus highlands. Pahoehoe 15 Huarei 15 Corona –20 Kali Tesserae, corona structures less than 6,054 km radius, and some lava hb Pavlova Corona cu Very smooth ponded pahoehoe Mons Dzalarhons 6,050 flows have enhanced emissivity due to high wavelength-scale rough- BACKSCATTER COEFFICIENT, IN DECIBELS COEFFICIENT, BACKSCATTER Average backscatter fc ld Mons ness. Red arrows denote locations of deposits of unit hb; deposits are ld cMu fM characterized by high emissivity relative to the surrounding corona –25 B 6,048 20 25 30 35 40 45 50 30° flows, which is consistent with an interpretation as coarse fragmental EISTLA REGIO 0° C INCIDENCE ANGLE, IN DEGREES pyroclastic material. Green arrows show areas of enhanced emissivity cMu Figure 1. (A) Mercator projection radar image of the Mead quadrangle (V–21), Venus, showing major ld cMt correlated with radar-dark flows from Kali Mons and Calakomana Figure 3. Radar correlation charts of selected material in Mead quad- fc features. (B) Topographic map of Mead quadrangle with colors corresponding to planetary radius shown in Corona. (B) Rms slope map of Mead quadrangle. Black corresponds to rangle (V–21), Venus, and terrestrial lavas. Average backscatter behav- perspective view. Minimum planetary radius within the quadrangle, 6,048.04 km; maximum radius, 6,054.95 hb ld fc values of 0°, white to values greater than 6° rms slope. Yellow arrows ior of Venus surface from Muhleman law (Campbell, 1995). (A) Flow km. View toward northeast. denote major regions of smooth terrain corresponding to fine-grained, units of central volcanoes and localized sources, corona material; (B) cMf tessera and plains material; (C) lava flows on Kilauea volcano, cMu mantling deposits of Mead crater. Green arrows denote similar mantled hb regions attributed to craters younger than Mead. Large, digitate, low- Hawaii—rough a’a, pahoehoe, and very smooth ponded pahoehoe. Isong cu Mead rms-slope region near bottom center of image corresponds to smooth pr de Ayala fc hb lava flows from Ptesanwi Mons. Corona fc

ld cMt 51.7° 54.5° 35.6° 39.2° 37.6° 44° cMu 67° 20.5° 22°

ld cMu fc pr

ld fc dome fc field fc 10° 10° cu a fK Gwynn ld Mafdet Tesser pr pr t cu Romola ld Kali ld fc Mons ld * pr s e Didilia t l l Corona

phO a

V

Kuro

cu a Figure 5. Magellan left-looking radar image of channel feature in g north-central Disani Corona, Mead quadrangle (V–21), Venus. This fl ld n a channel appears to have exploited pre-existing fracture and graben Calakomana G t fc structures. Image center lat 5.1° N., long 56.8° E. North at top; image width 72 km. dome a

Corona pit crater chains hb Pavlova ld Corona fC fC ld 16.7° 15.1° Figure 6. Magellan left-looking radar image of densely lineated mate- t Figure 7. Magellan left-looking radar image of flows from Didilia and Orczy rial forming the interior (fc) and rim structures (ld) of Didilia Corona, Pavlova Coronae, Mead quadrangle (V–21), Venus. Green line shows Mead quadrangle (V–21), Venus. We interpret radar-bright material at z Dors t boundary between corona flow (unit fc) and regional plains (unit pr) ld lower left to be coarse pyroclastic debris (unit hb). North at top; image Oju * 3.3° materials. Yellow line shows approximate boundary of flow complexes 5° s 5° e width 360 km. t l cu l Figure 4. Magellan left-looking radar image of plains material north- related to the two coronae; flows from Didilia Corona end at, or are a

Farida V east of Orczy crater in Mead quadrangle (V–21), Venus. Yellow arrows diverted by, the higher-standing Pavlova Corona flows. White arrows a ng show trace of sinuous channel system (Ganga Valles*). Green arrows show flow directions. Red arrows denote proximal terminations of pr a G show trace of wider, more subdued channel structure. Dome field and rough, radar-bright lava flows that are buried by younger, radar-dark pit craters may have also contributed to the broad homogeneous plains materials. North at top; image width 675 km. pr deposits in this region. North at top; image width 295 km. fP Orczy phO cu Disani t Ptesanwi t Corona 29° 33° 54° 61° 36° 38.1° Mons 13.5° 16° 14.5° pr t ld

fc

fD Manatum Tessera Nekhebe t Fluctus Gbadu phO Dzalarhons t Ovda Regio ld t Salus Tessera t Tessera phO de Ayala t ld Mons t pr 0° 0° 30° 35° 40° 45° 50° 55° 60° hb Descriptions of nomenclature used on map are listed at SCALE 1:5 198 991 (1 mm = 5.199 km) AT 0° LATITUDE Prepared on behalf of the Planetary Geology and Geophysics http://planetarynames.wr.usgs.gov/ 1:4 711 886 AT 25° LATITUDE Program, Solar System Exploration Division, Office of Space MERCATOR PROJECTION Science, National Aeronautics and Space Administration Edited by Jan L. Zigler 500 400 300 200 100 0KILOMETERS 100 200 300 400 500 Cartography by Darlene A. Ryan 25° Manuscript approved for publication September 12, 2005 20°

