Xing-Meng Orogenic Belt Research Articles

Geochronology, Geochemical Characterization and Tectonic Background of Volcanic Rocks of the Longjiang Formation in the Lengjimanda Plate Area, Middle Da Hinggan Mountains

The Lengjimanda plate is situated in the middle section of the Da Hinggan mountains, in the eastern section of the Tianshan Xingmeng orogenic belt. To determine the formation age of the volcanic rocks in the Longjiang formation in this area, to explore their origin and tectonic background, and to reconstruct the geodynamic evolution of the region, this study conducted petrological, zircon U–Pb geochronological, geochemical, and isotopic analyses of the volcanic rocks in the Longjiang formation. The Longjiang formation’s volcanic rocks are primarily composed of trachyandesite, trachyte trachydacite, and andesite, which are intermediate basic volcanic rocks. They are enriched in large-ion lithophile elements, are depleted in high-field-strength elements, are significantly fractionated between light and heavy rare earth elements, and exhibit a moderate negative Eu anomaly in most samples. The results of the LA–ICP–MS zircon U–Pb dating indicate that the volcanic rocks in this group were formed in the Early Cretaceous period at 129.1 ± 0.82 Ma. The zircon εHf(t) ranges from +1.13 to +43.77, the tDM2 ranges from +655 to +1427 Ma, the initial Sr ratio (87Sr/86Sr)i ranges from 0.7030 to 0.7036, and the εNd(t) ranges from +2.1 to +6.6. Based on the geochemical compositions and isotopic characteristics of the rocks, the initial magma of the volcanic rocks in the Longjiang formation originated from the partial melting of basaltic crustal materials, with a source material inferred to be depleted mantle-derived young crustal. These rocks were formed in a superimposed post-collisional and continental arc environment, possibly associated with the Mongol-Okhotsk Ocean closure and the oblique subduction of the Pacific plate. This study addresses a research gap regarding the volcanic rocks of the Longjiang formation in this area. Its findings can be applied to exploration and prospecting in the region.

Sediment provenance and dispersal in the early Eocene Dongying Depression, Bohai Bay Basin, Eastern China: Evidence from detrital zircon geochronology, geochemistry and petrology

Comprehensive provenance studies of syn-rift basin fills are required to better understand possible sources of clastic detritus and sediment routing systems. The Eocene fill of the Bohai Bay Basin in eastern China represents a syn-rift succession, where subsurface datasets permit investigation of sediment sources and sinks. New detrital zircon U–Pb samples (441 detrital zircon grains) from six wells were combined with elemental geochemical analysis of siliciclastic sediment, sandstone petrography and palynology to investigate depositional ages and provenance. This study demonstrates the importance of integrating geochronometry, geochemistry, petrology and palynology datasets to fully unravel syn-rift sediment provenance and routing. Zircons of the Dongying Depression were derived principally from an active continental margin island-arc setting characterized by felsic acid magmas, and subordinately from a recycled orogenic belt. The Shicun and Binnan faults controlled the relationship between sediment routing systems and source areas, explaining spatial differences of provenance signals in the depression. The routing system around the Shicun fault is characterized by a dominance of late Paleozoic and Paleoproterozoic zircons and subordinate Mesozoic zircons. In contrast, increased Mesozoic zircons in samples from south of the Binnan fault provide evidence of Mesozoic magmatism in this area. The early Eocene sediments record the signal of early Cretaceous magmatism in the North China Craton, but lack a record of substantial syn-depositional magmatic activity since the Paleogene in the Dongying Depression. Zircons from early Cretaceous strata and pre-existing zircons from the Xing-Meng Orogenic Belt and Inner Mongolia paleo-uplift were transported to the Yanshan and Luxi areas together. These sediments entered the Dongying Depression in the early Eocene, following a period of recycling. In addition, a Precambrian basement signal indicates possible denudation of Neoarchean to Proterozoic rocks in the Luxi uplift and from the Binnan fault footwall. Overall, the provenance signals of the basin reflect zircon recycling from an Early Cretaceous succession, denudation of ancient magmatic rock masses and the absence of syn-sedimentary magmatism.

