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LIPs - The Panjal Volcanics and Emeishan flood basalts

The oldest and most deformed of known CFBPs from the Phanerozoic are the Panjal Volcanics. Covering an area of approximately 12,000 km2 of NW reached a peak of thickness of 2.5 km in the Kashmir Valley (Honnegger et al., 1982). The main phase of volcanism is marked by basaltic lavas and lesser volumes of rhyodacitic tuffs, although minor alkali volcanics persisted in the Kashmir region into the Early Triassic (Veevers & Tewari, 1995). Lower and Middle Permian subaerial to marginal marine strata are overlain by basalt lavas and they are in turn overlain by Late Permian (Kazanian) pelagic strata (Nakazawa et al., 1975). It is suggested by this facies change that their emplacement is probably related to rifting and the development of a distal passive margin (Papritz & Rey, 1989). Estimation of the original volume of the province is made problematic by the subsequent deformation of the Panjal volcanics, and metamorphism to amphibolite grade, though it is not likely the region constituted a “super province” of a size that is comparable to that of the Deccan Traps.

The eruption of the Emeishan flood basalts in South China was contemporaneous and comparable in volcanicity. These are also associated with a probable rifting event (probably the Qiangtang Terrane from the South China Block, which began in the Early Permian, and they also subsequently deformed during the closure of Tethys (Chung et al., 1998). Their outcrop, which consists of flood basalts with lesser flows of picritic flows and trachytic and rhyolitic tuffs, covers 3.3 x 105 km2 of SW China (Chung et al., 1998; Jin & Shang, 2000). The lavas average 705 m thick and they reach 5 km in thickness locally. It has been estimated (Yin et al., 1992) that the original volume of the province was 0.6 x 106 km3, while half this figure was suggested (Jin & Shang, 2000).

It has yet to be determined what the precise age of Emeishan flood basalts province is. The lavas rest on carbonates from the Middle Permian (the Maokou Formation)       and marine strata from the Late Permian and Early Triassic directly overlie them (Yin et al., 1992); Chung & Jahn, 1995). The presence of fusulinid foraminifera has been reported recently (Jin & Shang, 2000), from shallow marine limestones that are interbedded by basal lava flows, which indicates unequivocally a Guadalupian (Middle Permian) age. Magnetostratigraphic results that were obtained from a thin (532 m thick) development of the flood basalt in western Guizhou Province indicates that the lower 450 m had been erupted during a single, chron of normal polarity and the upper 82 m during a reversal (Huang & Opdyke, 1996). Therefore, the Meishan CFBP, as was the case with the Panjal volcanics, appear to have been erupted over a brief interval that was suggested (Huang & Opdyke to be less than 1 Myr) around the Middle to Late Permian boundary. Acidic ash bands are, however, widespread in Permian-Triassic boundary sections in South China, and they are widely regarded to have been derived from the Emeishan Province (Yin et al., 1992; Chung &Jahn, 1995; Chung et al., 1998), which implies there was a prolonged interval of acidic volcanic activity which spanned the entre Late Permian and lasted into the Early Triassic. Thick, coarser-grained acidic-intermediate tuff bands that are 15-25 m thick are also known from the boundary interval in south Primorie (SE Siberia), which suggests that this area lay closer to the eruptive centre than South China, where the tuffs are finer grained and are thinner by an order of magnitude (Kozur, 1998). According to Wignall it is clear that more work is needed on the provenance of these P-Tr boundary tuffs.

Attempts to relate the Emeishan flood basalts in [?to] to end-Permian mass extinction event (e.g. Yin et al., 1992) are probably inappropriate, though it is suggested by the dating from the region that it may be implicated, Along with the Panjal Volcanics, with the end-Guadalupian mass extinction event (Hallam & Wignall, 1997). This earlier event, which has been identified within the last few years, had a primary effect on equatorial marine invertebrate taxa, notably the fusulinid foraminifera (Leven, 1993; Jin et al., 1994; Stanley & Yang, 1994). The best of the data was from the southwestern US and South China, 2 places where the extinctions appear to be related to major regional regressions which eliminated the shallow marine carbonate habitats which were the repository of much marine diversity in the Middle Permian. It was suggested (Hallam & Wignall, 1999) that the Middle-Late Permian boundary may mark an all-time low point of the sea level in the Phanerozoic. This sea level fall within South China itself could reflect regional doming that occurred prior to the eruption of the Emeishan flood basalts (Chung et al., 1998), though on a global scale some other mechanism must be invoked.

Sources & Further reading

Wignall, P. B. (2001). "Large igneous provinces and mass extinctions." Earth-Sci. Rev. 53: 1-33.


Author: M. H. Monroe
Last Updated 19/07/2019
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