RESEARCH Rifting of the Northern Margin of the Indian Craton in the Early Cretaceous: Insight from the Aulis Trachyte of The

RESEARCH

Rifting of the northern margin of the Indian craton in the Early Cretaceous: Insight from the Aulis Trachyte of the Lesser Himalaya (Nepal)

Saunak Bhandari1,2, Wenjiao Xiao1,2,3,4,*, Songjian Ao1,2, Brian F. Windley5, Rixiang Zhu1, Rui Li1,2, Hao Y.C. Wang1,2, and Rasoul Esmaeili1,2 1STATE KEY LABORATORY OF LITHOSPHERIC EVOLUTION, INSTITUTE OF GEOLOGY AND GEOPHYSICS, CHINESE ACADEMY OF SCIENCES, BEIJING 100029, CHINA 2COLLEGE OF EARTH AND PLANETARY SCIENCES, UNIVERSITY OF CHINESE ACADEMY OF SCIENCES, BEIJING 100049, CHINA 3XINJIANG RESEARCH CENTER FOR MINERAL RESOURCES, XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY, CHINESE ACADEMY OF SCIENCES, URUMQI 830011, CHINA 4CENTER FOR EXCELLENCE IN TIBETAN PLATEAU EARTH SCIENCES, CHINESE ACADEMY OF SCIENCES, BEIJING 100101, CHINA 5DEPARTMENT OF GEOLOGY, UNIVERSITY OF LEICESTER, LEICESTER LE1 7RH, UK

ABSTRACT

To reconstruct the early tectonic history of the Himalayan orogen before final India-Asia collision, we carried out geochemical and geochronological studies on the Early Cretaceous Aulis Trachyte of the Lesser Himalaya. The trace-element geochemistry of the trachytic lava flows suggests formation in a rift setting, and zircon U-Pb ages indicate that volcanism occurred in Early Cretaceous time. The felsic volcanics show enrichment of more incompatible elements and rare earth elements, a pattern that is identical to the trachyte from the East African Rift (Kenya rift), with conspicuous negative anomalies of Nb, P, and Ti. Although much of the zircon age data are discordant, they strongly suggest an Early Cretaceous eruption age, which is in agreement with the fossil age of intravolcanic siltstones. The Aulis Trachyte provides the first corroboration of Cretaceous rifting in the Lesser Himalaya as suggested by paleomagnetic data associated with the concept that the northern margin of India separated as a microcontinent and drifted north in the Neo-Tethys before terminal collision of India with Asia.

LITHOSPHERE; v. 11; no. 5; p. 643–651; GSA Data Repository Item 2019291 | Published online 12 July 2019 https://doi .org /10 .1130 /L1058 .1

INTRODUCTION al., 2016; Xiao et al., 2017; Ao et al., 2018; Chen et al., 2018). However, there is still insufficient geological evidence to substantiate any of the The tectonic evolution of the Himalayan orogen was the result of the extension necessary to enable rifting of the terranes. closure of the Neo-Tethys Ocean and the terminal collision of India with To help resolve these problems, we present new data on trachytic Eurasia (Searle et al., 1987; DeCelles et al., 2000; Yin, 2006; van Hins- alkaline rocks from the Gondwana sequence of the Lesser Himalaya in bergen et al., 2012). It has long been considered that an integral Indian central Nepal in order to help constrain the Cretaceous history of the plate drifted northward and collided with Tibet (Searle et al., 1987), but northern part of the Indian craton, and we discuss their significance for recent advances have reported that the northern margin of India was the tectonic evolution of the Himalayan orogen. separated as microcontinents that moved northwards to collide with Tibet (van Hinsbergen et al., 2012). This has created controversy about the GEOLOGICAL SETTING nature of amalgamation between India and Eurasia and, thus, their final collision time. Traditionally, the Himalaya is divisible into four major lithotectonic The northern margin of the Indian craton has been variously consid- units (Figs. 1A and 1B): the Sub-Himalaya, Lesser Himalaya, Greater ered to consist of a passive margin south of the Yarlung-Tsangpo suture Himalaya, and Tethys Himalaya (Gansser, 1964; Yin, 2006). The Sub- (Myrow et al., 2003), or early Paleozoic accreted terranes (DeCelles et al., Himalaya comprises a Cenozoic foreland basin with synorogenic sediments, 2000), or Late Jurassic to Early Cretaceous juxtaposed suspect terranes whereas the other units are pre-Himalayan. (Martin, 2017). However, van Hinsbergen et al. (2012) controversially The Lesser Himalaya, which is the oldest and stratigraphically lowest considered that the Tibetan Himalaya was separated from the northern unit, contains Proterozoic gneisses and Paleozoic and Mesozoic sediments margin of the Indian craton in the Early Cretaceous. Recently, further (Robinson and Pearson, 2013). Near its southern border (Fig. 1B), at an data have accrued that suggest there were several rifted terranes in the elevation of ~1500 m, the 250-m-thick Cretaceous Taltung Formation Tethys that collided with Asia before the terminal collision (Aitchison et (Fig. 1C) consists of fining-upward fluvial cycles of alternating cross- al., 2007; Li et al., 2013; Xiao, 2015; Yang et al., 2015a, 2015b; Ma et bedded sandstones and mudstones interbedded with 100-m-thick alkaline trachytic lava flows that belong to the 200-m-thick pillow lava–bearing, Wenjiao Xiao http://orcid.org/0000 -0003 -3518 -0526 vesicular Aulis volcanic rocks. These volcanic rocks are interbedded *Corresponding author: [email protected] with fluvial, imbricated pebble conglomerates and carbonaceous black

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/11/5/643/4829918/643.pdf by guest on 27 September 2021 BHANDARI ET AL. | Rifting of northern Indian craton in the Early Cretaceous RESEARCH

B A T n ib a e t I t is nd k u a s P G S er u 84°E iv a tu s R n re du g N In e ep 30°N s a R l N iv Bhutan er

India 2 o 0 N S o 500Km T 70 E D S

80°E R M M CT 29°N T MBT Sub Himalaya Kathmandu H Leucogranite FT Tibetan Himalaya Greater Himalaya Lesser Himalaya 1C Lesser Himalaya (RMT sheet) 0 100km

STDS—South Tibetan Detachment System, MCT—Main Central Thrust, RMT—Ramgarh Thrust, MBT—Main Boundary Thrust, HFT—Himalayan Frontal Thrust

C 83°35'0"E 83°36'0"E 83°37'0"E 83°38'0"E

900 Rupse Maulathar

900

1100 1300 Gijindanda Khapur

1100 50 Gheraudi 900 NA18 27°47'0"N Aules 1500 1300 27°47'0"N Kokaldanda 40 NA12 40 NA23 NA06 NA08 1500 1300 Marmera 1700 1100 1700 1500km 1100 0 1

27°46'0"N 83°35'0"E 83°36'0"E 83°37'0"E 83°38'0"E 27°46'0"N Contour MBT Bhainskati Formation Aulis Trachyte Stream Siwaliks Amile Quartzite Sisne Formation Sample location Dumri Formation Taltung Formation Kerabari Formation

Figure 1. (A) Position of Nepal in South Asia after DeCelles et al. (2001). (B) Position of Nepal within the Himalaya modified from Robinson and Pearson (2013). (C) Detailed geological map of the Aulis-Marmera area with sample locations modified after Sakai et al. (1992).