Petrogenesis and tectonic settings of epithermal mineralization-related granites in the Xinchenggou area, NE China

The Xinchenggou area is located in the northeast part of the eastern segment of the Xingmeng orogenic belt (EXOB), NE China and has been demonstrated to be a promising exploration target for epithermal deposits. Although previous studies have shown that syenogranite and monzogranite occurring in the Xinchenggou area are promising in forming epithermal mineralization, the petrogenesis and geodynamic settings in which these granites were emplaced are still unclear. To address these problems, in this study detailed whole-rock major and trace element analyses for these granites were conducted. Combined with previously published data, we show that both syenogranite and monzogranite in the Xinchenggou area are high-K calc-alkaline and peraluminous with high SiO2. Their rare earth element concentrations are low (ΣREE = 72.35 × 10−6–217.64 × 10−6) and show obvious differentiation between LREE and HREE (LaN/YbN=2.74–11.37), with apparent Eu negative anomalies (δEu = 0.14–0.83) and indistinctive Ce anomalies (δCe = 0.96–1.11). Combined with petrographical observations, it is suggested that both syenogranite and monzogranite are (slightly fractionated) I-type granite. Nb/Ta ratios of syenogranite and monzogranite range from 6.18 to 26.33, indicating that the granitic magma was derived from the upper mantle or the lower crust. Both syenogranite and monzogranite were emplaced in a continental arc setting, which was related to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate during the Late Triassic to Early Jurassic.

New geochronological and provenance constraints on the Late Mesozoic sedimentary formations in the western Shandong Province and Tanlu fault zone, China

We present new LA-ICP-MS detrital zircon U-Pb age and trace element data of the Late Mesozoic sedimentary sequences from the western Shandong and Tanlu fault zone, with the aim to constrain the depositional ages and sedimentary sources. The samples from the western Shandong have similar U-Pb age spectra, which can be divided into three major age groups, peaking age at circa 2,475–2,540 Ma, 1820–1870 Ma and 257–285 Ma, with minor Mesoproterozoic, Neoproterozoic and Paleozoic detrital zircon grains. The sample JN recovered from the Tanlu fault zone has an overwhelming majority of the Early Cretaceous detrital zircons with the age peak at circa 125 Ma, whereas the Archean and Paleoproterozoic detrital zircons are subordinate. The weighted average age of the youngest zircons show that the Santai Formation probably had begun deposition at circa 158 Ma and terminated deposition at circa 150 Ma, and the Tianjialou Formation of the Dasheng Group had begun deposition at circa 122 Ma. Our study indicates that the activity of the dinosaurs might occur during the Late Jurassic rather than the Cretaceous in the Shandong province. In addition, most detrital zircons of the studied samples are characterized by the high Th/U ratios and left-inclined REE patterns, revealing a magmatic origin. Morphologically, most detrital zircon grains characterized by angular to sub-rounded shapes indicate a middle-short distance transport from the source regions, whereas minor detrital zircon grains show rounded shapes, indicating a long-distance transport or multiphase recycling. According to detrital age populations in this study, combined with previously published data, we conclude that depositional provenances of the Santai Formation were mainly derived from the western Shandong and Jiao-Liao Belt, and minor detritus were derived from the northern part of the North China Craton and Xing-Meng orogenic belt. The sediments deposited in the Tanlu fault zone were mainly derived from the volcanic and subvolcanic rocks of the Qingshan period in the eastern Shandong, and subordinate depositional sources were from the Jiao-Liao and the basement uplift of the western Shandong, with minor supplier being derived from the Yinshan-Yanshan orogenic belt. The detrital provenance of the Santai Formation indicates that extension of the eastern NCC occurred during the Late Jurassic. The Neoproterozoic detrital zircons play a minor role in the studied strata, indicating that the large sinistral movement of the Tanlu fault zone might have occurred at the Early-Middle Jurassic and formed a paleogeographic separation of the western Shandong and eastern Shandong (Sulu orogenic belt).

Paleozoic sedimentary processes and magmatism in Zamenwude area, Mongolia, and their implications for tectonic evolution of the Xingmeng orogenic belt

兴蒙造山带属于中亚造山带的东段,关于其演化过程存在两种主要观点:一种观点认为它是由古亚洲洋经历整个古生代的连续俯冲-碰撞过程后在早三叠世形成;另一种观点则认为古亚洲洋在晚泥盆世之前就通过俯冲-碰撞过程闭合,形成早-中古生代造山带,随后在石炭-二叠纪又经历了从陆内伸展到再次闭合的过程,并形成陆内造山带。蒙古国东南部扎门乌德地区出露各类古生代沉积岩和岩浆岩,可以为解决上述争议提供典型研究实例。本文通过沉积学、年代学和地球化学等多种手段综合研究,取得以下研究成果:(1)根据年代学和岩性特征,在该地区识别出三类古生代岩石组合,第一类是以黑云母二长花岗岩为代表的中志留世侵入岩,第二类是中泥盆世大套的粗碎屑岩-火山岩沉积旋回,第三类是不整合地沉积于早期造山带之上的二叠纪巨厚火山-沉积岩系。这三类岩石组合分别属于俯冲阶段的大陆边缘岛弧带岩浆岩、碰撞造山后期的上叠盆地以及叠加在早期造山带岩石圈之上的晚古生代陆内伸展时期的裂谷盆地的沉积。(2)利用研究区所有古生代碎屑锆石和岩浆岩全岩资料,揭示了该地区古生代时期地壳厚度变化趋势如下:500~425Ma的俯冲-碰撞过程造成地壳加厚;425~375Ma的碰撞造山后伸展过程使地壳变薄;375~350Ma地壳再次加厚,可能与造山带物质堆叠有关;350~275Ma地壳再次减薄,对应于广泛而强烈的晚石炭世-早二叠世火山岩,证明此时期岩浆活动的构造背景是区域伸展而不是挤压作用。(3)根据研究区出现的三类岩石组合特点,结合研究区以南的艾力格庙地区已有的研究成果,可以划分出五个早-中古生代造山带构造单元和两个叠加其上的晚古生代陆内造山带构造单元,揭示蒙古国扎门乌德地区经历了早-中古生代加积造山带和晚古生代陆内造山带等两个构造演化过程。本文研究为认识兴蒙造山带的两阶段构造发展提供了新资料。

