RESEARCH Multisystem Dating of Modern River

RESEARCH

Multisystem dating of modern river detritus from Tajikistan and China: Implications for crustal evolution and exhumation of the Pamir

Barbara Carrapa1,*, Fariq Shazanee Mustapha1, Michael Cosca2, George Gehrels1, Lindsay M. Schoenbohm3, Edward R. Sobel4, Peter G. DeCelles1, Joellen Russell1, and Paul Goodman1 1DEPARTMENT OF GEOSCIENCES, UNIVERSITY OF ARIZONA, TUCSON, ARIZONA 85721, USA 2U.S. GEOLOGICAL SURVEY, DENVER FEDERAL CENTER, DENVER, COLORADO 80225, USA 3DEPARTMENT OF CHEMICAL AND PHYSICAL SCIENCES, UNIVERSITY OF TORONTO–MISSISSAUGA, MISSISSAUGA, ONTARIO L5L 1C6, CANADA 4INSTITUTE OF EARTH AND ENVIRONMENTAL SCIENCES, UNIVERSITY OF POTSDAM, POTSDAM-GOLM 14476, GERMANY

ABSTRACT

The Pamir is the western continuation of Tibet and the site of some of the highest mountains on Earth, yet comparatively little is known about its crustal and tectonic evolution and erosional history. Both Tibet and the Pamir are characterized by similar terranes and sutures that can be correlated along strike, although the details of such correlations remain controversial. The erosional history of the Pamir with respect to Tibet is significantly different as well: Most of Tibet has been characterized by internal drainage and low erosion rates since the early Cenozoic; in contrast, the Pamir is externally drained and topographically more rugged, and it has a strongly asymmetric drainage pattern. Here, we report 700 new U-Pb and Lu-Hf isotope determinations and >300 40Ar/ 39Ar ages from detrital minerals derived from rivers in China draining the northeastern Pamir and >1000 apatite fission-track (AFT) ages from 12 rivers in Tajikistan and China draining the northeastern, central, and southern Pamir. U-Pb ages from rivers draining the northeastern Pamir are Mesozoic to Proterozoic and show affinity with the Songpan-Ganzi terrane of northern Tibet, whereas rivers draining the central and southern Pamir are mainly Mesozoic and show some affinity with the Qiangtang terrane of central Tibet. Theε Hf values are juvenile, between 15 and −5, for the northeastern Pamir and juvenile to moderately evolved, between 10 and −40, for the central and southern Pamir. Detrital mica 40Ar/39Ar ages for the northeastern Pamir (eastern drainages) are generally older than ages from the central and southern Pamir (western drainages), indicating younger or lower-magnitude exhumation of the northeastern Pamir compared to the central and southern Pamir. AFT data show strong Miocene–Pliocene signals at the orogen scale, indicating rapid erosion at the regional scale. Despite localized exhumation of the Mustagh-Ata and Kongur-Shan domes, average erosion rates for the northeastern Pamir are up to one order of magnitude lower than erosion rates recorded by the central and southern Pamir. Deeper exhumation of the central and southern Pamir is associated with tectonic exhumation of central Pamir domes. Deeper exhumation coincides with western and asymmetric drainages and with higher precipitation today, suggesting an orographic effect on exhumation. A younging-southward trend of cooling ages may reflect tectonic processes. Overall, cooling ages derived from the Pamir are younger than ages recorded in Tibet, indicating younger and higher magnitudes of erosion in the Pamir.

LITHOSPHERE; v. 6; no. 6; p. 443–455; GSA Data Repository Item 2014332 | Published online 27 August 2014 doi: 10.1130/L360.1

INTRODUCTION of the Pamir with respect to Tibet but differ in Rohrmann et al., 2012). Cenozoic exhuma- the magnitude of offset along the Karakorum tion is localized around Miocene rifts (Kapp The Pamir Mountains form the western fault as well in the width of individual geologic and Guynn, 2004) and the southeastern exter- prolongation of the Tibetan-Himalayan col- terranes across the orogenic system and in the nally drained margin of the plateau (Clark et lisional orogenic system (Fig. 1), which is the degree of correlation (Fig. 2). In particular, al., 2005) and on the frontal (southern) flank locus of Earth’s highest mountains and largest early work by Tapponnier et al. (1981) and the of the Himalaya (Thiede and Ehlers, 2013). continental plateau. Although both Tibet and more recent correlation of Schwab et al. (2004) Because of the aridity, glaciers are for the most the Pamir are characterized by similar rocks call for a large magnitude of slip (~250 km), part restricted to the crests of mountain ranges and tectonostratigraphic architecture (Şengör, whereas others (Searle, 1996; Robinson et al., north of the Himalaya (Owen, 2009), and 1984; Dewey et al., 1988; Burtman and Mol- 2004; Robinson, 2009) suggest a much smaller glacial erosion has not significantly affected nar, 1993; Schwab et al., 2004; Robinson et al., offset (~150 km). landscape morphology. The Pamir, in contrast, 2007, 2012; Robinson, 2009), current debate Tibet and the Pamir are strikingly different is mostly externally drained, has high topo- exists about the exact correlation of terranes in terms of morphology and exhumation his- graphic relief (>2–3 km), and contains widely and sutures along strike (Schwab et al., 2004; tory. Tibet is largely characterized by internal exposed high-grade metamorphic domes that Robinson et al., 2004, 2012; Robinson, 2009). drainage, high elevation, relatively low inter- have been exhumed since early Miocene time All models suggest northward displacement nal relief (Fielding et al., 1994), and limited (Fig. 1; Schwab et al., 2004; Schmidt et al., erosion since the early Cenozoic (Rowley and 2011; Lukens et al., 2012). A striking feature *[email protected] Currie, 2006; DeCelles et al., 2007a, 2007b; of the Pamir is the asymmetry in morphology

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444 www.gsapubs.org | Volume 6 | Number 6 | LITHOSPHERE Multisystem dating of modern river detritus from the Pamir | RESEARCH

