The Causes and Consequences of the Crustal Dichotomy and Their Implications for the Early Evolution of Mars
نویسنده
چکیده
Introduction: The two most striking surface features on Mars are the crustal dichotomy and the Tharsis Rise [1]. While it is generally accepted that the Tharsis Rise is formed as a result of plume related volcanism [2], the formation mechanism for the crustal dichotomy is controversial with two main competing proposals: endogenic (mantle convection and flow) [3-5] and exo-genic (mega-impact) mechanisms [6]. Recent studies on modeling mega-impact and reconstructing dichot-omy boundary revive the mega-impact mechanism for the crustal dichotomy [7-9]. However, because the crustal dichotomy, as the oldest feature on Mars (i.e., the pre-Noachian or >4.1 Ga) [10], has been significantly modified by later processes such as the Tharsis formation, it is difficult to constrain the formation mechanism for the crustal dichotomy. The Tharsis Rise is a younger feature and is formed during the Noachian (4.1-3.8 Ga) [11]. Both the crustal dichotomy and Tharsis Rise represent hemispheric asymmetric structrures (i.e., degree-1 feature) in that the crustal dichotomy marks the difference between the northern and southern hemispheres, while the Tharsis Rise repressents the difference between the western and eastern hemispheres. Although the center of Thar-sis is near the dichotomy boundary at the equator, geo-physical and geological observations suggest that Thar-sis volcanisms may have initiated in the southern highlands (e.g., the Thaumasia region at ~40 o S) and subsequently migrated to the current positions [12,13]. Recently, Zhong [14] suggested that the crustal di-chotomy has an important effect on formation and evolution of the Tharsis Rise and volcanism. The key to Zhong's proposal is that the crustal dichotomy repressents lateral variations in lithospheric shell thickness which interacts with one-plume convection to give rise to the differential rotation between the lithospheric shell and the underlying mantle with one-plume con-vection, thus explaining the migration of Tharsis vol-canisms. This indicates that the Tharsis volcanism and tectonism may provide important constraints on the formation mechanism of the crustal dichotomy. The goal of this study is to critically examine both endogenic and exogenic formation mechanisms for the crustal dichotomy. In particular, we seek constraints on the formation mechanism, by further exploring the consequences of the crustal dichotomy from these two different mechanisms on volcanisms and tectonisms and their relation to the Tharsis Rise.
منابع مشابه
On The Dynamic Origin Of The Crustal Dichotomy and Its Implications For Early Mars Evolution
متن کامل
Geochemical evolution and petrogenesis of the eocene Kashmar granitoid rocks, NE Iran: implications for fractional crystallization and crustal contamination processes
Kashmar granitoids of Taknar zone, in north part of Lut block, intruded into volcanic rocks and consist of granites, granodiorites, monzodiorite and gabbrodiorites. They are composed of mainly plagioclase, alkali-feldspar, quartz, amphibole, biotite and pyroxene minerals. Harker diagram variation, including negative correlations CaO, MgO, FeO, TiO2 and V and positive correlations K2O, Rb, Ba, a...
متن کاملAge and Origin of the Crustal Dichotomy in Eastern Mars
The topography associated with the fundamental crustal dichotomy in much of eastern Mars can be largely ascribed to a single event: the very large impact which produced the Utopia Basin. Subsequent internal and surficial processes have been unable to remove the topographic signature of this basin. In particular, endogenic processes appear to have been ineffective in contributing to the basic di...
متن کاملPolar Wander of Mars Driven by Degree-1 Mantle Convection and Its Implications for the Formation of the Crustal Dichotomy and the Tharsis Rise
The topography on Mars is dominated by the crustal dichotomy between the northern and southern hemispheres and the Tharsis rise on the equator[1]. No explanation has been offered so far as to why the dichotomy should be in its current orientation rather than another. The geoid is currently dominated by Tharsis [2] and rotational stability suggests that a Tharsis-sized load would induce polar wa...
متن کاملLithospheric flexure and the evolution of the dichotomy boundary on Mars
[1] The boundary of the Martian crustal dichotomy in the eastern hemisphere is one of the most striking topographic features on the planet. The long wavelength topography of much of the boundary is expressed by a broad rise and an arched ramp that slopes downward from the southern highlands into the northern lowlands and often ends in a steep scarp. Lithospheric flexure of the southern highland...
متن کامل