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 644

shales with silicified wood up to 40 cm in diameter and silicide wood 150 fragments (Sakai, 1983). Sakai et al. (1992) reported three lava flows, each silty sandstone 5–100 m thick, which are interbedded with conglomerates, sandstones, silty shale tuffs, tuffaceous shales, and sediments that include considerable volcanic lava 3 Aulis Trachyte detritus derived from the Aulis volcanics. Figure 2 shows a representative columnar section with three distinct lava flows from the Marmera purple shale 100 olivegreen area (Fig. 1C). The Taltung Formation formed in a shallow-water, coastal, sandstone fluvial, volcaniclastic environment with episodic marine transgressions imbricated pebble and that was very similar to the shallow-marine, volcaniclastic, continental cobble conglomerate shelf–type environment of the Rajmahal sediments in eastern India. Early lava 2 Cretaceous rift- and plume-related alkaline and basaltic lavas were then erupted into both of these successions (Sakai, 1983). The Early Cretaceous Figure 2. Columnar section breakup of Gondwana was assisted by several mantle plumes, such as the 50 of the lower part of Tal- Kerguelen Plume (Chatterjee et al., 2013). Such plume-related magmatic tung Formation showing intercalation of the Aulis products typically occur along continental margins of continents that have Trachyte and fluvial strata, been separated from another continent. lava 1 modified from Sakai et al. Na23 (1992). METHODOLOGIES 0m

We collected five samples of the Aulis Trachyte (NA6, NA8, NA12, NA18, and NA23) for geochemical and geochronological studies, as shown in Figure 1C. As Sakai (1983) reported, all lava flows in the Himalayan orogenic events (Fig. 1C), older tectonic imprints might have Aulis-Marmera belt have identical lithologies, textures, and petrographic been concealed by succeeding deformation events. assemblages. Hence, our five collected samples are representative of the Representative trachyte samples from the Aulis Trachyte were crushed lava sequence; among them, we selected two for zircon data analysis using a tungsten carbide mill, and the powder was passed through a 200 (NA18 and NA23). mesh. Glass beads were made by fusing this powder at 1050–1100 °C. Geological mapping around the volcanic lava flows was expected to Major- and trace-element concentrations for the sample were determined encounter evidence for an extensional event, but we did not document any by X-ray fluorescence (XRF; Rikagu RIX 2100) and PerkinElmer Elan such structures. The area has been investigated regionally by Sakai (1983), 9000 inductively coupled plasma–mass spectrometry (ICP-MS), respec- who defined many lithostratigraphic strata and reported several local and tively, at the Mineral Division of ALS Chemex, Co., Ltd., Guangzhou, regional structures. However, he did not demonstrate any regional exten- China. For the XRF analysis, analytical procedures were as described by sional structure either. Since the area was intensely deformed during the Goto and Tatsumi (1996) with analytical precision within 1%, whereas

A B

Figure 3. Photographs of outcrops and microphotographs of the Aulis Trachyte: (A) outcrop of gray-green 3cm trachyte band; (B) trachyte in hand sample; (C) phenocrysts of plagioclase within a groundmass with plagioclase microlites; (D) rock C fragments (xenolith), which are D rare, composed of quartz, and which might be the cause of old zircons in trachyte.