70°E 80°E90°E100°E and climate from west to east (Fig. 3). The Tien Shan 40°N A west side of the range receives up to 60 cm/yr Altyn Tagh Fault 40°N in rainfall, dominantly delivered by the midlat- A MPT Tajik B Tarim Basin itude westerlies during the spring (Aizen et al., RPS TS depression 2001). Rivers are deeply incised, and the drain- Pamir Qaidam C SS age divide is displaced far to the east within D AKMS the range. The western Pamir hosts some of Songpan-Ganzi the largest glaciers outside of the polar regions K JS a Qiangtang ra k and the Himalaya and Karakoram (Fuchs et o r Tibetan Plateau a 30°N m al., 2013), including the Fedchenko glacier in F a BNS u lt Lhasa 30°N Tajikistan. Precipitation drops off dramatically eastward across the Pamir to less than 10 cm/yr Him IYS M alayas by the midpoint of the range. Glaciers and per- ain Fro ntal manent snow cover correspondingly decline India Thr ust 0 200km (Fuchs et al., 2013). Eastern drainages are much less dissected and are dominated by the 70°E 80°E90°E 100°E structural basin in the hanging wall of the Kon- gur extensional system (Robinson et al., 2004). 70°E 80°E 90°E 100°E A wealth of thermochronological, geochro- Tien Shan 40°N B nological, and structural data exists from Tibet Altyn Tagh Fault 40°N (e.g., Copeland et al., 1995; Ratschbacher et al., A MPT Tajik Tarim Basin B RPS TS 1996; Murphy et al., 1997; Kapp et al., 2007; depression Pamir Qaidam Jolivet et al., 2001; Kirby et al., 2002; Rohrmann C SS D AKMS et al., 2012), whereas only sparse data exist for the Pamir (e.g., Amidon and Hynek, 2010; Rob- Songpan-Ganzi K JS a Qiangtang inson et al., 2012; Sobel et al., 2013; Stübner et ra k o r Tibetan Plateau al., 2013a, 2013b; Thiede et al., 2013), leaving a 30°N m F a BNS u the exhumation and tectonic history of this part lt Lhasa 30°N of the orogenic system largely unresolved. Here, Him IYS we apply geochronology, thermochronology, M alayas ain and Hf isotope geochemistry to modern river Fro ntal India Thr sand grains in order to determine the timing of ust 0 200km crustal evolution and the timing and pattern of 70°E 80°E 90°E 100°E exhumation of the Pamir. The rivers sampled for this study drain not only metamorphic domes

70°E 80°E90°E100°E but also Paleozoic–Mesozoic and older rocks (Fig. 1); therefore, the ages presented here rep- 40°N Tien Shan C resent the timing of regional tectonic and ero- Altyn Tagh Fault 40°N Tajik A MPT sional processes. We also discuss the role that Tarim Basin depression B RPS TS climate-enhanced erosion may play in explain- Pamir Qaidam C SS ing the geomorphic and erosional differences D AKMS between the Pamir and Tibet.

Songpan-Ganzi K JS a Qiangtang ra GEOLOGICAL SETTING OF THE PAMIR k o r Tibetan Plateau a 30°N m F a BNS u The Pamir Mountains occupy a roughly lt 30°N Lhasa 120,000 km2 region extending ~360 km north Him IYS from the Hindu Kush Mountains to the Alai M alaya ai s n F River valley and the Main Pamir thrust system ront India al Th rus 0 200km t (Fig. 1), a group of south-dipping thrust faults along which crust of the Tarim Basin and Tajik 70°E 80°E90°E 100°E depression has been underthrust beneath the Pamir to a depth of at least 200 km (Schneider Figure 2. Simplified tectonic map of the Indo-Asian collision zone showing major active structures et al., 2013). The Pamir is bounded by major and suture zones (after Burtman and Molnar, 1993; Yin and Harrison, 2000). (A) Terrane correlations strike-slip faults on its eastern and western after Schwab et al. (2004); (B) terrane correlations after Robinson et al. (2004); (C) terrane correla- flanks, and it is composed internally of three tions after Robinson (2009) and Robinson et al. (2012). Abbreviations: MPT—Main Pamir thrust; or four large crustal blocks (or terranes) that IYS—Indus-Yarlung suture; BNS—Bangong-Nujiang suture; JS—Jinsha suture; AKMS—Ayimaqin- Kunlun-Muztagh suture; RPS—Rushan-Pshart Suture; TS—Tanymas Suture. Terranes of western accreted onto Eurasia from Paleozoic to early Indo-Asian collision zone are: A—Northern Pamir; B—Central Pamir; C—Southern Pamir–Karako- Cenozoic time (Burtman and Molnar, 1993). rum–Hindu Kush; D—Kohistan arc. The regional geology of the Pamir is dominated

LITHOSPHERE | Volume 6 | Number 6 | www.gsapubs.org 445 CARRAPA ET AL. E precipitation (cm/a) 00 60 0 60 50 40 30 20 10 0 00 00 50 07 60 e ) /srtm/). Sample loca - /srtm/). 00 40 00 elevation (m .nasa.gov drainage divid 00 .jpl 30 05 40 00 ilometers) 20 1 0

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- respec with stars and shaded regions, marked are areas drainage tions and upstream symbols. structural lines and standard with black indicated are Major structures tively. (Fig. profile Location of swath 3. (A) Digital elevation model (DEM) and shaded relief map of the Pamir on Shuttle on Shuttle map of the Pamir model (DEM) and shaded relief (A) Digital elevation 3. Figure base (http://www2 Mission (SRTM) Topography Radar - (December-January-Feb winter showing and precipitation, with drainages of the Pamir SRTM on shaded relief data shown mean (1948–2007) rainfall long-term average, ruary) Land data set Over Reconstruction the Precipitation from data are Precipitation base. Location of the metamorphic of 0.5° × 0.5°. 2002) with a spatial resolution (Chen et al., that the location of Sares Note outlines with labels. black by domes is indicated (2004). et al. the location in Schwab from and differs (2011) et al. Schmidt dome is from - and precipita profile (C) Swath indicated. (stars) are and sample sites (gray) Watersheds maximum and mini - indicates shaded region Gray A and B. in shown box tion data for the east, to pushed far divide, Drainage mean. line indicates and black mum elevation, a data show Precipitation side of the Pamir. Relief is higher on the western is indicated. (cool western for curves hypsometric (D) Cumulative east. to west from decrease strong less-incised eastern for curves lower Note colors) drainages. (warm colors) and eastern shape of eastern plateau-like Note (same colors as D). curves (E) Hypsometric drainages. drainages from Colors in D and E are drainages. peaks of western and sharper drainages Suture. SS—Shyok A. in