A study on geological structure prediction based on random forest method

The Xingmeng orogenic belt is located in the eastern section of the Central Asian orogenic belt, which is one of the key areas to study the formation and evolution of the Central Asian orogenic belt. At present, there is a huge controversy over the closure time of the Paleo-Asian Ocean in the Xingmeng orogenic belt. One of the reasons is that the genetic tectonic setting of the Carboniferous volcanic rocks is not clear. Due to the diversity of volcanic rock geochemical characteristics and its related interpretations, there are two different views on the tectonic setting of Carboniferous volcanic rocks in the Xingmeng orogenic belt: island arc and continental rift. In recent years, it is one of the important development directions in the application of geological big data technology to analyze geochemical data based on machine learning methods and further infer the tectonic background of basalt. This paper systematically collects Carboniferous basic rock data from Dongwuqi area of Inner Mongolia, Keyouzhongqi area of Inner Mongolia and Beishan area in the southern section of the Central Asian Orogenic Belt. Random forest algorithm is used for training sets of major elements and trace elements in global island arc basalt and rift basalt, and then the trained model is used to predict the tectonic setting of the Carboniferous magmatic rock samples in the Xingmeng orogenic belt. The prediction results shows that the island arc probability of most of the research samples is between 0.65 and 1, which indicates that the island arc tectonic setting is more credible. In this paper, it is concluded that magmatism in the Beishan area of the southern part of the Central Asian Orogenic belt in the Early Carboniferous may have formed in the heyday of subduction, while the Xingmeng orogenic belt in the Late Carboniferous may have been in the late subduction stage to the collision or even the early rifting stage. This temporal and spatial evolution shows that the subduction of the Paleo-Asian Ocean is different from west to east. Therefore, the research results of this paper show that the subduction of the Xingmeng orogenic belt in the Carboniferous has not ended yet.

Petrogenesis and tectonic significance of Late Paleozoic magmatism in the Xilinhot micro-continent, central Xingmeng orogenic belt

ABSTRACT The evolution history of the Hegenshan Ocean is an important part of studying the evolution of the Xingmeng orogenic belt, but it is still controversial. Here we present an integrated study of petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotopes on a series of intrusive rocks from the Baiyinguole area, Xiwuqi, central Inner Mongolia, NE China. Chronological data indicate that the intrusive rocks can be divided into three stages: 326–317, 297–295, and 259–254 Ma. The 326–317-Ma gabbros and diorites belong to the calc-alkaline series, and are characterized by positive whole-rock εNd(t) values (+1.1–+6.7), relatively low La/Ba ratios (0.04–0.10), and high La/Nb ratios (1.82–3.18), indicating that the magma source is from a subduction-modified lithospheric mantle. These samples have arc features owing to the southward subduction of the Hegenshan oceanic crust. The 297–295-Ma granodiorites and monzogranites show positive εNd(t) values (+1.9–+2.4), low 87Sr/86Sri ratios (0.704185–0.705234), and young Nd two-stage model ages (TDM2), which is consistent with typical I-type granites. On various tectonic setting discrimination diagrams, the granodiorites and monzogranites are plotted in the syn-collisional field. The 259–254-Ma syenogranites have low abundances of mafic minerals, low contents of Zr/Hf (18.31–31.35) and Nb/Ta (6.80–11.80) values, high SiO2 (76.36–78.54 wt.%) content, A/CNK (1.08–1.76), and D.I. of 96.8–97.4 (average 97.1), and notable negative Eu anomalies (δEu* = 0.07–0.17) and weakly tetrad-effects in REE pattern, which is affinity to the characteristics of highly differentiated granites. Moreover, they have positive εNd(t) values (+2.0–+2.1) with scattered TDM2 of 730–1217 Ma and low Nb/U ratios. This study suggests that the syenogranites are formed in a post-collisional tectonic setting, which is related to the closure of the Hegenshan Ocean. In addition, based on a review of the pre-existing literature data, a model of southward ridge subduction is proposed to explain the tectonic evolution of the Hegenshan Ocean.

