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1.
Rowe M. C.; Wolff J. A.; Gardner J. N.; Ramos F. C.; Teasdale R.; Heikoop C. E. 《Journal of Petrology》2007,48(11):2063-2091
The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO2)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements 相似文献
2.
Gray crystalline hematite on Mars has been detected in three regions, Sinus Meridiani, Aram Chaos, and Valles Marineris, first by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor (MGS) orbiter, and then confirmed by other instruments. The hematite-rich spherules were also detected by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum (Sinus Meridiani). Formation mechanisms of the hematite-rich spherules have been discussed widely since then. Here, we argue for an alternative formation mechanism, that is, the spherules originally formed at Valles Marineris due to the interaction of volcanic deposits and acidic hydrothermal fluids, and then were transported to and deposited at Meridiani Planum and Aram Chaos as alluvial/fluvial sedimentary deposits with other materials such as sulfates and rock fragments during the wash-out flows from Valles Marineris to Meridiani Planum and Aram Chaos. Diagenesis of the hematite-rich spherules may have also been a possible mechanism following sediment transport and emplacement. The hypothesis is consistent with available relevant information to date and provides an insight into the understanding of Martian surficial processes. 相似文献
3.
Most valley networks have been identified primarily in the heavily cratered uplands which are Noachian in age (>3.5 Gyr). A striking exception to this general observation is Warrego Valles located on the southeastern part of the Tharsis bulge. Recent data obtained by the Mars Orbiter Laser Altimeter, the Thermal Emission Imaging System (THEMIS) spectrometer and the Mars Orbiter Camera give new insight into the formation of valley networks and the early Mars climate. We focus our study on the southern Thaumasia region especially on Warrego Valles and determine the organisation of valleys in relation to regional topography and structural geology. Warrego Valles is the most mature valley network that incised the southern side of Thaumasia highlands. It developed in a rectangular-shaped, concave-up drainage basin. Four times more valleys are identified in THEMIS infrared images than in Viking images. Valleys exist on both sides of the main tributary contrary to what was visible in Viking images. Their distribution is highly controlled by topographic slope, e.g. there is a parallel pattern on the sides and dendritic pattern on the central part of Warrego Valles. We quantitatively analyse valley morphology and morphometry to determine the processes responsible for valley network formation. Warrego Valles displays morphometric properties similar to those of a terrestrial fluvial valley network. This valley network is characterised by seven Strahler's orders, a bifurcation ratio of 3, a length ratio of 1.7, a drainage density of 0.53 km−1 and a ruggedness number of 3.3. The hypsometric curve and integral (0.46) indicate that Warrego Valles reached the mature Davis’ stage. Valleys have undergone external degradation since their incision, which masks their main morphological characteristics. Our study supports the assertion that valley networks formed by fluvial processes controlled by an atmospheric water cycle. Further, they seem to develop by successive stages of erosion that occurred during Noachian through the late Hesperian. 相似文献
4.
Landslides in Valles Marineris (Mars): A possible role of basal lubrication by sub-surface ice 总被引：1，自引：0，他引：1
Fabio Vittorio De Blasio 《Planetary and Space Science》2011,59(13):1384-1392
There is much interest on the occurrence of water and ice in the past history of Mars. Because landslides on Mars are much better conserved than their terrestrial counterparts, a physical examination and morphological analysis can reveal significant details on the depositional environment at the instant of failure. A study of the landslides in Valles Marineris based on their physical aspect is presented and the velocity of the landslides is calculated with a stretching block model. The results show that the landslides were subject to strong basal lubrication that made them travel at high speed and to long distances. We use physical analysis to explore the four alternative possibilities that the natural lubricant of the landslides in Valles Marineris was either ice, deep water, a shallow carpet of water, or evaporites. Examination of the furrows present on the surface of the landslide deposits shows that either sub-surface ice or evaporites were likely present on the floor of Valles Marineris during the mass failures. 相似文献
5.
