Detrital Zircon Trace Elements from the Mesozoic Jiyuan Basin, Central
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Open Geosci. 2019; 11:125–139 Research Article Min Wang, Wenfei Guo, and Wentao Yang* Detrital zircon trace elements from the Mesozoic Jiyuan Basin, central China and its implication on tectonic transition of the Qinling Orogenic Belt https://doi.org/10.1515/geo-2019-0011 trace element distribution in zircons, it can also be an in- Received Apr 26, 2018; accepted Nov 17, 2018 dispensable tool that should be developed for application in discriminating the host rock types [5–9], magmatic evo- Abstract: The Qinling Orogen and the Jiyuan Basin consti- lution and metamorphism [10, 11], crustal evolution [12], tute a basin-mountain system during the Early Mesozoic. reconstructing mountain-basin interaction [14, 15]. Therefore, sediments from the Jiyuan Basin can be used to Many investigations, concerning detrital zircon deduce the orogenic process of the Qinling Orogen. This chronology, have been successfully performed in the sur- paper attempts to use detrital zircon trace elements with rounding basins of the Qinling Orogen [4, 16–25]. The ages ranging from the Late Carboniferous to the Middle Qinling Orogen emerged as the closure of the Mianlve Triassic that were obtained from the Jiyuan Basin to dis- Ocean, which resulted in the final amalgamation of the cuss the tectonic evolution of Qinling Orogen. On the tec- South China Block and the North China Block [26, 27]. But tonic setting discriminating diagrams, most grains are con- the Mianlve suture is now largely buried by later long- centrated in convergent continental margins/orogenic set- distance overthrusting [28, 29]. Therefore, to investigate tings, whereas the remaining samples (268 Ma, 265Ma, 264 the tectonic evolution of the Mianlve Ocean seems difficult. Ma and 254Ma) are plotted in anorogenic field. Compared However, the Late Paleozoic detrital zircons largely perse- to the Early Paleozoic (400-500Ma) zircons, 306Ma and vered in the surrounding basins of the Qinling Orogen are 281Ma grains represent higher Th/Nb ratios, which might suggested to be related to the Mianlve suture zone [18]. be related to the Mianlve oceanic crust subduction. The These zircons can be a good object to collect some impor- lower Th/Nb ratios containing 268 Ma, 265Ma, 264 Ma and tant information about the development of the Mianlve 254Ma grains might indicate lithospheric extension subse- Ocean. In addition, provenance analysis of the Late Paleo- quently. The final continent-continent collision between zoic sediments on the southern North China Block reveals South China and North China blocks took place after the that the tectonic uplift of the Qinling Orogen retreated Middle Triassic (242Ma). during the Permian [20, 30–33]. However, there is a lack Keywords: Zircon, Basin-mountain interaction, of data describing the Permian tectonic transition of the Subduction-collision transition, Mianlve Ocean Qinling Orogen. There are some important achievements regarding in- teractions between Jiyuan Basin and Qinling Orogen dur- 1 Introduction ing Middle Triassic to Middle Jurassic. These works mainly focus on the filling feature of sediments [34, 35], geochem- istry of mudstones [36, 37], detrital zircon geochronology Zircon has strong resistance to weathering and/or alter- and Hf isotopes [24, 33, 38], and suggest that the Late ation during sedimentation, magmatism, and metamor- Triassic was the critical period to the formation of the phism. Therefore, zircon U-Pb ages, along with Hf and O Jiyuan Basin controlled by the Qinling orogenesis. This isotopes, are widely used in earth science researches [1– paper focuses on the detrital zircons from the Middle 4]. The trace element composition of magmatic zircon is Triassic-Middle Jurassic Jiyuan Basin and integrated zir- strongly controlled by the composition of parental melts [5, con geochronology with geochemistry, to unravel the evo- 6]. Although some challenges exist like the complicated lutional process of the Mianlve Ocean during the Late Pa- leozoic to the Middle Triassic. *Corresponding Author: Wentao Yang: Henan Polytechnic Univer- sity, China; Email: [email protected] Min Wang, Wenfei Guo: Henan Polytechnic University, China Open Access. © 2019 W. Yang and M. Wang, published by De Gruyter. This work is licensed under the Creative Commons Attribu- tion 4.0 License 126 Ë W. Yang and M. Wang Figure 1: (a) the location of the Qinling Orogen and the Jiyuan Basin in China. (b) schematic tectonic map of the Qinling Orogen and the surrounding basins. (c) geological sketch map of the Jiyuan Basin defined by the Mesozoic strata, and showing the sampled location. 2 Geological setting to Early Triassic indicate the subduction of the Mianlve Ocean along the southern margin of the South Qinling Belt [45, 46]. The Mianlve Ocean closed at the Late Triassic, The Qinling Orogen is expressed as the South China, Qin- which resulted in the Triassic orogeny between the South ling, and North China blocks converged along the Shang- China Block and the North China Block [47]. The syncol- dan and Mianlve suture zones [26, 27]. These two sutures, lisional granites with the ages of 220-210 Ma are largely integrated with the Luanchuan fault, separate the Qinling distributed in the South Qinling Belt [48], and the post- Orogen into the North Qinling and the South Qinling belts collision process occurred subsequently during ca. 210- (Figure 1-a, b). 