Tectonic-magmatic setting for Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt: Constraints from zircon U–Pb and Hf isotopic data of wulaga deposit, NE China

The Xing–Meng Orogenic Belt hosts an amount of low-sulfidation epithermal gold deposits. However, the tectonic-magmatic setting remains problematic, which hinders understanding the factors that control the gold endowment in the region. Wulaga deposit is the largest low-sulfidation epithermal gold deposit in the northeastern Xing–Meng Orogenic Belt. Gold mineralization occurs in the crypto-explosive breccia zone of subvolcanic granodiorite porphyry. Zircon U–Pb ages of three granodiorite apophyses and previous pyrite Rb–Sr dating (113.8 ± 4.4 Ma) indicate granodiorite porphyry and gold mineralization was coeval. The ore-related granodiorite porphyry is moderate SiO2, high-K calc-alkaline, and metaluminous, suggesting an I-type granite. Moreover, Wulaga granodiorite porphyry displays low initial 87Sr/86Sr ratios and positive εNd(t) values with TDM2(Nd) of 799.7–897.4 Ma and εHf(t) values with TDM2(Hf) of 652–785 Ma, indicating that it was derived from partial melting of the Neoproterozoic juvenile mafic lower crust. Ti-in-zircon thermometry, medium–high Sr/Y ratio, high Ba/La, and fO2 value indicate that Wulaga granodiorite porphyry formed at relatively low temperatures (∼700 °C), rich water, and high fugacity within the stability field of garnet in the juvenile lower crust. Combined with ore-related tectonic-magmatic activities in the Wulaga, Dong'an, and Sandaowanzi gold deposits, the Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt were formed from magmatic-hydrothermal events triggered by mutual interaction between post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean and arc-back extension associated with rollback of the Paleo-Pacific Ocean plate. These data indicate the potential existence of the Early Cretaceous epithermal gold deposits that are related to the contemporaneous igneous activity.

Significance of sandstone provenance in tracking potential uranium reservoirs: A case study of the Middle Jurassic Zhiluo Formation, western Ordos Basin, northern China

The Middle Jurassic Zhiluo Formation is the main uranium-bearing sequence in the western Ordos Basin, northern China. Provenance studies of clastic rocks in the Zhiluo Formation are important to provide guidelines for uranium exploration. In this paper, we describe the sandstones from the Zhiluo Formation and report their bulk rock elemental compositions by using samples that were collected from the Lingwu area, western Ordos Basin. Our main objective is to provide constraints on the provenance of the sandstones and thus new insights into uranium exploration. The results show that the sources of the Zhiluo Formation sandstones have TTG (trondhjemite-tonalite-granodiorite) attributes and mainly consist of magmatic arc orogenic belts that were mixed with continental blocks and recycled orogenic belt materials. The paleocurrent measurements that average 144° suggest that the provenance supply direction of the sandstones is from northwest to southeast. Combined with the regional tectonic settings, it can be inferred that the sandstone provenance was mainly provided by the Xingmeng Orogenic Belt, while the Alxa Block and Helan Mountain complex rocks also contributed. Our research might provide a crucial reference for predicting the locations of potential uranium reservoirs, i.e., the search for uranium mineralization should target the northwest of the Ordos Basin, especially near regions where intermediate-acid rocks are present. This information is integrated into a predictive model in which tracking along the provenance supply directions of clastic sediments is an efficient method for conducting uranium exploration in a sedimentary basin.

Lithospheric structure beneath the boundary region of North China Craton and Xing Meng Orogenic Belt from S-receiver function analysis