15° hb 10°

5° 9° 0°

ld Kali Mons 0.70 0.90 CORRELATION OF MAP UNITS AND MAJOR EVENTS poses regional plains material (unit pr) and flow materials of fracturing of deposit during cooling. Low emissivity suggests tion; typically of moderate radar brightness. Superposes 12° modest increase in bulk dielectric constant relative to planetary surrounding units and crater material, undifferentiated (unit MICROWAVE EMISSIVITY SOUTHERN coronae (unit fc); primarily occurs on exterior corona flank Figure 11. Magellan radar image of bright halo material (unit hb) WESTERN OVDA EASTERN EISTLA REGIO MATERIALBELL REGIO WIDESPREAD MAJOR EVENTS average cu). Interpretation: Melt generated by the impact event escapes slopes, with at least one point of contact with densely lineated 8.5° Figure 9. Color overlay of Magellan horizontally polarized emissivity associated with Pavlova Corona and a coronalike deformation zone to REGIO MATERIAL MATERIAL MATERIAL material (unit ld). Interpretation: Rough pyroclastic material from the crater cavity to form a lavalike flow deposit cMu Mead crater distal ejecta material—Radar-bright hummocky or Figure 8. Magellan left-looking radar image of central and northern data on radar image of Mead crater, Mead quadrangle (V–21), Venus. the southwest, Mead quadrangle (V–21), Venus. Unit designations erupted in most recent period of corona volcanism, likely by a patchy terrain. Features typically radial to Mead crater. Super- pr Regional plains material—Radar backscatter properties variable Kali Mons flow field, Mead quadrangle (V–21), Venus. Arrows show Green tones denote emissivity close to the planetary average of 0.84. correspond to densely lineated material (unit ld) and corona flow mate- ground-hugging surge mechanism rather than by airfall. poses unit pr; embayed by units fc and fM. Interpretation: due to density of ridges, but background terrain characterized — Small impacts margins of lava flows associated with enhanced microwave emissivity Lowest value of emissivity, in northeastern portion of crater floor, about rial (unit fc). Note radar-dark wind streaks along margins of bright Radar-dark streaks likely wind-deposited, fine material that Rugged ejecta from Mead crater impact event, embayed by by moderate to low radar backscatter, low rms slope. Embays (fig. 2). North at top; image width 420 km. 0.72. North at top; image width 740 km. regions, suggesting burial by relatively thin layers of fine material tens hb cu co blankets rough surface later flows from coronae to the west and other sources east and tessera and densely lineated material. High density of wrinkle — Eruption of pyroclastic material Figure 10. Sketch map of tectonic features surrounding Mead crater (lat 9°–16° N., of centimeters thick. North at top; image width 220 km. Localized flow material—Lobate deposits radiating from a central north of the crater ridges or fractures. Interpretation: Smooth complexes of sheet- fl long 54°–61° E.), Mead quadrangle (V–21), Venus. Wrinkle ridges, shown by heavy depression, low-relief dome, or chain of small domes in the like or flood lavas that have undergone extensive tectonic defor- cMt Mead crater terrace material—Moderate to low radar return; solid lines, are predominantly located on elevated terrain; ridges in the regional plains. Typically less than 200 km in radial extent; variable mation and formation of coronae and coronalike annular mottled image texture. Occurs on gently sloped terrain concen- plains material (unit pr) are overlain by younger materials (units fc and fM) that radar brightness. Superposes regional plains material (unit pr). tric to Mead crater floor. Interpretation: Topographic terrace features fN3 embay the crater ejecta blanket. North at top; image width 740 km. fM In northwestern portion of quadrangle, superposed by lobate formed as part of collapse of Mead crater cavity during impact t Tessera material—Radar-bright regions elevated relative to, and materials of unit fc. Interpretation: Lava flows associated with event. Surface materials likely represent overturned target embayed by, regional plains material (unit pr), flow material of — Extended period of effusive small shield volcanoes and calderas in the plains fc volcanism from coronae and terrain, because low-emissivity signature associated with crater coronae (unit ), and edifices; abundant fractures, ridges, and fc floor material (unit cMf) is not evident graben with multiple principal orientations. Interpretation: phO fl major shields Flow material of coronae—Low- to moderate-radar-return depos- cMf Highly deformed terrain. Original nature of material indetermi- 0° phB its radial to coronae and corona-like deformation patterns in ld Densely lineated material—Bright radar return, with typically 75° 75° 60° fP fD fc fK fC nate. Relative ages of isolated tessera outcrops indeterminate, eastern Eistla