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446 www.gsapubs.org | Volume 6 | Number 6 | LITHOSPHERE Multisystem dating of modern river detritus from the Pamir | RESEARCH by five domal structures (Fig. 3) developed in ing these suture zones, the Central Pamir terrane ~350–80 °C temperature window (McDougall medium- to high-grade metamorphic rocks is matched to the Songpan-Ganzi, the Southern and Harrison, 1999; Gleadow and Duddy, 1981; that yield pressure-temperature-time estimates Pamir terrane is matched to the Qiangtang, and Green et al., 1986), which corresponds to ~12– consistent with exhumation from midcrustal the Kohistan arc is correlated to the Lhasa ter- 2.5 km of crust removal (assuming a conserva- depths, mostly during the Miocene (Schmidt et rane (Searle, 1996; Searle et al., 1998; Murphy tive 30 °C/km paleogeothermal gradient). Ero- al., 2011; Stübner et al., 2013b). et al., 2000). Yin and Harrison (2000) consid- sion and normal faulting (tectonic exhumation) The Pamir terranes are referred to as the ered the Lhasa terrane and Kohistan arc to be a are responsible for cooling and exhumation of Northern, Central, and Southern Pamir (Fig. 1) continuous magmatic arc. Earth’s crust (England and Molnar, 1990). High and have been correlated in different ways to The correlation model of Robinson (2009) relief, precipitation, and active deformation can terranes in Tibet (e.g., Schwab et al., 2004; (Fig. 2C) is a slight modification of the Robin- enhance exhumation (Ring et al., 1999). Robinson et al., 2007, 2012; Robinson, 2009). son et al. (2004) model and is based on remote Detrital thermochronology is particularly Different correlation models (Fig. 2) have been mapping of the Late Triassic–Early Jurassic useful in areas where sampling in situ rocks discussed in detail by Schwab et al. (2004) and Aghil Formation, which implies 149–167 km of is challenged by high relief and the paucity of Robinson et al. (2004, 2012). The Schwab et offset along the northern and southern portions roads, such as in the Pamir. In this study, we al. (2004) correlation model is based on geo- of the Karakorum fault. This study suggests a let nature do the job of sampling the orogenic logic structures and geochemistry of magmatic correlation between the Bangong-Nujiang and system by utilizing rivers. We collected 12 sam- belts in the Pamir-Tibet orogen. This study cor- Shyok sutures, consistent with the interpreted ples of medium-grained sand from major rivers relates the Karakul granites, which are found maximum offsets of the Miocene Baltoro gran- draining catchments within the Northern, Cen- in parts of the Northern Pamir terrane, to the ite (40–150 km). Further analysis of the Aghil tral, and Southern Pamir terranes (Figs. 1 and Songpan-Ganzi terrane in Tibet. This corre- Formation shows that the antiforms in both 3); of these, nine samples yielded mica, and 11 lation is supported by a continuous chain of the Central Pamir and Qiangtang are not off- yielded apatites. We present data from four river ca. 200 Ma plutons with similar geochemical set by the Karakorum fault. This model corre- samples from the Central and Southern Pamir signatures that wraps around the Pamir from lates the Northern Pamir with Songpan-Ganzi, (western drainages), one from the interior of the the Karakul Basin into the Mazar region of the Southern Pamir with Qiangtang, and the Pamir (TJK4) of Tajikistan, and seven river sam- western Kunlun (Schwab et al., 2004). In the Kohistan arc with Lhasa. This model also sug- ples from the northeastern Pamir of China. The Central Pamir terrane, the presence of mid- gests that the Central Pamir is a crustal fragment Tajik Pamir samples were previously analyzed Triassic granitoids similar to those observed with no equivalent in Tibet (Burtman and Mol- for zircon U-Pb and 40Ar/ 39Ar geochronology in the Qiangtang block led the same authors to nar, 1993; Robinson, 2009). Burtman (2010) and thermochronology (Lukens et al., 2012). propose a correlation between these terranes. interpreted the Central Pamir to be a partially Lu-Hf geochemistry and AFT thermochronol- Schwab et al. (2004) also documented a long- rifted portion of the Southern Pamir–Qiangtang ogy are here applied to all samples; U-Pb geo- lasting Cretaceous magmatic history of intru- terrane. More recent geochronological data chronology and 40Ar/39Ar thermochronology are sions in the Southern Pamir terrane. U-Pb geo- from the northeastern Pamir support correlation applied to the northeastern Pamir samples. chronology of xenoliths in this region yielded of the Northern Pamir with the Songpan-Ganzi The Tajik river samples were collected clusters of ages at 84–57 Ma, 170–146 Ma, terrane (Robinson et al., 2012). Despite differ- from the Vanj, Yazgulem, Bartang, Gunt, and 465–412 Ma, 890 Ma, and 1400 Ma, with the ences between correlation models, all agree that Murghab Rivers and drain a larger area than youngest zircon age at 56.7 ± 5.4 Ma (Ducea et Pamir terranes have been offset northward rela- the Chinese rivers, including mainly the Cen- al., 2003). These ages correlate with magmatic tive to their Tibetan counterparts by slip along tral and Southern Pamir and only part of the activity of the Tirich Mir–Karakoram–Gang- the Karakoram strike-slip fault (Burtman and Northern Pamir (Fig. 3). Drainage areas of dese arc, which was active in the northernmost Molnar, 1993; Lacassin et al., 2004; Schwab et the Tajik rivers include Paleozoic sedimen- part of the Southern Pamir and Hindu Kush– al., 2004; Robinson, 2009; Peltzer and Tappon- tary and basement rocks, Mesozoic and Ceno- Lhasa block and includes suites of granite and nier, 1988). zoic magmatic rocks, and large metamorphic granodiorites that yield crystallization ages of domes (Vlasov et al., 1991; Burtman and Mol- ca. 1624 Ma, 902 Ma, 417 Ma, 355 Ma, and DETRITAL APPROACH TO RESOLVING nar, 1993). The samples from the northeastern 196 Ma (Schwab et al., 2004). The proposed TECTONICS AND EROSION Pamir were collected from the Kalate and Gez correlation of the Northern Pamir terrane to Rivers and tributaries of the Tashkorgan River Songpan-Ganzi, the Central Pamir terrane to Geochronology and thermochronology that flow eastward, debouching into the Tarim Qiangtang, and the Southern Pamir terrane to applied to detrital minerals provide informa- Basin (Fig. 3). The Chinese rivers drain the Lhasa by Schwab et al. (2004) implies a dis- tion on the timing of crystallization, cooling, northeastern Pamir, which is dominated by placement of ~250 km along the Karakorum and exhumation of the river catchment areas Triassic and Jurassic sedimentary and meta- fault (Fig. 2A). and thus on regional tectonic and erosional morphic rocks (Fig. 1; Robinson et al., 2007). The correlation model proposed by Robin- processes (e.g., Hodges et al., 2005; Carrapa, Out of the seven samples we collected from son et al. (2004) (Fig. 2B), suggests a smaller 2010). In particular, U-Pb geochronology com- the northeastern Pamir, four (1071-1, 1071-2, offset along the Karakorum fault of <200 km bined with Lu-Hf geochemistry applied to zir- 1071-4, 1071-6) come from the footwall of the (120–150 km—Searle, 1996; Searle et al., 1998; cons provide information on crystallization age Kongur Shan normal fault, whereas the other 60–70 km—Murphy et al., 2000). This model and crustal evolution (e.g., Patchett et al., 1982; three (1071-3, 1071-5, 1071-7) come from correlates the Tanymas suture south of the Griffin et al., 2000; Dickinson and Gehrels, the hanging wall. Together, the sampled rivers Northern Pamir to the Ayimaqin-Kunlun-Muz- 2009). The 40Ar/39Ar thermochronology method drain a land surface area, representing roughly tagh suture, suggesting a correlation between applied to white mica and apatite fission-track 90% of the Pamir; the data provide the first the Northern Pamir terrane and the Kunlun- (AFT) thermochronology document the time of regional-scale assessment of exhumation ages Qaidam terrane in Tibet. Similarly, by correlat- mineral crystallization and cooling through the for almost the entire range.

