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K. L. Tanaka

Publications and source records attributed to K. L. Tanaka.

At least 55 records · Page 3Linked to original sources
USGS1999

Debris-flow origin for the Simud/Tiu deposit on Mars

A late Hesperian smooth plains deposit on Mars interpreted as a debris flow extends more than 2000 km from Hydraotes Chaos, through Simud and Tiu Valles, and into Chryse Planitia. The Simud/Tiu deposit widens out to >1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity. Morphologic features of the Simud/Tiu deposit observed in Viking and Pathfinder images are generally consistent with a debris-flow origin, but some of the deposit's salient features are not readily explained by catastrophic flooding or ice flow. Internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow. Possible flow lobes within the deposit may have formed by successive flow surges within the flow unit. The Pathfinder landing site is on the Simud/Tiu deposit, and the observations there are consistent with debris flow. The low, longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt. Imbricated, planar rocks on the ridges, such as in the Rock Garden, also may have been emplaced by debris or ice flow. However, stream energy calculations at Ares Vallis and channel geology indicate that flooding probably was incapable of emplacing the meter-size boulders observed at the Pathfinder site. Dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long. Local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material. The debris-flow unit apparently coalesced from outflows of water-fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of Simud and Tiu Valles. The deposit is onlapped from the north by another flow deposit originating from Acidalia Planitia. If the Simud/Tiu debris flow had entered a standing body of water, a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the Acidalia deposit.

Journal of Geophysical Research E: Planets↗
USGS1998

Erosional valleys in the Thaumasia region of Mars: Hydrothermal and seismic origins

Analysis of erosional valleys, geologic materials and features, and topography through time in the Thaumasia region of Mars using co-registered digital spatial data sets reveals significant associations that relate to valley origin. Valleys tend to originate (1) on Noachian to Early Hesperian (stages 1 and 2) large volcanoes, (2) within 50–100 km of stages 1 and 2 rift systems, and (3) within 100 km of Noachian (stage 1) impact craters >50 km in diameter. These geologic preferences explain observations of higher valley-source densities (VSDs) in areas of higher elevations and regional slopes (>1°) because the volcanoes, rifts, and craters form high, steep topography or occur in terrain of high relief. Other stage 1 and stage 2 high, steep terrains, however, do not show high VSDs. The tendency for valleys to concentrate near geologic features and the overall low drainage densities in Thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation (as is proposed in wann, wet climate scenarios) except perhaps during the Early Noachian, for which much of the geologic record has been obliterated. Instead, volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation, melting of ground ice and snow, and groundwater sapping. However, impact-crater melt would provide a heat source at the surface that might drive away water, fonning valleys in the process. Post-stage 1 craters mostly have low nearby VSDs, which, for valleys incised in older rocks, suggests burial by ejecta and, for younger valleys, may indicate desiccation of near-surface water and deepening of the cryosphere. Later Hesperian and Amazonian (stages 3 and 4) valleys originate within 100–200 km of three young, large impact craters and near rifts systems at Warrego Valles and the southern part of Coprates rise. These valleys likely developed when the cryosphere was a couple kilometers or more thick, inhibiting valley development by hydrothermal circulation. However, eruption of groundwater may have occurred from impact-induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping. The two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau. In the case of the larger crater (Lowell, 200 km in diameter), potential aquifers would likely be at depths of kilometers below the cryosphere. Seismic energy generated by the Lowell impactor would have been much greater, pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit. Along the margin of Thaumasia, tectonic pressurization of groundwater also may have contributed to valley formation. Dissection of rim materials of the Argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta.

Journal of Geophysical Research E: Planets↗
USGS1998

Digital structural mapping of Mars

Magmatic and tectonic activity have both contributed significantly to the surface geology of Mars. Digital structural mapping techniques have now been used to classify and date centers of tectonic activity in the western equatorial region. For example, our results show a center of tectonic activity at Valles Marineris, which may be associated with uplift caused by intrusion. Such evidence may help explain, in part, the development of the large troughs and associated outflow channels and chaotic terrain. We also find a local centre of tectonic activity near the source region of Warrego Valles. Here, we suggest that the valley system may have resulted largely from intrusive-related hydrothermal activity. We hope that this work, together with the current Mars Global Surveyor mission, will lead to a better understanding of the geological processes that shaped the Martian surface.

