Glacial and Climate History of Central Asia and TibetA Purdue research team led by Nat Lifton and Jon Harbor is a part of a long-term international effort (including Kyrgyz, American, Swedish, Russian, and Chinese scientists) to reconstruct patterns and timing of past glaciation along major transects across Central Asia and Tibet (Figure 1). This systematic approach utilizes cosmogenic nuclide (CN) dating of moraines and other landforms (primarily using 10Be) that constrain the former maximum extents of glaciers. Comparing consistently dated glacial histories along each transect will allow us to achieve the aim of identifying shifting dominance of patterns of precipitation over time in Central Asia. This is because differences in glacier extent on different parts of the same mountain range are more likely due to long-term differences in moisture sources and precipitation than differences in temperature. In planned work, our consistent working methodology developed in studies on the Tibetan Plateau (Heyman et al., 2008, 2009, 2011, in press; Morén et al., in press; Stroeven et al., 2009), will be applied to Central Asian mountain ranges, including the Tianshan and Altai Mountains and the Tibetan Plateau.
As a first step in developing a work plan for the Tianshan, members of our Purdue group traveled to the Inylchek Valley in the Kyrgyz Tianshan in August 2011 for a field planning meeting with our international colleagues (Figure 2). Field reconnaissance of the easily accessible parts of the valley indicated a major terminal moraine complex at the western valley end with numerous large boulders, many of which were deeply weathered (suggesting a pre-global Last Glacial Maximum age for the moraine) (Figure 3). Two large boulders were sampled for preliminary CN dating. An additional deposit of large boulders was also noted well above the moraine crest along an adjacent hillside, potentially suggestive of an even older glacial deposit. Somewhat surprisingly, additional unambiguous glacial deposits in the main valley were quite limited. However, we observed widespread evidence of active tectonism along the length of the valley, in the form of numerous vertically and laterally offset fluvial features and/or fault scarps (we could only observe these features from a distance, so we could not confirm a definite origin) (Figure 4). The north and south flanks of the valley exhibited distinctly different geomorphology, with hanging glacial valleys on the north side containing active glaciers (not visible from the valley floor, but obvious on Google Earth), and more gently incised fluvial and glacial valleys along the south side. Further investigation of the tectonic setting of the valley upon our return indicated that a major crustal suture (the Atbashi-Inylchek fault) bounds the north side of the valley, and a second major suture lies beneath the next valley to the north. Interestingly, glaciers draining into that valley from the north side of the intervening range exhibit much longer valleys (Figure 2). As part of our research in the area, we want to understand how differences in the active tectonics between the two valleys affect the style and preservation of glacial geomorphology on either side of this range.
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Morén, B., et al. Palaeoglaciology of the Central Tibetan Plateau. J Maps (in press).
Stroeven, A.P., et al., 2009, Geomorph. 103, 212-26.
Figure 1 – Overview map showing the scope of the international project of which our Purdue team is a part. To date our group has completed mapping and chronology reconstructions in Areas H and F, and mapping in Area M. Over the next five years members of our team will work in the Tianshan, Altai and Kunlun ranges.
Figure 2 - Preliminary glacial geomorphological map of Inylchek Valley study area, based on DEM and remote sensing interpretation. The extent of glacial valleys (purple) hummocky terrain (yellow) and end moraines (red) indicate the furthest extent of ice as seen in satellite imagery, which we consider the minimum extent of maximum glaciation, and show that the Tianshan were formerly heavily glaciated. The Inylchek Valley is the nearly linear glacial valley running ENE-WSW in the center of the map, with a right angle turn to the SE at its western end. Note the asymmetric glacial pattern in the range to the north of the Inylchek Valley. An exciting potential avenue of research is to study the interaction of active tectonics and glacial geomorphology on either side of this range.
Figure 3A – End moraine in the Inylchek Valley, about 60 km downvalley form the current glacier terminus, showing eratic boulders on the end moraine complex.
Figure 3B - End moraine in the Inylchek Valley, showing a distinct paleo ice-contact surface between the former glacier and its outwash plain. There are no published ages for this major feature, nor for almost all moraines in the Kyrgyz Tianshan.
Figure 4A – Fluvial terraces and/or fault scarps along the north side of the Inylchek Valley.
Figure 4B – Fluvial terraces and/or fault scarps along the north side of the Inylchek Valley. View looking eastward up-valley along the braided outwash plain toward the modern glacier terminus (not visible).