| Popis: |
The Cretaceous rocks of the central Tethyan Himalayas display different types of deep-sea olistostromes and chaotic deposits which are accompanied by turbidites. The deposits were incorporated into an accretionary prism and more or less deformed. According to the composition and provenance of their clasts, we distinguish four types of olistostromes: (1) P-type, derived from the passive (Indian) continental margin; (2) PO-type, derived from both the passive Indian margin and ocean floor (pelagic sediments and oceanic crust); (3) POA-type with clasts from the same sources as the PO-type, but also containing material from the active margin along the Lhasa block; and (4) A- and OA-type, mainly derived from the active margin (accretionary prism and magmatic arc). The occurrence of these different types of deep-sea chaotic deposits in space and time is closely related to the evolution of the Neo-Tethyan basin from a wide open ocean basin to a narrowing remnant and trench basin prior to collision. Whereas pure P-type olistostromes formed when the basin was still wide, predominating A-type deposits characterize a late stage of basin evolution prior to collision. Mixed-type olistostromes record an intermediate stage of basin evolution and require specific syn-sedimentary tectonic activity. |
Full Text from ScienceDirect