The boundary region of the North China Craton (NCC) and Xing-Meng Orogenic Belt (XMOB), including the northern boundary of the NCC and the southern XMOB, is the ideal area to investigate the spatially uneven lithospheric deformation and associated tectonic evolution in the boundary region of the craton and orogen. The depths and structures of the lithosphere–asthenosphere boundary (LAB) and mid-lithosphere discontinuity (MLD) are the key information to describe the nature and deformation pattern of the lithosphere, and thus can provide basic constraints on the associated tectonic processes and mechanism of the lithospheric deformation. Based on waveform data collected from 226 broadband seismic stations, high resolution spatial variations in the LAB and MLD depths were obtained by using the wave equation migration method for the S-receiver functions. The migrated images show a lateral variation in the LAB depth from 100–120 km in the northern boundary of the NCC to 120–140 km in the southern XMOB. The imaged LAB within the NCC is much shallower than that revealed by mantle xenoliths enclosed in the nearby Early Paleozoic kimberlites (~180 km), suggesting that the cratonic lithosphere of the area may have undergone significant thinning during the Phanerozoic evolution. Furthermore, a coherent MLD is identified at depths of 70–90 km beneath the northeastern NCC, which corroborates the speculation that the MLD probably existed in the eastern NCC before lithospheric destruction in the Mesozoic. The spatial variations in the LAB and MLD depths probably reflect complex lithospheric deformation and thinning around the boundary region of NCC and XMOB. The properties, including the gradient thickness and S-wave velocity contrast, of the two discontinuities further indicate that lithospheric deformation and thinning might be related to partial melting induced by the Big Mantle Wedge associated with the subducting Paleo-Pacific plate and its stagnation during the Late Mesozoic.

Extensive mineralization in the eastern segment of the Xingmeng orogenic belt, NE China: A regional view

• There are four types of EXOB deposits: porphyry , skarn , hydrothermal vein, and epithermal types. • There are five stage mineralizations in EXOB: 480–440, 300–220, 200–165, 155–130, and 125–100 Ma. • The five metallogenic periods correspond to different geological setting. The eastern segment of the Xingmeng orogenic belt (EXOB) hosts numerous Mo, polymetallic Ag, Pb–Zn , Sn, Cu, Au (Ag), and rare-earth element (REE) deposits and is one of the most important polymetallic-ore regions globally. The mineralization type includes i) porphyry Cu (Mo, Au), Mo (Cu, Pb–Zn, W), Sn (Cu–Ag) deposits, ii) skarn Cu–Au, polymetallic Pb–Zn and Fe–Sn deposit, and iii) veined polymetallic Ag, Pb–Zn, Sn, Cu deposits and W, Mo deposits, with an REE deposit related to magmatic hydrothermal fluid; and iv) epithermal Ag and Au (Ag, Te) deposits, respectively. The mineralization-related rocks in the EXOB are mainly high-K calc-alkaline granites together with minor alkaline granites that were derived from the melting of juvenile crust. The mineralizations in the EXOB are typically related to magmatic-hydrothermal events. In this study we attempt a systematic analysis of the temporospatial distribution of ore deposits in the EXOB, in order to constrain the geodynamic setting of mineralization. Based on available geochronological data, we suggest five mineralization stages for the EXOB at 480–440, 300–220, 200–165, 155–130, and 125–100 Ma, respectively. The porphyry Cu–Mo mineralization occurred during the early Paleozoic (480–440 Ma). The extensive Mo (W, Sn), and Ag (Pb–Zn) polymetallic mineralization was formed during the Mesozoic. The Ordovician–Triassic mineralization (480–220 Ma) is related to the Paleo-Asian Ocean tectonism and developed in an island arc setting. The Permian–Triassic mineralization (300–220) was formed in a post-collisional tectonic setting related to the development of Hegenshan suture. The early–middle Jurassic deposits (200–165 Ma) are related to the subduction of the Paleo-Pacific oceanic plate on the East Asian continental margin. The Late Jurassic–Early Cretaceous deposits (155–130 Ma) were formed in an extensional setting related to rollback of the Paleo-Pacific Plate. The Jurassic–Cretaceous mineralization (200–100 Ma) in the northern segment of the Da Hinggan Mountains is associated with the subduction and post-collisional tectonic setting of the Mongol–Okhotsk oceanic plate. The latest stage of epithermal deposits (125–100 Ma) were developed in a continental margin back-arc setting associated with subduction of the Paleo-Pacific Plate beneath the Eurasia.

Oxidation-reduction state of lithospheric mantle in northern Xingmeng orogenic belt

Xingmeng orogenic belt is located in the eastern part of East Asian orogenic belt, which is a typical area of superimposition and reconstruction of multiple tectonic systems. Spinel peridotite captives have been found in Nuo Min and Kolo areas in the north of Xingmeng orogenic belt. The olivine Mg# of lherzolite is 0.895 ∼ 0.911, which is slightly smaller than that of lherzolite (0.912 ∼ 0.928), and the high Mg# of lherzolite also indicates that the upper mantle in the study area is refractory. The lherzolite and lherzolite in the study area show high fO2 values, FMQ+1.947 ∼ 3.145, which is in sharp contrast with the relatively reduced ancient lithospheric mantle facies in general. The fundamental reason may be that the Paleozoic ancient Asian Ocean and the Mesozoic ancient Pacific Ocean successively subducted under the Xingmeng orogenic belt, resulting in the sharp rise of fO2 in the lithospheric mantle at that time.