LITHOSPHERE | Volume 6 | Number 6 | www.gsapubs.org 447 CARRAPA ET AL.

U-Pb and Lu-Hf Geochronology Methods Northeastern Pamir and Results A P09D 1071-4 (n=65)

Zircon U-Pb and Hf geochronology was P09D 1071-5 (n=92) conducted by laser ablation–multicollector– inductively coupled plasma–mass spectrometry P09D 1071-1 (n=90) (LA-MC-ICP-MS) at the Arizona LaserChron P09D 1071-2 (n=98)

Center (Gehrels et al., 2006, 2008; Cecil et al.,

2011; Gehrels and Pecha, 2014). For details on P09D 1071-7 (n=87) analytical procedure, we refer the reader to the GSA Data Repository1 and https://sites.google .com/a/laserchron.org/laserchron/. For zircon P09D 1071-3 (n=85) Age probability U-Pb data from the Tajik rivers, see Lukens et Southern Pamir source al. (2012). In total, 700 zircons from all seven samples from the northeastern Pamir were analyzed. Out of the 700 grains, 605 were included in the data reduction processes (Table DR1 [see footnote P09D 1071-6 (n=88) 1]). The excluded grains include those with high 0 500 1000 1500 2000 2500 3000 206Pb/238U error (>20%), high 204Pb (>100 cps B Northeastern Pamir, [counts per second]), and grains that produced Eastern drainages analyses that were >20% discordant or >5% (this study; Bershaw et al., 2012) reverse discordant. Selected zircons were analyzed for Lu/Hf geochemistry, with an average of 20 grains analyzed per sample. Samples 1071-1, 1071-2, 1071-3, 1071-4, and 1071-5 from the Gez and Tashkorgan Rivers Central, Southern Pamir, show mainly Permian–Triassic zircon U-Pb ages Western drainages (ca. 200–300 Ma; Fig. 4). A minor component at (Lukens et al., 2012) Age probability 400–500 Ma is present in most samples. Sample 1071-6, and to a lesser extent sample 1071-1, contains a component at ca. 80 Ma. Sample 1071-4 contains a small Miocene (ca. 16 Ma) component. Zircons from the Tajik rivers draining the Central and Southern Pamir terranes pro- 0 500 1000 1500 2000 2500 3000 duced Proterozoic through Cenozoic U-Pb ages, C TIBET exhibiting affinity with Asian rocks. These data Northern Tibet/Songpan Ganzi (Weislogel et al., 2006; n=807) were presented by Lukens et al. (2012) and will be further discussed in this paper.

The Hf isotopic data from the zircon grains Central Tibet/Qiangtang (Gehrels et al., 2011; n=2431) exhibit widely variable ε values (Table DR2

Hf [see footnote 1]), ranging from +15 to −40 (Figs. 5A and 5B). A few highly juvenile values Souther Tibet/Lhasa (Gehrels et al., 2011; n=733) (within 5 epsilon units of the depleted mantle array) are present for grains between 300 and Southern Pamir source PAMIR 900 Ma from the northeastern Pamir. Zircon Age probability Northern Pamir (n=605) grains that crystallized between 600 and 200 Ma have intermediate εHf values (near chondrite uniform reservoir [CHUR]). Central Pamir (n=169)

U-Pb and Lu-Hf Data Interpretation Southern Pamir (n=87) We interpret the zircon U-Pb ages from the northeastern Pamir to dominantly reflect Trias- 0 500 1000 1500 2000 2500 3000 Age (Ma) 1GSA Data Repository Item 2014332, Ana- Figure 4. Age probability plots for U-Pb geochronology. (A) Crystallization ages for northeastern lytical details and data tables, is available at www Pamir samples. (B) Comparison of crystallization ages between northeastern and western Pamir. .geosociety.org/pubs/ft2014.htm, or on request from (C) Comparison of crystallization ages between Pamir and Tibet terranes. Shaded dark-green and editing@geosociety.org, Documents Secretary, GSA, red box highlight the similarities between the corresponding signals from the different terranes P.O. Box 9140, Boulder, CO 80301-9140, USA. (Gehrels et al., 2011; Weislogel et al., 2006).

448 www.gsapubs.org | Volume 6 | Number 6 | LITHOSPHERE Multisystem dating of modern river detritus from the Pamir | RESEARCH

20 Northeastern Pamir sic magmatism recorded in the Kunlun arc of the A Karakul-Mazar Songpan-Ganzi terrane (Schwab 15 Eastern drainages DM et al., 2004). Early Paleozoic ages (ca. 400– 10 500 Ma) may be associated with sources from 5 the northern and southern Kunlun magmatic CHUR 0 belts as suggested by Schwab et al. (2004). Sam- -5 ples 1071-5 and 1071-7, which were collected -10 close to the village of Oytag and the easternmost

-15 section of the Tashkorgan River, record a differ-

Epsilon Hf ent signal mainly characterized by early Paleo- -20 1071-1 zoic ages (ca. 400–600 Ma). Cretaceous ages -25 1071-2-P1 in sample 1071-6, and to a lesser extent sample 1071-3-P1 -30 1071-4-P1 1071-1, could be derived from Cretaceous plu- -35 1071-5 P1 tons (Jiang et al., 2014). In general, the zircon 1071-6-P1 U-Pb ages from rivers draining the northeastern -40 1071-7-P1 Pamir differ from the zircon U-Pb ages of rivers -45 0 200 400 600 800 1000 1200 1400 1600 1800 draining the central and southern Pamir (Fig. 4); Age (Ma) western Pamir Rivers contain stronger 300 and 20 500 Ma components. B Central, Southern Pamir Juvenile ε values for grains between 900 15 Western drainages Hf DM and 300 Ma record the generation of new con- 10 tinental crust during Neoproterozoic through 5 middle Paleozoic time. Intermediate values CHUR εHf 0 (near CHUR) record interaction with older -5 crust, perhaps of Mesoproterozoic age (Fig. 5).

