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The Tharsis region is an 8000-km-wide structural dome that incorporates a concentration of the main volcanic and tectonic activity on the Planet Mars. The area of structural doming is characterised by giant radial graben-dike systems. Nested on a set of these giant dikes to the northern side of Tharsis, is Alba Patera, one of the largest volcanoes in the planetary system. The regional dikes there are in arcuate arrangement and imply an E-W to NW-SE regional extension at Alba Patera. To assess the influence of regional and local tectonics, we studied the dike orientations on the volcano with Viking mosaic data and simulated plausible stress fields with finite element modelling. We found that the influence of a NW-SE regional extension was strong near the volcano centre but decreased rapidly in importance towards the northern pole, i.e., far from the Tharsis centre. By combining this regional stress with a broad uplift that is due to a buoyancy zone of about 1400 km in lateral extent and centred under Alba Patera, we reproduced the radial pattern of dike swarms that diverge from the Tharsis trend. Regional tectonics may have dominated the early stages of dike injection. During the evolution of Alba Patera, however, local updoming controlled the dike pattern, supporting the idea of a hotspot under Alba Patera. The well-expressed dike geometry and characteristics of Alba Patera provide an ideal example for comparative study with analogue hotspots on Earth where plate tectonics and active erosion may complicate the reconstruction of volcanic and tectonic history and the understanding of involved geodynamic processes. 相似文献
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Alberto G. Fairén James M. Dohm Miguel A. de Pablo Javier Ruiz Robert C. Anderson 《Icarus》2003,165(1):53-67
Throughout the recorded history of Mars, liquid water has distinctly shaped its landscape, including the prominent circum-Chryse and the northwestern slope valleys outflow channel systems, and the extremely flat northern plains topography at the distal reaches of these outflow channel systems. Paleotopographic reconstructions of the Tharsis magmatic complex reveal the existence of an Europe-sized Noachian drainage basin and subsequent aquifer system in eastern Tharsis. This basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels, and ponded to form various hypothesized oceans, seas, and lakes episodically through time. These floodwaters decreased in volume with time due to inadequate groundwater recharge of the Tharsis aquifer system. Martian topography, as observed from the Mars Orbiter Laser Altimeter, corresponds well to these ancient flood inundations, including the approximated shorelines that have been proposed for the northern plains. Stratigraphy, geomorphology, and topography record at least one great Noachian-Early Hesperian northern plains ocean, a Late Hesperian sea inset within the margin of the high water marks of the previous ocean, and a number of widely distributed minor lakes that may represent a reduced Late Hesperian sea, or ponded waters in the deepest reaches of the northern plains related to minor Tharsis- and Elysium-induced Amazonian flooding. 相似文献
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We documented the distribution and the time-variation of the specific dark wind streaks at Pavonis Mons. We focused on the streaks we named “Spire Streaks”, which are overlapping spindle shaped dark streaks at the upper boundary of the coalesced dark streaks on Tharsis volcanoes. We investigated both visible and infrared images obtained by Viking orbiter camera, Mars Orbiter Camera (MOC), THEMIS, CTX and HiRISE of the spire streaks at Pavonis Mons. We also used topographic data obtained by Mars Orbiter Laser Altimeter (MOLA) to see the relationship between the topography and the distribution of the spire streaks. The spire streaks at Pavonis Mons provide us high-resolution information about the direction of the nighttime slope wind, and could be indirect clues for the time-variation of the nighttime environment. We conclude that the spire streaks are erosional features. However, some features of the spire streaks reported in this paper are outside the scope of previous modeling for erosional process, and we need a new category of model for the formation. 相似文献
