U-Pb Detrital Zircon Ages and Geochemical Features Of

Article U-Pb Detrital Zircon Ages and Geochemical Features of the Jingxing Formation, (Qamdo Basin, Tibet: Implications): Inferences for the Metallogenic Model of the East Tethys Evaporite

Wenhua Han 1,2,3,*, Haizhou Ma 1,2,*, Weixuan Fang 4, Huaide Cheng 1,2, Yongshou Li 1,2, Binkai Li 1,2, Weiliang Miao 1,2 and Qinyu Hai 1,2

1 Key Laboratory of Comprehensive and Highly Efﬁcient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China; [email protected] (H.C.); [email protected] (Y.L.); [email protected] (B.L.); [email protected] (W.M.); [email protected] (Q.H.) 2 Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Xining 810008, China 3 University of Chinese Academy of Sciences, Beijing 100049, China 4 China Non-Ferrous Metals Resource Geological Survey, Beijing 100012, China; [email protected] * Correspondence: [email protected] (W.H.); [email protected] (H.M.)

Abstract: Qamdo basin is located between the suture zone of Jinsha River (Ailao Mountains) and that of Ban Gong Lake (Nujiang) in the eastern Tethys. Part of the Jingxing Formation is deposited in Citation: Han, W.; Ma, H.; Fang, W.; the southwest of the basin. In this study, two proﬁles were investigated from the north and south of Cheng, H.; Li, Y.; Li, B.; Miao, W.; Hai, Qamdo basin. The characteristics of detrital zircon LA-ICP-MS U-Pb age, and the main and trace Q. U-Pb Detrital Zircon Ages and elements of sandstone were analyzed. The characteristics of major and trace elements showed that the Geochemical Features of the Jingxing tectonic setting of the study area is mainly composed of a relatively stable active continental margin Formation, (Qamdo Basin, Tibet: and a passive continental margin, showing characteristics of a continental island arc. The weathering Implications): Inferences for the degree of Jingxing Formation in the Qamdo area is lower than that in the Lanping-Simao area, which Metallogenic Model of the East may be closer to the origin. The age distribution characteristics of detrital zircon grains indicate Tethys Evaporite. Minerals 2021, 11, that the Qiangtang Block, Youjiang basin, and Yangtze area jointly constitute the provenance of the 745. https://doi.org/10.3390/ min11070745 Qamdo-Lanping-Simao basin. Both basins may be part of a large marine basin with uniﬁed water conservancy connection before evaporite deposition. Metamorphic seawater from the Qamdo basin

Academic Editor: may migrate to the Lanping-Simao basin and even the Khorat basin, where evaporite was deposited. Krzysztof Bukowski Keywords: Jingxing Formation; provenance; geochemistry; U-Pb detrital zircon age; Qamdo basin Received: 22 May 2021 Accepted: 30 June 2021 Published: 9 July 2021 1. Introduction Publisher’s Note: MDPI stays neutral The formation and evolution of the Tethys, which encompasses the five current conti- with regard to jurisdictional claims in nents of Europe, Asia, Africa, South America, and North America, exerted an important published maps and institutional affil- influence on the global structure. The Tethys tectonic area is rich in salt resources, and iations. reaches from northern to eastern Europe, north Africa, west Asia, and central Asia to China [1,2]. Qiangtang basin is located in the northern part of the Qinghai-Tibet Plateau and the eastern part of the Tethys-Himalayan tectonic domain (Figure1). It is the largest Meso-Cenozoic sedimentary basin in the Qinghai-Tibet Plateau [3–6]. In recent years, Copyright: © 2021 by the authors. a giant Jurassic potash deposit has been discovered in the Karakum basin in the north Licensee MDPI, Basel, Switzerland. margin of the Qiangtang basin [7–10]. Several Jurassic gypsum beds and gypsum mound This article is an open access article outcrops at different scales were also found in the northern Qiangtang basin, especially distributed under the terms and many salt springs in the northern Qiangtang basin, whose water composition reached conditions of the Creative Commons the deposition index of magnesium sulfate, which was close to that of potassium salt. Attribution (CC BY) license (https:// Qiangtang basin has better salt-forming geological conditions and potassium-forming creativecommons.org/licenses/by/ potential [11,12]. Qamdo basin is located in the east of Qiangtang basin. This area has an 4.0/).

Minerals 2021, 11, 745. https://doi.org/10.3390/min11070745 https://www.mdpi.com/journal/minerals Minerals 2021, 11, 745 2 of 21

abundance of salt spring water, gypsum salt, dolomite, and magnesite. Qamdo basin is con- nected with Lanping-Simao basin in the south, and extends to Laos, Thailand, and Nakhon Lat plateau in the south, which together constitute a large rift basin system. The Mengye jing potash deposit in Jiangcheng, Lanping-Simao basin is the only ancient solid potash deposit of mining value in China. Its ore-bearing stratum is the Mengye jing Formation, which, along with rock salts and clastic rocks, is part of the Mengye jing Formation [13]. A number of scholars inferred that the sedimentary age of the Mengye jing Formation was the late Early Cretaceous by studying the tuff interlayer (SHRIMP dating), palynol- ogy, and high-precision paleomagnetism of the formation [14,15]. Microaenator chagyabi, Asiatosaurus kwangshiensis, Monkonosaurus lawulacus, and other dinosaur fossils have been found in the Jingxing Formation of Qamdo. The sedimentary age of Jingxing Formation in Qamdo area may be the Early Cretaceous, and the lithologic assemblage and paleon- tological fossils of Jingxing Formation in the study area are basically identical to those of Jingxing Formation in the Lanping-Simao area [16]. Wang and Li studied the provenance of detrital zircon grains from Mengye jing Formation and Baishahe Formation in the Simao area of Lanping, and concluded that Qiangtang Block, Ailaoshan tectonic belt, Yangtze, and other areas jointly constituted the provenance of the Lanping-Simao basin [17,18]. Geochemistry and sulfur isotopic characteristics of anhydrite indicate that the evaporite deposits in the Qamdo-Lanping-Simao basin have marine facies genesis [18–20]. Hite and Japalcaster (1979) inferred that the Khorat area (such as the ocean) has a water conservancy contact to the southwest [21]. Wang (2014) studied the Lanping area and suggested that the formation of evaporite was related to the transgression of the Neo-Tethys Ocean in the middle Cretaceous [19]. Wang further pointed out that the Lanping-Simao-Vientiane-Khorat basin is in the transgression period for unified large evaporation basin systems, which are interconnected [17]. Recent studies have shown that large-scale evaporites, developed in the Qamdo-Lanping-Simao basin, were concentrated metamorphic seawater after the Neo-Tetyan Ocean seawater passed through the North Qiangtang confined sea and entered the basins of the salt-forming zone. This is a concentrated metamorphic migration model of multi-stage basin seawater into salt-forming potassium [18]. However, direct evidence for the provenance of Early Cretaceous strata in the Qamdo-Lanping-Simao basin is still lacking. Therefore, it is of great significance to study the provenance of the Early Cretaceous Jingxing Formation in Qamdo basin. Zircon grains are highly refractory during cycles of geologic history. Over the last 20 years, hundreds of published studies using detrital zircon grains indicate the increasing success in evaluations of provenance and paleogeography and developing tectonic recon- structions [22,23]. U-Pb ages of detrital zircon grains can therefore effectively constrain the sources and origins of detrital zircon grains in sedimentary rocks [24,25]. The whole-rock geochemistry of sandstones can also be used for provenance analysis [26,27]. In this study, an integrated approach of whole-rock geochemistry and detrital zircon U-Pb was used. The obtained data are used to constrain the sedimentary provenance of the Late Cretaceous Jingxing Formation and study the relationship between Jingxing Formation and Meyejing Formation. New evidence for the mineralization model of evaporite deposit is put forward. Minerals 2021, 11, 745 3 of 21 Minerals 2021, 11, x 3 of 21

Figure 1. (A) geological map (modified after Song et al., 2011 [28]; salt springs after Qin et al., 2017 [29]; salts after Wang Figure 1. (A) geological map (modified after Song et al., 2011 [28]; salt springs after Qin et al., 2017 [29]; salts after Wang et al., 2018 [30]); (B) Schematic tectonic map of Qamdo: Notes: Ⅰ: North China Block; Ⅱ: Songpan-Ganzi Block; Ⅲ: Yidun et al., 2018 [30]); (B) Schematic tectonic map of Qamdo: Notes: I: North China Block; II: Songpan-Ganzi Block; III: Yidun Arc Terrane; Ⅳ: Qamdo-Simao Block; Ⅴ: Indochina Block; Ⅵ: Baoshan Block; Ⅶ: Qiangtang Block; Ⅷ: Gangdisi Arc; Ⅸ: HimalayanArc Terrane; Block; IV: Qamdo-Simao Ⅹ: Himalayan Block; Front V: Thrust Indochina Belt; Block; Ⅺ: Qinghai–Tibet VI: Baoshan Block; Plateau; VII: ① Qiangtang Longmenshan Block; Fault VIII: GangdisiZone; ② Daofu- Arc; IX: LuhuoHimalayan Fault Block; Zone; X:③Himalayan Garze-Litang Front Suture Thrust Zone; Belt; ④ XI: Jinshajiang-Ailaos Qinghai-Tibet Plateau;han Suture 1 Longmenshan Zone; ⑤ Shuanghu-Lancangjiang Fault Zone; 2 Daofu-Luhuo Suture Zone;Fault Zone;⑥ Bangong-Nujiang 3 Garze-Litang suture Suture Zone; Zone; ⑦ 4 Yarlung-ZangboJinshajiang-Ailaoshan Suture SutureZone; ⑧ Zone; Himalayan 5 Shuanghu-Lancangjiang Thrust Belt (modified Suture after Zone;Hou et 6 al.,Bangong-Nujiang 1996 [31]); (C) Stratigraphic suture Zone; column 7 Yarlung-Zangbo (modified after Suture Miao Zone; [32]). 8 Himalayan Thrust Belt (modified after Hou et al., 1996 [31]); (C) Stratigraphic column (modified after Miao [32]). 2. Geological Setting 2. GeologicalQamdo Basin Setting is located at 96°30’–99°30’ E and 29° 00’–31°40’ N of the eastern Qing- hai-Tibet Plateau, with NNW-SSE direction (Figure 1), covering an area of about 4.8 × 104 Qamdo Basin is located at 96◦30’–99◦30’ E and 29◦00’–31◦40’ N of the eastern Qinghai- km2. The Qamdo basin developed in the Qiangtang, Qamdo-Simao Block, and the Tibet Plateau, with NNW-SSE direction (Figure1), covering an area of about 4.8 × 104 km2. Jinshajiang-Ailaoshan suture zone is in the northeast, which is characterized by the final The Qamdo basin developed in the Qiangtang, Qamdo-Simao Block, and the Jinshajiang- extinction of Jinshajiang-Ailaoshan in the Late Triassic and the collision of the Qamdo Ailaoshan suture zone is in the northeast, which is characterized by the final extinction block and Songpan-Ganzi block since the Late Triassic. In the southwest, the Bangong-