-10 Beginning at ca. 180 Ma, more variable εHf values, with some values near CHUR, record the -15

Epsilon Hf presence of younger (Neoproterozoic) crust as -20 well as more negative values that record the -25 presence of evolved crust. Overall ,the Hf data TJK-04 -30 TJK-05 are broadly similar to Hf results that have been -35 TJK-06 reported from Tibet (Fig. 5), supporting the idea TJK-07 -40 TJK-08 that crustal domains of the Pamir and Tibet have common petrogenesis. -45 0 200 400 600 800 1000 1200 1400 1600 18002000 2200 2400 Age (Ma) 40Ar/39Ar and AFT Thermochronology 20 Methods and Results C Pamir vs. Tibet 15 The 40Ar/39Ar analyses of white mica from 10 DM the northeastern Pamir samples were con- 5 ducted at the U.S. Geological Survey Labora- CHUR 0 tory in Denver. Samples were irradiated for -5 10 MWH (Megawatt per hour) in the central -10 thimble position of the Denver USGS TRIGA

-15 reactor with cadmium shielding. Sanidine from

Epsilon Hf the Fish Canyon Tuff was used as the neutron -20 influence monitor with a reference age of 28.20 -25 ± 0.8 Ma (Kuiper et al., 2008). For more details, -30 Central-S. Pamir 40 39 NE Pamir see Table DR3 (see footnote 1). For Ar/ Ar -35 Qiangtang analyses of Tajik rivers draining the central and Songpan Ganzi -40 Lhasa southern Pamir, we refer the reader to Lukens -45 et al. (2012). AFT analyses were conducted 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 at the University of Arizona following proce- Age (Ma) dures described in Table DR4 (see footnote

Figure 5. (A–B) εHf data of the analyzed zircons from the (A) northeastern Pamir and (B) western Pamir. 1). In total, 330 white micas were analyzed by (C) Compilation of Pamir vs. Tibet Hf data (Songpan-Ganzi terrane data from Zhang et al. [2013]; Qiang- 40Ar/39Ar thermochronology from the northeast- tang terrane data from Zhai et al. [2013a, 2013b, 2013c]; Lhasa terrane data from Wu et al. [2010]). Refer ern Pamir rivers, and 1154 grains from the 12 to Table DR2 (see text footnote 1) for more details and to Lukens et al. (2012) for zircon U-Pb ages from the central and southern Pamir (western drainages). The gray arrow shows typical crustal evolution samples draining both the northeastern and cen- with 176Lu/177Hf = 0.0115 (Vervoort and Patchett, 1996; Vervoort et al., 1999). Chondrite uniform reservoir tral and southern Pamir were analyzed for AFT (CHUR)—Bouvier et al. (2008). Deplete mantle (DM)—Vervoort and Blichert-Toft (1999, 2009). ). thermochronology.

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The 40Ar/39Ar single-grain ages range from al., 2013b). Older Cenozoic thermochronologi- DISCUSSION ca. 350 Ma to ca. 8 Ma (Fig. 6A). AFT age cal ages in the northeastern Pamir have been density distributions and detrital populations interpreted to be the result of an early phase of Terrane Correlation and Crustal Evolution (calculated using DensityPlotter and Binomfit; subduction erosion along the Trans-Alai intrac- Brandon, 2002; Vermeesch, 2012) are mainly ontinental suture (Sobel et al., 2013). The zircon U-Pb data from modern fluvial late Cenozoic, but with a tail of early Cenozoic The new AFT ages from western Pamir range sediments in rivers draining the Pamir document ages (Fig. 6B); the youngest AFT population from early to late Cenozoic. In particular, ages an Asian crustal provenance. Compiled ages is ca. 6 Ma (Fig. 7; Tables DR4 and DR5 [see from the Bartang River draining the southern yield three main zircon U-Pb age components footnote 1]). Samples from the Vanj (TJK-8), Pamir, including the Shakdara dome, show a sig- in the Pamir (Fig. 4). The youngest age group Yazgulem (TJK-7), Gunt (TJK-5), Bartang nificant late Cenozoic component (ca. 8–13 Ma; contains Cenozoic and Cretaceous populations (TJK-6), and Murghab (TJK-4) Rivers in Tajiki- Fig. 6) that is consistent with ages recorded in younger than 100 Ma and constitutes more than stan, draining mostly the central and some of basement rocks of the Shakdara dome (Stübner 50% of the age spectra. The other two major age southern Pamir, including the Yazgulen, Sares, et al., 2013b), suggesting that late-stage exhuma- components are the Permian–Triassic (ca. 200– Muskol, and Shakdara metamorphic domes, tion of the dome occurred during the late Mio- 300 Ma) and Paleozoic (ca. 400–600 Ma), which have prominent 40Ar/39Ar age components at cene. The same signal is present in the Gunt and together represent less than 50% of the entire ca. 18 Ma and ca. 25 Ma (Lukens et al., 2012) Yazgulem River samples, indicating regional age spectra. A striking regional difference is the and late Miocene AFT ages (Fig. 6), with exhumation of the Northern, Central, and South- higher proportion of younger grains in central youngest AFT populations between ca. 8 Ma ern Pamir terranes during the Cenozoic. and southern Pamir (western drainages) com- and ca. 13 Ma (Fig. 7). Samples from the Kalate pared with northeastern Pamir rivers (Fig. 4). River (1071-4) and tributaries of the Gez (1071- Hypsometric Analysis The younger (<100 Ma) detrital zircon U-Pb 1, 1071-2) and Tashkorgan (1071-3, 1071-7, ages from rivers draining the central and south- 1071-6) Rivers, draining the northeastern Pamir, Hypsometry, hypsometric integral, and ern Pamir are consistent with Cenozoic intru- including the Kongur Shan and Mustagh Ata cumulative hypsometry were calculated using sions in the central Pamir domes (Schwab et al., domes (Fig. 3), have prominent 40Ar/39Ar age Shuttle Radar Topography Mission (SRTM) 2004). Therefore, we interpret the younger than components at ca. 80 Ma, 100 Ma, and between 90 m digital elevation data (bin size 100 m) 100 Ma detrital ages to mostly represent sources ca. 150 Ma and 200 Ma (Fig. 6) and early to for four drainages in the central and south- from these domes and deep exhumation. late Cenozoic AFT ages; the youngest AFT age ern Pamir representing the upstream drainage Schwab et al. (2004) correlated the central populations are between ca. 6 Ma and 22 Ma areas for samples TJK-8, TJK-7, TJK-6, and Pamir to the Qiangtang block in Tibet. Detrital (Fig. 7; Table DR5 [see footnote 1]). TJK-5, and three drainages in the northeastern U-Pb ages from our river samples support this Pamir representing upstream drainage areas interpretation (Fig. 4). However, apart from the 40Ar/39Ar and AFT Data Interpretation for samples 1071-4, 1071-1, 1071-2, 1071-3, small but significant presence of Paleozoic sig- 1071-7, and 1071-6 (Fig. 3). nals (ca. 400–600 Ma) in all the samples drain- Overall, the 40Ar/ 39Ar ages from rivers Hypsometric integrals for the western ing the central and southern Pamir (western draining the northeastern Pamir are older than drainages are, from north to south, 0.46 (cor- drainages), all samples are dominated by grains 40Ar/ 39Ar ages from rivers draining the central responding to TJK-8), 0.51 (TJK-7), 0.49 younger than 100 Ma, suggesting an affinity and southern Pamir, indicating older exhuma- (TJK-6), and 0.57 (TJK-5), with an average of with Gangdese arc rocks of the Lhasa terrane in tion for the northeastern Pamir. Alternatively, 0.51 ± 0.4. Cumulative hypsometric curves are Tibet (Ji et al., 2009). In contrast, zircon U-Pb this pattern could indicate that exhumation in S-shaped (Fig. 3D), and hypsometry displays ages from the northeastern Pamir are mostly the northeastern Pamir has been insufficient a prominent peak at around 4200 m (Fig. 3E). older than 100 Ma and show affinity with the to expose rocks recording Cenozoic 40Ar/ 39Ar The two smaller, northern drainages are more Kunlun and Songpan-Ganzi arc rocks (Robin- ages. Higher-magnitude exhumation of the asymmetric, with longer tails at low elevations. son et al., 2012). We note that sample 1071-6 western Pamir is supported by Miocene syn- Hypsometric integrals for the eastern drain- (located in northeastern Pamir) contains a large orogenic deposits >6 km thick preserved in the ages are lower. From north to south, values are group of 80–100 Ma grains. We attribute this Tajik depression (Nikolaev, 2002), indicating 0.49 (corresponding to 1071-4), 0.42 (1071-1, to the fact that this sample comes from a river rapid erosion of the Pamir at this time. 1071-2), and 0.45 (1071-7), with an average draining part of the Southern Pamir terrane. Fig- Detrital AFT ages of ca. 22–24 Ma are of 0.45 ± 0.04. Curves are S-shaped but plot ure 4 illustrates the similarity of detrital patterns consistent with initiation of exhumation of the slightly lower than the western cumulative hyp- between the Northern Pamir terrane (including northeastern Pamir, possibly as the result of sometries (Fig. 3D). The hypsometry displays sample TJK-8 from Lukens et al., 2012) and southward-directed subduction or underthrust- a broad plateau from ~3500 to 5000 m for the Songpan-Ganzi with two distinctive peaks at ing of Asia (Amidon and Hynek, 2010; Sobel southern two drainages. The plateau in the east- ca. 200 Ma and ca. 550 Ma. Gehrels et al. (2011) et al., 2013). The presence of sparse late Mio- ern drainage hypsometry could reflect glacial reported 212–537 Ma ages from the Songpan- cene 40Ar/39Ar and AFT ages (between ca. 6 and erosion or the presence of the depositional basin Ganzi complex with peaks at ca. 264 Ma and ca. 9 Ma) in the northeastern Pamir coincides in the hanging wall of the Kongur extensional 440 Ma, 720–850 Ma ages with age peaks at with the timing of tectonic exhumation of the system at an elevation of 3500–4500 m. Higher 770 and 793 Ma, 1730–2100 Ma ages with an Kongur Shan detachment system as recorded by hypsometric integrals in the western drainages age peak at 1870 Ma, and 2360–2630 ages with regional in situ thermochronological and struc- are consistent with evidence for more intense an age peak at 2515 Ma. tural data (Robinson et al., 2004, 2007; Sobel fluvial erosion on that side of the range, which Based on the U-Pb zircon analyses of rivers et al., 2011, 2013; Thiede et al., 2013; Cao et includes higher precipitation, higher relief, and draining the Northern Pamir terrane, we make al., 2013a) and supported by detrital zircon the position of the divide well east of the mid- the following interpretations: (1) The strong fission-track ages from the Gez River (Cao et point of the range (Fig. 3). 200–300 Ma age component coincides with