500µm 100µm

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 645

trace-element compositions were measured by the method described by TABLE 1. MAJOR ELEMENTS (WT%) AND TRACE ELEMENTS (PPM) Wu et al. (2015), and analysis precision was well within 5%. FROM THE AULIS TRACHYTE OF THE LESSER HIMALAYA (NEPAL) We collected two samples (each >5 kg) of the Aulis Trachyte for Sample no.: NA 06 NA 08 NA 12 NA 18 NA 23 zircon dating. Zircon grains were separated from rock samples using Trace elements conventional heavy liquid and magnetic separation methods. Zircons were Ba 423 1600 486 726 684 handpicked and mounted in epoxy resin. They were polished and cath- Ce 295 322 287 306 339 odoluminescence images were acquired, which helped to check internal Cr <10 10 <10 10 <10 structures and potential target sites. U-Pb geochronological analyses of Cs 0.31 0.81 0.47 0.39 0.27 Dy 7.21 8.12 8.14 8.12 8.94 zircon were conducted using laser-ablation (LA)–multicollector (MC) Er 3.53 4.14 4.42 4.13 4.44 ICP-MS at the Key Laboratory of Mineral Resources Evaluation in North- Eu 2.78 3.2 2.88 3 3.02 east Asia, Ministry of Land and Resources of Changchun, China. The Ga 26.6 29.6 27.4 27.2 27.9 instrument was used with the automatic positioning system. It couples Gd 9.7 11.6 10.75 11.2 11.6 a quadrupole ICP-MS (Agilient 7900) and 193 nm ArF Excimer laser Hf 15.4 17.1 16 16.2 16.8 Ho 1.3 1.51 1.56 1.5 1.66 (COMPexPro 102, Coherent). The analysis involved a laser spot size La 170 179.5 158.5 182 194 of 32 μm for all analyses, laser energy density at 10 J/cm2, and repeti- Lu 0.43 0.46 0.59 0.49 0.56 tion rate at 8 Hz. The procedure of laser sampling was 30 s blank, 30 s Nb 132.5 151 151.5 145.5 147 sampling ablation, and 2 min sample-chamber flushing after the abla- Nd 109.5 122 109.5 117.5 129 Pr 31.3 33.2 30.7 33.4 36.5 tion. The ablated material was carried into the ICP-MS by a high-purity Rb 141.5 140 178 170 139 helium gas stream with a flux of 1.15 L/min. In order to increase energy Sm 15.25 17.4 16 16.7 18.1 stability, the whole laser path was fluxed with Ar (600 mL/min). The Sn 5 5 5 6 5 counting time was set as 20 ms for 204Pb, 206Pb, 207Pb, and 208Pb, 15 ms Sr 155.5 411 181.5 257 241 for 232Th and 238U, 20 ms for 49Ti, and 6 ms for other elements. Zircon Ta 6.4 7.4 7.1 7.1 7.3 Tb 1.37 1.59 1.5 1.55 1.67 91500 was used as the external standard for U-Pb isotope fractionation Th 22.4 24.3 23.8 23.9 23.8 effect correction, whereas NIST 610 glass as an external standard and Tm 0.49 0.55 0.65 0.59 0.63 Si as internal standard were used for calibrations for the zircon analyses. U 4.77 4.26 5.49 4.37 5.2 For secondary standard zircon, standard Plesovice (337 Ma) was also V <5 6 <5 <5 7 used to supervise the deviation of age measurement/calculation. Glit- W 2 2 2 2 2 Y 36 45.1 45.5 44.6 50 ter was used to calculate isotopic ratios and element concentrations of Yb 2.97 3.3 4.09 3.35 3.82 zircons. Similarly, concordia age and weighted average diagrams were Zr 704 790 727 765 763 made using Isoplot/Ex (3.0). The analytical data are presented on U-Pb Major oxides concordia diagrams with 2σ errors. Al2O3 17.66 18.54 17.59 18 18.22 BaO 0.05 0.18 0.06 0.09 0.08 RESULTS CaO 1.24 0.59 1.13 0.96 1.15 Cr2O3 <0.01 <0.01 <0.01 <0.01 <0.01 *TFe O 4.44 3.41 4.7 3.81 3.78 The lava flows are of different thicknesses, chemically homogeneous, 2 3 K2O 6.15 6.23 7.34 6.78 6.65 and variably weathered (Fig. 3A). Our chosen fresh samples were plagio- MgO 1.14 0.74 1.14 0.98 1.01 clase-phyric and had typical trachytic textures with euhedral phenocrysts MnO 0.05 0.04 0.08 0.07 0.04 of plagioclase, sanidine, kaersutite, and anorthoclase in a matrix of minute Na2O 5.03 5.22 4.27 4.65 5.3 P O 0.19 0.24 0.18 0.19 0.21 lath-shaped plagioclase microlites (Figs. 3B and 3C); the feldspar pheno- 2 5 SiO 60.93 62.11 61.15 62.24 61.33 crysts were up to 5mm long and had oscillatory zones. Some trachytes 2 SO3 <0.01 <0.01 <0.01 <0.01 <0.01 also included small rock fragments that might have been the source for SrO 0.02 0.05 0.03 0.03 0.03

old zircons in trachyte (Fig. 3D). TiO2 0.98 1.03 0.99 1.01 1.02 LOI ×1000 1.51 1.45 1.56 1.7 1.32 Geochemistry Note: LOI—loss on ignition. *Total iron. Major- and trace-element data from the Aulis Trachyte are listed in Table 1. The major-element abundances confirm the acidic alkalinity of the

lavas. On plots of (Na2O + K2O) versus SiO2 (Fig. 4A) and Nb/Y versus extensional rift at Karaburhan in Turkey (Sarıfakıoğlu et al., 2009) are

Zi/TiO2 (Fig. 4B), the samples cluster in the trachyte field (Le Bas et al., almost identical (Fig. 4C), as also are trachytes from the East African Rift 1986; Winchester and Floyd, 1977, respectively). (Kenya rift) (White et al., 2012) in a chondrite-normalized multi-element A chondrite-normalized rare earth element (REE) plot (Nakamura, spider diagram (Fig. 4E; Thompson, 1982). The Zr-Ti diagram (Pearce, 1974) depicts enrichment of light (L) REEs relative to heavy (H) REEs 1982) demonstrates that the Aulis Trachyte is a within-plate lava (Fig. 3F). (Fig. 4C), and a mid-ocean-ridge basalt (MORB)–normalized spider diagram (Fig. 4D; Pearce, 1983) shows distinct positive anomalies of K, Ages Rb, and Th, and pronounced negative anomalies of Sr, Ba, P, and Ti. In general, the volcanic rocks are enriched in the more incompatible ele- Even after careful examination of the zircons, we were unable to obtain ments. Pronounced negative anomalies of Nb, P, and Ti and enrichments a precise age of eruption. Most of the determined ages have a discordance in more incompatible elements are well-established characteristics of lavas that is due to Pb loss and/or inheritance. A major Pb-loss event might be in continental rifts (Storey et al., 1992; Singh and Bikramaditya Singh, associated with movement on the once-overlying Main Central Thrust. 2012). The REE patterns of the Aulis Trachyte and a trachyte from an Sakai et al. (1992) found a K-Ar whole-rock age of 17.4 ± 0.9 Ma in this

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 646

TAS (Le Bas et al., 1986) A B Nb/Y-Zr/TiO2 plot (Winchester and Floyd, 1977)

Ultrabasic Basic Intermediate Acid

5.00

Phonolite Cornentite Pantellerite Phonolite

Tephri- phonolite Trachyte

Foidite Trachydacite 0.500 Rhyolite

10 Phono Trachyte O

2 -tephrite Trachy- 2 andesite Rhyolite Rhyodacite/Dacite Basaltic

O+K Tephrite trachy- Trachy-

0.050 Basanite andesite Zr/TiO Andesite andesite Trachy-

Na basalt 5 Basanite Basalt Andesite Andesite/Basalt Nephelinite andesite Dacite

Basalt 0.005 Alkaline-Basalt Subalkaline Basalt

Alkaline Picrobasalt Subalkaline/Tholeiite

0.001 40 50 60 70 80 0.01 0.05 0.10 0.5 1 5.00 10.00

SiO2 Nb/Y

C Spider plot -REE chondrite (Nakamura, 1974) D Spider plot - MORB (Pearce, 1983)

1000

100 Field of extension related trachyte from Karaburhan Turkey (after Sarifakioglu et al., 2009)

100

Sample/MORB

Sample/REE chondrite

0.1 10 Er Tm Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Yb Sr K Rb Ba Th Ta Nb Ce P Zr Hf Sm Ti Y Yb

Spider plot - Chondrite (Thompson, 1982) E F Zr-Ti (Pearce, 1982)