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Mars Global Surveyor (MGS) observations of crustal magnetic fields over Tharsis provide new constraints on models for the thermal and magmatic evolution of this region. We analyze the distribution of magnetic field anomalies over Tharsis surface units of Noachian, Hesperian and Amazonian age. These data suggest that early Noachian crust underlies the Tharsis province, and formed contemporaneously with the existence of a martian dynamo. This crust either pre-dates the formation of Tharsis, or formed during the earlier phases of Tharsis volcanism. The preservation of strong magnetic field anomalies over some of the earliest Noachian and topographically high units, together with the observation of magnetic field anomalies over Hesperian- and Amazonian-age surface units, indicate that a large fraction of the magnetized crust has remained cool (below the blocking temperature of the magnetic carrier) throughout the construction of Tharsis. Moreover, the distributions of magnetic anomaly amplitudes over Noachian, Hesperian, and Amazonian surface units suggest that the youngest units overlie sites of prolonged intrusion and have undergone a greater extent of thermal demagnetization. The absence of magnetic anomalies around the Tharsis Montes and Olympus Mons argues for strong, localized heating, as would be expected at volcanic centers. We show that end-member models for progressive thermal demagnetization of a Noachian magnetized crustal layer are consistent with the anomaly amplitude distributions. We integrate the magnetic field observations with constraints from tectonics, gravity, and topography, and present a revised scenario for the evolution of the Tharsis region. 相似文献
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Hlne Rouby Marianne Greff-Lefftz Jean Besse 《Earth and Planetary Science Letters》2008,272(1-2):212-220
Motion of the entire solid planet with respect to its spin axis have been proposed on Mars. This movement is known as True Polar Wander (TPW). According to the conservation of angular momentum with no external torque, on geological time scales the axis of maximum inertia of a planet is aligned with the rotation axis. Then rearrangement of masses within the mantle disturbs the planet's inertia and induces TPW. The convection pattern on Mars is possibly controlled by a sequence of single plumes originating from the core-mantle boundary. Using a homogeneous model of the martian mantle and modelling the plume as a sphere, we calculate the inertial tensor perturbations caused by the plume mass anomaly. We investigate the stabilizing influence of the remnant rotational bulge due to the lithosphere elasticity on these perturbations. It appears that, during early martian history, the elastic lithosphere was thin enough to allow its fractures under the inertia perturbations induced by a hot plume. Consequently, the lithosphere's behaviour became effectively viscoelastic and the plume could induce large TPW. We conclude that one plume convection pattern should have greatly influenced the rotation pole behaviour during early Mars history: around 4 Gyr ago, Mars already could have experienced two TPW events lasting possibly only a few million years each. We then compare our scenario with others already published in the literature. 相似文献
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D. L. Huston 《Journal of Geochemical Exploration》2001,72(1):135
The Western Tharsis disseminated Cu–Au orebody, which occurs within the Cambrian Mt Read Volcanics of Western Tasmania, is surrounded by a pyritic halo that extends 100–200 m stratigraphically above and below the ore zone. Although this halo extends laterally along the same stratigraphic position to the south, it probably closes off to the north based on limited surface and drill hole data. The ore zone is characterized by extreme enrichment (the enrichments and depletions referred to herein are relative to background; these have not been established using mass balance techniques) in As, Bi, Ce, Cu, Mo, Ni, S and Se; with the exception of Mo, these elements are also enriched, but at a much lower level, in the pyrite halo.Pronounced depletion in K, Cs and Mg occurs in 20–30 m wide stratiform zones that flank the orebody on both sides within the pyritic halo. These anomalies and depletions in Be, Ga, Rb, Y, MREE and HREE are associated with a pyrophyllite-bearing alteration zone that wraps around the main pyrite–chalcopyrite-bearing ore zone. This zone is also characterized by positive Eu anomalies which persist up to 150 m both into the hanging wall and footwall of the orebody. The depletion of these elements is consistent with the advanced argillic alteration assemblage developed about acid-sulfate Cu–Au deposits.The pyrite halo is surrounded by a peripheral carbonate halo which is highly enriched in C, CaO and MnO, and weakly enriched in Zn and Tl. Zinc and Tl are most enriched in the upper 100–150 m of the stratigraphically lower halo. In the stratigraphically upper halo, Zn and Tl values are anomalously high but erratic.Barium and Sr enrichment, although mainly restricted to the pyrite halo, extends into the stratigraphically lower carbonate halo by up to 100 m. A Na depletion anomaly extends from 150 m below the orebody and to at least the Owen contact (i.e. ≥400 m)in the hanging wall.The dispersion patterns observed at Western Tharsis are quite unlike those of Zn–Pb-rich volcanic-hosted massive sulfide (VHMS) deposits in western Tasmania. Rather, the dispersion patterns observed at Western Tharsis are more akin to those surrounding porphyry Cu deposits and related acid-sulfate Cu–Au deposits. 相似文献
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