450 www.gsapubs.org | Volume 6 | Number 6 | LITHOSPHERE Multisystem dating of modern river detritus from the Pamir | RESEARCH

AB1071-4 Gez, Kalate rivers (nKalate River; =84) (1071-1, 2, 4; n=300)

1071-1, n=78

Gez River 0102030405060708090 100 1071-2, n=83 Tashkorgan tributaries (1071-3, 6, 7) 1071-6 n=242 (Tashkorgan tributary; n=85) Northern Pamir

0102030405060708090 100

Eestern Pamir drainages Vanj River n=100

TJK8 (Vanj River; n=69)

TJK7 (Yazgulem River; n=84) 10 20 30 40 50 60 70 80 90 100

Yazgulem River n=100

0 10 20 30 40 50 60 70 80 90 100

TJK4 (Murghab River; n=54)

Murghab River n=100 Central Pamir

0102030405060708090100 estern Pamir drainages W

Bartang River n=100 TJK6 (Bartang River; n=69)

0102030405060708090100 TJK5 (Gunt River; n=58) Gunt River, n=102 Southern Pamir 0102030405060708090100 020406080 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 40Ar/39Ar Age (Ma) AFT Age (Ma) Figure 6. Kernel density distributions curves of detrital 40Ar/39Ar and apatite fission-track (AFT) ages (calculated using DensityPlotter; Vermeesch, 2012). 40Ar/39Ar ages for the western Pamir drainages are from Lukens et al. (2012).

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Age (Ma) 02468101214161820222426283032343638404244464850 N

Kalate River 1071-4 Figure 7. Distribution of younger r than 30 Ma 40Ar/39Ar and apatite 1071-1 Mustagh-Ata Dome fission-track (AFT) ages and AFT 40 39

1071-2 Gez Rive r >50 Ma Ar/ Ar ages youngest populations (calcu- 1071-7 r lated using Binomfit; Brandon, 1071-3 Northern Pami 2002) from north to south; note 40 39 Eastern drainages that most Ar/ Ar ages for the Footwall of Kongur Shan detachment system 1071-6 northeastern Pamir are older

shkorgan Rive than 30 Ma. The majority of the

e 40 39 Ta r reported Ar/ Ar ages have TJK-8 Vanj River uncertainties of <2% (Table DR3 [see text footnote 1]). Errors for TJK-7 Yazgulem River the reported AFT ages are gener- zgulem Dom Central Pami ally ~10% (Tables DR4 and DR5 Ya Muskol Dome [see text footnote 1]). We note TJK-4 Murghab River stern drainages that the youngest AFT peaks gen- Sares and Muskol Domes Bartang River r We erally include >50% of the whole TJK-6 detrital spectrum for each sample

Relative distance from the main Pamir thrust Shakdara Dome Gunt River (Table DR5 [see text footnote 1]). TJK-5

