Pebbles within the Indus Molasse
The molasse displays an overall decrease in pebble size away from the northern tectonic contact (i.e. larger pebbles occur at the contact compared to the distal zone). The percentage of pebbles in the groundmass of the molasse also decreases away from the northern contact, suggesting the initial deposition was adjacent to the batholith. The pebbles from our study location vary in size and character (e.g., rock type and protolith), ranging in size from ~3 cm to ~30 cm. Water tumbling and abrasion during transportation has produced rounded pebbles. The pebbles themselves have well-preserved original mineralogy and microfabrics (Figure 3). Weathering has not taken place and the pebbles are exceptionally well preserved. Note that the term pebble used in this paper refers to the layman use of the term and that the official terminology should be cobble but is not used here (cf. pebble (4mm-16mm), cobble (16mm-256mm) and boulder (+256mm).
The most prominent geomorphical features in the Indus Formation are bedding and a pervasive and penetrative slaty cleavage overprint. This cleavage occurs only within the shaley non-competent layers (Figure 3b) and is axial planar to large-scale upright folds (Figure 4). The overlying Indus Molasse is also affected by this folding event. In addition a previous recumbent folding event is preserved within the limbs of the upright folds (Figure 4).
As mentioned above the molasse is folded by the same generation upright folding as the underlying Indus Formation, however in the molasse the folding is on a smaller-scale. The pervasive axial planar fabric also occurs in the molasse, however it is not well-defined. For example, the fabric in the molasse is discernible but weak and anastomoses around even the small pebbles and commonly lies along the weaker zones (Figure 5).
Figure 4. Folded Indus Formation.
When the Indus Formation is viewed approximately perpendicular to the contact with the Ladakh Batholith (along strike of the Indus suture), several generations of folding are observed. The older generation of folds are characterised as recumbent folds (the axial plane marked in red = FR), these are overprinted by a younger upright folding event (FU) with the axial plane marked in purple (therefore the FR is followed by FU). The multiply-folded fabric is highlighted with black lines. The upright folds are on the scale of hundreds of metres. The upright fold nearest the river is approximately 300 metres in the gully.
The deformational fabrics in the structurally lower zones of the molasse were observed to be more intense closer to the contact with the Ladakh Batholith. In contrast, the Indus Formation displays spectacular original depositional layering that can be observed from the air as one flies into Leh, or with satellite imagery such as displayed on Google Earth. The deposition of the Indus Formation was independent to the overlying molasse, however after the period of deposition of the molasse (Thakur and Misra 1984), both units were then deformed as a single unit.
Figure 5. Example of the molasse.
The molasse has been folded with the underlying Indus Formation. The deformational fabric that has formed within the molasse due to the folding, is irregular in character and anastomoses around the larger pebbles (rocks) and irregularities in the molasse. Even though the fabric is irregular, it occurs on the mm-scale. It is not brittle jointing.
The structures with the Indus Molasse and the Indus Formation do not resemble those within the Ladakh Batholith (e.g. the Thanglasgo Shear Zone of Weinberg and Dunlap 2000).