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Downloaded from gsabulletin.gsapubs.org on 18 September 2009 Geological Society of America Bulletin Stratigraphic correlation of Cambrian−Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region Paul M. Myrow, Nigel C. Hughes, Michael P. Searle, C.M. Fanning, S.-C. Peng and S.K. Parcha Geological Society of America Bulletin 2009;121;323-332 doi: 10.1130/B26384.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. 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Notes © 2009 Geological Society of America Downloaded from gsabulletin.gsapubs.org on 18 September 2009 Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region Paul M. Myrow† Department of Geology, Colorado College, Colorado Springs, Colorado 80903, USA Nigel C. Hughes Department of Earth Sciences, University of California, Riverside, California 92521, USA Michael P. Searle Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK C.M. Fanning Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia S.-C. Peng State Key Laboratory on Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Nanjing, 210008, China S.K. Parcha Wadia Institute of Himalayan Geology, Dehra Dun, Uttranchal, 248001, India ABSTRACT contain a similar age spectrum to those from echino derm fragments taken from ~6 m below Middle Cambrian strata in northern India, as the summit to the Carboniferous or Permian. In The depositional age and stratigraphic well as grains as young as ca. 526 Ma, both of the 1970s, the summit rocks were reinterpreted correlations of metamorphosed and varia- which support the depositional age and conti- as being Ordovician in age (Mu et al., 1973; bly deformed rocks of Mount Everest are nuity of depositional systems along the length Wang and Zhen, 1975; Yin and Kuo, 1978; poorly known because of limited recovery of the Himalaya. Highly fractured rocks of Yin, 1987). After the comprehensive geologi- of diagnostic fossils. Detailed study of Cam- the Ordovician lower Chiatsun Group in the cal investigation of the northern slope of Mount brian and Ordovician strata from along hanging wall of the South Tibetan detach- Qomolangma by the Chinese Academy of Sci- the length of the Himalaya has produced a ment system in Nyalam, 75 km to the west ences in 1975, a stratigraphic division was pro- coherent stratigraphy that stretches from of Everest, correlate with Ordovician strata posed, and the summit limestone was assigned northern India to Tibet. Our work also dem- of the Mount Qomolangma Formation on to the Lower to Middle Ordovician (Yin and onstrates that the North Col Formation rocks Mount Everest. Our correlations indicate Kuo 1978; Yin, 1987). This stratigraphy was (= Everest series), between the Qomolangma that the base of the summit pyramid of Ever- also used by Burchfi el et al. (1992) in their and Lhotse detachments of the South Tibetan est, the foot of the “Third Step,” is composed study of the structures associated with the South detachment system, still locally preserve sedi- of a 60-m-thick, white-weathering thrombo- Tibetan detachment, a low-angle north-dipping mentary textures and primary stratigraphy lite bed. The top of this ancient microbial normal fault that separates the “Tethyan” sedi- that match those within Cambrian strata deposit crops out only 70 m below the sum- mentary series above from the Greater Hima- ~1100 km to the west in northern India. This mit of Mount Everest. layan sequence of high-grade metamorphic demonstrates a coherency of depositional sys- rocks and crustal melt granites below. tems and stratigraphic architecture for Cam- Keywords: India, Himalaya, Parahio Forma- Although the strata near the summit of Mount brian deposits along much of the Himalaya tion, Cambrian, Tethyan, Everest. Everest have been correlated with Lower to Tethyan margin. It also allows, for the fi rst Middle Ordovician rocks (Yin and Kuo, 1978; time, identifi cation of precise depositional INTRODUCTION Yin, 1987; Burchfi el et al., 1992), almost no age ages of several units in the Everest region, in constraint exists for underlying strata that extend particular, the Yellow Band carbonate and The age and character of the rocks exposed down to the high-grade rocks of the Greater directly underlying siliciclastic strata, which on the summit pyramid of Mount Everest have Himalayan sequence in the Everest