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of Jinshajiang-Ailaoshan in the Late Triassic and the collision of the Qamdo block and Songpan-Ganzi block since the Late Triassic. In the southwest, the Bangong-Nujiang Suture Zone closed with the Bangonglake-Nujiang basin in the middle and late middle Jurassic [33–35]. The tectonics of Qamdo area belong to the eastern section of the East Tethys tectonic domain, which is an arc-continental collision orogenic belt that formed since the Late Paleozoic. Since the Paleozoic, three major tectonic system changes have occurred, namely, the Late Paleozoic to Middle Triassic multi-arc basin to orogenic belt transition, the Late Triassic to Cretaceous basin-mountain transition, and the Cenozoic large-scale intracontinental tectonic convergence [36–40]. The strata exposed in Qamdo basin are mainly Pre-Ordovician, Ordovician, Upper Paleozoic, Mesozoic, and Cenozoic. The Mesozoic middle and lower Triassic strata are mainly distributed in the east of the basin, and in the narrow zone from the south of Yushu to the area of Mangkang. The distribution in the basin is sporadic. These strata are purplish red, grayish green, and gray medium thin layers of sandstone and shale interbedded with volcanic rocks [41]. The Mesozoic strata in the southern part of the basin are relatively well preserved in the Mangkang area. The denudation in the northern Qamdo area is relatively large, and the Upper Triassic-Jurassic strata are only exposed in Mangda Town. The main Triassic formations are Jiapila Formation (T3j), Bolilia Formation (T3b), Adula Formation (T3a), and Duogaila Formation (T3d). The Jiapila Formation is interbedded with purplish red conglomerate, sandstone, and shale. The bottom is unconformable above the Upper Permian strata, and the top is conformable covered with limestone of Bolila Formation. Bolila Formation is a set of carbonate formations with the bottom integrated over Jiapila Formation. Bolila Formation is composed of light gray medium-thick stratified limestone, micritic limestone, nodular limestone, and bioclastic limestone, and its distribution is stable. Adula Formation is composed of gray and dark gray thin-bedded to intermediate mudstone, siltstone interbedded with feldspar quartz sandstone, and coal lines, containing plant fragments. Duogaila Formation is a set of coastal and lagoonal facies deposited with abundant plant fossils and a small amount of brackish bicrustal fossils, which are interbedded with grey-black thin-bedded sandstones and shales. Triassic strata present a set of gypsum deposits. The Jurassic is mainly composed of fluvio-lacustrine clastic rock deposits, interbedded with marine strata, generally consisting of a set of red and purplish red strata. Together with the Cretaceous system, these constitute the so-called “red basin” of Qamdo basin, with a main distribution in Qamdo-Mangkang. Jurassic strata include Wangbu Formation (J1w), Dongdaqiao Formation (J2d), and Xiaosuoka Formation (J3x). Jurassic lithology in Qamdo basin is mainly composed of purplish red sand and argillaceous rocks, and deposits of thick layers of gypsum ore [42]. Cretaceous strata include the Jingxing Formation (K1j), Nanxin Formation (K2n), and Hutousi Formation (K2h), which are in parallel unconformable contact with underlying strata. Nanxin Formation consists of a set of purplish red sandstone, complex lithic conglomerate, and conglomerate. It is a fluvial facies deposit, and the strata only outcropped in the north of Mangkang area. Hutousi Formation is a large set of cross-bedding with thick bedded sandstone and purple mudstone. This belongs to river and arid hot salt water lacustrine deposits, and few outcrops can be found in the study area. The strata of Jingxing Formation (K1j) are local outcrops in Jiangda County and Mangkang County, and are the target strata of this study. The lithology is mainly composed of purplish red feldaceous conglomerate, mud- bearing coarse sandstone with color, and silty mudstone, which belongs to fluvio-lacustrine deposits. The strata are integrated on the Xiaosuoka Formation (J3x) [16]. On the whole, the area of Cretaceous strata outcrops in Qamdo basin is small; therefore, the research foundation of Cretaceous strata in this area is relatively weak.

3. Materials and Methods The geochemical analysis of the major and trace elements of the samples was com- pleted in the laboratory of the Beijing Research Institute of Uranium Geology, Beijing, China. The working environment temperature was 20 ◦C and humidity was 40%. The major ele- Minerals 2021, 11, 745 5 of 21

ments were tested and analyzed by X-ray fluorescence spectrometry on a Panaco AXIOS X-ray fluorescence spectrometer (Malvern Panalytical, Malvern, UK), with an analysis error of less than 5%. Trace elements were measured using a Finnigan MAT (Thermo Fisher Sci- entific, Waltham, MA, USA) high-resolution inductively coupled plasma mass spectrometer (ICP-MS). The details of this analytical procedure have been described by Cullen et al. [43]. The accuracy of the analyses was better than 2.5%. Samples for this study were collected from the section in Mangda Town and west of Mangkang County, where the Mesozoic strata of Jingxing Formation are well exposed. A total of 23 sandstone samples were collected from two sections of the Jingxing Formation, and the contents of major elements and rock slices of samples were studied. Two samples from the Jingxing Formation were collected from Mangda and Mangkang areas and were subjected to U-Pb geochronology by the State Key Laboratory of Continental Dynamics, Northwest University, Xian, China. Each sample was selected from fresh sandstones. Zircon grains were separated using conventional heavy liquid and magnetic techniques and were purified by handpicking under a binocular microscope. A total of 204 representative grains of each sample were mounted in a 25-mm epoxy-resin mount and then polished and coated with gold film. Cathodoluminescence images of zircon grains were used to assess the internal growth structures of the zircon grains. The best zircon particles without inclusions and cracks were selected for LA-ICP-MS test. The analytical instrument was an Agilent 7700X ICP-MS (MicroLas, Göttingen, Germany) and the matching GeoLas2005 laser erosion system was used. During the experiment, He was used as carrier gas, and the diameter of the laser beam spot was 25 µm. Zircon 91500 was used as external standard for U-Pb dating, and NIST SRM 610 was used as external standard for both the U and Th contents. The zircon U-Pb age concordia and probability density plots were drawn using the Isoplot (version 3.0) software of Ludwig and Hou [44,45].

4. Results 4.1. Petrography The lithology of the Cretaceous Jingxing Formation in the study area is mainly medium-fine feldspar lithic sandstone and siltstone. Its structural components are characterized by fine particle size of 0.06–0.5 mm, pore type of cementation, good to medium sorting, sub-angular grinding degree, and moderate weathering degree, indicating relatively weak hydrodynamic conditions during deposition. The contents of quartz, feldspar, and lithic fragments in the detrital composition are 51%, 14%, and 35%, respectively. The ce- ment content is 3–6%. Feldspar is widely distributed in the study area (Figure2), mainly as plagioclase, potassium feldspar, sericited and kaolinited plagioclase are common, resulting in a dirty surface. Occasionally, the plagioclase secondary increase phenomenon can be observed, increasing the side for albitization. Feldspar is often selectively dissolved and metasomatized by carbonate along cleavage fractures. The higher the content of feldspar and lithic fragments, the lower the compositional maturity of the rock. The content of lithic fragments in this study area is relatively high, and their types are complex and diverse. The volcanic rock lithic fragment in magmatic rocks are the main fragments (Figure2B,D), and contain a small amount of granite, metamorphic quartzite, micritic limestone, and siliceous rocks. Volcanic rock lithic fragment is dominated by acid extrusive rock lithic fragment, which is characterized by porphyritic structure or the lack thereof. The phe- nocryst is quartz or transfeldspar, its matrix has either a felsic structure, radiating spherular structure, or microscopic cryptocrystalline structure, and the structures are massive, occasionally showing a flow structure and felsic mineral composition. The granite lithic fragment has a semi-idiomorphic granular structure (i.e., granitic structure) and massive structure. The main mineral components are quartz, potassium feldspar, and plagioclase. Metamorphic quartzite is generally composed of two or more quartz particles, which are colorless and transparent. Quartz particles are inlaid and contacted with each other, and show clear wavy (or banded) extinction. Micritic limestone lithic fragment generally has a micritic structure, mineral composition of micritic calcite, with an extremely unstable Minerals 2021, 11, 745 6 of 21

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nature, similar to near provenance lithic fragment. The cuttings of siliceous rock are colorless and transparent, and show smooth surface, small grain structure, or radial spherular are colorless and transparent, and show smooth surface, small grain structure, or radial structure, and a mineral composition of cryptocrystalline quartz. spherular structure, and a mineral composition of cryptocrystalline quartz.

