Geologic map of the Agnesi quadrangle (V-45), Venus

Hansen, Vicki L.; Tharalson, Erik R.

doi:10.3133/sim3250

“…The contacts between adjacent units vary from well‐defined whereas in other cases are approximate or gradational, due to the angular nature of individual contacts or the style of the units or terrains. For example, shield terrain (unit st) consists of a thin veil of numerous in situ locally sourced deposits associated with individual shields, typically on the order of a few km or less across (Guest et al, 1992; Hansen, 2005); the location of the mapped contact could vary across tens and locally perhaps even hundreds of kilometers given the inherent challenges in recognizing individual shields and the wide variation in shield density (e.g., Hansen, 2009; Hansen & Tharalson, 2014). In the case of some basal terrains that were cut by fractures following host unit formation, and later locally buried by younger material, the contact between the basal terrain and younger units can be sharp, marked by fracture truncation.…”

Section: The Nma Geologic Mapmentioning

confidence: 99%

Geologic Map of the Niobe Planitia Region (I‐2467), Venus

López

¹

,

Hansen

²

2020

Earth and Space Science

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We present a 1:10M scale geologic map of the Niobe Planitia region of Venus (0°N-57°N/ 60°E-180°E). We herein refer to this area as the Niobe Map Area (NMA). Geologic mapping employed NASA Magellan synthetic aperture radar and altimetry data. The NMA geologic map and its companion Aphrodite Map Area (AMA) cover~25% of Venus' surface, providing an important and unique perspective to study global and regional geologic processes. Both areas display a regional coherence of preserved geologic patterns that record three sequential geologic eras: the ancient era, the Artemis superstructure era, and the youngest fracture zone era. The NMA preserves a limited record of the fracture zone era, contrary to the AMA. However, the NMA hosts a diverse and rich assemblage of material and structures of the ancient era and structures that define the Artemis superstructure era. These two eras likely overlap in time and account for the formation of basement materials and lower plain units. Impact craters formed throughout the NMA recorded history. Approximately 40% of the impact craters show interior flood deposits, indicating that a significant number of NMA impact craters experienced notable geological events after impact crater formation. This and other geologic relations record a geohistory inconsistent with postulated global catastrophic resurfacing. Together, the NMA and the AMA record a rich geologic history of the surface of Venus that provide a framework to formulate new working hypotheses of Venus evolution and to plan future studies of the planet.

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“…The contacts between adjacent units vary from well-defined whereas in other cases are approximate or gradational, due to the angular nature of individual contacts or the style of the units or terrains. For example, shield terrain (unit st) consists of a thin veil of numerous in situ locally sourced deposits associated with individual shields, typically on the order of a few km or less across (Guest et al, 1992;Hansen, 2005); the location of the mapped contact could vary across tens and locally perhaps even hundreds of kilometers given the inherent challenges in recognizing individual shields and the wide variation in shield density (e.g., Hansen, 2009;Hansen & Tharalson, 2014). In the case of some basal terrains that were cut by fractures following host unit formation, and later locally buried by younger material, the contact between the basal terrain and younger units can be sharp, marked by fracture truncation.…”

Section: Map Unitsmentioning

confidence: 99%

Geologic Map of the Niobe Planitia Region (I-2467), Venus.

López

¹

,

Hansen

²

2020

Preprint

Self Cite

View full text Add to dashboard Cite

We present a 1:10M scale geologic map of the Niobe Planitia region of Venus (0°N-57°N/ 60°E-180°E). We herein refer to this area as the Niobe Map Area (NMA). Geologic mapping employed NASA Magellan synthetic aperture radar and altimetry data. The NMA geologic map and its companion Aphrodite Map Area (AMA) cover~25% of Venus' surface, providing an important and unique perspective to study global and regional geologic processes. Both areas display a regional coherence of preserved geologic patterns that record three sequential geologic eras: the ancient era, the Artemis superstructure era, and the youngest fracture zone era. The NMA preserves a limited record of the fracture zone era, contrary to the AMA. However, the NMA hosts a diverse and rich assemblage of material and structures of the ancient era and structures that define the Artemis superstructure era. These two eras likely overlap in time and account for the formation of basement materials and lower plain units. Impact craters formed throughout the NMA recorded history. Approximately 40% of the impact craters show interior flood deposits, indicating that a significant number of NMA impact craters experienced notable geological events after impact crater formation. This and other geologic relations record a geohistory inconsistent with postulated global catastrophic resurfacing. Together, the NMA and the AMA record a rich geologic history of the surface of Venus that provide a framework to formulate new working hypotheses of Venus evolution and to plan future studies of the planet.

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“…Similarities between the two include the following: (i) each records a unique geodynamic process restricted to early planet evolution; (ii) both record extremely rich geologic histories, reflecting a progressive evolution of the specific terrain through time; (iii) the number, size and geometry are similar. For example, although the original areal extent of granite-greenstone terrain is unknown, the Superior Province is similar in size to crustal plateaux; (iv) both display gentle, subhorizontal, upright, long-wavelength folds (50-200 km; Abitibi Subprovince [96,97]; Yilgarn craton [98]; crustal plateaux [69,70,79,80]), with (v) upward stratigraphic facing [69,80,94,96,99]; (vi) both preserve evidence of high-strain, strike-parallel ductile shear zones that commonly terminate along strike and/or merge [89][90][91][92][93][94]97,98]; (vii) deformation accompanied by magmatic activity; (viii) both formed early, yet survived, at least locally, to modern time; and (ix) both involve high-T, high-fraction melting of the sublithospheric mantle, with melt rising to form the surface igneous province, and the melt residue forming a strong, buoyant root, which ultimately preserves the overlying surface igneous province.…”

Section: (C) Crustal Plateaux As An Analogue For Archaean Cratonsmentioning

confidence: 99%

“…Complex graben would form, cutting gentle long-wavelength folds. Ductile strike-parallel shear zones could develop locally [89][90][91][92][93], and large coherent tessera blocks within plateaux could translate or rotate [94,95].…”

Section: (B) Ancient Era Mechanismsmentioning

confidence: 99%