Astronomy and Geophysics↗
USGS1997

Sedimentary history and mass flow structures of Chryse and Acidalia Planitiae, Mars

Geologic mapping and crater counting in Chryse and Acidalia Planitiae (GAP) reveal five major sedimentary deposits of Hesperian to Early Amazonian age, including (1) a mass flow deposited during the Early Hesperian near Deuteronilus Mensae (northeast of the map region) that may have resulted from the carving of Kasei Valles, >3000 km southwest of the exposed part of the deposit; (2) knobby plains material consisting of channel (likely; from Simud and Tiu Valles and possibly Ares and Shalbatana Valles) and mass-wasting deposits in central and eastern CAP; (3) material largely from Maja and Ares Valles emplaced in at least western and southern CAP (outcrops in southern Chryse Planitia developed thermokarst); (4) a thin mass flow covering much of southern Chryse Planitia that emanated from Simud and Tiu Valles; and (5) a thick, extensive (perhaps >3500 km across) mass flow deposit in central and northern CAP derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits. Other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature. Various associated landforms appear to be consistent with the mass flow interpretations, including lobate and linear scarps along deposit edges, fractures related to desiccation of thick sediments, troughs, and ridges near the edges of the deposit indicative of secondary mass movement and deformation, pitted domes and fissure-fed flows possibly formed by sedimentary (mud) eruptions, and longitudinal channel grooves perhaps formed by roller vortices. No convincing evidence for paleoshorelines or stagnant ice sheets is found in CAP. These findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow-channel dissection in CAP. Elsewhere in the northern plains, similar landforms are prevalent. The mass flow interpretation does not require either multiple episodes of extraordinarily high water-discharge rates achieved by freeing huge volumes of water from the crust, repetitive recycling of immense volumes of water into highland aquifers at the heads of Chryse channels, or profound climate change. Mars Pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of Simud and Tiu Valles.

Journal of Geophysical Research E: Planets↗
USGS1996

Extension across Tempe Terra, Mars, from measurements of fault scarp widths and deformed craters

Two independent methods, with no common assumptions, have been used to estimate the extension across the heavily deformed Tempe Terra province of the Tharsis region of Mars. One method uses measurements of normal fault scarp width with average scarp slope data for simple grabens and rifts on Mars to estimate the fault throw, which, combined with sparse fault dip data, can be used to estimate extension. Formal uncertainties in this method are only slightly greater than those in other methods, given that the total uncertainty is dominated by the likely uncertainty in the fault dip (assumed to be 60° ± 15°). Measurement of normal fault scarp widths along two N25°–50°W directed traverses across Tempe Terra both yield about 22 ± 16 km of extension (or ∼2% strain across the northern traverse and nearly 3% across the southern one). About three quarters of the extension has occurred during the two main phases of Tharsis-related deformation from Middle/Late Noachian to Early Hesperian and from Late Hesperian to Early Amazonian, with more extension closer to the center of Tharsis during the first phase. Extension across the region was also determined by measuring the elongation and elongation direction of all ancient Noachian impact craters without ejecta blankets, which predate most of the deformation. Results have been corrected for initial non circularity of craters, established from similar measurements of young (post deformation) impact craters, yielding a statistically significant mean strain of 1.96 ± 0.35% in a N38° ± 10°W direction across Tempe Terra (extension of ∼20 ± 4, comparable in magnitude and direction to the average result from the scarp measurement method). Both methods indicate an average extension for single normal fault scarps (and shortening across wrinkle ridges for the crater method) of ∼100 m. The agreement between the results of the two independent methods in overall extension and average single normal fault extension argues that the average scarp slope and fault dip data in the fault scarp width method accurately represent the actual extension across the observed structures. This conclusion supports existing geometric and kinematic models for structural features on Mars. A preliminary estimate of the total circumferential extension around Tharsis (at a radius of ∼2500 km) is roughly 60 ± 42 km; total hoop strain is about 0.4% distributed heterogeneously (Tempe Terra is the most highly strained region on Mars).

Journal of Geophysical Research E: Planets↗
USGS1995

Geologic/geomorphologic map of the Chryse Planitia region of Mars

Since the 1970’s, when the Mariner 9 spacecraft revealed the geologic diversity of Mars, the Chryse Planitia region has been noted for its immense outflow channels and chaotic terrain (McCauley and others, 1972; Sharp and Malin , 1975; Baker, 1982, chap. 3; Mars Channel Working Group , 1983). Various proposals for the origin of these features have been offered; most workers have favored a mechanism in which ground water or water-rich debris was expelled from beneath a frozen crust, leading to catastrophic debris flows o r floods that may have contained significant amounts of ice (Baker and Milton, 1974; Carr , 19 79; Nummedal and Prior, 1981; Lucchitta , 1982 ; MacKinnon and Tanaka, 1989). The channels originated on or near the flanks of the volcanotectonic rises of Tharsis (whose east margin is in the west edge of the map region) and Valles Marineris , which suggests that tectonics and igneous activity led to the conditions for discharge. Estimated discharge rates for some channels exceed thos of prehistoric floods on Earth ( Carr , 1979; Komar , 1979; Robinson and Tanaka, 1990) . Some workers think that the discharges may have led to the development of temporary oceans that filled the northern lowlands (Parker and others, 1989; Baker and others, 1991). The Chryse basin ( Chryse and southern Acid alia Planitiae ), which is part of those lowlands, apparently has been the site of lava and sediment deposition (Greeley and others, 1977; Scot and T anaka, 1986).

