Research Paper GEOSPHERE Geologic framework of the northern Indo-Burma Ranges and lateral correlation of Himalayan-Tibetan lithologic units across the GEOSPHERE, v. 15, no. 3 eastern Himalayan syntaxis https://doi.org/10.1130/GES02054.1 Peter J. Haproff1,2, Andrew V. Zuza3, An Yin2, T. Mark Harrison2, Craig E. Manning2, Chandra S. Dubey4, Lin Ding5, Chen Wu6, and Jianlin Chen7 1Department of Earth and Ocean Sciences, University of North Carolina, Wilmington, North Carolina 28403, USA 17 figures; 3 tables; 1 set of supplemental files 2Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095, USA 3Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557, USA 4 CORRESPONDENCE: [email protected] Department of Geology, Delhi University, Delhi 110007, India 5Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China 6Structural Geology Group, China University of Geosciences, Beijing 100083, China CITATION: Haproff, P.J., Zuza, A.V., Yin, A., Harrison, 7State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China T.M., Manning, C.E., Dubey, C.S., Ding, L., Wu, C., and Chen, J.L., 2019, Geologic framework of the north- ern Indo-Burma Ranges and lateral correlation of ■ ABSTRACT the northern Indo-Burma Ranges, including the Mesozoic–Cenozoic southern Himalayan-Tibetan lithologic units across the eastern Himalayan syntaxis: Geosphere, v. 15, no. 3, p. 856– Gangdese batholith belt and its cover sequence of the Linzizong volcanic 881, https:// doi.org /10.1130 /GES02054.1. The Cenozoic India-Asia collision generated both the east-trending Hi- rocks, Xigaze forearc basin, Tethyan Himalayan Sequence, and Greater Hi- malayan orogen and the north-trending Eastern and Western Flanking Belts malayan Crystalline Complex of south-central Tibet and the central Himalaya. Science Editor: Raymond M. Russo located along the margins of the Indian subcontinent. Although the tectonic We interpret the absence of these lithologic units to be a result of a greater development of both flanking belts is key to understanding mechanisms of magnitude of crustal shortening and/or underthrusting of the Indian cratonal Received 17 August 2018 continental deformation during indenter-induced collision, few field-based rocks than that across the Himalayan orogen to the west. This interpretation Revision received 19 December 2018 Accepted 27 February 2019 studies coupled with geochronological and geochemical methods have been is supported by a southward decrease in the map-view distance between applied to these tectonic domains. In this study, we investigate the lateral the active range-bounding thrust and the Indus-Yarlung suture zone in the Published online 9 April 2019 correlation of lithologic units between the northern Indo-Burma Ranges, the northern Indo-Burma Ranges, from ~200 km in the north near the eastern northernmost segment of the Eastern Flanking Belt, and the eastern Hima- Himalayan syntaxis to ~5 km in the south across a distance of ~200–300 km. layan-Tibetan orogen by integrating field observations, U-Pb zircon geochro- nology, and whole-rock geochemistry. Our findings provide new quantitative constraints to interpretations that the northern Indo-Burma Ranges expose ■ INTRODUCTION the eastward continuation of several lithologic units of the Himalayan oro- gen and Lhasa terrane. Our field work documents a stack of thrust-bounded The Cenozoic India-Asia collision generated the Himalayan collisional sys- lithologic units present in the study area. The northernmost and structurally tem, which consists of the convergence-perpendicular Himalayan orogen and highest Lohit Plutonic Complex consists of Mesoproterozoic basement rocks convergence-parallel flanking belts located along the eastern and western (ca. 1286 Ma) and Late Jurassic–Cretaceous granitoids (ca. 156–69 Ma) with margins of the Indian subcontinent (Gansser, 1964; Yin, 2006) (Fig. 1A). Al- 87 86 positive εNd values and initial Sr/ Sr ratios of ~0.705, which are correlative though the geology and tectonic evolution of the Himalayan orogen are well to the Bomi-Chayu complex and the northern Gangdese batholith, respec- documented (Le Fort, 1975; Le Fort, 1996; DeCelles et al., 2000, 2001; Hodges, tively. The structurally lower Tidding-Mayodia mélange complex, composed 2000; Yin and Harrison, 2000; Yin, 2006, 2010; Webb et al., 2013, 2017), rela- of basalt, gabbro, ultramafic rocks, and mafic schist of a dismembered ophi- tively few geologic studies have focused on the flanking belts (cf. Tapponnier olite sequence, is interpreted in this study as the eastward extension of the et al., 1981; Ni et al., 1989; Mitchell, 1993; Haq and Davis, 1997; Haproff et al., Indus-Yarlung