50000

1000

20000

100 Within-Plate Ti Lavas

10000 MORB

5000

10 Island Arc Lavas

Reference pattern from KS/94/29 trachyte of Kenya rift

Sample/chondrite

2000 (after White et al., 2012) KS/94/33

Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y Tm Yb 1000 10 20 50 100 200 500 Zr

Sample symbols NA06 NA08 NA12 NA18 NA23

Figure 4. (A) Total alkali-silica (TAS) diagram plotting (Na2O + K2O) vs. SiO2 (in wt%; Le Bas et al., 1986). (B) Nb/Y vs. Zi/TiO2 diagram (Winchester and Floyd, 1977). (C) Chondrite-normalized rare earth element (REE) plot (Nakamura, 1974), where the pattern is compared with the field for trachyte of the extensional setting from Karaburhan, Turkey (Sarıfakıoğlu et al., 2009). (D) Mid-ocean-ridge basalt (MORB)–normalized multi- element spider diagram (Pearce, 1983). (E) Chondrite-normalized multi-element variation diagram (Thompson, 1982) compared with the trachyte from the Kenya rift (White et al., 2012). (F) Tectonic setting discrimination Zr-Ti plot (in ppm) showing within-plate lava character (Pearce, 1982).

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 647

NA18 13 9 1 43 25 19 44 21 119Ma 127Ma 107Ma 113Ma Figure 5. Representative cathodoluminescence 112Ma 119Ma 111Ma 113Ma (CL) images of zircons used for volcanic eruption age determination; red circles indicate positions NA23 of laser spot. 34 17 6 29 24 23 15 13 118Ma 127Ma 128Ma 126Ma 130Ma 127Ma 114Ma 115Ma

volcanic unit, which they ascribed to partial thermal alteration caused by reported extensive alternating volcanism and sedimentation. Intravolcanic southward thrusting of the Main Central Thrust in the Miocene. siltstones of the Taltung Formation contain fossil plants (Sakai, 1983; Sample NA18 is from Aulis village (Fig. 1C), the type locality of Kimura et al., 1985) of four genera belonging to Ptillophylum, Ptero- the Aulis Trachyte. We separated 60 zircon grains from 5 kg of sample, phyllum, Cladopherebis, and Elatocladus, which have been assigned among which 45 were large enough for ICP-MS dating. Most zircons a Late Jurassic to Early Cretaceous age, and which are well known in were very small and subhedral to round (Fig. 5). Of 45 analyses, only 13 sediments within the Rajmahal Traps. The wide fossiliferous age range were considered to be close to the age of eruption, because other grains does not provide a precise date of the alkaline magmatism. Sakai et al. were either old inherited zircons or were highly discordant. Sample NA23 (1992) obtained a Rb-Sr mineral isochron age of 96.7 ± 2.8 Ma on a pho- from Marmera village (Fig. 1C) produced 40 zircons, of which only 35 notephrite; however, this Rb-Sr isotopic technique still requires a more grains were useful for LA-ICP-MS dating, with the other zircons being precise confirmation if we are to understand the timing of the alkalic too small (Fig. 5). Among the 35 analyses, only 13 grains were consid- material. Furthermore, the age was obtained from a single phonotephrite ered to be close to the age of eruption of trachyte volcanism, because the gravel “probably eroded out from the Taltung Formation” (Sakai et al., other grains were either very old and xenocrystic, or highly discordant, 1992, p. 65), and the mean square of weighted deviates (MSWD) was similar to sample NA18 (Fig. 5). Since most of the ages obtained from not reported. the trachyte samples ND18 and ND23 were discordant, we carried out Our zircon dates strongly suggest an Early Cretaceous age for Aulis U-Pb geochronological analysis of 37 zircons from the specimen NA06 by Trachyte volcanism, which is consistent with previous radiometric dates LA-ICP-MS at the Institute of Geology and Geophysics, Chinese Acad- as well as biostratigraphic ages from interbedded sedimentary rock. emy of Sciences (IGGCAS) in Beijing for independent confirmation of the suggested age. The configuration of the LA-ICP-MS and the method TECTONIC IMPLICATIONS for age determination are very similar to those of the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and The Late Cretaceous and Paleocene history of the Neo-Tethys Ocean Resources of China. Among 37 zircons, 6 grains resemble the Cretaceous has long been well defined because of paleomagnetically determined, events, but most of them are highly discordant, like the other samples Early Cretaceous positions of the Lhasa terrane, the Himalayan sequences, (Fig. 6; GSA Data Repository Item1). LA-ICP-MS zircon U-Pb age data and India (Besse et al., 1984; Patzelt et al., 1996; Tong et al., 2008; Lip- are given in the Data Repository Item. pert et al., 2011; Yi et al., 2011; Chen et al., 2012; Torsvik et al., 2012; Among 13 zircons from sample NA18, six zircons were obviously Liebke al., 2013; Ma et al., 2014; Huang et al., 2015; Xiao, 2015; Yang et discordant, and seven zircons were internally concordant but externally al., 2015a, 2015b). The argument about the Early Cretaceous rifting of the discordant (they fall on concordia but do not overlap with each other). northern Indian craton was already hypothesized with the study of Early The spread in age is from ca. 110 Ma to ca. 125 Ma. Two clusters at ca. Cretaceous volcaniclastics in the Tethys Himalaya of southern Tibet and 110 Ma and ca. 125 Ma, each with three zircons, are separated by 120 Ma central Nepal (Jadoul et al., 1998; Hu et al., 2010). However, the idea has zircon. A similar spread and two concentrations at ca. 115 Ma and ca. 125 come under debate after recent paleomagnetic studies (van Hinsbergen Ma (with two and four internally concordant zircons, respectively) were et al., 2012; Yang et al., 2015a, 2015b). Recently, van Hinsbergen et al. demonstrated by sample NA23. Among six zircons of sample NA06, three (2012) suggested that there was an ocean, called the Greater India Basin, were obviously discordant, and three were internally concordant. Two of between the Tibetan Himalaya and the Lesser Himalaya and India to the them fall at ca. 112 Ma, and one falls at ca. 125 Ma on a concordia line. south. However, no geological evidence has since been recorded from the Some external discordance (points fall on concordia but do not overlap Lesser Himalaya to confirm rifting and extension of the predicted Tibetan- with each other) might be due to slight Pb loss and/or inheritance of Himalayan microcontinent (van Hinsbergen et al., 2012). slightly older (but still Early Cretaceous) igneous zircon. Although most The Aulis Trachyte in the current work provides the first evidence that ages were discordant, all three samples gave the same Early Cretaceous supports the start of rifting and extension in the Early Cretaceous in the age, which is consistent with the fossil occurrence of intravolcanic strata present-day Lesser Himalaya. Reconstruction of Late Cretaceous and (as described in the Geological Setting section). The range of ages might Paleocene paleolatitudes of the Tibet Himalaya and the calculated apparent point to inheritance of zircon from protracted magmatism. Sakai (1983) polar wander paths (APWPs) of India (Torsvik et al., 2012; van Hinsber- gen et al., 2012) clearly imply considerable extension and rifting, because 1 GSA Data Repository Item 2019291, U-Pb age data, is available at http://www the amount of crustal shortening during the Himalayan orogeny is far less .geosociety.org/datarepository/2019, or on request from [email protected]. than the 2675 ± 700 km allowed by the Late Cretaceous latitude difference