Regio. Morphology varies from sheetlike to single principal lineament orientation. Forms parts of corona V–1 fN but trend and shape of Gbadu and Mamitu Tesserae similar to cMu cMt 1 narrow lobes. Embays tectonically deformed rim and central rim deposits. Occurs as isolated outcrops embayed by regional — Mead Impact corona structures; superposes regional plains material (unit pr); plains (unit pr) and corona flow materials (unit fc). Interpreta- outcrops southwest and west of Bell Regio suggest a shared V–6 V–3 50° 50° topographically, is confined to south by deformation associated tion: Material of uncertain origin (though likely regional plains, contractional regime V–7 V–2 with Calakomana Corona. For Didilia and Pavlova Coronae, unit pr) that has been pervasively deformed by compression Mead narrow, lobate, radar-bright deposits are stratigraphically lower; Contact—Dashed where approximately located later materials form low-radar-return, sheetlike aprons that SOUTHERN BELL REGIO MATERIAL Sinuous rille V–17 V–10 fc embay and flood earlier lobate terrain. Interpretation: Lava fN3 Upper flow material of Nyx Mons—Complex of radar-bright, V–18 V–9 Isong ld flows erupted in association with corona formation. Relative lobate-margined deposits that is typically radial to Nyx Mons. Fracture V–19 V–8 Corona Calakomana 25° 25° age of flows from individual coronae, in general, indeterminate. Superposes radar-dark material of units fN1 and fN2 (in quad- Ninmah Corona — Uplift and coronae formation in For Didilia and Pavlova Coronae, earlier eruptions appear to rangle V–9) and regional plains material (unit pr) to the south. Wrinkle ridge heavily Dzalarhons wind ld Corona eastern Eistla Regio have higher volume or are more viscous, while later eruptions mantled pr Interpretation: Lava flows from a variety of source vents streaks Mons are characterized by lower eruption rate or lower viscosity Ridge associated with Nyx Mons that postdate unit pr and the materi- V–29 V–22 V–30 V–21 — Formation of Calakomana fK Flow material of Kali Mons—Low- to moderate-radar-return, als of units fN1 and fN2. Enhanced radar backscatter likely due V–31 V–20 Graben 30° Corona structure lobate deposits radial to Kali Mons. Superposes regional plains to rough surface texture at the 12.6-cm scale of the illuminating Pavlova 0° material (unit pr). To the northeast, characterized by moderate wavelength Calakomana Corona boundary 270° 300° 330° 0° 30° 60° 90° Corona 0° 0° to low radar backscatter and enhanced emissivity. Interpreta- fN1 Lower flow material of Nyx Mons—Low- to moderate-radar- — Beginning of regional plains tion: Lava flows from Kali Mons. Areas of enhanced emissivity return, lobate, and sheet-like deposits radial to Nyx Mons. Flow direction heavily emplacement may indicate a low-density, surface-mantling deposit or highly Superposes regional plains material (unit pr) and tessera mate- V–43 V–32 mantled Dome V–42 V–33 Didilia vesicular lava flow texture rial to the south. Interpretation: Lava flows from Nyx Mons V–41 V–34 pr ld t lobate Corona Planetary fC Flow material of Calakomana Corona—Low- to moderate- that postdate unit pr. Backscatter coefficients are consistent — Regional tectonic deformation Dome or circular scarp—Hachures point downslope margin radius (km) radar-return, lobate, and mottled deposits interior to Calakom- with terrestrial, smooth pahoehoe flows N 6,055 ana Corona, with low domical edifice in center of deposit; phB Homogeneous plains material of Bell Regio—Homogeneous Caldera or pit crater ° ° Figure 12. Magellan left-looking radar image of region southeast of moderate-radar-return, lobate deposits east of Calakomana that radar image texture. Superposes regional plains material (unit –25 –25 Crater rim showing crest V–55 V–44 Isong Corona (lat 7.0°–9.3° N., long 49.0°–52.6° E.), Mead quadrangle superpose local structure and regional plains material (unit pr). pr) in northwest corner of quadrangle. Moderate radar V–54 V–45 DESCRIPTION OF MAP UNITS high surface roughness from Dzalarhons Mons. Areas of high (V–21), Venus. Arrows denote areas of low radar return, inferred to be radar backscatter and low emissivity associated with formation Interpretation: Lava flows related to Calakomana Corona backscatter coefficient; low rms slope. Interpretation: Moder- V–53 V–46 Chain craters heavily mantled, and margins of mantling material that are lobate or 6,052 WESTERN OVDA REGIO MATERIAL fM Flow material near Mead crater—Moderate- to low-radar- ately rough plains formed by volcanic flooding, with relatively of surface coating or inclusions of high-dielectric phases conform to local topography. Unit designations correspond to densely fP backscatter, low-rms-slope deposits that embay Mead crater little post-emplacement deformation Surficial materials—Fine-grained material, likely produced by Flow material of