B. Imre 《Planetary and Space Science》2004,52(14):1303-1319
Valles Marineris offers a deep natural insight into the upper crust of Mars. The morphology of its slopes reflects the properties of the wall materials, thus constraining in models of composition and evolution of the upper layers of the Martian crust. Hence, knowledge about the lithological composition of these wall rocks is of major interest to the understanding of the geological and climatic history of Mars. This study investigates mechanical rock mass parameters of the northern wall of eastern Candor Chasma (between 290°E and 296°E longitude, −8° to −5° latitude). These are inferred from its present-day morphology and a proposed slope-forming history, applying a distinct element code to simulate the stability and the tectonic history of this slope within a parameter study. Additionally, a mathematical denudation model is applied to take into account the effect of exogenic processes on the slope. The study results show that two periods of normal faulting in conjunction with massive interim denudational scarp recess is a valid model for the evolution of the northern wall of eastern Candor Chasma. The estimated rate of scarp recess of 60 m Myr−1 is comparable with certain terrestrial scarp retreat rates. The best-fit models yield a homogenous distribution of low-level rock mass strength and deformability properties distributed over the entire stratigraphic column of the northern wall of eastern Candor Chasma. The values are 5.0 (±0.7) MPa for the uniaxial compressive strength, 1.6 (±0.2) MPa for the Brazilian tensile strength, 4.7 (±1.5) GPa for the Young's modulus, 0.2 (±0.15) for the Poisson's ratio, 22 (±2)° for the internal friction angle, 1.6 (±0.2) MPa for the cohesion and 2200 (±500) kg m−3 for the density. This study favors columnar jointed basalt as the material that builds up the northern wall of eastern Candor Chasma and other walls within central Valles Marineris. The best-fit denudational model of the upper slope section of the northern wall of eastern Candor Chasma indicates a distinct cap rock unit of lesser susceptibility to denudation than the wall rock below. 相似文献
6.
How do sediment yields from post‐wildfire debris‐laden flows depend on terrain slope,soil burn severity class,and drainage basin area? Insights from airborne‐LiDAR change detection 
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下载免费PDF全文 We derived a high‐resolution, spatially continuous map of erosion and deposition associated with the debris‐laden flows triggered by the 2011 Las Conchas wildfire and subsequent rainstorms over a 197 km2 area in New Mexico, USA. This map was produced using airborne‐LiDAR‐derived bare‐earth digital elevation models (DEMs) acquired approximately one year before and one year after the wildfire. Differencing of the pre‐wildfire and post‐wildfire‐and‐rainstorm bare‐earth DEMs yielded a DEM‐of‐difference (DoD) map that quantifies the magnitude of ground‐surface elevation changes due to erosion/deposition within each 1 m2 pixel. We applied a 0.3 m threshold filter to our DoD to remove changes that could have been due to artifacts and/or imperfect georeferencing. The 0.3 m value for the threshold filter was chosen based on the stated accuracy of the LiDAR as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the DoD filter. We developed an automated procedure that accepts the DoD map as input and computes, for every pixel in the DEM, the net sediment volume exported through each pixel by colluvial and/or fluvial processes using a digital routing algorithm. An analysis of the resulting sediment volume map for the Las Conchas fire demonstrates that sediment volume is proportional to upstream contributing area. After normalized by contributing area, the average sediment yield (defined as the sediment volume divided by the contributing area) increases as a power‐law functions of the average terrain slope and soil burn severity class (SBSC) with exponents equal to approximately 1.5. Our analysis quantifies the relationships among sediment yield, average terrain slope, and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire‐affected drainage basins. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