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 648

Data-point error ellipses are 2σ Data-point error ellipses are 2σ

0.4 NA18 0.022 NA18 140 1800

0.3 130

U 0.020 1400

238

U 120 0.2

238

Pb/

1000 0.018

206 Pb/ 110

206

600

0.1 0.016 100

0.014 0.0 2 6 8 0.11 0.13 1 4 0.09 0.15 0.15 0.19 0.21 207 235 Pb/ U 207Pb/235U

Data-point error ellipses are 2σ Data-point error ellipses are 2σ

0.4 145 NA23 0.023 NA23 900

135

0.3 0.021

U 700

U 238 125

238 0.2

Pb/ 500 0.019

Pb/

206 115

206

300

0.1 0.017 105

100

0.0 0.015 0.0 0.4 0.8 1.2 1.6 0.06 0.10 0.14 0.18 0.22 207Pb/235U 207Pb/235U

Data-point error ellipses are 2σ Data-point error ellipses are 2σ

2600

0.5 NA06 NA06

145 0.023

2200 0.4

135 0.021

U 1800

238 0.3 125 1400 238

Pb/ 0.019

Pb/

206 0.2 1000 115

206 0.017

0.1 600 105 0.0 2 4 6 8 10 12 0.015 0.10 0.12 0.14 0.16 0.18

207Pb/235U 207Pb/235U

Figure 6. U-Pb concordia diagrams for the Aulis Trachyte zircon samples from rock specimens NA18, NA23, and NA06.

