A walk in cold desert

The most interesting fact about Ladakh is the barren nature of the landscapes. It ensures that the geological evolution of the region is right in front of the observer. Although I have visited Leh and nearby areas a couple of times, mainly to trek along remote valleys and scale peaks, what aroused my interest in the geology of the area is a photograph of my recent trek. Probably us petroleum geologists are so busy in interpreting subsurface geology that we fail miserably in identifying the geology in and around us. I cannot deny the fact that in every trek or climb, my priority was always to survive, return home safely from that anoxic- strenuous condition so didn’t have much leisure to ponder on geology. 

The photograph was taken from a gully looking northeast while descending from Zalung Karpo La (4200m) on the way to Konka Wangpo La (5090m). Being a non-technical summit climb in Kang Yaste-II (6250m) this trip has exhilarating views all throughout. That view, however, grabbed my attention, mainly because sheer extent of the feature. The recumbent fold mesmerized everyone. I searched for the same structure in Google Earth (link). The more I look at Google Earth, the more I feel how underutilized it is. Mostly our trek team comprising of petroleum geologists, use it to find new treks, obstacles, distances to cover and the like, but never really dive into the geological realm. 

The trek started through exotic looking horizontal terraces along rivers valleys, mainly products of neotectonics. Over next 6 days we covered almost 72km by foot, reaching a maximum elevation of 6250m, a gain by 1900m from where we started.

While virtually flying through the trekked section, I could find geological reasons for some hurdles we faced while crossing the 3 main passes or ‘La’ in that trek (Figure 1). By looking at the colour one can loosely mark the different bedrocks in that region. Once tied to the on-ground observations, comparatively persistent bedrock in Zulong Karpo La belongs to the Zanskar Tethyan Zone comprised of carbonates and siliciclastics, whereas Gongmaru La rocks belongs to the subduction related lithology potpourri- Lamayuru Complex. The coexistence of these varied lithologies can be explained by a low angle thrust at the southern boundary of Markha Valley. The crown of the valley, Kang Yatse, lies in a hard-resistant buff coloured section, and is of granitic composition. Konka Wangpo La probably lies on a fault that separates this rock and Zanskar Formation. These changes in lithology and structural position resulted in significant amount of loose rocks to be tackled while crossing the later passes.Bedrocks across Gongmaru La are brightly coloured and steeply dipping. In this part they are dominantly radiolarian cherts with serpentinite, sensu stricto mud-matrix mélange and oceanic exotics. The whole sequence is part of ‘ophiolitic melange’ and an intercalation of ultrabasic rocks, volcanoclastics and cherts.

Figure 1: The trek route marked on a quickdrawn lithological map of the area. The 3 passes in the question are marked, the boundaries between individual lithologies are reverse faults. Pictures along trek route with description are posted in the google map (link)

As I think back now, the fact that I had walked my steps through remnant subduction/accretion units gives me goose bumps. Similarly, it struck me, that the Namgyal-Tsemo trail, we climbed on the first evening as an acclimatization climb, was situated on the Leh Batholith, “ring of fire” (Figure 2). 

Figure 2: Schematic diagram of depositional environments though which we traversed 72km during our trek

Our final leg journey by car to Leh is through spectacular nearly horizontal terraces on the floor of the actual Indus river valley unconformably overlying the mélange. These were developed after the main collisional phase of Indian plate and Ladakh arc (50-60 Ma) along Indus suture. It seemed like a circle of life, we started and ended in similar geomorphic setup. 

North of this suture zone is Shyok suture zone formed between 74 Ma and 97 Ma with Karakoram batholith as the island arc equivalent (Figure 3). 

Figure 3: Main structural elements of Ladakh region marked on Google Map image (courtsey: Sandipan Dutta)

There is so much detail that one can divulge just from Google Earth imagery. And yet we do not value this wealth of information enough. The more we take advantage of this technology, the better we will be in honing our core skills, as over the years we all have become ‘Desktop’ geologists, finding answers with simulated models. It can serve the purpose of a free of cost virtual field guide for any subsurface problem, especially in this current time where “going” to the field remains a distant dream.