Figure 2. Photomicrographs of typical lithics in sandstones of the Jingxin Formation under cross- Figure 2. Photomicrographs of typical lithics in sandstones of the Jingxin Formation under cross- polarized light. (A,B), sample MP4 in section of Mangda. (C,D), sample MK11 in section of polarized light. (A,B), sample MP4 in section of Mangda. (C,D), sample MK11 in section of Mangkang. Mangkang. Abbreviations: Q, quartz; Cal, calcite; Pl, Plagioclase; Kf, K-Feldspar; Lv, volcanic rock Abbreviations:fragment. Q, quartz; Cal, calcite; Pl, Plagioclase; Kf, K-Feldspar; Lv, volcanic rock fragment. 4.2. Whole Rock Geochemistry 4.2. Whole Rock Geochemistry The results of the major elements from the Jingxing Formation sandstone in the QamdoThe Basin results show of thatthe major the data elements of the majorfrom elementsthe Jingxing from Formation both sections sandstone are basically in the identical,Qamdo Basin and theshow variation that the range data isof weak.the major The elements results of from the elements both sections data areare givenbasically in identical, and the variation range is weak. The results of the elements data are given in Supplementary Data Table S1. According to the data of both sections, SiO2 ranges from 54.68%Supplementary to 79.72%, Data with Table an average S1. According of 66.42% to (n the = 23).data This of both is consistent sections, withSiO2 theranges average from 54.68% to 79.72%, with an average of 66.42% (n = 23). This is consistent with the average value of the upper crust (65.89 wt.%) [46]. Al2O3 ranges from 3.80% to 20.09%, with an 2 3 T averagevalue of of the 11.86%, upper which crust (65.89 is lower wt.%) than [46]. the averageAl O ranges of the from ucc(15.17 3.80%wt.%) to 20.09%, [46]. Fewith2O 3an rangesaverage from of 11.86%, 1.13% to which 8.12% is with lower an than average the ofaverage 4.38%; of MgO the ucc ranges (15.17 from wt.%) 0.31% [46]. to 2.78%Fe2O3T withranges an averagefrom 1.13% of 1.74%, to 8.12% Na2 withO ranges an average from 0.06% of 4.38%; to 1.51% MgO with ranges an average from 0.31% of 0.99%; to 2.78% K2O rangeswith an from average 0.46% of to1.74%, 4.82% Na with2O ranges an average from 0.06% of 2.56%; to 1.51% CaO with ranges an average from 0.49% of 0.99%; to 9.00% K2O withranges an averagefrom 0.46% of 4.29%; to 4.82% TiO 2withranges an fromaverag 0.20%e of to2.56%; 0.86% CaO with ranges an average from of0.49% 0.60%; to MnO9.00% rangeswith an from average 0.02% of to 4.29%; 0.16% TiO with2 ranges an average from of0.20% 0.07%; to and0.86% P2 withO5 ranges an average from0.05% of 0.60%; to 0.18% MnO withranges an from average 0.02% of 0.13%.to 0.16% Geochemistry with an average classiﬁcation of 0.07%; diagrams and P2O (Figure5 ranges3 A)from show 0.05% that to samples0.18% with from an the average Jingxing of 0.13%. Formation Geochemistry of both the classification Mangda section diagrams and Mangkang (Figure 3A) section show arethat located samples in thefrom area the of Jingxing arkose sandstoneFormation and of both lithic the greywacke. Mangda section These show and Mangkang a low number sec- oftion samples are located in sublithic in the sandstone, area of arkose and have sandstone a tendency and tolithic transform greywacke. to subarkose These show sandstone. a low Innumber the Na of2O-K samples2O diagram in sublithic (Figure sandstone,3B), a large and part have of samplesa tendency from to transform both sections to subarkose fall into thesandstone. quartz rich In the and Na quartz-intermediate2O-K2O diagram (Figure categories 3B), ofa large subarkose part of sandstone. samples from both sections fall into the quartz rich and quartz-intermediate categories of subarkose sandstone.

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Figure 3. GeochemistryFigure 3. Geochemistry classiﬁcationFigure 3. classification diagramsGeochemistry of diagrams sandstones classification of ofsandstones thediagrams Jinxing of Formation sandstonesthe Jinxing in of Formation Qamdo the Jinxing basin in Formation Qamdo (A, after Pettijohnin Qamdo et al., 1972 [basin47]; B ,(A after, after Asiedu Pettijohnbasin et al.,(A et, 2000after al., 1972 [Pettijohn48]). [47]; etB ,al., after 1972 Asiedu [47]; B et, after al., 2000 Asiedu [48]). et al., 2000 [48]).

In the process InInof the themagma processprocess or of fluidof magma magma evolution, or or fluid fluid compatible evolution, evolution, compatible elementscompatible elements(e.g., elements Ni (e.g.,and (e.g., Co) Ni Ni and and Co) Co) mostly mostly enter theentermostly mineral the enter mineral phase the phasemineral or the or residuphase the residual alor phase,the phase,residu while whileal phase, incompatible incompatible while incompatible elements elements are areelements more inclined are more inclined tomore enter inclined thethe meltmelt to phase.enterphase. the Therefore,Theref melt phase.ore, in in contrast Therefcontrastore, to to thein the contrast major major elements, to elements, the major trace trace elements, elements trace record elements recorddifferentelements different geological record geological different activities activities geological in a in unique a activities unique way way[in46 ].a unique As[46]. shown As way shown in [46]. Figure in As Figure4 shownA, all samples in Figure have 4A, all samplessimilar4A, have all similar chondritesamples chondrite have normalized similar normal chondrite rareized earth rare normal element earthized (REE)element rare profiles.earth (REE) element Theprofiles. normalized (REE) The profiles. distribution The normalized distributionpatternsnormalized of patterns REEs distribution in of chondrites REEs patterns in showchondrites of REEs that lightin show chondrites REE that are light enriched,show REE that are while light enriched, REE the contents are enriched, of heavy while the contentsREEwhile of are theheavy low. contents TheREE total areof heavy low. amount The REE oftotal are REE low. amount (Σ TheREE) totalof ranges REE amount (Σ betweenREE) of REE ranges 66.48 (ΣREE) betweenµg/g ranges and 243.25betweenµg/g, 66.48 μg/g andwith 66.48243.25 an μ g/gμ averageg/g, and with 243.25 value an averageμ ofg/g, 145.2 with valueµ g/g.an average of The 145.2 total value μg/g. amount of The 145.2 oftotal μ lightg/g. amount rareThe earthtotal of light amount elements of (lightΣLREE) rare earth elementsrangesrare earth(Σ fromLREE) elements 59.89 rangesµ g/g(Σ LREE)from to 223.0 59.89 rangesµ g/g,μg/g from withto 59.89223.0 an averageμ μg/gg/g, to with 223.0 value an μ ofg/g, average 131.14 with µanvalueg/g. average The content value of of 131.14 μg/g. The content of heavy rare earth elements (ΣHREE) ranges from 60.59 μg/g of 131.14 μg/g.heavy The content rare earth of heavy elements rare ( ΣearthHREE) elements ranges ( fromΣHREE) 60.59 rangesµg/g from to 20.61 60.59µg/g, μg/g with an average to 20.61 μg/g, with an average value of 14.07 μg/g. The ratio of LHREE to heavy rare earth to 20.61 μg/g, withvalue an of average 14.07 µ valueg/g. Theof 14.07 ratio μg/g. of LHREE The ratio to of heavy LHREE rare to earth heavy elements rare earth (LHREE/HREE) elements (LHREE/HREE) ranges from 7.23 μg/g to 11.01 μg/g with an average of 9.23 μg/g. elements (LHREE/HREE)ranges from ranges 7.23 µ fromg/g to7.23 11.01 μg/gµ g/gto 11.01 with μg/g an averagewith an average of 9.23 µ ofg/g. 9.23 Theμg/g. Eu element has The Eu element has an obvious negative anomaly. Figure 4B shows that the Jingxing For- an obvious negative anomaly. Figure4B shows that the Jingxing Formation sandstone in The Eu elementmation has an sandstone obvious negative in Qamdo anomaly. area has Figurelow contents 4B shows of high that field the strength Jingxing elements For- such as Qamdo area has low contents of high field strength elements such as K, Nb, Sr, P, and Ti. mation sandstoneK, Nb, in Qamdo Sr, P, and area Ti. has low contents of high field strength elements such as K, Nb, Sr, P, and Ti.

FigureFigure 4.4. (A) Chondrite-normalized Chondrite-normalized rare rare earth earth element element (R (REE)EE) patterns patterns of sandstones of sandstones of the of Jingxing the Jingxing FormationFormation (after Taylor and and McLennan McLennan 1985 1985 [46]). [46]). (B ()B Chondrite-normalized) Chondrite-normalized trace trace element element spider spider Figure 4. (A) Chondrite-normalizeddiagram of the sandstones rare earth of Jingxing element Fo (RrmationEE) patterns (after Taylor of sandstones and McLennan of the Jingxing 1985 [46]). Formation (afterdiagram Taylor and of the McLennan sandstones 1985 of Jingxing[46]). (B) FormationChondrite-normalized (after Taylor andtrace McLennan element spider 1985 [46]). diagram of the sandstones of Jingxing Formation (after Taylor and McLennan 1985 [46]). 4.3.4.3. U-PbU-Pb Geochronology In this study, 102 detrital zircon grains from sample MP4 were tested, which is lo- 4.3. U-Pb GeochronologyIn this study, 102 detrital zircon grains from sample MP4 were tested, which is located incated the Mangdain the Mangda Town. Town. Among Among them, them, three three did not did meet not meet the requirements the requirements of concordance of con- In this study, 102 detrital zircon grains from sample MP4 were tested, which is lo- (concordancecordance (concordance <90% and <90% >110%), and >110%), and the and remaining the remaining 99 samples 99 samples met the met research the research require- cated in the Mangda Town. Among them, three did not meet the requirements of con- ments.requirements. The effective The effective data accounted data accounted for about for about 97% of 97% the of data. the Thedata. U-Pb The U-Pb data aredata given are in cordance (concordance <90% and >110%), and the remaining 99 samples met the research 206 238 Supplementarygiven in Supplementary Data Table Data S2. Table The interpreted S2. The interpreted ages are ages based are on based the 206 onPb/ the238 UPb/ for <1000U requirements. The effective data accounted for about 97% of the data. The U-Pb data are Ma grains and on the 207Pb/206Pb for >1000 Ma grains [49]. In sample MK11, which was given in Supplementary Data Table S2. The interpreted ages are based on the 206Pb/238U

Minerals 2021, 11, 745 8 of 21 Minerals 2021, 11, x 8 of 21

located in Mangkang County, 102 detrital zircon grains were tested, two of which also failed for <1000 Ma grains and on the 207Pb/206Pb for >1000 Ma grains [49]. In sample MK11, which towas meet located the requirementsin Mangkang County, of concordant 102 detrital degree, zircon and grains the were remaining tested, 100two metof which the research requirements.also failed to meet The the effective requirements age data of co accountsncordant degree, for about and 98% the remaining of the overall 100 met analyzed the data (Tableresearch S2). requirements. The U-Pb data The foreffective each sampleage data are accounts presented for about in concordia 98% of the diagrams overall ana- and relative probabilitylyzed data (Table plots S2). (Figure The U-Pb5). These data for data each are sample discussed are presented together in in concordia view of thediagrams two samples withand relative similar probability detrital age plots compositions (Figure 5). These according data are todiscussed the age together distribution in view characteristics. of the Basedtwo samples on the with age similar distribution detrital characteristics age compositions of according the two samples to the age from distribution Jingxing char- Formation, theacteristics. minimum Based age on is the 195.4 age Ma,distribution the youngest characteristics cluster of of the ages two ranges samples within from 194–218Jingxing Ma, the peakFormation, age for the this minimum age group age is 195.4 220 Ma, Ma, andthe yo theungest maximum cluster ageof ages is 2734.2 ranges Ma.within The 194– age of two samples218 Ma, the is mainlypeak age concentrated for this age group in 198–608 is 220 Ma, Ma, and 721–1006 the maximum Ma, and age 1694–2082 is 2734.2 Ma. Ma. In the detritalThe age zirconof two grainsamples age is spectrummainly concentr diagram,ated in the 198–608 ages of Ma, coarse 721–1006 sandstone Ma, and in 1694– the Jingxing 2082 Ma. In the detrital zircon grain age spectrum diagram, the ages of coarse sandstone Formation mainly showed three peaks of 450 Ma and 1870 Ma. in the Jingxing Formation mainly showed three peaks of 450 Ma and 1870 Ma.

