Lake Hovsgol: An Integrative Natural Laboratory for Quaternary Tectonics, Glaciation, and Climate Change in Northern Mongolia

What:  The 2010 Mongolia Keck project is designed to improve our understanding of the dynamics of crustal deformation associated with convergent to extensional transition zones by studying the coupling between atmospheric, Earth surface, and lithospheric processes across Quaternary time scales within the active Lake Hovsgol intracontinental rift zone of northern Mongolia. This project will integrate field studies of active faults, timing and extent of late Pleistocene glaciations, lake level history, and the paleoenvironmental ecology of the northern Hovsgol Rift zone (Figure 1).

When: July 12-August 8

Where: Northwestern shore of Lake Hovsgol, Mongolia (Latitude: 51.570° N; Longitude: 100.462°E)

Who: Karl Wegmann (North Carolina State University), Kurt Frankel (Georgia Institute of Technology), Anne Meltzer (Lehigh University), A. Bayasaa Bayasgalan and Tsolman Amgaa (Mongolian University of Science and Technology) and 8 students.

Project description and goals

Mongolia occupies a peculiar place in Asia at the transition between a N-S convergent province to the south in the Tien Shan and an E-W to NW-SE extensional province to the north in the Baikal rift zone (e.g. Baljinnyam et al., 1993; Cunningham et al., 1996; Bayasgalan et al., 1999). Molnar and Tapponnier (1975) first suggested that post-collisional “rigid” indentation of India into Asia since ~50 Ma is responsible for Cenozoic deformation throughout the whole of Central Asia, including crustal extension in the Baikal-Hovsgol system of rifts (Fig. 2). South of the Mongolian Plateau, deformation presumably related to India-Asia convergence has propagated northward since ~50 Ma, as marked by the progression in the timing of range uplift (e.g., Jolivet et al., 2001) and by movements along major strike-slip faults such as the Altyn Tagh (Fig. 2). Relative to stable Eurasia, western Mongolia and adjacent parts of central Asia (west of 100° E) currently accommodate ~10 mm/yr of northward-directed shortening related to the India-Asia collision, while the ~2000 km long Baikal rift system is presently extending at ~4 mm/yr (Calais et al., 2003). Situated in this complex juncture between regions of active shortening and extension, the Hovsgol rift [2010 Keck project] and Hangay Mountains [2006 Keck project] are broad dome-shaped areas of elevated topography and relief comprising the Mongolian Plateau. Both regions are associated with Pliocene and Quaternary volcanics and moderate heat flow (Windley and Allen, 1993). The Hovsgol rift and Hangay Mountains demarcate a kinematic transition between predominantly oblique contractions to the south and transtensional deformation to the north (Fig. 2; Baljinnyam et al., 1993).

The proposed project is designed to improve our understanding of the dynamics of crustal deformation associated with oblique-contractional to transtensional transition zones in intracontinental settings and the interactions between atmospheric, Earth surface, and lithospheric processes within the active Hovsgol rift. The proposal is built around several key observations. First, rift bounding faults exhibit geomorphic evidence for recent activity, and discrepancy exists as to how far-field stresses are being transferred from the Hovsgol graben northward into the Tunka basin and southwestern Baikal rift. Second, variability in the down-valley extent of Pleistocene glaciers may reflect on-going tectonic uplift of the Bayan and Vostoch Mountains, resulting in an effective lowering of the equilibrium line altitude (ELA) between marine isotope stage (MIS) 6 and MIS 2. The opportunity now exists to develop a detailed late Quaternary chronostratigraphy for the northern Lake Hovsgol rift that will encompass glacial, fluvial, and littoral sequences anchored by high-precision radiometric age control. These terrestrial records in turn may be integrated with high-resolution paleoclimate proxy records recently retrieved from Lake Hovsgol via sediment coring by members of the International Continental Drilling Program (e.g. Hovsgol Drilling Project Members, 2009).

The primary goal of the proposed research is to engage senior undergraduate-level geoscience majors in testing hypotheses via independent field research around a coupled tectonic-geomorphic problem. Cross-cultural scientific exchange is also of significant importance to our project. Furthermore, improving our understanding of the dynamics of crustal deformation associated with oblique-contractional to transtensional transition zones in intracontinental settings is one of the most important topics in modern tectonics. Specifically, it appears that the Hovsgol rift system plays an important role in the transfer of far-field strain across central Asia to the Baikal rift, accommodating a significant fraction of the intracontinental deformation related to the India-Asia collision in the process (e.g., Calais et al., 2003). Yet the lack of field-based investigations and numerical chronologies has made it difficult to assess the exact role this system plays in accommodating this deformation.