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 649

between India and the Tibet Himalaya (Schelling, 1992; DeCelles et al., convincing with respect to Himalayan metamorphic and deformational 2001). The paleolatitude of the Tibet Himalaya in the Early Cretaceous history. Furthermore, multiple rifting and subsequent accretion events is significantly different from that in the Late Cretaceous, and that dif- might have occurred before final collision. ference increased with time, supporting the idea of van Hinsbergen et al. Chatterjee et al. (2013) identified five volcanic events around the Indian (2012) that the Tethys Himalaya and Indian craton were a single body Shield that were related to different plumes. Among them, similarities during the Early Cretaceous. Van Hinsbergen et al. (2012) demonstrated in fossil content of intravolcanic siltstone show that the Aulis Trachyte that before and until the Early Cretaceous (120 Ma), the Tethys Himalaya was coeval with the Rajmahal flood basalt (118–115 Ma) related to the and India were separated by 2.1° ± 5.5° of latitude, whereas in the Late Kerguelen plume (118 Ma; Baksi, 1995; Ray et al., 2005; Ghatak and Cretaceous to Paleocene, the separation was 24.1° ± 3.0° relative to India. Basu, 2013; Ghose et al., 2017). The two most favored environments for Ma et al. (2016) predicted that the extension and separation of the Tibet rifting and continental extension are an old collisional suture zone and a Himalaya from the Indian craton occurred after 130 Ma, which is similar mantle plume or hotspot (Vink et al., 1984; Chatterjee et al., 2013). Both to the interpretation of Yang et al. (2015a), who, from a paleomagnetic of these conditions were attained during the separation of the Tibetan- study of Cretaceous lava flows in the Tethys Himalaya, demonstrated an Himalayan microcontinent because the rifted portion of the Indian craton ~2.1° paleolatitude difference and separation after 134–130 Ma between was comparable to the early Paleozoic accreted terranes (DeCelles et the Tethys Himalaya and the Indian craton. al., 2000) and the Kerguelen plume was coeval with the extension event. Because the eruption time of the Aulis Trachyte was broadly synchro- nous with the paleomagnetically determined time of separation of the CONCLUSION Tibetan-Himalayan microcontinent, we present a tectonic model for the Early Cretaceous separation of the Tibetan-Himalayan microcontinent By comparing our age and geochemical data from the Aulis Trachyte including geological evidence from the present-day Lesser Himalaya with recent paleomagnetic data, we conclude that the Aulis Trachyte (Fig. 7). We agree with the data of van Hinsbergen et al. (2012), which erupted in an extensional tectonic setting, probably in a plume-generated, indicate that the Tibet Himalaya started to drift at ca. 117 Ma, and by rifted continental margin, when the Tibetan-Himalayan microcontinent ca. 68 Ma, it had drifted northwards by 2675 ± 700 km from the Indian began to drift to the north in the Early Cretaceous. Our evidence of exten- caton (Fig. 7). The presence of this wide oceanic basin (the Greater India sion, along with recent documentation of Cretaceous rift-related volcanism Basin) is consistent with the two-phase collision of India and Eurasia from the Tethys Himalaya, supports the concept that there might have been (Xiao, 2015). The first “soft” collision of a Tibet-Himalaya microconti- several different terranes in the Neo-Tethys Ocean before the terminal nent with Asia was at ca. 55 Ma, and it was followed by subduction of the collision between India and Eurasia. oceanic plate of the Greater India Basin under Tibet, enabling the final “hard” collision of the main Indian craton with Asia at ca. 25–20 Ma (van ACKNOWLEDGMENTS Hinsbergen et al., 2012). This study was funded by the National Natural Science Foundation of China (41888101), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (CAS; Recently, Early Cretaceous mafic rocks generated in a continental XDB18020203), and the CAS–The World Academy of Sciences (TWAS) President’s Fellowship rift setting were reported from the Tethys Himalaya, and they imply the program. This is a contribution to International Geoscience Programme (IGCP) Project 662, separation of the Tethyan Himalaya from the Indian craton and a two- “Orogenic Architecture and Crustal Growth from Accretion to Collision.” stage India-Asia collision (Chen et al., 2018). The model of Chen et al. (2018) considers the extension in the Tethys Himalaya. Hence, part of REFERENCES CITED Aitchison, J.C., Ali, J.R., and Davis, A.M., 2007, When and where did India and Asia col- the Tethys Himalaya and Greater Himalaya should have been part of lide?: Journal of Geophysical Research, v. 112, no. B5, B05423, https://doi .org/10.1029 the Indian craton during the final collision. However, this assumption /2006JB004706. Ao, S., Xiao, W., Windley, B., Zhang, J., Zhang, Z., and Yang, L., 2018, Components and struc- is unable to address the middle Eocene metamorphism and exhumation tures of the eastern Tethyan Himalayan Sequence in SW China: Not a passive margin of the Greater Himalaya (Carosi et al., 2016). An early Eocene (54 Ma) shelf but a mélange accretionary prism: Geological Journal, v. 53, p. 2665–2689, https:// metamorphic event has been documented from north Himalayan gneiss doi.org/10.1002/gj.3103. Baksi, A.K., 1995, Petrogenesis and timing of volcanism in the Rajmahal flood basalt prov- domes (Smit et al., 2014), which are considered to be the upper part of ince, northeast India: Chemical Geology, v. 121, p. 73–90, https://doi.org/10.1016/0009 the Greater Himalaya (Ding et al., 2016). Hence, rifting of the Indian cra- -2541(94)00124-Q. Besse, J., Courtillot, V., Pozzi, J.P., Westphal, M., and Zhou, Y.X., 1984, Paleomagnetic esti- ton along the southern part of the present-day Greater Himalaya is more mates of crustal shortening in the Himalayan thrusts and Zangbo suture: Nature, v. 311, p. 621–626, https://doi.org/10.1038/311621a0. Carosi, R., Montomoli, C., Iaccarino, S., Massonne, H.J., Rubatto, D., Langone, A., Gemignani, L., and Visona, D., 2016, Middle to late Eocene exhumation of the Greater Himalayan A. Early Cretaceous Sequence in the Central Himalayas: Progressive accretion from the Indian plate: Geo- S Aulis Trachyte N logical Society of America Bulletin, v. 128, p. 1571–1592, https://doi.org/10.1130/B31471.1. Chatterjee, S., Goswami, A., and Scotese, C.R., 2013, The longest voyage: Tectonic, magmatic, Extension and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia: Gondwana Research, v. 23, no. 1, p. 238–267, https://doi .org /10 .1016 /j .gr .2012 .07 .001 . India THM Chen, S.S., Fan, W.M., Ren, D.S., and Xiao, H.L., 2018, 118–115 Ma magmatism in the Tethyan Himalaya igneous province: Constraints on Early Cretaceous rifting of the northern mar- B. ca. 68 Ma gin of Greater India: Earth and Planetary Science Letters, v. 491, p. 21–33, https://doi .org 2675±700 km /10.1016/j.epsl.2018.03.034. Chen, W., Yang, T., Zhang, S., Yang, Z., Li, H., Wu, H., Zhang, J., Ma, Y., and Cai, F., 2012, Paleo- S (after van Hinsbergen et al., 2012) N magnetic results from the Early Cretaceous Zenong Group volcanic rocks, Cuoqin, Tibet, and their paleogeographic implications: Gondwana Research, v. 22, no. 2, p. 461–469, https://doi.org/10.1016/j.gr.2011.07.019. India THM DeCelles, P.G., Gehrels, G.E., Quade, J., Lareau, B., and Spurlin, M., 2000, Tectonic implications of U‐Pb zircon ages of the Himalayan orogenic belt in Nepal: Science, v. 288, p. 497–499, Figure 7. Simplified tectonic model for Tibetan-Himalayan microcontinent https://doi.org/10.1126/science.288.5465.497. DeCelles, P.G., Robinson, D.M., Quade, J., Ojha, T.P., Garzione, C.N., Copeland, P., and (THM) rifting. (A) During the Early Cretaceous, the northern margin of the Upreti, B.N., 2001, Stratigraphy, structure, and tectonic evolution of the Himalayan India craton started to drift, forming the Aulis Trachytes. (B) At ca. 68 Ma, fold-thrust belt in western Nepal: Tectonics, v. 20, no. 4, p. 487–509, https://doi.org/10 there was an ocean between the India craton and the Tibet Himalaya. .1029/2000TC001226.

