Stress field evolution in the northwest Himalayan syntaxis, northern Pakistan

Abstract

pp. 26International audienceWe have conducted a systematic inversion of striated fault planes throughout northern Pakistan in order to better depict the temporal and spatial variations in stress patterns. Two domains are evidenced at a regional scale, separated by the active Raikhot fault, the western boundary of the Nanga Parbat spur. West of this fault, a wrench-type stress field with σ1 axis oriented around N–S predominates in the Karakorum and in Kohistan. It predates Pliocene-Quaternary exhumation of Nanga Parbat and corresponds to the Miocene or earlier regional stress field related to Indian-Asian convergence. East of the Raikhot fault, compression parallel to the belt accounts for initiation of the Nanga Parbat anticlinorium after 5 Ma. It is followed by predominant post-2 Ma extension, both parallel to the belt and NNE–SSW oriented. Thus, in the N–W Himalayan syntaxis, multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt. Such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence

Paleostress regimes from brittle structures of the Karakoram–Kohistan Suture Zone and surrounding areas of NW Pakistan

“…Our aim is to clarify the chronology and the orientation of recorded stress fields along the suture zone and to integrate this new information in a larger regional frame, concentrating on the Miocene to Quaternary evolution of the Western Himalayas. Our results complement previous kinematic analyses of faults in adjacent areas (Zanchi, 1993;Zeilinger et al, 2000;Burg et al, 2005;Pêcher et al, 2008), thus consolidating knowledge of the geological background of such major earthquakes as that of Kashmir in October 2005 (e.g. Avouac et al, 2006;Kaneda et al, 2008).…”

“…18e and f). This sorting does not reflect the relative importance of these regimes because the data aggregate local determinations (our three new sites) and 'regionalized' determinations from Zeilinger et al (2000) and Pêcher et al (2008). Comparing regionalized with local results gives an idea of the possible bias this aggregation introduces.…”

“…Beyond this fault (zone G, Fig. 1), mainly N-S extension is documented by Pêcher et al (2008). Our compilation includes three new tensors obtained from three new stations (Table 1, zone C) dominated by strike-slip faults (Fig.…”

“…Our compilation includes three new tensors obtained from three new stations (Table 1, zone C) dominated by strike-slip faults (Fig. 17), the four 'regional tensors' obtained by Zeilinger et al (2000) and 10 determinations by Pêcher et al (2008) (Table 2, zone C).…”

“…A relative chronology was proposed by Zeilinger et al (2000) and Pêcher et al (2008). The oldest regime would predate initiation of the Nanga-Parbat system and is ascribed to the Mid-to Late Miocene.…”