Figure 5. U-Pb concordia diagrams and age probability plots for samples of Jingxing at Qamdo Ba- Figure 5. U-Pb concordia diagrams and age probability plots for samples of Jingxing at Qamdo Basin. sin. (A,B) Sample MP4 of Mangda section. (C,D) Sample MK11 of Mangkang section. (A,B) Sample MP4 of Mangda section. (C,D) Sample MK11 of Mangkang section. The Cathodoluminescence (CL) images of representative zircon grains and the spot ages Theare shown Cathodoluminescence in Figure 6. The morphologies (CL) images of of these representative zircon grains zircon vary grainswidely andfrom the spot agesprismatic are shown crystals into Figureoval shapes.6. The These morphologies zircon grains of can these be divide zircond into grains two vary groups: widely (1) from prismaticeuhedral, subhedral, crystals to anhedral, oval shapes. elongated, These and zircon zoned grains grains can were be dividedassignedinto to the two ‘idio- groups: (1) euhedral,morphic’ group, subhedral, while anhedral,(2) rounded elongated, and subround anded zoned zircon grains grains wereconstitute assigned the ‘rounded’ to the ‘idiomorphic’group. group, Several while grains (2) were rounded broken and and may subrounded have been zircondamaged grains during constitute transport. theOther ‘rounded’ group.grains are Several subrounded grains wereor have broken rounded and corners. may have Thisbeen rounding damaged of grains during suggests transport. pro- Other grainslonged aretransport subrounded or multiple orhave cycles rounded of transport, corners. whereas This euhedral rounding grains of typically grains suggests sug- pro- longedgest short transport transport or distances. multiple Most cycles zircon of transport, grains have whereas well-developed euhedral oscillating grains typically zoning suggest shortor striped transport zoning distances. structures, Mostshowing zircon magmatic grains origin have under well-developed CL. Other grains oscillating have in- zoning or ternal structures that indicate a typical metamorphic origin, i.e., unzoned, weakly zoned, striped zoning structures, showing magmatic origin under CL. Other grains have internal cloudy-zoned, sector-zoned, planar-zoned, and patched-zoned [50]. Zircon grains of mag- structuresmatic origin that generally indicate have a typicala high Th/U metamorphic value (usually origin, exceeding i.e., unzoned, 0.4), while weakly metamorphic zoned, cloudy- zoned, sector-zoned, planar-zoned, and patched-zoned [50]. Zircon grains of magmatic origin generally have a high Th/U value (usually exceeding 0.4), while metamorphic zircon grains generally have a Th/U ratio below 0.1. Fast-growing metamorphic zircon grains

have relatively high Th/U ratios, and incomplete recrystallized zircon grains may also have relatively high Th/U ratios [51,52]. A number of metamorphic zircon grains even Minerals 2021, 11, 745 9 of 21

Minerals 2021, 11, x 9 of 21

have a Th/U ratio ofzircon 0.7 [53 grains]. About generally 63% have ofa Th/U the ratio zircon below grains 0.1. Fast-growing from the metamorphic Mangda zircon section have Th/U ratios exceedinggrains have 0.4, relatively and about high Th/U 5% ratios, of the and zircon incomplete grains recrystallized have Th/Uzircon grains ratios may less also have relatively high Th/U ratios [51,52]. A number of metamorphic zircon grains even than 0.1%. About 66%have of thea Th/U zircon ratio of grains 0.7 [53]. from About the63% Mangkangof the zircon grains section from havethe Mangda Th/U section ratios exceeding 0.4, and abouthave 3%Th/U have ratios exceeding Th/U ratios 0.4, and below about 5% 0.1%. of the Basedzircon grains on thehave Th/UTh/U ratios ratios less of both sections, most ofthan the zircon0.1%. About grains 66% of are themagmatic zircon grains zirconfrom the grains.Mangkang Cathodoluminescence section have Th/U ratios exceeding 0.4, and about 3% have Th/U ratios below 0.1%. Based on the Th/U ratios of images of zircon grainsboth show sections, a cloudy most of the structure zircon grains with are magmatic Th/U ratio zircon belowgrains. Cathodoluminescence 0.1, which may be the product of metamorphism.images of zircon grains show a cloudy structure with Th/U ratio below 0.1, which may be the product of metamorphism.

Figure 6. Representative cathodoluminescence images for detrital zircon grains of sandstone samples from Qamdo. The Figurelaser 6. spotsRepresentative and corresponding cathodoluminescence ages are marked. (A) Sample images MP4 of for Mangda detrital section. zircon (B) Sample grains MK11 of sandstone of Mangkang samples fromsection. Qamdo. The laser spots and corresponding ages are marked. (A) Sample MP4 of Mangda section. (B) Sample MK115. Discussion of Mangkang section. 5.1. Source Area Weathering and Sediment Recycling 5. Discussion The contents of unstable oxides (e.g., CaO, Na2O, K2O, and MgO) and relatively sta- 5.1. Source Area Weatheringble oxides and (e.g., Sediment Al2O3, ZrO Recycling2, and TiO2) contained in the parent rocks in the region of origin will change significantly after weathering or chemical metasomatism during diagenesis The contents of unstable[54]. Wedepohl oxides [55] suggested (e.g., that CaO, the upper Na2O, crust K is2 O,composed and MgO)of about 21% and quartz, relatively 41% stable oxides (e.g., Alplagioclase,2O3, ZrO and2, and21% potassium TiO2) contained feldspar; therefore, in the feldspar parent minerals rocks play in a the very region im- of origin will changeportant signiﬁcantly role in the afterweathering weathering process of th ore upper chemical crust. The metasomatism weathering of the upper during crust is a process of feldspar degradation accompanied by the formation of clay minerals. diagenesis [54]. WedepohlThe loss of [55 elements] suggested such as potassium, that the sodium, upper and crustcalcium isfrom composed feldspar minerals of about re- 21% quartz, 41% plagioclase,sults in the andaccumulation 21% potassium of silica-alumina feldspar; minerals therefore,in the products feldspar of weathering. minerals To play a very importantquantify role in the the degree weathering of weathering, process the chemical of the index upper of alteration crust. (CIA) The was weathering used. The CIA was calculated using the molecular proportions according to Equation (1): of the upper crust is a process of feldspar degradation accompanied by the formation CIA = Al2O3 / (Al2O3 + CaO* + Na2O + K2O) × 100 (1) of clay minerals. The loss of elements such as potassium, sodium, and calcium from feldspar minerals results in the accumulation of silica-alumina minerals in the products of weathering. To quantify the degree of weathering, the chemical index of alteration (CIA) was used. The CIA was calculated using the molecular proportions according to Equation (1): CIA = Al2O3/(Al2O3 + CaO* + Na2O + K2O) × 100 (1) where CaO* represents the amount of CaO incorporated in the silicate fraction of the rock [56]. Because of the absence of a CO2 value, the assumption proposed by Bock et al. was used [57]. After correcting for P2O5, if the mole fraction of CaO is less than that of Na2O, the value of CaO is accepted. If, however, the mole fraction of CaO exceeds that of Na2O, the mole fractions of CaO and Na2O were assumed to be equal. In general, the CIA value of sandstone generated by weathering is ~70%, and it is unlikely to be lower than 50%. The average CIA value of the upper crust is ~47% [58], and a CIA value of 45–55% identiﬁes unweathered sandstone. The CIA of the Jingxing Formation sample in the Munda section ranges from 59% to 78% (Table S1), with an average of 67%. The CIA of the Jingxing Formation sample of the Mangkang section ranged from 57% to 83%, with an average of Minerals 2021, 11, x 10 of 21

where CaO* represents the amount of CaO incorporated in the silicate fraction of the rock [56]. Because of the absence of a CO2 value, the assumption proposed by Bock et al. was used [57]. After correcting for P2O5, if the mole fraction of CaO is less than that of Na2O, the value of CaO is accepted. If, however, the mole fraction of CaO exceeds that of Na2O, the mole fractions of CaO and Na2O were assumed to be equal. In general, the CIA value of sandstone generated by weathering is ~70%, and it is unlikely to be lower than 50%. The average CIA value of the upper crust is ~47% [58], and a CIA value of 45-55% identi- fies unweathered sandstone. The CIA of the Jingxing Formation sample in the Munda Minerals 2021, 11, 745 section ranges from 59% to 78% (Table S1), with an average of 67%. The CIA10 of of the 21 Jingxing Formation sample of the Mangkang section ranged from 57% to 83%, with an average of 68%. The samples from both sections follow a trend of moderate chemical weathering. The CIA values of the Baishahe Formation (K1p) in the Lanping-SiMao area 68%.range The from samples 58% to from 95%, both with sections an average follow value a trend of of82%. moderate CIA values chemical of mudstone weathering. samples The CIAfrom values the Mengye of the Baishahe jing (K2me) Formation Formation (K1p) range in the from Lanping-SiMao 45% to 55%, areawith range an average from 58% of 74% to 95%,[17,32]. with The an averageweathering value intensity of 82%. of CIA the values Simao of area mudstone in Lanping samples is clearly from the lower Mengye than jing that (Kin2 me)the Qamdo Formation basin. range from 45% to 55%, with an average of 74% [17,32]. The weathering intensityAn ofA-CN-K the Simao triangle area diagram in Lanping is a is further clearly representation lower than that of in the the CIA Qamdo value. basin. This dia- gramAn can A-CN-K show the triangle distribution diagram of the is aanalys furtheris results representation of samples of with the CIAdifferent value. CIA This val- diagramues, and can can show be used the to distribution assess the ofcompositio the analysisn of resultssource ofrocks samples and the with characteristics different CIA of values, and can be used to assess the composition of source rocks and the characteristics of the potassium metasomatism of samples [58,59]. The A-CN-K diagram (Figure 7) shows the potassium metasomatism of samples [58,59]. The A-CN-K diagram (Figure7) shows that both the Mangda and the Mangkang section reflect the same transition trend from that both the Mangda and the Mangkang section reﬂect the same transition trend from low low weathering to medium weathering, and the projected value is consistent with the cal- weathering to medium weathering, and the projected value is consistent with the calculated culated results. The weathering trend line slightly shifted to the right relative to the A-C- results. The weathering trend line slightly shifted to the right relative to the A-C-N edge, N edge, indicating that late weathering may have yielded in a small amount of elemental indicating that late weathering may have yielded in a small amount of elemental K. K.