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 650

Ding, H.X., Zhang, Z.M., Dong, X., Tian, Z.L., Xiang, H., Mu, H.C., Gou, Z.B., Shui, X.F., Li, W.C., Sakai, H., 1983, Geology of the Tansen Group of the Lesser Himalaya in Nepal: Memoirs of and Mao, L.J., 2016, Early Eocene (c. 50 Ma) collision of the Indian and Asian continents: the Faculty of Science, Kyushu University, ser. D, v. 25, p. 27–74. Constraints from the North Himalayan metamorphic rocks, southeastern Tibet: Earth Sakai, H., Hamamoto, R., and Arita, K., 1992, Radiometric ages of alkaline volcanic rocks from and Planetary Science Letters, v. 435, p. 64–73, https://doi.org/10.1016/j.epsl.2015.12.006. the upper Gondwana of the Lesser Himalayas, west central Nepal, and their tectonic Gansser, A., 1964, Geology of the Himalayas: London, Wiley Interscience, 289 p. significance: Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Ghatak, A., and Basu, A.R., 2013, Isotopic and trace element geochemistry of alkalic–mafic– Nepal, v. 2, p. 65–74. ultramafic–carbonatitic complexes and flood basalts in NE India: Origin in a heteroge- Sarıfakıoğlu, E., Özen, H., and Hall, C., 2009, Petrogenesis of extension-related alkaline volca- neous Kerguelen plume: Geochimica et Cosmochimica Acta, v. 115, p. 46–72. nism in Karaburhan (Sivrihisar-Eskisehir), NW Anatolia, Turkey: Journal of Asian Earth Ghose, N.C., Chatterjee, N., and Windley, B.F., 2017, Subaqueous early eruptive phase of the Sciences, v. 35, no. 6, p. 502–515, https://doi.org/10.1016/j.jseaes.2009.03.002. late Aptian Rajmahal volcanism, India: Evidence from volcaniclastic rocks, bentonite, Schelling, D., 1992, The tectonostratigraphy and structure of the eastern Nepal Himalaya: black shales and oolite: Geoscience Frontiers, v. 8, p. 809–822, https://doi.org/10.1016 Tectonics, v. 11, p. 925–943, https://doi.org/10.1029/92TC00213. /j.gsf.2016.06.007. Searle, M.P., Windley, B.F., Coward, M.P., Copper, D.J.W., Rex, A.J., Tingdong, L., Xuchang, Goto, A., and Tatsumi, Y., 1996, Quantitative analysis of rock samples by an X-ray fluorescence X., Jan, M.Q., Thakur, V.C., and Kumar, S., 1987, The closing of Tethys and the tectonics spectrometer (II): Rigaku Journal. v. 13, p. 20–39. of the Himalaya: Geological Society of America Bulletin, v. 98, p. 678–701, https://doi .org Hu, X., Jansa, L., Chen, L., Griffin, W.L., O’Reilly, S.Y., and Wang, J., 2010, Provenance of Lower /10.1130/0016-7606(1987)98<678:TCOTAT>2.0.CO;2. Cretaceous Wölong volcaniclastics in the Tibetan Tethyan Himalaya: Implications for the Singh, A.K., and Bikramaditya Singh, R.K., 2012, Petrogenetic evolution of the felsic and mafic final breakup of Eastern Gondwana: Sedimentary Geology, v. 223, no. 3–4, p. 193–205, volcanic suite in the Siang window of Eastern Himalaya, northeast India: Geoscience https://doi.org/10.1016/j.sedgeo.2009.11.008. Frontiers, v. 3, no. 5, p. 613–634, https://doi.org/10.1016/j.gsf.2012.01.004. Huang, W., van Hinsbergen, D.J.J., Lippert, P.C., Guo, Z., and Dupont-Nivet, G., 2015, Paleo- Smit, M.A., Hacker, B.R., and Lee, J., 2014, Tibetan garnet records early Eocene initiation of magnetic tests of tectonic reconstructions of the India-Asia collision zone: Geophysical thickening in the Himalaya: Geology, v. 42, p. 591–594, https://doi.org/10.1130/G35524.1. Research Letters, v. 42, no. 8, p. 2642–2649, https://doi.org/10.1002/2015GL063749. Storey, B.C., Alabaster, T., Hole, M.J.J., Pankhurst, R., and Wever, H.E., 1992, Role of subduc- Jadoul, F., Berra, F., and Garzanti, E., 1998, The Tethys Himalayan passive margin from Late tion plate boundary forces during the initial stages of Gondwana break-up: Evidence Triassic to Early Cretaceous (South Tibet): Journal of Asian Earth Sciences, v. 16, p. 173– from the proto-Pacific margin of Antarctica,in Storey, B.C., Alabaster, T., and Pankhurst, 194, https://doi.org/10.1016/S0743-9547(98)00013-0. R.J., eds., Magmatism and the Causes of Continental Break-up: Geological Society [Lon- Kimura, T., Bose, M.N., and Sakai, H., 1985, Fossil plant remains from Taltung Formation, Palpa don] Special Publication 68, p. 149–163, https://doi.org/10.1144/GSL.SP.1992.068.01.10. district, Nepal Lesser Himalaya: Bulletin of the National Science Museum, Tokyo, v. 11, Thompson, R.N., 1982, Magmatism of the British Tertiary Volcanic Province: Scottish Journal p. 141–150. of Geology, v. 18, p. 49–107, https://doi.org/10.1144/sjg18010049. Le Bas, M.J., Le Maitre, R.W., Streckeisen, A., and Zanettin, B., 1986, A chemical classifica- Tong, Y., Yang, Z., Zheng, L., Yang, T., Shi, L., Sun, Z., and Pei, J., 2008, Early Paleocene paleo- tion of volcanic rocks based on the total alkali-silica diagram: Journal of Petrology, v. 27, magnetic results from southern Tibet, and tectonic implications: International Geology p. 745–750, https://doi.org/10.1093/petrology/27.3.745. Review, v. 50, no. 6, p. 546–562, https://doi.org/10.2747/0020-6814.50.6.546. Li, J.T., Li, Y., Klaus, S., Rao, D.-Q., Hillis, M., and Zhang, Y.P., 2013, Diversification of rhacopho- Torsvik, T.H., Van der Voo, R., Preeden, U., Mac Niocaill, C., Steinberger, B., Doubrovine, rid frogs provides evidence for accelerated faunal exchange between India and Eurasia P.V., van Hinsbergen, D.J.J., Domeier, M., Gaina, C., Tohver, E., Meert, J.G., McCaus- during the Oligocene: Proceedings of National Academy of Science of the United States land, P.J.A., and Cocks, L.R.M., 2012, Phanerozoic polar wander, palaeogeography and of America, v. 110, p. 3441–3446. dynamics: Earth-Science Reviews, v. 114, no. 3–4, p. 325–368, https://doi .org/10.1016/j Liebke, U., Appel, E., Ding, L., and Zhang, Q., 2013, Age constraints on the India-Asia collision .earscirev.2012.06.007. derived from secondary remanences of Tethyan Himalayan sediments from the Tingri area: van Hinsbergen, D.J.J., Lippert, P.C., Dupont-Nivet, G., McQuarrie, N., Doubrovine, P.V., Spak- Journal of Asian Earth Sciences, v. 62, p. 329–340, https://doi .org /10 .1016 /j .jseaes .2012 .10 .012 . man, W., and Torsvik, T.H., 2012, Greater India Basin hypothesis and a two-stage Cenozoic Lippert, P.C., Zhao, X., Coe, R.S., and Lo, C.