Ptesanwi Mons—Low to moderate radar return; phO Homogeneous plains material of Ovda Regio—Homogeneous lineated material (unit ld), corona flow material (unit fc), and regional low rms slope. Lobate deposits radial to Ptesanwi Mons. Super- ejecta (units cMu, cMt) along north, south, and east sides of impact events, that mantles the underlying surface and reduces V–61 V–56 radar image texture. Superposes regional plains material (unit WIDESPREAD MATERIAL –50° –50° plains material (unit pr). North at top; image width 380 km. 6,050 poses regional plains material (unit pr) and embays north edge pr) and embays densely lineated material (unit ld) in southeast- crater. Image texture often featureless. Superposes regional backscatter return. Radar-dark deposits with feathery margins V–60 V–57 of Salus Tessera. At elevations above ~6,054 km radius, charac- ern portion of quadrangle. Low- to moderate-radar-backscatter plains material (unit pr), wrinkle ridges, pit craters, and other cu Crater material, undifferentiated—Radar-bright material occur as regional deposits, linear or arcuate streaks, and terized by very high radar backscatter and low emissivity. Inter- features in low terrain surrounding Mead crater. Contact with surrounding a central depression, rim materials, and floor mate- accumulations along east edges of topographic features such as V–62 coefficient; low rms slope. Associated with numerous pit 6,048 pretation: Lava flows of relatively low surface roughness from craters and small shield-like edifices. Interpretation: Plains unit fc uncertain and likely controlled by topography. Interpre- rials of radar-bright and radar-dark varieties; exterior deposits wrinkle ridges –75° –75° 30° 25° Ptesanwi Mons. Areas of high radar backscatter and low tation: Lava flows generated by volcanic sources north and east typically lobate, with patchy radar image texture and bright formed by volcanic flooding, with relatively little post- QUADRANGLE LOCATION Figure 13. Topographic map of Mead quadrangle (V–21), Venus, presented as a perspective view toward the emissivity associated with formation of surface coating or of Mead crater streaks radial to the central cavity. Superposes surrounding emplacement deformation. Possible sources include Verdandi Photomosaic showing location of map area. An outline of southwest. Radar-bright lineaments, interpreted as tectonic fractures, shown as white lines. Note that inclusions of high-dielectric phases units. Interpretation: Crater formed by impact. Hummocky (in quadrangle V–22) and Disani Coronae and small shield cMf Mead crater floor material—Moderate-radar-return, patchy 1:5,000,000-scale quadrangles is provided for reference. fractures associated with Pavlova Corona are largely confined to high-standing rim materials, while fractures texture of near-rim material reflects distribution of continuous fD Flow material of Dzalarhons Mons—Low- to moderate-radar- volcanoes and pit craters northeast of Orczy crater image texture; emissivity lower than planetary average in associated with Didilia Corona cut both rim and flank materials. return, moderate-rms-slope, lobate deposits radial to Dzalar- eastern portion of crater. Central region characterized by short, ejecta. Radar-bright floors may be fractured impact melt, while hons Mons. Superposes regional plains material (unit pr) and EASTERN EISTLA REGIO MATERIAL radar-bright lineaments; margins characterized by localized radar-dark floors may reflect post-emplacement volcanic flood- embays west edge of Gbadu Tessera. At elevations above hb Bright halo material—Localized deposits of very high radar return lobate or patchy variations in radar brightness. Interpretation: ing or smooth impact melt ~6,054 km radius, characterized by very high radar backscatter and high microwave emissivity have homogeneous appearance, Impact melt sheet formed during impact event or post- co Crater outflow material—Mottled or swirled radar image texture, and low emissivity. Interpretation: Lava flows of moderate to with radar-dark streaks at margins and feathery edges. Super- excavation lava flows. Crater floor lineaments may reflect with lobate margins and streaks parallel to the downhill direc-

Any use of trade, product, or firm names in this publication is for Geologic Map of the Mead Quadrangle (V–21), Venus descriptive purposes only and does not imply endorsement by the U.S. Government For sale by U.S. Geological Survey, Information Services, Box 25286, *Name provisionally accepted by International Astronomical Union By Federal Center, Denver, CO 80225, 1–888–ASK–USGS 1 2 Available on World Wide Web at http://pubs.usgs.gov/sim/2006/2897 1Center for Earth and Planetary Studies, Smithsonian Institution, Washington, DC Bruce A. Campbell and David A. Clark 2Department of Mathematics, University of California, San Diego, CA 2006 Printed on recycled paper