region. Work are both shown to be late Middle Cambrian been highly contested. Early geologists con- by Searle (1999, 2003), Law et al. (2004), Searle in age. Detrital zircon data presented herein sidered the upper part of Everest, including the et al. (2003, 2006), and Jessup et al. (2006) in for a sample from these siliciclastic strata Yellow Band, to be Permian or younger in age the Everest massif led to the identifi cation of (Odell, 1925; Wager, 1934). Gansser (1964) two north-dipping low-angle normal faults, an †E-mail: [email protected]. assigned limestone samples with abundant upper brittle Qomolangma detachment that cuts GSA Bulletin; March/April 2009; v. 120; no. 3/4; p. 323–332; doi: 10.1130/B26384.1; 8 fi gures; Data Repository item 2008214. For permission to copy, contact [email protected] 323 © 2008 Geological Society of America Downloaded from gsabulletin.gsapubs.org on 18 September 2009 Myrow et al. through the summit rocks, and a lower ductile of Mount Everest, as well as several sections at a locality 30 km north of the town of Nyalam, Lhotse detachment that separates greenschist– measured in Cambrian strata along the length of Tibet. The rocks are exposed in cliffs along lower-amphibolite-facies pelites of the North the Indian Himalaya, to demonstrate a coherent the north side of a river valley ~5 km along an Col Formation (= Everest series) above from stratigraphic framework along the Himalayan unpaved road that branches off the Friendship high-grade sillimanite gneisses, migmatites, and Tethyan margin. New detrital zircon data from Highway (Fig. 1). In addition, we examined leucogranites beneath. From restoration of the the Nyalam section verify the stratigraphic cor- the same units at a locality 18 km north of the South Tibetan detachment system faults, these relations and help provide precise depositional Rongbuk Monastery, the latter of which is a few authors interpreted the North Col Formation ages of strata on Everest. The correlation of the kilometers north of Everest base camp. These (Everest series) pelites as representing Cam- youngest part of the section also allows for the units are exposed at an altitude of ~5000 m brian and Neoproterozoic protoliths beneath identifi cation of the age and nature of the rocks due to the northward regional dip. Stratigraphic the Yellow Band carbonate, which they inter- that make up the base of the summit pyramid on units at this section are similar to those exposed preted as Ordovician, following earlier reports the top of Mount Everest. in Nyalam (described next) and are easily traced (e.g., Burchfi el et al., 1992). An understanding to Everest itself. of stratigraphic and age relationships of these LOCATION rocks is critical for deciphering the tectonic STRATIGRAPHY: NYALAM history of the Himalaya, particularly the meta- We measured a stratigraphic section across morphic protolith of rocks beneath the South the South Tibetan detachment system, a major Across the Himalaya, the South Tibetan Tibetan detachment system. down-to-north normal fault that stretches the detachment system separates high-grade We present a detailed measured section from length of the Himalaya (Burg, 1983; Burg et al., meta morphic rocks of the Greater Himalaya above the town of Nyalam, Tibet, 75 km west 1984; Burchfi el et al., 1992; Carosi et al., 1998), sequence (GHS) from sedimentary strata of 70°E 80° 90° 64 72 80 88 96°E N 40 Tibetan Plateau 32 0 500 km 24 35° Peninsular South Tibetan detachment system 16 India Zanskar Valley TIBETAN 8°N Main Central thrust Spiti Valley PLATEAU Main Boundary thrust Kumoan Krol–Tal belt Indus Tsangpo suture zone 30°N INDIAN PENINSULA Nyalam Everest Lesser Himalaya Greater Himalaya KATHMANDU KLIPPE Tethyan Himalaya and major Lesser Himalayan klippen Figure 1. Simplifi ed lithotectonic zones of Himalaya and locations of sections illustrated in Figure 4. Box in inset map shows boundaries of Himalayan map. 324 Geological Society of America Bulletin, March/April 2009 Downloaded from gsabulletin.gsapubs.org on 18 September 2009 Cambrian–Ordovician of the Himalaya the Tethyan Himalaya (TH) to the north. At this site near Nyalam, Burchfi el et al. (1992) A mapped the South Tibetan detachment system at a contact between sheared sedimentary rocks Thrombolite of the footwall and lower-grade Ordovician 400 QD Yellow carbonate in the hanging wall.