Lunar and Planetary Science XXXIV (2003) 1314.pdf GEOLOGICAL PROCESSES IN THE BAIKAL RIFT ZONE: POSSIBLE TERRESTRIAL ANALOGS FOR THE VALLES MARINERIS REGION ON MARS. G. Komatsu, International Research School of Plane- tary Sciences, Universita’ d’Annunzio, Viale Pindaro 42, 65127 Pescara, Italy, [email protected] Introduction: Recent researches are shedding new their formation coincided with extensive glaciation in lights on the evolution of Valles Marineris and neigh- the region. The ice caps of various sizes developed boring chaotic terrain and outflow channels. For ex- over high plateaus of southern Siberia during the Qua- ample, Chapman and Tanaka [1] proposed a hypothe- ternary [4]. The drainage system of the region was sis with an emphasis on magma-ice interactions for the reorganized due to changes in precipitation, tempera- formation of chasmata, interior deposits, chaotic ter- ture and humidity, but also because the ice caps rain, outflow channels, and surface materials. Terres- blocked water flows [5]. Cataclysmic floods also oc- trial analog studies are useful in providing examples of curred along the Yenisei River as ice-dammed lakes processes that may have operated in this complex re- upstream collapsed. Jökulhlaup-type floods due to the gion on Mars. I here introduce some geological proc- subice eruptions of the Azas Plateau and other volcanic esses of the Baikal Rift Zone in southern Siberia, provinces related to the Baikal Rifting are a distinct which could be compared with those in the Valles possibility. Permafrost is widely developed in Siberia Marineris region. Many of the proposed geological and magma-groundice interactions could have played activities of the Valles Marineris region have occurred an important role in the geomorphology of the region. also in the Baikal Rift Zone. Therefore, comparisons Comparisons with the Valles Marineris Region: of these two unique regions on Earth and Mars could Many geological processes that characterize the Ice provide potentially very rich understanding of how Age southern Siberia can be envisaged in the ancient elements such as rift volcanism and climate influence Valles Marineris region. The Valles Marineris has each other, and of the important role hydrology plays been proposed to be a rift system (e.g., [6]) probably in forming landforms. caused by one or multiple mantle plumes, although its Interactions of Tectonism, Volcanism, Ice and development certainly involved other processes in- Water in the Baikal Rift Zone: The Baikal Rift Zone cluding erosion and collapsing [7]. Internal layered including northern Mongolia is a vast land character- deposits (ILDs) in Valles Marineris are characterized ized by complex geological history (Figure 1). The by their extensive thin layering and their unique rela- geology of this region reflects continental formation tionships with the canyons. The subice volcanism processes based on interactions of cratons and arcs [2]. hypothesis [8, 9] has a strong possibility to explain the The basement rocks are comprised of ancient passive formation of at least some of the ILDs as well as other and active margin terrains as old as the Proterozoic and suspected volcanic features in Valles Marineris. Cata- they were accreted over successively forming foldbelts clysmic floods have occurred repeatedly as evidenced of sedimentary-volcanic formations. These formations by the presence of outflow channels connected to the are usually extensively folded and underpinned by a canyons. The ice bodies and ground ice in the canyons variety of granitic plutons. The Cenozoic Baikal Rift may have been melted by eruptions, thus producing with Lake Baikal occupying in the middle is as deep as jökulhlaup-type floods [1]. 8-9 km with a thick accumulation of sediments filled in The origin of great bodies of ice that may have and it is one of the deepest active rifts on Earth. The filled the Valles Marineris is an interesting question. main Baikal Rift is associated by many sub-parallel Under the current climatic regime, mobilizing and de- grabens with volcanism as young as the Holocene. positing water from the polar caps to the equatorial The Tuva volcanic province is the westernmost lava regions is impossible, and hence the ice formation field linked with the Baikal Rift System and the largest should be attributed to major climatic shifts such as the lava field in the province is the Azas Plateau. The ones hypothesized as temporal climatic changes [10]. Tuva volcanic province is related to the South Baikal The surface ages of the ILDs are estimated to be Late Hot Spot that forced domal uplifting with the highest Hesperian to Early Amazonian, approximately the altitude above 3000 m a.s.l. at the triple junction of same period as the activities of outflow channels [7]. Hovsgol Basin, Tunka valley and Oka-Azas toughs It is possible that this was a period of active volcanism, (Figure 1). The compositions of Baikal Rift Zone vol- which influenced hydrology and the climatic regime. canics are trachybasalt and basanite [3]. The Azas lava Alternatively, the ice bodies may have derived locally plateau began to form from the Late Pliocene and its from subsurface aquifers and/or ground ice perhaps by volcanism continued to the Holocene. magmatic heating. A potential problem for this idea is The rift volcanism in the cold and wet climatic re- that such sources may not be enough for the ice bodies gime caused subice volcanism in Siberia. The subice sometimes as thick as the canyons themselves. How- volcanism of the Azas Plateau records climatic epi- ever, this scenario does not require major climatic sodes significantly different from today. The tuya edi- shifts. fices on the Azas Plateau are Pleistocene in age and Lunar and Planetary Science XXXIV (2003) 1314.pdf THE BAIKAL RIFT ZONE AND VALLES MARINERIS: G. Komatsu References: [1] Chapman M. G. and Tanaka K. L. (2002) Icarus, 155, 324-339. [2] Sengör A. M. C. and Natal’in B. A. (1996) In: The tectonic evolution of Asia, Cambridge University Press, 486-640. [3] Lita- sov Y. et al. Northeast Asian Studies, n. 6, Tohoku University, in press. [4] Grosswald M.G. (1999) Cata- clysmic megafloods in Eurasia and the polar ice sheets, Scientific world, Moscow (in Russian). [5] Komatsu G. et al. (2002) Submitted. [6] Blasius K. R. et al. (1977) JGR, 82, 4067-4091. [7] Lucchitta B. K. et al. (1992). In: Mars, University of Arizona Press, pp. 453-492. [8] Chapman M. G. and Tanaka K. L. (2001) JGR, 106, 10,087-10,100. [9] Komatsu G. and Litasov Y. (2002) LPSC XXXIII. [10] Baker V. R. et al. (1991) Nature, 352, 589-594. Figure 1. Geographical locations of places discussed in this abstract..