200 Ma. The Shangdan Ocean is considered to be formed at The Jiyuan Basin is located to the north of Qinling Oro- least before the Cambrian [26]. The northward subduction gen, and adjacent to the Taihang Mountains (Figure 1-b, c). of the Shangdan Ocean plate didn’t happen until the early During the Early to Middle Triassic, the Jiyuan Basin was time of Cambrian [39–41]. A large number of subduction- an intracratonic terrestrial depression in the south mar- related intrusions, mainly concentrated at 514-420 Ma, are gin of the North China Block and developed a suit of red found in the North Qinling Belt [27, 42]. The closure of beds with stable distribution [35, 49, 50]. The Liujiagou the Shangdan Ocean, constrained by the detrital zircons Formation in the low part of the Early Triassic strata mainly from the Liuling Group [43], is considered to have occurred represents several layers of light red conglomerates inter- in the Early Devonian. Thereafter the North Qinling Belt calated in purple red thick-bed middle-fine grained sand- was exhumed and denudated [44], however the deposi- stones and thin-bed mudstones. The Heshanggou Forma- tion continued on the South Qinling Belt. A continent- tion in the upper part of the Lower Triassic strata is com- continent subduction model, expressed as the subduction posed of bright red siltstones and mudstones with inciden- of the South Qinling Belt underneath the North Qinling tal fine grain conglomerates. The Middle Triassic strata can Belt, is proposed to visualize the tectonic evolution along be divided into two formations by the occurrence of green the Shangdan suture during the Late Paleozoic [26, 27]. mudstones. The lower part named Ermaying Formation is The Mianlve Ocean might be formed at the Devonian characterized by grayish yellow sandstones interbedded and constrained from expanding before the Carbonifer- with purple red siltstones and mudstones, whereas the up- ous [27, 40]. The island-arc volcanics from the Permian Zircon trace elements indicate orogenic evolution Ë 127 Figure 2: Measured section from the Middle Triassic to Middle Jurassic Youfangzhuang, Chunshuyao, Tanzhuang, Anyao, Yangshuzhuang and Maao formations. per part named Youfangzhuang Formation contains yel- and petrographic features, which indicated the tectonic at- low green fine grained sandstones interbedded with pur- tribute of Jiyuan Basin alternated from a part of intracra- ple red and green siltstones, muddy sandstones and sandy ton to a foreland basin [34, 35, 51]. The lithofacies evolved mudstones. As the South China Block collided with the into thick conglomerates and coal beds in the southern North China Block in the Late Triassic, the eastern part part of the Basin and lacustrine turbidites in the north- of North China Block was extensively uplifted, whereas ern part of the Basin were controlled by the intense thrust- the western part underwent tectonic subsidence [34, 35, ing of Qinling Orogen during the Early Jurassic [52, 53]. 51]. Continuous deposition occurred in the Jiyuan Basin This unit named the Anyao Formation mainly consists of forming the Chunshuyao and Tanzhuang formations in as- gray yellow thick layered fine-grained sandstones, gray cending order. Both of the formations represent gray yel- green mudstones, muddy sandstones and siltstones. The low fine-grained sandstones, siltstones, sandy mudstones Middle Jurassic Yangshuzhuang Formation records a se- and mudstones, but the Tanzhuang Formation contains quence of a shore-shallow lacustrine sedimentary sys- 9-10 layers of black oil shales. Great changes took place tem, with gray yellow and gray green mudstones, interca- in the depositional environment, sedimentary sequence lated with yellow muddy sandstones, siltstones and fine- 128 Ë W. Yang and M. Wang Figure 3: The relative probability density diagrams of detrital zircon U-Pb ages for the analyzed samples [24]. (a) detrital zircon U-Pb ages from the Middle Triassic Youfangzhuang Formation; (b) detrital zircon U-Pb ages from the Late Triassic Chunshuyao Formation; (c) detrital zircon U-Pb ages from the Late Triassic Tanzhuang Formation; (d) detrital zircon U-Pb ages from the Early Jurassic Anyao Formation; (e) detrital zircon U-Pb ages from the Middle Jurassic Yangshuzhuang Formation; (f) detrital zircon U-Pb ages from the Middle Jurassic Maao Formation. grained sandstones. The Jiyuan foreland basin was closed but two samples are collected from the Middle Triassic in the late Middle Jurassic as the Taihang Mountains up- Youfangzhuang Formation and Middle Jurassic Maao For- lift. The Maao Formation, unconformable to the underly- mation respectively to have a comparison between each ing Yangshuzhuang Formation, was formed during this pe- stage of the basin-mountain interaction (Figure 2).