IMAP↗
USGS1994

Geologic maps of the Olympus Mons region of Mars

Olympus Mons is one of the broadest volcanoes and certainly the tallest in the Solar System. It has been extensively described and analyzed in scientific publications and frequently noted in the popular and nontechnical literature of Mars. However, the first name given to the feature-Nix Olympica (Schiaparelli, 1879)-was based on its albedo, not its size, because early telescopic observations of Mars revealed only albedo features and not topography (lnge and others, 1971). After Mariner 9 images acquired in 1971 showed that this albedo feature coincides with a giant shield volcano (McCauley and others, 1972), the name Olympus Mons was adopted for the shield to distinguish it from the albedo feature. Olympus Mons is one of the most photographed features on the planet. The Mariner 9 spacecraft obtained 126 images of Olympus Mons with resolutions of 60 m/pixel to 2.5 km/pixel. Later, the two Viking orbiters greatly enlarged this dataset, acquiring more than 2,150 images of the Olympus Mons region at various resolutions and altitudes; 925 images have resolutions of better than 50 m/pixel. More than 150 of the Viking images provide stereoscopic coverage of the shield region (Blasius and others, 1982).

IMAP↗
USGS1992

Geologic map of the Elysium region of Mars

The region centered at Elysium Mons contains that second largest volcanic complex on Mars, surpassed in size by only the Tharsis complex. The Elysium region also has been a center of tectonic, fluvial , and mass-wasting activity. After degradation of ancient cratered terrain within the northern lowlands, volcanic rocks erupted from Elysium Mons, Hecta s Tholus, and Albor Tholus in Elysium Planitia. The volcanic activity was associated with episodes of channel formation, faulting, and apparent volcano/ground-ice modifications of some areas . On this map sheet we portray, describe, and interpret the rich geologic history of the region.

IMAP↗
USGS1991

Geologic map of the Valles Marineris region, Mars

The Valles Marineris region lies east of Thar sis Montes (which extend from lat 12 ˚ to 16˚., long 101 ˚ to 125˚). Part of the region is in the midst of a vast plateau bounded on the west and east by Claritas and Nectaris Fossae, respectively; the remainder extends farther east into southern Xanthe Terr and western Margar itifer Terra. Channel trends, stereophotogrammetry , and radar altimetery indicate that the surface north and east of the canyons sl o pes toward Chryse Planitia ( centered at about lat 25˚ N., long 45˚). Within the broad Valles Marineris region, three distinct physiographic provinces are recognized (fig. 1): (1) the Noctis Labyrithus province, consisting of a high plateau cut by a network of structurally controlled troughs; (2) the Valles Marineris province, characterized by broad, linear valleys hundreds of thousands of kilometer s long; (3) the eastern canyon province , containing irregular depressions as much as 900 km across. Topography has been determined from a preliminary stereophotogrammetric map having a contour interval and a precision of about 1 km (Wu and others, 1986) and from latitudinal tracks of radar altimetry have a pre cision of 200 m (Roth and others, 1980).

IMAP↗
USGS1987

Geologic map of the polar regions of Mars

These geologic maps of the north and south polar regions of Mars, extend ing to 55 ˚ north and south latitudes, overlap by 2 ˚ the geologic maps of the western and eastern regions, which extend to lat ± 57 ˚ . The maps were compiled from Viking medium-resolution photomosaics at scales of 1:2,000,000 and from higher resolution Viking images. The quality and resolution of the Viking pictures are superior to those of Mariner 9 used to prepare the previous maps (Scott and Carr , 1978) that includes these two regions. Because of the Viking orbital configuration, a vast number of high-resolution images of the area within 10 ˚ of the north pole was obtained, whereas many areas in lower northern latitudes were covered only by low-resolution images. In contrast, the south polar region is nearly completely covered by images at medium resolution but is not image d at high resolution.