Geological, Fluid Inclusion, H-O-S-Pb Isotope Constraints on the Genesis of the Erdaogou Gold Deposit, Liaoning Province

The Erdaogou gold deposit is located in the conjuncture of North China Carton and Xingmeng orogenic belt. The ore-forming process of Erdaogou gold deposit is divided into three stages (I to III), which are quartz-pyrite stage (stage I), quartz-polymetallic sulfide stage (stage II) and quartz-calcite stage (stage III). Two types of fluid inclusions is distinguished in the ore-forming stage, i.e., aqueous type (W-type) and aqueous-carbonic type (C-type) inclusions. From the stage I to III, the homogenization temperature of fluid inclusions are respectively 334–395, 214–364 and 172–272 °C, with salinities of 7.72 wt.%–11.23 wt.% NaCl equiv., 0.20 wt.%–23.18 wt.% NaCl equiv., and 0.35 wt.% to 5.25 wt.% NaCl equiv. The ore-forming fluids of the Erdaogou deposit have the characteristics of medium-low temperatures, moderate salinities and low densities. And the fluids belong to the CO2-H2O-NaCl system. The values of δ34SV-CDT in sulphide samples at different stages (stages I to III) are between −2.2‰ to 2.3‰, indicating sulfur source from magma volatiles or subvolcanic rock leaching. The lead isotopes suggest that ore-forming metals may be derived from a mixture of lower crust and mantle materials. Oxygen and hydrogen isotope data at Erdaogou indicate that magmatic fluid and meteoric water may both be involved in the hydrothermal system. Based on the geological characteristics, fluid inclusion results, stable and radiogenic isotope results of Erdaogou gold deposit, we believe that the temperature decrease, fluid boiling are the key factors leading to the ore precipitation and the genetic type of Erdaogou gold deposit is low-sulfidation epithermal deposit.

Late Paleozoic tectonic framework of the central Xing-Meng Orogenic Belt: Constrains from detrital and igneous zircon U-Pb geochronology of Late Devonian-Early Carboniferous Seribayanaobao Formation in southern Sunid Zuoqi

内蒙古苏尼特左旗地区位于兴蒙造山带中段，是研究古生代俯冲-增生造山作用和地壳生长的关键地区。在苏尼特左旗南部，晚泥盆-早石炭世色日巴彦敖包组角度不整合在早古生代增生楔之上，已有研究对于其沉积环境、盆地属性及区域构造意义一直存在较大分歧。本文对色日巴彦敖包组敖木根呼都格剖面和阿拉塔特剖面碎屑岩和火山岩夹层开展锆石U-Pb测年及Hf同位素分析，并进行了沉积相分析，进一步查明了地层层序、时代及物源特征，并对沉积环境和盆地属性进行了探讨。研究表明，敖木根呼都格剖面色日巴彦敖包组底部含砾粗砂岩最小谐和碎屑锆石年龄为391±5Ma，中下部凝灰质砂岩最小谐和碎屑锆石年龄为338.2±4.3Ma，凝灰岩锆石年龄为336±2Ma、333±3.5Ma，结合古生物化石，表明底部形成于晚泥盆世，中上部地层形成于早石炭世晚期。阿拉塔特剖面中上部安山质火山碎屑岩最小谐和碎屑锆石年龄加权平均值为320.4±6.2Ma，表明其形成于晚石炭世。碎屑锆石年龄谱及Hf同位素组成表明，底部及中部砂岩碎屑物主要来自近源的早古生代白音宝力道和二连东乌旗地区弧岩浆岩，少量来自北侧南蒙古弧。结合沉积相分析，推测苏尼特左旗南部色日巴彦敖包组下部为一套形成于弧陆碰撞后被动陆缘滨浅海相沉积建造，中上部为形成于弧前盆地的一套杂砂岩夹火山岩建造。以上资料表明，该区从早石炭世开始转为活动陆缘背景，暗示古亚洲洋中东段在晚古生代仍未封闭。

Detrital zircon geochronology and provenance of sediments within the Mesozoic basins: New insights into tectonic evolution of the Qinling Orogen

Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen (QO). This study uses new detrital zircon U–Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao, Taizishan, Nanzhao, and Mashiping formations of the North Qinling Orogen (NQO). The detrital zircons can be split by age peaks into five major groups, including Early Cretaceous, Late Triassic, Early Paleozoic, Neoproterozoic and Paleoproterozoic age peaks. On the basis of the youngest zircon ages and age-diagnostic fossils, we conclude that the Taishanmiao (youngest age of 234 Ma) and Taizishan (216 Ma) formations were deposited during the Late Triassic, whereas the Nanzhao Formation (110 Ma) was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought. The Mashiping Formation (110 Ma) was also deposited during the Early Cretaceous. Combined with zircon Hf isotopic compositions, zircons from Late Triassic units were generally derived from the NQO, South Qinling Orogen (SQO), and North China Craton (NCC), with minor amounts derived from the Xing–Meng Orogenic Belt. The sediments within the Nanzhao Formation were mainly derived from the QO, with a minor contribution from the NCC. The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus. This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean, whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO. The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift, which was a process generated sediments that were deposited in a series of basins of this area.

