Quaternary Tectonic and Geomorphic Evolution of the Deluun Nuruu, Mongolian Altai, Western Mongolia

Figure 3. Oblique aerial view to NE across the Deluun Nuruu. The Tolbo Nuur Fault, which bounds the west side of the range, is in the foreground, while the Khovd Fault is in the background. The base camp location, denoted by the green tent symbol, is central to the individual project areas. Individual student project areas are outlined in blue boxes, with the number corresponding to the project designation (see text). The locations of Figures 4, 5, and 7 are shown. The image was generated from LandSat7 photography draped over an SRTM 90-m DEM and manipulated using NASA’s World Wind software.

What: In Central Asia, 2,500 km north of the India–Eurasia collision zone, a vast array of active intracontinental mountain belts are present. The Deluun Nuruu, a sub-range of the greater Mongolian Altai, is one of these. Paleozoic to Cenozoic sedimentary rocks crop out in the range and flanking hills, with minor amounts of late Paleozoic to Mesozoic intrusive rocks attesting to subduction, terrane collision and orogenesis during the Mesozoic when the Siberian and North China cratons collided (Tomurtogoo, 2003). Western Mongolia is host to many large active faults, including the Bulnay, Fu-yun, and Gobi Altai, which released three of the largest recorded intracontinental earthquakes in 1905 (Mw 8.1), 1931 (Mw 8), and 1957 (Mw 8.3), respectively (Baljinnyam et al., 1993).

The Deluun Range is flanked on its western side by the Tolbo Nuur Fault, which exhibits evidence for both recent right-lateral strike-slip and thrust rupture, but has never been studied beyond a reconnaissance level (Baljinnyam et al., 1993). The Mongolian Altai is the largest glaciated area in Mongolia (Lehmkuhl, 1998), and the Deluun range supports retreating glaciers that provide runoff critical to local peoples and endemic species.

This project will examine the neotectonics, geomorphology, and paleoecology – climatology of this geologically fascinating area.

When: July 15 – August 10, 2008 (tentative)

Where: Mongolia

Who: 8 students and 3 faculty – Professor Bob Carson, Department of Geology ,Whitman College; Karl Wegmann, Department of Earth and Environmental Sciences, Lehigh University; and Professor Amgalan (“Bayasaa”) Bayasgalan, GeoInformatics Center, Mongolian University of Science and Technology.

Project Description and Goals

Our motivations for the proposed research in western Mongolia are threefold: first, to provide constraints for models of active intracontinental faulting and orogenesis; second, to provide Late Quaternary paleoenvironmental proxy records of environmental change in this understudied portion of Central Asia; and third, to promote cross-cultural scientific exchange between U.S. and Mongolian geoscience students.

Student Projects

Student projects will be in 2 to 3 complimentary areas:

  1. neotectonic – tectonic geomorphology, fault characterization, and paleoseismology;
  2. glacial, periglacial, and fluvial geomorphology, and
  3. paleoclimatic proxies of Late Quaternary climate change.

Figure 5. Right-lateral displacement of drainages by the Tolbo Nuur Fault (TNF) at the northern end of the Deluun Nuruu, see Fig. 3 for location. A. A 90-m SRTM DEM showing present topography and drainage along the TNF. B. Approximately 750 m of restorative left-lateral displacement along the fault results in realignment of offset drainages. If the long-term slip rate for the TNF is 1 mm/yr, the amount of offset preserved by the drainages represents 750 ka of accumulated slip along the fault. If the slip rate is 3 mm/yr, the offsets would have accumulated in only 250 ka.

We have pre-identified nine individual projects (Fig. 3) and additional projects may be added based upon student-faculty sponsor interests and field opportunities.