IMAP↗
USGS1986

Migration of volcanism in the San Francisco volcanic field, Arizona

The remanent magnetization of volcanic rocks has been determined at 650 sites in the San Francisco volcanic field in the southern part of the Colorado Plateau. The polarity of remanent magnetization—combined with K-Ar age determinations, spatial and petrographic associations, stratigraphic relations, and state of preservation of the cinder cones—provides a basis for assignment to known magnetic polarity epochs of 610 mafic vents and >100 intermediate to silicic flows, flow sequences, and vents. The age assignments for basaltic rocks include 243 Brunhes (<0.73 Ma) vents, 220 Matuyama (0.73 to 2.48 Ma) vents, and 147 pre-Matuyama (2.48 to about 5.0 Ma) vents. Basaltic volcanism migrated northeastward before Matuyama time at a rate of ∼1.2 cm/yr and eastward (S87° ± 5°E) over the past 2.5 m.y. at a rate of 2.9 ± 0.3 cm/yr. Concomitant acceleration in total magma production (from 75 to 1,400 × 10 −6 km 3 /yr) and frequency of basaltic eruptions (from 1 per 17,000 yr to 1 per 3,000 yr) occurred between 5 and 0.25 Ma. For the past 0.25 m.y., magma production (∼180 × 10 −6 km 3 /yr) and perhaps eruption frequency have decreased. This evolutionary sequence, coupled with the lead and strontium-isotopic composition of the rocks, can be explained by magmatism caused by shear heating at the base of the lithosphere. We propose that this eastward drift of volcanic activity represents absolute westward motion of the North American plate. Our model is in agreement with a model in which the African plate is fixed to the deep mantle.

Arizona↗
USGS1986

Geologic map of the western equatorial region of Mars

The r egional topographic swell centered in the Tharsis Montes and Syria Planum extends over one-third of the map area (U.S. Geological Survey, 1976). Within this high region are the four largest and youngest volcanoes on Mars: Olympus Mons, Arsia Mons, Pavonis Mons, and Ascrae us Mons. The latter three collectively form the large northeast-trending, volcanic mountain chain of the Tharsis Montes. This volcanic chain lies athwart the global highland - lowland boundary that transects the western equatorial region. The boundary, where not covered b young lava flow s, is marked by a gentle, irregular scarp bordered by clusters of low knobby hills. It separates the relatively smooth, flat, spar sely cratered northern plains from the higher, rougher, more densely cratered plateau terrain of the southern highlands . A vast system of canyons, the Valles Marineris , originates in Noctis Labyrinthus , just east of the Tharsis -Sy ria swell, and extends eastward for several thousand kilo meters. Ancient rivers channels appear to have sources in canyons and chaotic terrain north of Valles Ma rineris and in a large fissure at the head of the Mangala V alles. Visible remnants of large circular basins are not as common on Mars as on the Moon, probably because of more active erosion and deeper burial on Mars by eolian and fluvial activity and by widespread volcanism on both the highlands and plains. The youngest and b est preserved impact basin on Mars, lying in the western hemisphere , is more than 1,00 0 km across. It has a broad flat floor ( Argyre Planitia) covered by eolian materials and volcanic flows ; the floor is several kilometers below its encompassing rough mountainous rim.

IMAP↗
USGS1985

Ice-lubricated gravity spreading of the Olympus Mons aureole deposits

Gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of Olympus Mons. Detachment sliding could have occurred around the volcano if either pore-fluid pressures were exceptionally high (greater than 90%) or the rocks had very low resistance to shear (about 1 × 10 5 Pa or 1 bar). Because of the vast areal extent and probable shallow depth of the detachment zone, development of ubiquitous, high pore-fluid pressures beneath aureole-forming material was unlikely. However, a zone of sufficiently weak material consisting of about 10% interstitial or interbedded ice could have been present. If so, a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer. According to this model, extensional deformation would have occurred near the shield and compressional deformation in its distal parts. Proximal grabens and distal corrugations on aureole surfaces support this model. A submarine slide at Kitimat Arm, British Columbia, is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits. Ground-ice processes have been considered the cause of many geologic features on Mars; a 3% average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere. Ice may have been deposited in higher concentrations below the aureole-forming material; the source of the ice could have been juvenile water circulated hydrothermally by Olympus Mons volcanism. The basal scarp of Olympus Mons apparently demarcates the transition between the upper, stable part of the shield and its lower part that decoupled and formed the aureole deposits. This transition may reflect a change in the bulk shear strength of the shield, caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano. Other Martian volcanoes exhibit virtually no evidence of similar large-scale gravity spreading and basal scarps. Perhaps such evidence, if it existed, has been buried by lava flows, or perhaps the smaller size of other volcanoes did not permit the development of these features.

Icarus↗