Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya

Paleocene–Eocene record of ophiolite obduction and initial India‐Asia collision, south central Tibet

“…The Gangdese ocean-continent subduction system in south central Tibet may have become intraoceanic to the east and west (Figure 11b; compare to similar tectonic reconstruction proposed by Beck et al [1996]), which could explain intraoceanic ophiolitic, subduction-accretion, and arc fragments near Zedong [Aitchison et al, 2000;Davis et al, 2002] and in the western Himalaya [e.g., Searle et al, 1987;Gnos et al, 1997]. An intraoceanic subduction system may have separated India and Asia prior to $65 Ma [e.g., Beck et al, 1996]; however, there is no evidence in the geologic and stratigraphic record of south central Tibet for its former existence or obduction onto the Indian margin. Onset of collision at $65 Ma may have induced rollback of a formerly shallow subducting Neo-Tethys oceanic slab, with associated asthenospheric upwelling initiating Linzizong volcanism (Figure 11a) .…”

“…This age has been difficult to constrain as reflected by the wide range of estimates for the onset of collision (70 -38 Ma), most of which are minimum estimates or are based on indirect evidence (see reviews and references from Butler [1995] and Yin and Harrison [2000]). Although specific geologic relationships are still debated, there is a general consensus that India-Asia collision initiated no later than $55 -52 Ma in the northwestern Himalaya on the basis of the ages of postcollisional stratigraphic assemblages [e.g., Searle et al, 1987;Gaetani and Garzanti, 1991;Beck et al, 1995Beck et al, , 1996Searle et al, 1997], high-pressure metamorphic rocks [e.g., Tonarini et al, 1993;Guillot et al, 1997;de Sigoyer et al, 2000], and paleomagnetic studies [e.g., Besse and Courtillot, 1988;Klootwijk et al, 1992Klootwijk et al, , 1994. A robust estimate for the maximum age of collision is provided by formation ages of the youngest ophiolitic fragments documented (70 -65 Ma [Gnos et al, 1997]).…”

“…Changes in sedimentation patterns and the appearance of accretionary prism and arc material within Maastrichtian strata of the southern Tibetan Tethyan Himalaya have been attributed to onset of interaction between India and Asia at this time [e.g., Liu and Einsele, 1994;Shi and Yin, 1995;Liu and Einsele, 1996;Willems et al, 1996]. However, these changes in sedimentation may be equally well explained by southward obduction of Neo-Tethys intraoceanic rocks, including ophiolitic fragments and subduction-accretion complexes, onto the northern margin of India during Late Cretaceous-early Tertiary time prior to India-Asia collision Burg and Chen, 1984;Burg et al, 1987;Searle et al, 1987;Beck et al, 1996;Gnos et al, 1997;Makovsky et al, 1999;Aitchison et al, 2000]. Further questioning an early age for collision in southern Tibet is the lack of evidence for Asian-derived detritus or increased rates of tectonic subsidence in Paleocene -Eocene strata of the Tethyan Himalaya [Rowley, 1996[Rowley, , 1998Aitchison et al, 2000Aitchison et al, , 2002.…”

Convergence history across Zagros (Iran): constraints from collisional and earlier deformation

“…Convergence was first accommodated by a northeastward subduction (with respect to the present geographic position) of the oceanic domain below the Iran block (itself earlier accreted to Eurasia by late Triassic; Besse et al 1998;Saidi et al 1997) from the late Triassic-early Jurassic (Berberian and King 1981;Davoudzadeh and Schmidt 1984) or the late Jurassic (Mohajjel and Fergusson 2000). A major obduction stage (running from Turkey to Oman and then onto the Himalayas; e.g., Beck et al 1996;Ricou 1971aRicou , 1994) is known to have taken place approximately 100-70 Ma ago in Iran (Lanphere and Pamic 1983;Ricou 1971a) .…”

Organic petrology of subbituminous carbonaceous shale samples from Chalāw, Kabul Province, Afghanistan: Considerations for paleoenvironment and energy resource potential

“…The presence of ophiolites at the margins of the Kabul Block has led most workers to infer that it was a peri-Gondwanan microcontinental fragment surrounded by oceans and emplaced against Eurasia near the Cretaceous-Paleocene boundary (e.g., Tapponnier et al, 1981;Sengör, 1984;Treloar and Izatt, 1993;Gnos et al, 1997). Alternatively, Beck et al (1996) hypothesized that the Kabul Block represented a leading element of the Indian Plate that was displaced southwestward and extruded during India-Eurasia collision in the Tertiary.…”