suture zone. Structurally below the suture zone are the Mayo- 2018). Establishing the geologic history of the two flanking belts is crucial for dia gneiss and Lalpani schist, which are interpreted to correlate with the understanding the holistic development of the Himalayan collisional system Lesser Himalayan Sequence based on comparable metamorphic lithologies, and differentiating the end-member models of continental deformation during negative εNd values, and similar Mesoproterozoic–Cambrian detrital zircon the India-Asia collision (e.g., Tapponnier et al., 1982, 2001; England and House- age spectra. In contrast to the above metamorphic units, the structurally man, 1986; Cobbold and Davy, 1988; Dewey et al., 1988; England and Molnar, lowest Tezu unit consists of siliciclastic strata that may be correlated with 1990; Royden et al., 1997; Zuza et al., 2019). This paper is published under the terms of the the Miocene–Pliocene Siwalik Group of the Himalayan orogen. Despite the In this study, we investigate the divisions of major lithologic units exposed CC-BY-NC license. above correlations, notable Himalayan-Tibetan lithologic units are absent in in the northern Indo-Burma Ranges, the northernmost segment of the Eastern © 2019 The Authors GEOSPHERE | Volume 15 | Number 3 Haproff et al. | Northern Indo-Burma Ranges framework and lateral correlation of Himalayan-Tibetan lithologic units Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/3/856/4701242/856.pdf 856 by University of Nevada Reno user on 01 August 2019 Research Paper 95°E N. Gangdese JF 100 km 94°30’E Jiali fault95°30’E 96°96966°°E Lhasa batholith A terrane B Lhasa C Tibet terrane S. Gangdese batholith N Himalayan IYSZ orogen E. Himalayan THS orogen D GHC Bomi-Chayu ST 29° India Shillong Plateau Complex Western 45’N SE Fig. 1C Flanking Belt Eastern MCT LHS Flanking Belt Asia Qal MFT IYSZ Sampling location Symbols of Xu et al. (2013) ? Parlung Thrust Namche Barwa faul fault t syntaxis (EHS) Indus-Yarlung Strike-slip suture zone fault 29° Figure 1. Geologic maps of (A) the Hima- 15’N Normal layan-Tibetan orogen; (B) the easternmost Walong fault Himalayan orogen and southeastern Ti- pЄ-K(elp) thrust betan Plateau (modified from Webb et al., Puqu Antiform 2017); and (C) the northern Indo-Burma fault N Ranges compiled from Ding et al. (2001) Lohit thrust Synform and Haproff et al. (2018). Abbreviations: EHS—eastern Himalayan syntaxis; GHC— Tidding 28° Fig. 3 Dibang Valley Lithologic Greater Himalayan Crystalline Complex; 45’N thrust units IYSZ—Indus-Yarlung suture zone; JF—Jiali IYSZ traverse 28° Quaternary fault; LHS—Lesser Himalayan Sequence; 45’N Qal MCT alluvium LPC—Lohit Plutonic Complex; MBT—Main Boundary thrust; MCT—Main Central thrust; Jr-K(wlp) Cenozoic MFT—Main Frontal thrust; STD—South Ti- (Cz)ms metasedim- entary rocks/ LHS MB Tidding betan detachment; THS—Tethyan Hima- T ? volcanics ml(t) thrust layan Sequence. cgl Tezu unit ? GHC GHC Cz(ms) Siang sch 28° ms Sewak unit 28° half- gn Lohit 15’N 15’N window Lalpani thrust sch ml(m) schist Lohit Mayodia ms gn MCT Jr-K(wlp) Valley gneiss traverse Mishmi thrust cgl Tidding/Mayodia LHS ml(t) ml(m/t) Qal mélange complex SHS Demwe thrust Fig. 5 Western Lalpani thrust Jr-K(wlp) T LPC belt MF 50 km MBT Tezu thrust 27° Eastern 96° pЄ-K(elp) 45’N LPC belt 95°E 95°30’E 30’E Flanking Belt (Fig. 1). We correlate these units with the classic lithologic divi- shortening and/or continental underthrusting across the northern Indo-Burma sions of the Himalayan orogen and the Lhasa terrane to the west. Correlations Ranges than across the Himalaya to the west. are based on U-Pb zircon geochronology, whole-rock geochemistry, bounding Cenozoic faults, and similar lithologies. From these findings, we conclude that several lithologic units of the Himalayan-Tibetan orogen, including the Greater ■ GEOLOGIC SETTING Himalayan Crystalline Complex, Tethyan Himalayan Sequence, Xigaze forearc basin, and Mesozoic–Cenozoic southern belt of the Gangdese batholith are To provide a regional context, we summarize the existing research across absent in the study area. If these lithologic units were present at the onset the eastern Himalayan orogen, the Indus-Yarlung suture zone, the Lhasa ter- of the India-Asia collision, our work implies a greater magnitude of crustal rane, cratonal rocks of northeast India, and the northernmost segment of the GEOSPHERE | Volume 15 | Number 3 Haproff et al. | Northern Indo-Burma Ranges framework and lateral correlation of Himalayan-Tibetan lithologic units Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/3/856/4701242/856.pdf 857 by University of Nevada Reno user on 01 August 2019 Research