FigureFigure 7. 7. A-CN-K diagram of of the the sandstones sandstones in in Qamdo Qamdo dist districtrict (after (after McLennan McLennan et al. et [60] al. [and60] andFedo et al.; [59]). Fedo et al.; [59]).

TheThe detrital detrital composition composition of sedimentaryof sedimentary strata strata changes changes because because of redeposition; of redeposition; therefore,therefore, it is necessary it is necessary to distinguish to distinguish samples samples for redeposition, for redeposition, i.e., by i.e., using by using the composition the compo- variationsition variation index, whichindex, iswhich expressed is expressed in Equation in Equation (2): (2):

ICV = [n(Fe2O3) + n(K2O*) + n(Na2O) + n(CaO*) + n(MgO) + n(MnO) + n(TiO2)] / n(Al2O3) (2) ICV = [n(Fe2O3) + n(K2O*) + n(Na2O) + n(CaO*) + n(MgO) + n(MnO) + n(TiO2)]/n(Al2O3) (2) where, n(CaO*) refers to n(CaO) in silicate, and n(K2O*) represents the corrected n(K2O), where,i.e., the n(CaO*) initial n(K refers2O) to[59]. n(CaO) in silicate, and n(K2O*) represents the corrected n(K2O), i.e., theICV initial > 1 indicates n(K2O) [59 that]. the rock contains little clay minerals, which represents the first depositionICV > 1in indicates a tectonically that theactive rock zone. contains ICV < little1 indicates clay minerals, that many which clay minerals represents exist the in ﬁrstthe depositionsediments, inwhich a tectonically may represent active zone.the first ICV deposition < 1 indicates under that the many conditions clay minerals of re- exist in the sediments, which may represent the ﬁrst deposition under the conditions of re-deposition or enhanced weathering [60]. The ICV value of the Jingxing Formation sample in the Mangda section ranged from 0.6 to 1.2, with an average of 0.96 (Table S1).

The ICV value of the Jingxing Formation in the Mangkang section ranged from 0.68 to 1.45, with an average of 1.2. This indicates that the Jingxing Formation in Qamdo Basin belongs to the ﬁrst deposition type under the background of tectonic activity. In the process of weathering, transporting, and sedimentation of rock, specific trace elements are not easily dissolved; therefore, they show the characteristics of parent rocks [61]. Cullers (1994) inferred that Cr/Th ratios of 2.5 to 17.5 are typical for felsic rocks [62]. The samples from the Jingxing Formation have Cr/Th ratios between 4.55 and 6.41, indicating a felsic source. The Th/Sc ratio is a good indicator of igneous chemical differentiation, and thus, a plot of Th/Sc versus Zr/Sc can reflect the degree of sedimentary sorting and recycling [58]. In Figure8A, a portion of the analyzed samples evolved along the compositional variation Minerals 2021, 11, x 11 of 21

deposition or enhanced weathering [60]. The ICV value of the Jingxing Formation sample in the Mangda section ranged from 0.6 to 1.2, with an average of 0.96 (Table S1). The ICV value of the Jingxing Formation in the Mangkang section ranged from 0.68 to 1.45, with an average of 1.2. This indicates that the Jingxing Formation in Qamdo Basin belongs to the first deposition type under the background of tectonic activity. In the process of weathering, transporting, and sedimentation of rock, specific trace elements are not easily dissolved; therefore, they show the characteristics of parent rocks [61]. Cullers (1994) inferred that Cr/Th ratios of 2.5 to 17.5 are typical for felsic rocks [62]. The samples from the Jingxing Formation have Cr/Th ratios between 4.55 and 6.41, indi- Minerals 2021, 11, 745 cating a felsic source. The Th/Sc ratio is a good indicator of igneous chemical differentia-11 of 21 tion, and thus, a plot of Th/Sc versus Zr/Sc can reflect the degree of sedimentary sorting and recycling [58]. In Figure 8A, a portion of the analyzed samples evolved along the compositional variation trend, but most samples belong to sediment recycling. More felsic trend,rocks butusually most contain samples higher belong LREE/HREE to sediment ratios recycling. and negative More felsic Eu rocksanomalies usually [63]. contain In this higherstudy, LREE/HREELREE/HREE ratios andranged negative between Eu 7.23 anomalies and 11.01 [63]. and In thisEu/Eu* study, ratios LREE/HREE ranged be- ratiostween ranged 0.56 and between 0.76, indicating 7.23 and a 11.01 mostly and felsic Eu/Eu* composition ratios ranged of the betweensource area. 0.56 This and is 0.76, con- indicatingsistent with a mostly the diagram felsic composition of Eu/Eu* vs of theTh/Sc source (Figure area. 8B). This Successive is consistent cycles with of the weathering diagram ofand Eu/Eu* redeposition vs Th/Sc can (Figure increase8B). the Successive Th/U rati cyclesos of ofsedimentary weathering rock ands redepositionand are thus cangood increaseindicators the of Th/U weathering ratios of and sedimentary sedimentary rocks re andcycling are thus[58,64]. good The indicators Th/U ratios of weathering of samples andrange sedimentary from 3.6 to recycling 8.0, with [58 ratios,64]. Theof most Th/U samples ratios of ranging samples between range from 3.6 and 3.6 to6.3, 8.0, slightly with ratiosexceeding of most the samples average ranging value betweenof the UCC 3.6 andof 3.8 6.3, [65]. slightly From exceeding the diagram the average of Th/U–Th, value ofan the UCC of 3.8 [65]. From the diagram of Th/U-Th, an increasing weathering trend can be increasing weathering trend can be observed, representing a moderate degree of weath- observed, representing a moderate degree of weathering (Figure8C). ering (Figure 8C).

FigureFigure 8. 8.Discrimination Discrimination diagrams diagrams illustrating illustrating sedimentary sedimentary provenance. provenance. (A ()A Th/Sc) Th/Sc versus versus Zr/Sc Zr/Sc plot plot of samples (after McLennan et al., 1993 [58]). (B) Eu/Eu* versus Th/Sc of samples. (after McLennan of samples (after McLennan et al., 1993 [58]). (B) Eu/Eu* versus Th/Sc of samples. (after McLennan et al., 1990 [66]). (C) Th/U versus Th, showing samples derived from felsic sources (after McLennan et al., 1990 [66]). (C) Th/U versus Th, showing samples derived from felsic sources (after McLennan et al., 1993 [58]). et al., 1993 [58]). The sandstone of Jingxing Formation in Qamdo basin has sub-angular roundness and The sandstone of Jingxing Formation in Qamdo basin has sub-angular roundness and a high content of feldspar and lithic fragments. This indicates that the rock has a low com- a high content of feldspar and lithic fragments. This indicates that the rock has a low compositional maturity and moderate weathering characteristics, reflecting the characteristics positional maturity and moderate weathering characteristics, reﬂecting the characteristics of strata close to the source area. The SiO2/Al2O3 of the Jingxing Formation sandstones in of strata close to the source area. The SiO2/Al2O3 of the Jingxing Formation sandstones in QamdoQamdo area area ranges ranges from from 2.79 2.79 to 20.98, to 20.98, with an with average an average of 7.91, indicatingof 7.91, indicating that the sandstone that the underwent moderate weathering [47]. The characteristics of Petrography, major elements, CIA values, and ICV together indicate that the weathering degree of the Early Cretaceous Jingxing Formation was low and characterized by near-source deposition. In this study, the trace elements of Jingxing Formation reﬂect a moderate degree of weathering and sediment recycling. By comparing the strata of the Jingxing Formation in the Qamdo basin with those of the Mengye jing Formation and the Baishahe Formation in the Lanping Simao basin shows that the weathering degree of the strata of Jingxing Formation in Qamdo area is lower than that of Lanping Simao area. The Early Cretaceous strata of the two basins have similar sediment recycling. It is possible that the sediments of the Early Cretaceous strata in this area are closer to the area of origin and have been deposited after a short transport. Minerals 2021, 11, x 12 of 21

sandstone underwent moderate weathering [47]. The characteristics of Petrography, major elements, CIA values, and ICV together indicate that the weathering degree of the Early Cretaceous Jingxing Formation was low and characterized by near-source deposition. In this study, the trace elements of Jingxing Formation reflect a moderate degree of weathering and sediment recycling. By comparing the strata of the Jingxing Formation in the Qamdo basin with those of the Mengye jing Formation and the Baishahe Formation in the Lanping Simao basin shows that the weathering degree of the strata of Jingxing For- mation in Qamdo area is lower than that of Lanping Simao area. The Early Cretaceous Minerals 2021, 11, 745 strata of the two basins have similar sediment recycling. It is possible that the sediments12 of 21 of the Early Cretaceous strata in this area are closer to the area of origin and have been deposited after a short transport.

