|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|156533||2017||22 صفحه PDF||سفارش دهید||16850 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Planetary and Space Science, Volume 144, 15 September 2017, Pages 49-70
In this paper, we present the results of our detailed study of morphology, topography, and age of the Deuteronilus contact that outlines Vastitas Borealis Formation (VBF) in the northern plains and the Isidis Planitia unit. The Deuteronilus contact represents a sharp and distinct geological boundary that can be traced continuously for many hundreds to thousands of kilometers. In the northern plains, segments of the Deuteronilus contact occur at two distinct topographic levels. In the northern plains, the long-wavelength topography of the Deuteronilus contact occur at two distinct topographic levels. In the Tempe, Chryse, Acidalia, and Cydonia-Deuteronilus regions (the total length is â¼14,000Â km), the contact is at the mean elevation of about â3.92Â km (the decile range is 180Â m, from â4.01Â km to â3.83Â km). In the Pyramus-Astapus, Utopia, and Western Elysium regions (the total length is â¼7700Â km), the mean elevation of the contact is about â3.58Â km (the decile range is 270Â m, from â3.73Â km to â3.46Â km). These levels to large extent (but not completely) correspond to the model geoids that may have been characterized the shape of Mars at the time of the VBF emplacement. Largest deviations of the actual topographic position of the contact from the model geoids occur in the Tantalus and Phlegra regions where the deviations are due to the post-VBF changes of the regional topography. The fact that the model geoids satisfactory describe the shape of the largest portion of the contact provides additional evidence for both the emplacement of the VBF edges near an equipotential surface and for relative stability of the shape of Mars during a long time interval of about 3.6 Ga. Within the northern plains in the Tempe Terra, Acidalia Planitia, Cydonia-Deuteronilus, Pyramus-Astapus, and the southern Utopia regions, the absolute model ages of the VBF surface near the Deuteronilus contact are tightly clustered around the age of â¼3.6 Ga, which we interpret as the age of the VBF emplacement. The surface of the VBF-like Isidis Planitia unit is distinctly younger, â¼3.50Â Â±Â 0.01 Ga, which suggests that this unit formed independently. Neither volcanic nor glacial modes of emplacement are consistent with the topographic configuration and the shape of the Deuteronilus contact within both the northern plains and in Isidis Planitia. The broad flooding and formation of extensive water/mud reservoirs remains to be the most plausible mode of formation of the VBF in the northern plains and the VBF-like unit on the floor of the Isidis basin.