Carboniferous ridge subduction in the Xingmeng Orogenic Belt: Constraints from geochronological, geochemical, and Sr-Nd-Hf isotopic analysis of strongly peraluminous granites and gabbro-diorites in the Xilinhot micro-continent

The Xingmeng Orogenic Belt evolved through a long-lived orogeny involving multiple episodes of subduction and accretion. However, there is a debate on its tectonic evolution during the Late Paleozoic. Here, we report geochemical, geochronological, and isotopic data from strongly peraluminous granites and gabbro-diorites from the Sunidzuoqi–Xilinhot region. Zircon U–Pb ages suggest that the intrusive rocks were emplaced during the Early Carboniferous (333–322 Ma). The granites exhibit geochemical characteristics similar to S-type granites, with high SiO2 (72.34–76.53 wt.%), Al2O3 (12.45–14.65 wt.%), and A/CNK (1.07–1.16), but depleted Sr, Nb, and Ta contents. They exhibit positive εNd(t) and εHf(t) values (−0.3 to 2.8 and 2.7–5.7, respectively) and young Nd and Hf model ages (TDM2(Nd)=853–1110 Ma and TDM2(Hf)=975–1184 Ma), suggesting that they may be the partial melting products of heterogeneous sources with variable proportions of pelite, psammite, and metabasaltic rocks. The meta-gabbro-diorites from the Maihantaolegai pluton have low SiO2 (47.06–53.49 wt.%) and K2O (0.04–0.99 wt.%) contents, and demonstrate slight light rare earth element (REE) depletion in the chondrite-normalized REE diagrams. They have high zircon εHf(t) values (14.41–17.34) and young Hf model ages (TDM2(Hf)= 230–418 Ma), indicating a more depleted mantle source. The variations of the Sm/Yb and La/Sm ratios can thus be used to assess the melting degree of the mantle source from 5% to 20%, suggesting a quite shallow mantle melting zone. We propose that the petrogenesis and distribution of the strongly peraluminous granites and gabbro-diorites, as well as the tectonic architecture of the region, can be explained by a ridge subduction model. Based on these results, and previous studies, we suggest a southward ridge subduction model for the Sunidzuoqi–Xilinhot region.

Evolution of central-southern margin of the Xing-Meng Orogenic Belt in the Late Paleozoic: Evidence from Carboniferous-Permian sedimentary formation and volcanic rock in Sonid Right Banner, Inner Mongolia

Evolution of central-southern margin of the Xing-Meng Orogenic Belt in the Late Paleozoic: Evidence from Carboniferous-Permian sedimentary formation and volcanic rock in Sonid Right Banner, Inner Mongolia

Early-Middle Triassic Intrusions in Western Inner Mongolia, China: Implications for the Final Orogenic Evolution in Southwestern Xing-Meng Orogenic Belt

The end-Permian to Early-Middle Triassic magmatic rocks in Inner Mongolia can provide valuable insights into the relationships between the collisional processes and the magmatic responses during the final orogenic evolution of Xing-Meng orogenic belt (XMOB). This paper presents zircon U-Pb ages and Hf isotopes, whole rock geochemical and Sr-Nd-Pb isotopic data for the Early-Middle Triassic diabases and monzogranites from the Langshan area, southwestern XMOB. Our results suggest that the studied diabases and monzogranites were respectively formed during Early Triassic and Middle Triassic. The Early Triassic diabases are characterized by “arc-like” geochemical signatures, including enrichment in Rb, U and K, and depletion in Nb, Ta, P and Ti. They have negative to weak positive eNd (t) values (−3.1 to +1.5) and relatively high initial ratios of 208Pb/204Pb (35.968–37.346), 207Pb/204Pb (15.448–15.508) and 206Pb/204Pb (16.280–17.492), indicating a subduction-metasomatized enriched lithospheric mantle source. Their low Ba/Rb (2.72–6.56), Ce/Y (0.97–1.39) and (Tb/Yb)N ratios (1.31–1.45) suggest that the parental magma was likely originated from low degree partial melting of the phlogopite-bearing lherzolite in a spinel-stability field. The Middle Triassic monzogranites show high Sr/Y ratios, low MgO, Cr and Ni contents, high Zr/Sm ratios (40–64), negative zircon eHf(t) values (−25.8 to −8.8), as well as relatively flat heavy rare earth element patterns. They were likely derived from low degree partial melting of a moderately thickened ancient lower crust. The diabases and the slightly postdated high Sr/Y granites in this study represent the magmatic responses to the final orogenic evolution in the southwestern XMOB. Together with regional works, we propose that the slab break-off of the Paleo-Asian oceanic lithosphere following the terminal collision between the North China Craton and the South Mongolia terranes triggered asthenospheric upwelling, and the ongoing convergence further initiated moderately crustal thickening and uplift in the XMOB.