5.2.5.2. GeochemicalGeochemical ProvenanceProvenance SignaturesSignatures RoserRoser andand KorschKorsch studiedstudied thethe compositioncomposition ofof sandstonesandstone protolithsprotoliths basedbased onon whole-whole- rockrock geochemistry. geochemistry. They They established established the the discriminant discriminant function function of theof the composition composition of F1-F2of F1- T sedimentaryF2 sedimentary rocks rocks based based on the on principal the principal elements elements TiO2, Al TiO2O32, FeAl22OO33, ,Fe MgO,2O3T, CaO,MgO, Na CaO,2O, andNa2 KO,2 O[and67 K].2O In [67]. this paper,In this fourpaper, sedimentary four sedimentar stratigraphicy stratigraphic types, including types, including felsic igneus felsic provenance,igneus provenance, intermediate intermediate igneus igneus provenance, provenance, quartzose quartzose sedimentary sedimentary provenance, provenance, and magﬁcand magfic igneus igneus provenance, provenance, are distinguished are distinguished effectively. effectively. In Figure In9, mostFigure samples 9, most originate samples fromoriginate the Jingxing from the Formation Jingxing plotFormation in the quartzose plot in the sedimentary quartzose sedimentary provenance and provenance felsic igneus and provenance.felsic igneusThis provenance. is basically This consistent is basically with consistent the lithogeochemical with the lithogeochemical classiﬁcation diagram,classifica- indicatingtion diagram, that indicating the rocks ofthat the the Jingxing rocks of Formation the Jingxing originate Formation from originate feldspar sandstonefrom feldspar to lithicsandstone greywacke. to lithic This greywacke. further indicates This further that the indicates Jingxing that Formation the Jingxing sandstone Formation in Qamdo sand- basinstonebelongs in Qamdo to thebasin category belongs of to quartz-rich the category sandstone. of quartz-rich sandstone.

FigureFigure 9.9. MajorMajor elemental elemental composition composition discriminatory discriminatory plots plots for the for provenance the provenance of sandstones of sand- in Qamdo basin (F1 = −1.773TiO2 + 0.607Al2O3 + 0.76Fe2OT3−1.5MgO + 0.616CaO + stones in Qamdo basin (F1 = −1.773TiO2 + 0.607Al2O3 + 0.76Fe2OT3−1.5MgO + 0.616CaO + 0.509Na2O−1.224K2O−9.09; F2 = 0.445TiO2 + 0.07Al2O3−0.25Fe2OT3−1.142MgO + 0.438CaO + 0.509Na2O−1.224K2O−9.09; F2 = 0.445TiO2 + 0.07Al2O3−0.25Fe2OT3−1.142MgO + 0.438CaO + 1.475Na2O + 1.426K2O−6.861, after Roser et al., 1988 [67]). 1.475Na2O + 1.426K2O−6.861, after Roser et al., 1988 [67]).

TheThe chemicalchemical propertiesproperties ofof alkalinealkaline earthearth metalsmetals (such(such asas SrSr andand Ba)Ba)are are similar, similar, but but thethe enrichmentenrichment degree of of these these elements elements is isslightly slightly different different in environments in environments such such as con- as continentaltinental facies, facies, alternating alternating sea-land sea-land phase, phase, and andmarine marine facies facies [68,69]. [68 ,According69]. According to previ- to previousous studies studies on the on characteristics the characteristics of sediments of sediments from the from Pearl the PearlRiver RiverDelta region Delta region of China, of China,the contents the contents of Sr and of Sr Ba and in Basediments in sediments of continental of continental facies facies are areless less than than 60 μ 60g/gµg/g and and 300 300μg/g,µg/g, while while those those in marine in marine sediments sediments exceed exceed 160 160μg/gµg/g and and400 400μg/g,µg/g, respectively. respectively. The Thedifferences differences between between marine marine and and continental continental faci facieses sediments sediments are are large. large. The The content content of ofSr Srinin the the sandstones sandstones of of the the Jingxing Jingxing Formatio Formationn from the QamdoQamdo areaarea rangesranges from from 32.1 32.1µ g/gμg/g to 269 µg/g, with an average of about 122 µg/g, representing characteristics of marine and continental sedimentary facies. The Ba content of 127.0 µg/g to 421 µg/g, with an average of about 259.69 µg/g, shows the characteristics of continental sediments. Combined with the content distribution characteristics of Sr and Ba, the Jingxing Formation in the Qamdo area is characterized by typical marine-continental alternating sedimentary facies [70]. The geochemical characteristics of clastic sedimentary rocks are mainly determined by their composition, which is closely related to their origin and tectonic environment. The tectonic setting of diagenesis also partly controls the origin, and the chemical composition of sediment records the changes of tectonic activities over the process of sedimentation and diagenesis. Therefore, the composition of sedimentary rocks plays an important role in the tectonic setting of the area of origin. A speciﬁc relationship exists between the chemical Minerals 2021, 11, x 13 of 21

to 269 μg/g, with an average of about 122 μg/g, representing characteristics of marine and continental sedimentary facies. The Ba content of 127.0 μg/g to 421 μg/g, with an average of about 259.69 μg/g, shows the characteristics of continental sediments. Combined with the content distribution characteristics of Sr and Ba, the Jingxing Formation in the Qamdo area is characterized by typical marine-continental alternating sedimentary facies [70]. The geochemical characteristics of clastic sedimentary rocks are mainly determined Minerals 2021, 11, 745 13 of 21 by their composition, which is closely related to their origin and tectonic environment. The tectonic setting of diagenesis also partly controls the origin, and the chemical composition of sediment records the changes of tectonic activities over the process of sedimen- compositiontation and diagenesis. of sediments Therefore, and the the composition composition of of clastic sedimentary minerals, rocks and plays their characteristicsan important role in the tectonic setting of the area of origin. A specific relationship exists be- differ in response to different tectonic environments. Therefore, the properties and tectonic tween the chemical composition of sediments and the composition of clastic minerals, and background of the area of origin can be determined according to the composition variation their characteristics differ in response to different tectonic environments. Therefore, the characteristics.properties and tectonic Based onbackground data of sandstone of the area and of origin arenaceous can be determined rocks, a series according of geochemical to endmemberthe composition maps variation of major characteristics. elements are Based proposed on data to of identify sandstone the and tectonic arenaceous setting of the passiverocks, a continentalseries of geochemical margin, endmember the active continental maps of major margin, elements the are oceanic proposed island to iden- arc, and the continentaltify the tectonic island setting arc. of Mutual the passive correction continental among margin, these thedifferent active continental endmember margin, maps has beenthe oceanic adopted island by arc, most and scholars the continental [26]. Theisland present arc. Mutual study correction adopted among the diagram these dif- of SiO2- Kferent2O/Na endmember2O[71] and maps (SiO has2 / been 20)—(K adopted2O + by Na most2O)—(TiO scholars2 + [26]. FeO The + MgO) present [72 study] to conduct dropadopted point the analysis diagram on of allSiO sandstone2-K2O/Na2O samples [71] and in (SiO the2 study/ 20)—(K area,2O + as Na shown2O)—(TiO in Figure2 + FeO 10 . Both Cretaceous+ MgO) [72] Jingxing to conduct Formation drop point samples analysis fall on all into sandstone the range samples of active in the continental study area, margin as and passiveshown in continental Figure 10. margin.Both Cretaceous Jingxing Formation samples fall into the range of active continental margin and passive continental margin.

FigureFigure 10. TectonicTectonic setting setting discrimination discrimination diagrams diagrams based on based the major on the elements major for elements Jingxing forFor- Jingxing mation sandstones of Qamdo district (A after Bhatia and Crook [71], and B after Kroonenberg [72]). FormationAbbreviations: sandstones OIA, ocean of Qamdo island arc; district CIA, (continA afterental Bhatia island and arc; Crook ACM, [71 active], and continentalB after Kroonenberg margin; [72]). Abbreviations:PM, passive margin. OIA, ocean island arc; CIA, continental island arc; ACM, active continental margin; PM, passive margin. The basic assumption of the geochemical discrimination of sedimentary rocks is that a closeThe relationship basic assumption exists between of the the geochemical plate tectonic discriminationenvironment and ofthe sedimentary origin of sedi- rocks is thatmentary a close rocks. relationship However, one exists of the between major unce the platertainties tectonic is that particular environment sediments and the may origin of sedimentarymigrate from rocks.the tectonic However, setting one of their of the origin major to uncertaintiesthe sedimentary is thatbasin particular of a different sediments maytectonic migrate setting. from In contrast the tectonic to major setting element of their analysis, origin the to contents the sedimentary of stable trace basin elements of a different tectonicand REE setting. are mainly In contrast controlled to by major the rock element composition analysis, of the their contents origin, reflecting of stable the trace ele- elements mental spherochemistry of their area of origin [73]. According to the discriminant diagram and REE are mainly controlled by the rock composition of their origin, reflecting the of the trace element tectonic background as proposed by Bhatia et al. (1986) [27], clastic elemental spherochemistry of their area of origin [73]. According to the discriminant rock deposits in the study area were analyzed. diagramFigure of the11 shows trace that element the stratigraphic tectonic background tectonic setting as proposed of the Cretaceous by Bhatia Jingxing et al. For- (1986) [27], clasticmation rock in Qamdo deposits basin in is the a relatively study area stable were active analyzed. continental margin and passive conti- nentalFigure margin, 11 withshows characteristics that the stratigraphic of a continental tectonic island arc. setting The Cr/Ni of the ratio Cretaceous ranges from Jingxing Formation1.0 to 2.5, indicating in Qamdo a very basin low is content a relatively of mafic stable or ultramafic active continental rocks in the marginsource region and passive continental margin, with characteristics of a continental island arc. The Cr/Ni ratio ranges from 1.0 to 2.5, indicating a very low content of mafic or ultramafic rocks in the source region [74]. At the crustal scale, most trace elements of Zr occur in zircon grains, and most

HREE and trace elements are affected by zircon grains. The Zr/Hf ratios of zircon grains range from 30 to 40 [75], and the Zr/Hf value of the JingXing Formation sandstones ranges from 30.17 to 34.73. These results indicate that the Zr and Hf contents are controlled by detrital zircon grains. The Nb/Ta ratio of the upper crust is about 12 [76], and the Nb/Ta ratio of the Jingxing Formation sandstone ranges from 10.28 to 12.03, with an average of 11.07. These geochemical characteristics indicate that both Nb and Ta elements in the sandstone may mainly originate from upper crustal rock units. The Sr/Ba ratio reﬂects the palaeosalinity characteristics of the sedimentary environment. It is generally assumed that the Sr/Ba ratio of marine sediments with high salinity exceeds 1.0, while the Sr/Ba ratio of freshwater sediments is generally lower than 1.0 [70]. The Sr/Ba ratio of sandstone samples from the Jingxing Formation is less than 1.0, except for MK15 (1.79), which indicates that Minerals 2021, 11, x 14 of 21