S Southern Pami 40Ar/39Ar ages (<50 Ma) youngest 40Ar/39Ar age population using DensityPlotter youngest AFT population using Binomfit difference between youngest AFT and 40Ar/39Ar age

youngest AFT population using DensityPlotter population (by DensityPlotter)

the Triassic magmatism recorded in the Kun- tion comprising 63% of the ages from the Gunt Excluding these two anomalous samples, lun arc in the Karakul-Mazar Songpan-Ganzi River (Fig. 6; Table DR5 [see footnote 1]), the bulk of the 40Ar/39Ar age spectra are pre- terrane (Schwab et al., 2004). This implies which is the largest drainage in the western Cenozoic. Although some young (ca. 2–5 Ma) that samples with these ages (1071-1, 1071- Pamir derived mostly from the Shakdara dome, 40Ar/39Ar ages have been recorded in the Kon- 2, 1071-3, 1071-4, 1071-6) have affinity with is 15.7 Ma. The main 40Ar/39Ar age population gur Shan gneiss dome (Robinson et al., 2004) the Permian–Triassic Karakul-Mazar terrane. consisting of 76% of the ages from the Tashk- and reflect localized tectonic exhumation, our (2) The early Paleozoic ages (ca. 400–600 Ma) organ River tributaries, derived mainly from data indicate that regional exhumation rates are represent a source from the northern and south- the Kongur-Shan and Mustagh Ata domes, is significantly higher in the central and southern ern Kunlun magmatic belts, as suggested by 78.6 Ma (Fig. 6; Table DR5 [see footnote 1]), Pamir, which is the western and wetter side of Schwab et al. (2004). and the main 40Ar/39Ar age populations made of the range compared to the northeastern Pamir.

Negative εHf values (as low as −42) in grains 61% and 42% of the ages from two tributaries AFT ages for the central, southern and north- between ca. 180 Ma and ca. 700 Ma are present of the Gez River are 172.4 Ma and 98.7 Ma, eastern Pamir are mid- to late Cenozoic, indicat- in samples derived from northeastern, central, respectively (Table DR5 [see footnote 1]). ing similar average rates of short-term exhuma- and southern Pamir, with higher proportions in Although the bulk of 40Ar/39Ar ages are mainly tion (0.4 mm/yr; Table DR5 [see footnote 1]). the central and southern Pamir samples, indi- pre-Cenozoic in the northeastern Pamir (Fig. 6), Late Cenozoic AFT ages (ca. 6 Ma) in samples 40 39 cating a more-evolved crustal source. The εHf two samples (1071-6, 1071-1) exhibit Ar/ Ar 1071-2 and 1071-3 from the northeastern Pamir, values of samples from northeastern Pamir are youngest population ages of 10.7 ± 0.2 Ma and both of which tap into the footwall of the Kon- consistent with values recorded in the Song- 14.5 ± 0.2 Ma, consistent with in situ thermo- gur Shan extensional system, likely reflect pan-Ganzi terrane, and εHf values from samples chronological ages (Thiede et al., 2013). These localized rapid exhumation associated with derived from the central and southern Pamir samples were both derived from granitic intru- movement along this young fault system. Mod- samples are consistent with εHf values recorded sions. The southern sample (1071-6) is from eling of thermochronologic data indicates exhu- in the Qiangtang and Lhasa terranes of Tibet a river that drains a Miocene granite that has mation of the Kongur Shan dome in the footwall (Fig. 5C). yielded biotite 40Ar/39Ar ages as young as 11.45 of the fault system at rates of 1.5–4 mm/yr since ± 0.3 Ma (Robinson et al., 2007), and could the late Miocene (Robinson et al., 2010; Thiede Exhumation History explain the presence of late Miocene 40Ar/39Ar et al., 2013). ages. The northern sample (1071-1) taps into Assuming a conservative paleogeothermal Cenozoic 40Ar/39Ar ages are widespread in an undated intrusion mapped as Triassic–Early gradient of 30 °C/km, and closure temperatures samples from central and southern Pamir (west- Jurassic (Robinson et al., 2007). Our data sug- for white mica 40Ar/39Ar of ~350–425 °C (for ern drainages), whereas northeastern Pamir is gest the true age may be younger. Interestingly, phengite—McDougall and Harrison, 1999; for mainly characterized by Mesozoic ages (Fig. 6). both samples are also located on the drainage muscovite—Harrison et al., 2009), we obtain For example, the main 40Ar/39Ar age popula- divide between the western and eastern Pamir. average Cenozoic exhumation rates between 0.4

452 www.gsapubs.org | Volume 6 | Number 6 | LITHOSPHERE Multisystem dating of modern river detritus from the Pamir | RESEARCH and 0.2 mm/yr for the northeastern Pamir and For example, northward subduction and under- much higher rates than those observed in Tibet. between 0.6 and 1.3 mm/yr for the central and thrusting of India under Asia has contributed We hypothesize that greater precipitation on the southern Pamir (Table DR5 [see footnote 1]). to Cenozoic crustal thickening and east-west upwind, western Pamir led to greater long-term For a lower paleogeothermal gradient, average extension in Tibet (DeCelles et al., 2002; Sun- exhumation, relief production, and migration exhumation rates would be higher. The highest dell et al., 2013) and most likely in the Pamir. of the drainage divide progressively toward exhumation rates are recorded by the Murghab If this is correct, the present-day location of the the east. Alternatively, asymmetric exhuma- and Gunt Rivers (2.4 mm/yr and 2 mm/yr). Indian slab under the Hindu Kush (Negredo et tion may be related to asymmetric tectonics. The high exhumation rates recorded by the al., 2007) requires southward slab rollback fol- However, based on the correlation between the Murghab River, which drains a small area, may lowing underthrusting, as proposed for Tibet locus of deep exhumation and higher precipita- reflect exhumation of the Muskol dome and or during the Oligocene–Miocene (DeCelles et tion (Fig. 3) in the Pamir, we favor climate as localized exhumation associated with move- al., 2011). Southward slab rollback of India the controlling factor on regional exhumation ment along the Karakorum fault (Amidon and and asthenospheric upwelling, accompanied by by deep dissection of the western flank of the Hynek, 2010). Exhumation rates between 0.6 upper-plate extension, could explain the south- orogen. This is supported by the highly asym- and 2 mm/yr recorded by the Gunt River detri- ward younging of thermochronological ages. metric Pamir drainage divide positioned near tus are interpreted here to reflect exhumation the eastern flank of the range and by the fact that of the Shakdara dome and are consistent with DISCUSSION AND CONCLUSIONS major rivers generally drain westward (Fig. 1). rates recoded by in situ thermochronology Reanalysis data (Fig. 3) show that precipitation (Stübner et al., 2013b). Although the similar- Although both the Pamir and Tibet are com- comes from the west and is most intense during ity between our detrital Cenozoic cooling ages posed of rocks with similar affinity, the exhu- the early spring. This precipitation is concen- and the cooling ages of the metamorphic domes mation history of the two regions appears to trated on the western side of the Pamir, which supports this interpretation, the fact that the be significantly different. Overall, zircon U-Pb forms an orographic barrier to eastward mois- sampled rivers also drain rocks other than the ages from modern river detritus derived from ture transport. We suggest that relatively intense domes (Fig. 1) allows for the possibility that the the central and southern Pamir are most simi- precipitation on the windward side of the Pamir grains with Cenozoic ages may be derived from lar to zircon U-Pb ages recorded in the Qiang- has been a major factor since at least the early Mesozoic–Paleozoic and older rocks. If this is tang terrane of central Tibet; U-Pb ages from Miocene in controlling bedrock exhumation and the case, it would suggest that Cenozoic exhu- modern rivers draining the northern Pamir are eastward retreat of the orogenic drainage divide. mation is orogen-wide rather than limited to the most similar to zircon U-Pb ages recorded in We also suggest that exhumation of the Pamir domes, and it would be consistent with erosion the Karakul-Mazar terrane (Fig. 1C), correlative domes was facilitated by erosion and should be controlled by climate, rather than localized tec- to the Triassic Songpan-Ganzi terrane of north- considered in tectonic models (Stübner et al., tonic exhumation. ern Tibet, and Kunlun magmatic belt. Detrital 2013a). A trend of southward-younging cooling