Similarly, continental rift basins, like Hovsgol, preserve sediment and paleoenvironmental proxy archives of climate variability and landscape response to tectonic and climatic forcing over tens to millions of years. These lake basin records, when combined with terrestrial records of late Pleistocene glacial extent and timing provide key constraints on central Asian climate dynamics and the synchroneity (or lack thereof) of environmental change across Central Asia, the northern hemisphere, as well as between hemispheres.

This Keck project is built around several key observations. First, both the Hovsgol rift-flank fault and the Tunka fault exhibit ample geomorphic evidence for late Pleistocene to Holocene activity. Geomorphic relationships suggest that the Hovsgol rift flank fault is predominantly normal. In contrast, there is much debate concerning the kinematics of the Tunka fault, with normal, reverse, and sinistral senses of shear all having been put forth as possibilities (e.g., Baljinnyam et al., 1993, McCalpin and Khromovskikh, 1995; Arjannikova et al., 2004; Vogt and Vogt, 2007). Second, the furthest downvalley moraines for glaciers heading along the western actively uplifting rift flank appear to be MIS 2 in age, whereas the furthest down-valley glacial deposits for valleys that head behind the active rift flank (e.g. Ih-Horoo valley) appear to be older than MIS 2.

Collectively, these observations lead us to hypothesize that the predominantly normal rift-flank fault on the west side of Hovsgol Nuur accommodates some portion of the indentation of India into Asia. Although there is a lack of consensus as to kinematics along the western portion of the Tunka fault, given its orthogonal orientation with respect to the Hovsgol rift, it is clear that this structure must play a major role in transferring far-field stresses northward into Siberia and the Baikal rift system.

Accordingly, glaciers of the LGM extended downvalley further than previous glacial advances due to on-going tectonic uplift of the Bayan and Vostoch Mountains, which resulted in an effective lowering of the equilibrium line altitude (ELA) between MIS 6 and MIS 2. Detailed mapping and geochronology of glacial deposits will help confirm or refute our hypothesis of ELA depression resulting from continued tectonic activity.

Student projects

We have outlined 13 potential research topics for students involved in this project to choose from (Figure 3). The projects include structural and geomorphic analysis of active faults, timing and extent of late Pleistocene glaciations, lake level history, and investigations of paleo-environment/ecology. Our goal is to have an integrated project whereby students’ individual research contributes to the broader overall understanding of the Quaternary tectonic and climatic history of the Hovsgol region.

  • Projects 1, 2, and 4 – Hovsgol Rift Flank Normal Fault: These projects will focus upon the geometry, kinematics, age, and evolution of the rift flank normal fault bounding the western edge of Lake Hovsgol (Figure 3).
  • Projects 3, 5, 6, 7, 8, and 9 – Timing and Extent of Late Pleistocene Glaciations: The northern Hovsgol rift is characterized by numerous glacial features including moraines and glacial deposits. These projects will focus on the number, extent, age, and climatic significance of glaciations in the Hovsgol region for comparison with similar studies in the Darhad Basin to the west (Figure 3; Gillespie et al., 2008) as well as other parts of central Asia.
  • Projects 10 and 11 – Western Tunka Fault Zone: These projects are similar to projects 1, 2, and 4 and will focus upon the geometry, kinematics, age, and evolution of the Tunka fault, which bounds the northern end of our field area (Figure 3).
  • Project 12 – Lake Hovsgol Shorelines: In places, evidence exists for paleo-shorelines around Lake Hovsgol (Figure 3). These shorelines can be used to determine lake level histories in addition to rates and style of tectonic activity. The student involved in this project will map and survey paleo-shorelines, including the use of differential GPS and Ground Penetrating Radar equipment to accurately determine the elevations and stratigraphic relationships of the shorelines.
  • Project 13 – Paleoclimate Coring and Dendrochronology: The student involved in this project will collect shallow (<10 m) sediment cores from marshes and shallow glacial lakes and dendrochronology cores from the surrounding forests to investigate Holocene environmental change in the Hovsgol region. This project will require significant post-field lab analysis of paleoenvironmental proxies, such as total organic carbon, loss on ignition, pollen, and perhaps stable isotope analyses and/or dendrochronologic analysis.