[74]. At the crustal scale, most trace elements of Zr occur in zircon grains, and most HREE and trace elements are affected by zircon grains. The Zr/Hf ratios of zircon grains range from 30 to 40 [75], and the Zr/Hf value of the JingXing Formation sandstones ranges from 30.17 to 34.73. These results indicate that the Zr and Hf contents are controlled by detrital zircon grains. The Nb/Ta ratio of the upper crust is about 12 [76], and the Nb/Ta ratio of the Jingxing Formation sandstone ranges from 10.28 to 12.03, with an average of 11.07. These geochemical characteristics indicate that both Nb and Ta elements in the sandstone may mainly originate from upper crustal rock units. The Sr/Ba ratio reflects the palaeosa- Minerals 2021, 11, 745 linity characteristics of the sedimentary environment. It is generally assumed that14 of the 21 Sr/Ba ratio of marine sediments with high salinity exceeds 1.0, while the Sr/Ba ratio of freshwater sediments is generally lower than 1.0 [70]. The Sr/Ba ratio of sandstone samples from the Jingxing Formation is less than 1.0, except for MK15 (1.79), which indicates that thethe sedimentary sedimentary environment environment of of Jingxing Jingxing Formation Formation is is continental. continental. Regional Regional lithofacies lithofacies paleogeographicpaleogeographic studies studies also also showed showed that that the the Tethys Tethys Ocean Ocean on on the the western western side side of of Qamdo Qamdo basinbasin gradually gradually closed closed from from the the Middle Middle and and Late Late Jurassic Jurassic to the to endthe ofend the of Early the Early Cretaceous. Creta- Afterwards,ceous. Afterwards, the Qamdo the Qamdo area, as area, a marginal as a marginal sea of the sea continental of the continental margin, endedmargin, marine ended sedimentationmarine sedimentation and formed and continental formed continental lacustrine lacustrine basin deposits basin [77 deposi]. Duringts [77]. the During evolution the ofevolution the Tethys of the Ocean, Tethys Qamdo Ocean, belonged Qamdo tobelonged a landmass to a landmass in a multi-island in a multi-island arc system arc [ 52sys-]. Previoustem [52]. studies Previous showed studies that showed the samples that the of samples Pashahe of Formation Pashahe andFormation Mangang and Formation Mangang ofFormation Early Cretaceous of Early strataCretaceous in the strata Lanping-Simao in the Lanping-Simao area, as well area, as the as provenance well as the provenance of Mengye jingof Mengye Formation jing of Formation Late Cretaceous of Late strata, Cretaceous mainly strata, originate mainly from originate passive continentalfrom passive margin conti- environment.nental margin A environment. small amount A originates small amount from originates an active continentalfrom an active margin continental environment. margin Few samples showed that the origin in this area had the nature of a continental island environment. Few samples showed that the origin in this area had the nature of a conti- arc [17,32], which was basically similar to the results of the present study. This indicates nental island arc [17,32], which was basically similar to the results of the present study. that the tectonic background of the Cretaceous strata in Qamdo area and Lanping Simao This indicates that the tectonic background of the Cretaceous strata in Qamdo area and Cretaceous strata were basically identical. Lanping Simao Cretaceous strata were basically identical.

FigureFigure 11. 11.Tectonic Tectonic setting setting discrimination discrimination diagrams diagrams based base ond the on trace the elementstrace elements of Jingxing of Jingxing Formation For- sandstonesmation sandstones from the from Qamdo the district.Qamdo Abbreviations:district. Abbrevia OIA,tions: ocean OIA, island ocean arc; island CIA, arc; continental CIA, continental island island arc; ACM, active continental margin; PM, passive margin (after Bhatia et al.; 1986 [27]). arc; ACM, active continental margin; PM, passive margin (after Bhatia et al.; 1986 [27]).

5.3.5.3. DetritalDetrital ZirconZircon Provenance Provenance TheThe LA-ICP-MS LA-ICP-MS concordant concordant ages ages of detritalof detrital zircon zircon grains grains from thefrom Jingxing the Jingxing Formation For- sandstonemation sandstone samples insamples Qamdo in area Qamdo mainly area range main fromly range 198 Ma from to 608 198 Ma, Ma 721 to 608 Ma toMa, 1006 721 Ma, Ma andto 1006 1694 Ma, Ma and to 2082 1694 Ma. Ma The to 2082 zircon Ma. ages The mainly zircon show ages twomainly peaks show at 450 two Ma peaks and at 1870 450 Ma. Ma Inand Lanping-Simao 1870 Ma. In Lanping-Simao basin, the youngest basin, cluster the youngest of ages cluster in Mengye of ages jing in Formation Mengye jing ranges For- frommation 215 ranges Ma to from 218 Ma,215 Ma shows to 218 a peakMa, shows of Late a Ordovicianpeak of Late agesOrdovician (at 449 ages Ma), (at with 449 ages Ma), rangingwith ages from ranging 414 Ma from to 472414 Ma [to17 472], and Ma is [17], similar and tois similar the peak to agethe ofpeak 450 age Ma of in 450 Qamdo Ma in basin.Qamdo The basin. latest The age latest of detrital age of zircondetrital grains zircon in grains sedimentary in sedimentary rocks indicates rocks indicates the lower the limitlower of limit their of formation their formation [78]. The [78]. minimum The minimum age of detrital age of zircon detrital grains zircon in thegrains Jingxing in the formationJingxing formation in the Qamdo in the area Qamdo is 195.4 area Ma, is which 195.4 representsMa, which therepresents lower limit the oflower its deposition. limit of its Thedeposition. deposition The of deposition the Jingxing of Formation the Jingxing in theFormation Qamdo in area the should Qamdo be area later should than the be early later Jurassic. According to the study of detrital zircon grains in the Mengye jing Formation, the provenance of the detrital zircon grains is mainly Qiangtang block, Ailaoshan tectonic belt, and Yangtze plate. In this study, the age range of 198–608 Ma is very consistent with the

age distribution characteristics of the southern Qiangtang Block, Songpan-Ganzi Block, Ailaoshan Tectonic Belt, Youjiang basin, and Lanping Simao basin. The age range from 721 Ma to 1006 Ma is consistent with the origin ages of the Southern Qiangtang Block, the Yangtze Block, and the Lanping Simao basin. The age range of 1694–2082 Ma is consistent with the age distribution characteristics of the Southern Qiangtang Block, Songpan-Ganzi Block, and Lanping Simao basin (Figure 12). Based on the age distribution characteristics of the three groups, the main detrital origin of the Jingxing Formation in the Qamdo area is concentrated in the Early Cambrian to Early Jurassic, and shares the age characteristics of the Neoproterozoic. The age distribution shows that the provenance area of the Jingxing Minerals 2021, 11, x 15 of 21

than the early Jurassic. According to the study of detrital zircon grains in the Mengye jing Formation, the provenance of the detrital zircon grains is mainly Qiangtang block, Ai- laoshan tectonic belt, and Yangtze plate. In this study, the age range of 198–608 Ma is very consistent with the age distribution characteristics of the southern Qiangtang Block, Songpan-Ganzi Block, Ailaoshan Tectonic Belt, Youjiang basin, and Lanping Simao basin. The age range from 721 Ma to 1006 Ma is consistent with the origin ages of the Southern Qiangtang Block, the Yangtze Block, and the Lanping Simao basin. The age range of 1694– 2082 Ma is consistent with the age distribution characteristics of the Southern Qiangtang Block, Songpan-Ganzi Block, and Lanping Simao basin (Figure 12). Based on the age dis- Minerals 2021, 11, 745 tribution characteristics of the three groups, the main detrital origin of the Jingxing15 of For- 21 mation in the Qamdo area is concentrated in the Early Cambrian to Early Jurassic, and shares the age characteristics of the Neoproterozoic. The age distribution shows that the provenance area of the Jingxing Formation is mainly north Qiangtang Block, Qiangtang FormationBlock, Songpan-Ganzi is mainly north Block, Qiangtang and Youjiang Block, Qiangtangbasin. The Block,clastic Songpan-Ganziages of the Qamdo-Lanping- Block, and Youjiangsimao basin basin. are The highly clastic consistent, ages of the indicating Qamdo-Lanpingsimao that the Cretaceous basin strata are highly of the consistent, two basins indicatinghave the thatsame the provenance. Cretaceous strata of the two basins have the same provenance.

FigureFigure 12. 12.Probability Probability density density plots plots and and histograms histograms of of LA-ICP-MS LA-ICP-MS detrital detrital zircon zircon U-Pb U–Pb ages ages of of the the Qamdo samples compared with those from Qiangtang (after Gehrels et al., 2011 [79]), Lhasa (after Qamdo samples compared with those from Qiangtang (after Gehrels et al., 2011 [79]), Lhasa (after Leier et al., 2007 [80]), Songpan-Ganzi (after Weislogel et al., 2010 [81]), Yangtze (after Zhao et al., 2010 [82]), Ailaoshan (after Lai, 2012 [83]), Youjiang basin (after Yang et al., 2012 [84]), Simao basin (after Wang et al., 2014 [17]), and Pashahe and Myejing Formations (after Li et al., 2015 [18]).

Previous studies showed that the basement of the Himalayan Block and Lhasa Block south of the Bangonglake-Nujiang Suture Zone is a pan-African basement. Pan-African tectono-magmatic heat events of the pre-Ordovician metamorphic basement are widely developed [85,86]. In recent years, Pan-African age records have been successively found in the metamorphic basement of the northern Qiangtang Block. The Pan-African orogeny occurred between 600 Ma and 500 Ma, and the age obtained from the Jitang metamorphic complex (520–570 Ma) is similar to that of the Pan-African orogeny [87,88]. The peak age of 450 Ma is close to that of the end of the Pan-African movement, indicating that the Minerals 2021, 11, 745 16 of 21

sediments of the Jingxing Formation in the Qamdo area may have originated from an orogenic source area that experienced Pan-African movement. The basement of the Qamdo basin consists of Jitang metamorphic rocks. Its formation age is generally considered to be ancient (i.e., either Mesoproterozoic or Precambrian). The composition and geochemical characteristics of the original rocks identiﬁed them as island arc volcanic rocks and pyroclastic rocks of 1700–1900 Ma, which are the volcanic products of the active continental margin west of the Yangtze continent. The Ningduo Group is distributed in the eastern part of the Qamdo-Simao Block and consists of a set of metamorphic gneiss, granulite, schist, and marble with medium depth. In the Ningduo black cloud plagenous gneiss U-Pb age curve, the upper intersection point is 1870 ± 280 Ma, and the lower intersection point is 490 ± 130 Ma. Sm-Nd isochron ages of 1593.975 ± 240.5 Ma have been obtained from the plagioclase gneiss of pomegranate musca [89]. In the present study, the peak age of this detrital zircon at 1870 Ma suggests that the metamorphic rock series of Jitang Group and Ningduo Group in the basement of the Qamdo Block provide abundant origin for the strata of the Jingxing Formation in the Qamdo Basin.