  • Projects 1-4: Tolbo Nuruu Fault: These projects will focus upon the geometry, kinematics, age and evolution of the Tolbo Nuruu Fault. Each project will cover ~25 km along strike that is characterized by differing geometry and apparent rupture behavior. Paleoseismic trenching is a possibility for each of these 4 projects. Projects 1 & 4 will focus upon the TNF near the ends of the Deluun Nuruu, where it is hypothesized that fault motion transitions from predominantly right-lateral strike-slip to a larger thrust component. Project 1 will utilize offset drainages to provide constraints on the amount of right-lateral slip (e.g. Fig. 5). Projects 2 and 3 will utilize alluvial fan relationships to characterize the style and amount of movement on the central part of the TNF (e.g. Walker et al., 2006).
  • Project 5: Fluvial terraces: This project will focus upon mapping and dating fluvial terrace deposits above and within the upper few kilometers of the Buyant Gol gorge, straddling the trace of the TNF. The student will use geomorphic and sedimentologic evidence to develop a terrace chronostratigraphy, augmented by radiocarbon and/or cosmogenic age control. Terrace longitudinal profiles will be constructed in order to provide constraints on the kinematics of deformation along this portion of the TNF (e.g. Fig. 6). It is anticipated that this student will collaborate with the student working on the southern segment of the TNF (Project 4).
  • Project 6: Pleistocene-holocene paleoclimatology: In sparsely populated western Mongolia, long-term climate measurements are rare. As a result paleo-records preserved in sedimentary or dendrochronologic archives may provide detailed information about past climate changes in this portion of central Asia. The focus of this project will be to retrieve proxy paleoclimatic records for the Holocene and possibly late Pleistocene. Examination of such records may reveal important climate forcing periodicities and potential driving mechanisms for climate change on various temporal scales. Predicative paleoclimate research is much needed in Mongolia, a dominantly agrarian society dependent upon dry-land grazing, especially in the face of warming temperatures during the 20th and 21st centuries. Paleoclimate records could be retrieved from Larix sibirica (Siberian larch) trees (e.g. Stratton et al., 2007; Jacoby et al., 1996), from sediment cores recovered small glacial lakes (e.g. Blyakharchuk et al., 2007), or from peat cores.
  • Figure 6. Longitudinal profile of channel elevation as a function of distance for the Buyant Gol from its headwaters in the NW Deluun Nuruu to just past Khovd (near its terminus in Khar-Us Nuur). Note the prominent knickpoint and steepening of the profile that occurs at the range front, where the river crosses the trace of the Tolbo Nuur Fault and enters into a ~30-km-long gorge. River terraces preserved at the head of the gorge might provide insights into the type and rate of deformation of the Tolbo Nuur Fault.
  • Projects 7 & 8: Glacial and periglacial geomorphology: These projects will focus upon the number, extent, age, and climatic significance of glaciations in the Deluun Nuruu region. Of importance is the validation (invalidation) that the OIS 2 glaciers extended further downvalley than previous glacial advances. Because several of the larger valley glacier systems exited onto the piedmont, there is the opportunity to constrain the rate of offset on the TNF by dating offset glacial features (moraines and outwash terraces). It is anticipated that the students working on Projects 7 & 8 will collaborate with those working on segments 2 & 3 of the TNF projects (Fig. 3). Additionally, Holocene and modern glacial and periglacial processes could be incorporated into these projects.
  • Figure 7. Oblique aerial view to NE of piedmont debris flow deposit. Sapping of a small moraine-dammed lake may have generated the debris flow. In addition the headward-retreating valley may capture the lake and upstream drainage in the near future. Dating of the debris deposit could constrain the rate of faulting along this portion of the Tolbo Nuur Fault.

    Project 9: Mass wasting deposit and incipient drainage capture: A conspicuous debris flow deposit is observable overlying Holocene alluvial fans (Figs. 3, 7). The deposit was derived from a deeply incised valley exiting the mountain front along the TNF, and may be cut by the fault. The head of this valley may be sapping a small glacial lake in a drainage exiting the east side of the range, and thus may be in the process of generating a near-future drainage capture. This student would collaborate with students on projects 3, 7, and 8.

Course Preparation

We will have two or three projects in each of the following subject areas: (1) neotectonics, (2) geomorphology, and (3) paleoecology – climatology. Students will be selected to fill these slots. A general requirement is a course in field methods or field camp. Those interested in geomorphology should have a course in geomorphology or Quaternary geology. Those interested in neotectonics should have courses in structure and geomorphology.

 

 

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