Field conditions

This project will take place in a remote location where medical attention is not readily available. Students should be prepared for all weather conditions from cold rain and snow to hot, dry, and windy. All project participants will camp for the duration of the project. Students should be in good physical condition as most of the projects will involve large amounts of off-trail hiking over steep and uneven terrain at relatively high elevations.

Course Preparation

Students should have field experience (4-6 credit Field Geology) combined with a sense of adventure. In addition, students should have completed at least two (2) of the following courses: geomorphology, structural geology, Quaternary geology, paleoclimatology, sedimentology and stratigraphy, geophysics, geodynamics, or tectonics. Courses in first aid, CPR, and wilderness medicine are also useful.

References

  • Arjannikova, A., Larroque, C., Ritz, J.-F., Deverchere, J., Stephan, J. F., Arjannikova, S., and San’kov, V., 2004, Geometry and kinematics of recent deformation in the Mondy-Tunka area (south-westernmost Baikal rift zone, Mongolia-Siberia): Terra Nova, v. 16, no. 5, p. 265-272.
  • Baljinnyam, I., Bayasgalan, A., Borisov, B. A., Cisternas, A., Dem’yanovich, M. G., Ganbaatar, L., Kochetkov, V. M., Kurushin, R. A., Molnar, P., Philip, H., and Vashchilov, Y. Y., 1993, Ruptures of major earthquakes and active deformation in Mongolia and its surroundings: Geological Society of America Memoir 181, 62 p.
  • Bayasgalan, A., 1999, Active Tectonics of Mongolia. Ph.D. Thesis, University of Cambridge, UK.
  • Calais, E., Vergnolle, M., San’kov, V., Lukhnev, A., Miroshnitchenko, A., Amarjargal, S., and Déverchere, J., 2003, GPS measurements of crustal deformation in the Baikal-Mongolia area (1994-2002): Implications for current kinematics of Asia: Journal of Geophysical Research, v. 108, no. B10, 2501, doi:10.1029/2002JB002373.
  • Cunningham, D. W., Windley, B. F., Dorjnamjaa, D., and Badamgarav, Z., 1996, A structural transect across the Mongolian Western Altai: Active transpressional mountain building in central Asia: Tectonics, v. 15, no. 1, p. 142-156.
  • Gillespie, A. R., Burke, R. M., Komatsu, G., and Bayasgalan, A., 2008, Late Pleistocene glaciers in Darhad Basin, northern Mongolia: Quaternary Research, v. 69, no. 2, p. 169-187.
  • Hovsgol Drilling Project Members, 2009, Sedimentary record from Lake Hovsgol, NW Mongolia: Results from the HDP-04 and HDP-06 drill cores: Quaternary International, v. 205, no. 1-2, p. 21-37.
  • Jolivet, M., Brunel, M., Seaward, D., Xu, Z., Yang, J., Roger, F., Tapponnier, P., Malavieille, J., Arnaud, N., and Wu, C., 2001, Mesozoic and Cenozoic tectonics of the northern edge of the Tibetan plateau: fission track constraints: Tectonophysics, v. 343, p. 111-134.
  • McCalpin, J. P., and Khromovskikh, V. S., 1995, Holocene paleoseismicity of the Tunka fault, Baikal rift, Russia: Tectonics, v. 14.
    Molnar, P., and Tapponnier, P., 1975, Tectonics of Asia: Consequences and implications of a continental collision: Science, v. 189, p. 419-426.
  • Vassallo, R., Jolivet, M., Ritz, J. F., Braucher, R., Larroque, C., Sue, C., Todbileg, M., and Javkhlanbold, D., 2007, Uplift age and rates of the Gurvan Bogd system (Gobi-Altay) by apatite fission track analysis: Earth and Planetary Science Letters, v. 259, no. 3-4, p. 333-346.
  • Vogt, H., and Vogt, T., 2007, Morphotectonic evolution of two depressions at the southern border of the Baikal rift system: Geomorphology, v. 86, no. 3-4, p. 480.

Pin It on Pinterest

Share This