The different magnitude of exhumation of the zircon εHf values in the Pamir river sands are ages between ca. 18 and ca. 6 Ma is observed central and southern Pamir (western drainages) consistent with εHf values reported for Songpan- throughout the Pamir and can be explained by versus northeastern Pamir is consistent with our Ganzi, Qiangtang, and Lhasa terranes in Tibet. southward migration of exhumation as a result geomorphic data, which indicate greater erosion Thermochronological ages from the Pamir of southward rollback of the subducting Indian on the western side of the range (Fig. 3). West- record younger (mid-late Miocene), and on slab under Asia. Overall, the magnitude of Ceno ern drainages exhibit higher hypsometric curves average much faster, exhumation than that zoic regional exhumation in the Pamir is greater and hypsometric integrals, and relief is higher recorded in Tibet. Lower magnitudes of exhu- than that observed in Tibet. on the western side of the range (Fig. 3). mation in Tibet are supported by the surficial Figure 7 presents the younger than 50 Ma geology, which is characterized by widespread ACKNOWLEDGMENTS 40Ar/39Ar ages and youngest 40Ar/39Ar and AFT exposures of young volcanic and Mesozoic sed- We would like to acknowledge the support of National Geo- graphic, the University of Wyoming, and the University of age populations. The most recent exhumation imentary rocks (Chung et al., 2005), indicating Arizona for funds to B. Carrapa. E.R. Sobel and L.M. Schoen- signals from rivers draining the central and a shallow level of erosion. Outside of late Mio- bohm thank the German Research Council (grant STR 373/20- southern Pamir domes occurred mainly between cene rifts and marginal areas (Clark et al., 2005), 1) for funding. We thank Jay Chapman, Peter Molnar, Steve Roecker, Rebecca Bendick, and Claire Lukens for help in the ca. 19 Ma and ca. 8 Ma, and exhumation sig- low-temperature thermochronological ages are field and for scientific discussions, and Chen Jie for help with nals from the rivers draining the Kongur Shan almost exclusively pre-Oligocene (Hetzel et Chinese river samples. U-Pb and Hf analyses were conducted at the Arizona LaserChron Center, which is supported by and Mustagh Ata domes are between ca. 15 and al., 2011; Rohrmann et al., 2012; Duvall et al., National Science Foundation grant EAR-1032156. ca. 6 Ma. The data also suggest a possible south- 2012). Together, these observations indicate that ward-younging trend of the youngest detrital most of the Tibetan Plateau has been internally REFERENCES CITED 40 39 Ar/ Ar ages and youngest detrital AFT popu- drained and did not experience significant exhu- Aizen, E.M., Aizen, V.B., Melack, J.M., Nakamura, T., and Ohta, lation ages for the central and southern Pamir mation during the Cenozoic. This is consistent T., 2001, Precipitation and atmospheric circulation patterns at mid-latitudes of Asia: International Journal of samples. Although this signal may be an arti- with increased aridification of large parts of the Climatology, v. 21, p. 535–556, doi:10.1002/joc.626. fact of sample size and or statistical treatment Tibetan Plateau during the Eocene–Oligocene Amidon, W.H., and Hynek, S.A., 2010, Exhumational his- of the data, the fact that both 40Ar/39Ar and AFT (Dupont-Nivet et al., 2007) and with high eleva- tory of the north central Pamir: Tectonics, v. 29, TC5017, doi:10.1029/2009TC002589. youngest components show the same trend, tions since at least the late Oligocene (Rowley Bershaw, J., Garzione, C.N., Schoenbohm, L., Gehrels, G., which is consistent with documented cooling and Currie, 2006; DeCelles et al., 2007b; Quade and Tao, L., 2012, Cenozoic evolution of the Pamir pla- ages of metamorphic domes that also young to et al., 2011). In contrast, numerous early Mio- teau based on stratigraphy, zircon provenance, and stable isotopes of foreland basin sediments at Oytag the south (Schmidt et al., 2011), suggests that cene detrital thermochronological ages derived (Wuyitake) in the Tarim Basin (west China): Journal of our trend is geologically meaningful. We specu- from the Pamir interior presented in this study Asian Earth Sciences, v. 44, p. 136–148, doi:10.1016/j .jseaes.2011.04.020. late that southward younging of exhumation of indicate that most of the Pamir was undergoing Bouvier, A., Vervoort, J.D., and Patchett, J.D., 2008, The Lu-Hf the Pamir may be related to tectonic processes. extensive exhumation during the Cenozoic at and Sm-Nd isotopic composition of CHUR: Constraints

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Erratum to this article.

Multisystem dating of modern river detritus from Tajikistan and China: Implications for crustal evolution and exhumation of the Pamir Barbara Carrapa, Fariq Shazanee Mustapha, Michael Cosca, George Gehrels, Lindsay M. Schoenbohm, Edward R. Sobel, Peter G. DeCelles, Joellen Russell, and Paul Goodman (this issue, v. 6; no. 6; p. 443–455; doi: 10.1130/L360.1)

On page 7 at the end of the first paragraph “western Pamir Rivers contain stronger 300 and 500 Ma components” should be: “eastern Pamir Rivers....”.

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