6. Implications for Late Cretaceous Potassium Mode in the Eastern Tethys The East Tethys lithofacies paleogeography shows that in the Late Triassic, the Nu- jiang Tethys oceanic crust subducted under the southern Qiangtang-Zuogong Block. The collision of the Dege Block with the Qamdo Block resulted in the uplift of the western margin of the southern Qiangtang-Zuogong Block and the eastern margin of the Qamdo- Simao Block, leading to the formation of the Qamdo-Mangkang basin. At this time, the basin developed fluvial-lacustrine facies, coastal facies, shallow marine facies, and sea– land intersedimentation [16]. In the Middle Jurassic, the Nujiang Tethys Ocean gradually closed from east to west. Furthermore, the Qamdo-Lanping-Simao land block closed and became a unified and large basin, with local residual sea areas of the Neo-Tethys Ocean and intercontinental marine deposits with continental crust as seafloor [16]. In the late Cretaceous period, the Qamdo-Simao-Khorat land distribution is nearly east–west oriented (paleomagnetic), and Qiangtang basin and Qamdo area are widely distributed shallow sea and coastal depositions [90]. Jurassic and Cretaceous gypsum deposits in Qamdo basin and magnesite deposits in the Middle Jurassic Yanshiping are typical representatives of this formation. According to the field geological characteristics, magnesite has typical sedimentary genetic characteristics in Baxia, Qamdo basin. When normal seawater evaporates to the end of the salt stage, magnesite can be precip- itated when the Mg/Ca ratio reaches suitable conditions and with the doping of terrestrial water containing Ca and HCO3− [18]. Analysis of the experimental model showed that the eastern Qiangtang area generally lacks salt mineral deposits, while the Lanping Simao area lacks the corresponding sulfate and magnesium-bearing carbonate (magnesite) precipita- tions, while it contains many potassium salt deposits. The sulfur isotopic composition of gypsum of the Yunlong Formation in the Lanping basin also indicates that it is of marine origin [19]. The Br geochemistry of potash evaporite rocks of the Mengye jing Formation in the Simao basin and the sulfur isotopic characteristics of anhydrite also indicates marine origin [18]. The sulfur and strontium isotopic values of gypsum in the Qamdo Basin also point toward marine origin [18]. In this study, the age distribution of detrital zircon grains in the Jingxing Formation indicates that the Qiangtang Block, the Ailaoshan Tectonic Belt, and the Yangtze area constitute the origin of the Qamdo-Lanping-Simao basin. The minimum age of detrital zircon grains from the Jingxing Formation in the Qamdo Basin is 195.4 Ma, and the minimum age of detrital zircon grains from the Baishahe Formation (K1P) in the Lanping-Simao basin is 210 Ma [18]. The above-mentioned studies further suggest that the two basins began to receive unified deposits after the Early Jurassic at the latest [78]. In this paper, petrographic and geochemical studies showed that Qamdo Basin is closer to the source area than the Lanping Simao basin. In the Late Cretaceous, the Qamdo basin was deposited in the Lanping Simao basin with a large number of potash deposits, which had a distinct characteristic of a preparatory basin. Minerals 2021, 11, x 17 of 21

Formation in the Simao basin and the sulfur isotopic characteristics of anhydrite also indicates marine origin [18]. The sulfur and strontium isotopic values of gypsum in the Qamdo Basin also point toward marine origin [18]. In this study, the age distribution of detrital zircon grains in the Jingxing Formation indicates that the Qiangtang Block, the Ailaoshan Tectonic Belt, and the Yangtze area constitute the origin of the Qamdo- Lanping-Simao basin. The minimum age of detrital zircon grains from the Jingxing For- Minerals 2021, 11, 745 mation in the Qamdo Basin is 195.4 Ma, and the minimum age of detrital zircon17 ofgrains 21 from the Baishahe Formation (K1P) in the Lanping-Simao basin is 210 Ma [18]. The above- mentioned studies further suggest that the two basins began to receive unified deposits after the Early Jurassic at the latest [78]. In this paper, petrographic and geochemical studies showed that Qamdo Basin is closer to the source area than the Lanping Simao basin. In conclusion, theIn the Qamdo-Lanping Late Cretaceous, the SimaoQamdo basin basin was has deposited a similar in the and Lanping unified Simao tectonic basin with evolution backgrounda large with number regard of to potash its regional deposits, evolution which had history.a distinct Incharacteristic terms of geochemicalof a preparatory characteristics of sedimentarybasin. strata and origin characteristics of detrital zircon grains, In conclusion, the Qamdo-Lanping Simao basin has a similar and unified tectonic many similarities existevolution between background both sources. with regard The to its Early regional Cretaceous evolution history. strata In of terms the of Qamdo- geochem- Lanping-Simao basinical began characteristics to receive of sedimentary a unified originstrata and deposit origin characteristics at the latest of after detrital the zircon Middle grains, Jurassic. Both basinsmany may similarities have been exist marine between submersion both sources. The basins Early withCretaceous a unified strata of hydraulic the Qamdo- connection before evaporiteLanping-Simao deposition. basin began Nujiang to receive Tethysa unified ended origin deposit its evolution at the latest in after the the Late Mid- dle Jurassic. Both basins may have been marine submersion basins with a unified hydrau- Cretaceous, and thelic Nujiang connection area before continued evaporite deposition. its collision Nujiang orogeny; Tethys ended therefore, its evolution the in meta- the Late morphic seawater remainingCretaceous, and in Qamdo the Nujiang basin area maycontinued have its migratedcollision orogeny; from therefore, Qamdo the basin metamor- to Lanping-Simao basinphic and seawater even to remaining Khorat basinin Qamdo under basin the may influence have migrated of orogeny. from Qamdo Thus, basin large to amounts of evaporiteLanping-Simao and potassium basin saltsand even were to depositedKhorat basin in under these the areas influence (Figure of orogeny. 13). Thus, large amounts of evaporite and potassium salts were deposited in these areas (Figure 13).

Figure 13. Metallogenic model of Cretaceous evaporation deposit in Lanping-Simao-Korat basin (modified after Li, 2015 Figure[18]). 13. Metallogenic model of Cretaceous evaporation deposit in Lanping-Simao-Korat basin (modiﬁed after Li, 2015 [18]). 7. Conclusions 7. Conclusions The petrography shows that the weathering degree of the sandstone in Jingxing For- The petrographymation shows is low. that The thegeochemistry weathering of sandston degreees also of indicates the sandstone moderate inweathering Jingxing conditions and a predominantly felsic source with minor recycled sediments. In combination, Formation is low. Thethe main geochemistry trace whole rock of sandstones geochemistry alsoand weathering indicates indexes moderate indicate weathering that the Early conditions and a predominantlyCretaceous Jingxing felsic Formation source in with the Qamdo minor basin recycled have a lower sediments. weathering In degree combi- than nation, the main tracethose whole in the rock Lanping geochemistry Simao district; and moreover weathering, the Qamdo indexes basin indicateis closer to that the source the Early Cretaceous Jingxingerosion Formationarea. in the Qamdo basin have a lower weathering degree The stratigraphic tectonic setting of the Early Cretaceous Jingxing Formation in the than those in the LanpingQamdo Simao basin is district; mainly composed moreover, of a the relatively Qamdo stable basin active is closercontinental to the margin source and a erosion area. The stratigraphic tectonic setting of the Early Cretaceous Jingxing Formation in the Qamdo basin is mainly composed of a relatively stable active continental margin and a passive continental margin, with continental island arc characteristics. Trace element data indicate that the sedimentary environment of the Jingxing Formation is continental. The Early Cretaceous Jingxing Formation in the Qamdo district and the Cretaceous strata in the Lanping Simao district share the same tectonic setting. The main age peaks of detrital zircon grains from the Jingxing Formation in the Qamdo area are 198–608 Ma, 721–1006 Ma, and 1694–2082 Ma. The minimum age is 195.4 Ma, which represents the lower limit of the deposition, and the deposition of the Jingxing formation most likely happened after the Early Jurassic. The age distribution characteristics of detrital zircon grains indicate that the origin of the Early Cretaceous strata in both Qamdo and Lanping Simao basin is related, and the main areas of origin are Qiangtang Block, Songpan-Ganzi Block, and Youjiang basin. Combined with the regional evolutionary background and analysis of the detrital zircon age, the Early Cretaceous strata in the Qamdo-Lanping-Simao basin began to receive the same deposits at the latest after the Early Jurassic. Both basins may have been marine submersion basins with the same water resource connection before evaporite deposition. Under the inﬂuence of tectonic movement, the residual metamorphic seawater in Qamdo basin may have migrated from Qamdo basin Minerals 2021, 11, 745 18 of 21

to Lanping-Simao basin and even to Khorat basin, where it may have deposited a large volume of evaporite and potassium salt.

Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/min11070745/s1, Table S1: Whole-rock geochemical compositions of Jingxing Formation sandstones from Qamdo, Table S2. LA-ICP-MS zircon U-Pb age data results of sandstones from Jingxing Formation in Qamdo Basin. References [91,92] are cited in Supplementary Materials. Author Contributions: Conceptualization, W.H. and H.M.; methodology, W.H.; software, W.H.; validation, H.M and H.C.; formal analysis, W.H.; investigation, W.H., H.M., H.C., B.L., Y.L., W.M., and Q.H; resources, H.M.; data curation, H.M.; writing—original draft preparation, W.H.; writing— review and editing, H.M., W.F., H.C., B.L., Y.L., W.M., and Q.H.; visualization, W.H. and H.M.; supervision, H.M.; project administration, H.M.; funding acquisition, H.M. All authors have read and agreed to the published version of the manuscript. Funding: This work was funded by the National Key Basic Research Project of China (973 program, No. 2011CB403004). Data Availability Statement: Not applicable. Acknowledgments: We are very grateful to the lab staff of the Beijing Research Institute of Ura- nium Geology, Beijing, China, and the State Key Laboratory of Continental Dynamics, Northwest University, Xian, China. Valuable comments and suggestions of three anonymous reviewers are ac- knowledged. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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