-H., 2011, Palaeomagnetism and 40Ar/39Ar geo- collision between India and Asia: Proceedings of National Academy of Sciences of the chronology of Upper Palaeogene volcanic rocks from Central Tibet: Implications for the United States of America, v. 109, no. 20, p. 7659–7664. Central Asia inclination anomaly, the palaeolatitude of Tibet and post–50 Ma shortening Vink, G.E., Morgan, W.J., and Zhao, W.-L., 1984, Preferential rifting of continents: A source of within Asia: Geophysical Journal International, v. 184, no. 1, p. 131–161, https://doi .org displaced terranes: Journal of Geophysical Research–Solid Earth, v. 89, no. B12, p. 10,072– /10.1111/j.1365-246X.2010.04833.x. 10,076, https://doi.org/10.1029/JB089iB12p10072. Ma, Y., Yang, T., Yang, Z., Zhang, S., Wu, H., Li, H., Li, H., Chen, W., Zhang, J., and Ding, J., White, J.C., Espejel-García, V.V., Anthony, E.Y., and Omenda, P., 2012, Open system evolution 2014, Paleomagnetism and U-Pb zircon geochronology of Lower Cretaceous lava flows of peralkaline trachyte and phonolite from the Suswa volcano, Kenya rift: Lithos, v. 152, from the western Lhasa terrane: New constraints on the India-Asia collision process and p. 84–104, https://doi.org/10.1016/j.lithos.2012.01.023. intracontinental deformation within Asia: Journal of Geophysical Research–Solid Earth, Winchester, J.A., and Floyd, P.A., 1977, Geochemical discrimination of different magma se- v. 119, p. 7404–7424, https://doi.org/10.1002/2014JB011362. ries and their differentiation products using immobile elements: Chemical Geology, v. 20, Ma, Y., Yang, T., Bian, W., Jin, J., Zhang, S., Wu, H., and Li, H., 2016, Early Cretaceous pa- no. 4, p. 325–343, https://doi.org/10.1016/0009-2541(77)90057-2. leomagnetic and geochronologic results from the Tethyan Himalaya: Insights into the Wu, C., Chen, H.Y., Hollings, P., Xu, D.R., Liang, P., Han, J.S., Xiao, B., Cai, K.D., Liu, Z.J., and Neotethyan paleogeography and the India-Asia collision: Nature Scientific Reports, v. 6, Qi, Y.K., 2015, Magmatic sequences in the Halasu Cu belt, NW China: Trigger for the p. 21605, https://doi.org/10.1038/srep21605. Paleozoic porphyry Cu mineralization in the Chinese Altay–East Junggar: Ore Geology Martin, A.J., 2017, A review of Himalayan stratigraphy, magmatism, and structure: Gondwana Reviews, v. 71, p. 373–404, https://doi.org/10.1016/j.oregeorev.2015.06.017. Research, v. 49, p. 42–80, https://doi.org/10.1016/j.gr.2017.04.031. Xiao, W., 2015, New paleomagnetic data confirm a dual-collision process in the Himala- Myrow, P.M., Hughes, N.C., Paulsen, T.S., Willlams, I.S., Parcha, S.K., Thompson, K.R., Bow- yas: National Science Review, v. 2, no. 4, p. 395–396, https://doi.org/10.1093/nsr/nwv056. ring, S.A., Peng, S.C., and Ahluwalia, A.D., 2003, Integrated tectonostratigraphic analysis Xiao, W.J., Ao, S.J., Yang, L., Han, C.M., Wan, B., Zhang, J.E., Zhang, Z.Y., Li, R., Chen, Z.Y., of the Himalaya and implications for its tectonic reconstruction: Earth and Planetary Sci- and Song, S.H., 2017, Anatomy of composition and nature of plate convergence: Insights ence Letters, v. 212, no. 3–4, p. 433–441, https://doi.org/10.1016/S0012-821X(03)00280-2. for alternative thoughts for terminal India-Eurasia collision: Science China–Earth Sciences, Nakamura, N., 1974, Determination of REE, Ba, Fe, Mg, Na & K in carbonaceous and ordinary v. 60, p. 1015–1039, https://doi.org/10.1007/s11430-016-9043-3. chondrites: Geochimica et Cosmochimica Acta, v. 38, p. 757–775, https://doi .org/10.1016 Yang, T., Ma, Y., Bian, W., Jin, J., Zhang, S., Wu, H., Li, H., Yang, Z., and Ding, J., 2015a, Paleo- /0016-7037(74)90149-5. magnetic results from the Early Cretaceous Lakang Formation lavas: Constraints on the Patzelt, A., Li, H., Wang, J., and Appel, E., 1996, Palaeomagnetism of Cretaceous to Tertiary paleolatitude of the Tethyan Himalaya and the India-Asia collision: Earth and Planetary sediments from southern Tibet: Evidence for the extent of the northern margin of India Science Letters, v. 428, p. 120–133, https://doi.org/10.1016/j.epsl.2015.07.040. prior to the collision with Eurasia: Tectonophysics, v. 259, p. 259–284, https://doi .org/10 Yang, T., Ma, Y., Zhang, S., Bian, W., Yang, Z., Wu, H., Li, H., Chen, W., and Ding, J., 2015b, .1016/0040-1951(95)00181-6. New insights into the India-Asia collision process from Cretaceous paleomagnetic and Pearce, J.A., 1982, Trace element characteristics of lavas from destructive plate boundaries, geochronologic results in the Lhasa terrane: Gondwana Research, v. 28, no. 2, p. 625–641, in Thorpe, R.S., ed., Orogenic Andesites and Related Rocks: Chichester, UK, John Wiley, https://doi.org/10.1016/j.gr.2014.06.010. p. 528–548. Yi, Z.Y., Huang, B., Chen, J., Chen, L., and Wang, H., 2011, Paleomagnetism of early Paleogene Pearce, J.A., 1983, Role of the sub-continental lithosphere in magma genesis at active con- marine sediments in southern Tibet, China: Implications to onset of the India-Asia col- tinental margins, in Hawkesworth, C.J., and Norry, M.J., eds., Continental Basalts and lision and size of Greater India: Earth and Planetary Science Letters, v. 309, p. 153–165. Mantle Xenoliths: Nantwich, UK, Shiva Publications, p. 230–249. Yin, A., 2006, Cenozoic tectonic evolution of the Himalayan orogen as constrained by along- Ray, J.S., Pattanayak, S.K., and Pande, K., 2005, Rapid emplacement of the Kerguelen plume– strike variation of structural geometry, exhumation history, and foreland sedimenta- related Sylhet Traps, eastern India: Evidence from 40Ar-39Ar geochronology: Geophysical tion: Earth-Science Reviews, v. 76, no. 1–2, p. 1–131, https://doi.org/10.1016/j.earscirev Research Letters, v. 32, no. 10, L10303, https://doi.org/10.1029/2005GL022586. .2005.05.004. Robinson, D.M., and Pearson, O.N., 2013, Was Himalayan normal faulting triggered by initiation of the Ramgarh-Munsiari thrust and development of the Lesser Himalayan du- MANUSCRIPT RECEIVED 20 DECEMBER 2018 plex?: International Journal of Earth Sciences, v. 102, no. 7, p. 1773–1790, https://doi .org REVISED MANUSCRIPT RECEIVED 9 MAY 2019 /10.1007/s00531-013-0895-3. MANUSCRIPT ACCEPTED 11 JUNE 2019

Geological Society of America | LITHOSPHERE | Volume 11 | Number 5 | www.gsapubs.org 651

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/11/5/643/4829918/643.pdf by guest on 27 September 2021