Magmatic and tectonic setting of the Permian Au mineralization in the Xing-Meng Orogenic Belt: constraints from the U–Pb ages, Hf–O isotopes and geochemistry of granitic intrusions in the Bilihe and Hadamiao gold deposits

The Xing-Meng Orogenic Belt (XMOB) hosts significant Au-dominant polymetallic mineral deposits. Although these deposits mostly formed in the Mesozoic, Permian Au deposits are also present but less well studied. In the Bilihe and Hadamiao gold mining areas, granitic intrusions that are associated with gold mineralization were dated by LA–ICP–MS at 272.7–259.7 Ma. These intrusions consist of granodioritic porphyry and quartz diorite that both represent calc-alkaline metaluminous I-type granites. These granitoids exhibit enrichment in LREEs and LILEs, depletion in HREEs and HFSEs, and low Sr/Y ratios, suggesting that these rocks have an island-arc affinity. The eHf(t) values of the Bilihe granodioritic porphyry and Hadamiao quartz diorite range from −0.3 to +8.9, with TDM2 values ranging from 0.7 to 1.3 Ga, and from +2.5 to +13.5, with TDM2 values ranging from 0.4 to 1.1 Ga, respectively. The zircon δ18O values of the granitic porphyry and quartz diorite range from 6.9 to 7.6‰ and from 5.0 to 6.4‰, respectively. A simple binary Hf–O isotope mixing model shows that the assimilation of 10–15% sediments by MORB could have generated the Bilihe granodioritic porphyry, and that the assimilation of less than 5% sediments by MORB could have generated the Hadamiao quartz diorite. Combined with previous studies of the Late Carboniferous to Permian igneous rocks in the southern region of the XMOB, these new data suggest that the Bilihe and Hadamiao ore-related intrusive rocks formed in a continental-arc setting associated with the subduction of the Paleo-Asian oceanic slab. This setting indicates the potential existence of subduction-related gold deposits that are related to contemporaneous igneous activity.

Fluid Inclusions and CHOSPb Isotopes: Implications for the Genesis of the Zhuanshanzi Gold Deposit on the Northern Margin of the North China Craton

AbstractThe Zhuanshanzi gold deposit lies in the eastern section of the Xingmeng orogenic belt and the northern section of the Chifeng‐Chaoyang gold belt. The gold veins are strictly controlled by a NW‐oriented shear fault zone. Quartz veins and altered tectonic rock‐type gold veins are the main vein types. The deposits can be divided into four mineralization stages, and the second and third metallogenic stages are the main metallogenic stages. In this paper, based on the detailed field geological surveys, an analysis of the orebody and ore characteristics, microtemperature measurement of fluid inclusions, the Laser Raman spectrum of the inclusions, determination of CHOSPb isotopic geochemical characteristics, and so on were carried out to explore the origin of the ore‐forming fluids, ore‐forming materials, and the genesis of the deposits. The results show that the fluid inclusions can be divided into four types: type I – gas–liquid two‐phase inclusions; type II – gas‐rich inclusions; type III– liquid inclusions; and type IV – CO2‐containing three‐phase inclusions. However, they are dominated by type Ib – gas liquid inclusions and type IV – three‐phase inclusions containing CO2. The gas compositions are mainly H2O and CO2, indicating that the metallogenic system is a CO2H2ONaCl system. The homogenization temperature of the ore‐forming fluid evolved from a middle temperature to a low temperature, and the temperature of the fluid was further reduced due to meteoric water mixing during the late stage, as well as a lack of CO2 components, and eventually evolved into a simple NaClH2O hydrothermal system. CHOSPb isotope research proved that the ore‐forming fluids are mainly magmatic water during the early stage, with abundant meteoric water mixed in during the late stage. Ore‐forming materials originated mostly from hypomagma and were possibly influenced by the surrounding rocks, suggesting that the ore‐forming materials were mainly magmatic hydrothermal deposits, with a small amount of crustal component. The fluid immiscibility and the CO2 and CH4 gases in the fluids played an active and important role in the precipitation and enrichment of Au during different metallogenic stages. The deposit is considered a magmatic hydrothermal deposit of middle–low temperature.