Noncondensible gases from hot springs, fumaroles, and deep wells within the Valles caldera geothermal system (210–300°C) consist of roughly 98.5 mol% CO2, 0.5 mol% H2S, and 1 mol% other components. 3He/4He ratios indicate a deep magmatic source (R/Ra up to 6) whereas δ13C–CO2 values (−3 to −5‰) do not discriminate between a mantle/magmatic source and a source from subjacent, hydrothermally altered Paleozoic carbonate rocks. Regional gases from sites within a 50-km radius beyond Valles caldera are relatively enriched in CO2 and He, but depleted in H2S compared to Valles gases. Regional gases have R/Ra values ≤1.2 due to more interaction with the crust and/or less contribution from the mantle. Carbon sources for regional CO2 are varied. During 1982–1998, repeat analyses of gases from intracaldera sites at Sulphur Springs showed relatively constant CH4, H2, and H2S contents. The only exception was gas from Footbath Spring (1987–1993), which experienced increases in these three components during drilling and testing of scientific wells VC-2a and VC-2b. Present-day Valles gases contain substantially less N2 than fluid inclusion gases trapped in deep, early-stage, post-caldera vein minerals. This suggests that the long-lived Valles hydrothermal system (ca. 1 Myr) has depleted subsurface Paleozoic sedimentary rocks of nitrogen. When compared with gases from many other geothermal systems, Valles caldera gases are relatively enriched in He but depleted in CH4, N2 and Ar. In this respect, Valles gases resemble end-member hydrothermal and magmatic gases discharged at hot spots (Galapagos, Kilauea, and Yellowstone). 相似文献
8.
This article documents the clastic nature of sulphate evaporite beds in the Tithonium Chasma located in the Valles Marineris region of Mars. These beds form a stratified succession characterised by very thick interbedded channel-fill breccia bodies. We infer that the bouldery channel-fills were deposited by voluminous mass-flow processes occurring in a relatively deep subaqueous environment. The redeposition of the coarse-grained evaporite would have responded to phases of high denudation rates in rapidly uplifting hinterlands. Tectonic activity also caused the diapiric uprise and exhumation of evaporite diapirs within the Valles Marineris chasmata, where the apparently young and well development karstic landforms probably formed during the late Amazonian age. These new data strongly suggest the deposition of both primary and resedimented evaporites in a marginal basin area, which effectively restricted ocean access through the proposed “proto-Valles Marineris Strait”. The associated ocean may be the “Ocean Borealis” of Late Noachian-Early Hesperian age. 相似文献
9.
The planet Mars has a bimodal albedo distribution with bright and dark regions. Earth-boundreflectance spectra ofbright Martian
regions are generally characterized by a flat to positive continuum slope in the near-infrared (NIR), while those of dark
regions tend to have a negative slope. Spectra obtained with the instrument ISM (Imaging Spectrometer for Mars) onboard the
Phobos 2 spacecraft usually show the same relationship between brightness and NIR continuum slope. Nevertheless, some ISM
spectra show deviations from this relationship, the most conspicuous ones being observed in the Syrtis Major and Valles Marineris
regions, where some dark areas are characterized by a flat continuum slope. So far, this was interpreted to indicate a basaltic
material covered with a weathering coating or a thin layer of dust. The results of a new spectroscopic investigation of analog
materials for the Martian crust revealed that reflectance spectra of bulk samples generally show a preference for a negative
NIR continuum slope, in contrast to spectra of powder samples. This suggests a different interpretation of the ISM spectra,
namely that the unusual dark regions, which are characterized by a flat NIR continuum slope, are covered by sand-sized basaltic
particles. In contrast, the common dark regions, which are characterized by a blue continuum slope, are dominated by bedrock
or blocky basalt rocks. This interpretation is in agreement with the findings of other methods of remote sensing.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Steve J. Chipera Fraser Goff Cathy J. Goff Melissa Fittipaldo 《Journal of Volcanology and Geothermal Research》2008
Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite–clinoptilolite–mordenite–silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow “caldera-type zeolitization” as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to “caldera-type zeolitization.” Resource Geol. Spec. Issue No. 20, 129–140]. Geology and 40Ar/39Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (≤ 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance. 相似文献