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Developments in Earth system research have led to widespread interest in multi‐sphere interactions that may have controlled bauxite formation. Although karst bauxite ores are abundant in the Tethyan Metallogenic Domain (TMD), their genesis and distribution are not yet fully understood. This study utilizes the Random Forest (RF) model to analyze geochemical data sets compiled from three bauxite provinces in the Tethys, including the Mediterranean, Central Asian, and Chinese provinces. Meaningful variables among the provenance, paleolatitude and tectonic setting that affected the formation of the bauxite deposits are identified. The Logistic Regression model is used to verify the importance of various factors. Our study shows that when RF model achieves the best classifier performance, TiO2 is the variable that has the greatest impact on the model. TiO2 content is the highest in the Central Asian Province. The high TiO2 content in bauxites indicates a provenance of magmatic origine associated with the Subduction Provenance Zone. Bauxites with TiO2 content similar to that of the continental basement are derived from siliciclastic and carbonate rocks, identified as the Orogenic Provenance Zone. This study illustrates a novel link between geochemical compositions (TiO2 content) of bauxites, provenance and regional tectonic setting. Plain Language Summary Abundant bauxite deposits formed in the Tethyan Metallogenic Domain are of great importance to bauxite research. However, previous studies generally focus on local bauxite occurrences formed over certain geologic time. A comprehensive understanding of the genesis and characteristics of bauxite deposits is hence essential. In this study, Machine learning methods (Random Forest and Logistic Regression) are applied to improve the understanding of Tethyan bauxite formation. Our research reveals that the TiO2 content in Tethyan bauxites is related to their provenance. The enrichment of TiO2 in bauxite deposits points to magmatic rock provenance that underwent subduction. Bauxites with a TiO2 content similar to that of continental basement are derived from siliciclastic and carbonate rocks exposed on orogenic belts. As such, this investigation elucidates a previously unexplored association between the geochemical characteristics (TiO2 content) of bauxite deposits, their provenance, and the regional tectonic context. Key Points Two Provenance Zones in the Tethys Domain are proposed: Subduction Provenance Zone and Orogenic Provenance Zone High TiO2 content in bauxites resulted from magmatic rocks of the Subduction Provenance Zone Ti in bauxites has the potential for tracing provenance and associated tectonic settings

The Qin-Fang Trough, South China, trends northeast-southwest, orthogonal to the adjoining southern margin of the craton. The Devonian strata within the trough are unconformable on late Neoproterozoic units of the Yunkai Massif, indicating that strata within the trough are autochthonous. U-Pb ages and Hf isotope compositions of detrital zircons from the Silurian to Devonian succession are consistent with derivation from the massif. In comparisons of our data with those from equivalent units in the Ailaoshan Belt and Hainan Island, detrital zircons from the Silurian strata show similar age distributions and Hf isotope compositions, indicating that the three areas shared a common source and were adjacent to each other during the Silurian. In contrast, the age distributions of detrital zircons preserved in Devonian strata in the Qin-Fang area are different from those of equivalent units in the Ailaoshan Belt. This, along with the absence of Devonian strata on Hainan Island, suggests that the Qin-Fang area had separated from the Ailaoshan Belt by the Devonian. This change is linked to opening of the Ailaoshan Ocean, which was synchronous with expansion of the Qin-Fang Trough and the adjoining Youjiang Basin into epicontinental basins during the Devonian and Carboniferous. Combining these findings with temporal and spatial correlations, we conclude that the Qin-Fang Trough originated as an aulacogen: a “failed” rift of a three-armed rift system, with the other two rift arms evolving into the Ailaoshan Ocean during the opening of Paleo-Tethys. The Ailaoshan Ocean was an Atlantic-type oceanic basin with rifting commencing in the Early Silurian.

Original sedimentary manganese (Mn) deposits and supergene Mn ores are important Mn resources in China. However, the geochemical information from Chinese supergene Mn ores is scarce, and the relationship between sedimentary Mn deposits and supergene Mn ores is ambiguous. In this study, we collected the original Mn-bearing dolomitic sandstones (ZK20-3 drillcore) and supergene Mn ores (Longmen Section) from eastern Hebei, North China for systematic petrographic, mineralogical and geochemical analyses. Our new data help us to figure out the transformation from original Mn-bearing deposits to supergene ores. The main minerals of original Mn-bearing dolomitic sandstones are quartz and feldspar, with minor muscovite, dolomite, rhodochrosite, ankerite, and kutnohorite. Supergene Mn-oxide ores only emerged in the middle part of the Longmen (LM) Section, and mainly contain quartz, pyrolusite, cryptomelane, todorokite and occasional dolomite. The possible transformation sequence of Mn minerals is: kutnohorite/rhodochrosite → pyrolusite (I) → cryptomelane (todorokite) → todorokite (cryptomelane) → pyrolusite (II). For Mn-oxide ores, Fe, Na and Si are enriched but Al, Ca, Mg and K are depleted with the enrichment of Mn. For original and supergene ores, the total rare earth element + ytterbium (Σ REY) contents range from 105.68 × 10 −6 to 250.56 × 10 −6 and from 18.08 × 10 −6 to 176.60 × 10 −6 , respectively. Original Mn ores have similar slightly LREE-enriched patterns, but the purer Mn-oxide ore shows a HREE-enriched pattern. In the middle part of the LM Section, positive Ce anomalies in Mn-oxide ores indicate the precipitation of Ce-bearing minerals. It implies the existence of geochemical barriers, which changed pH and Eh values due to the long-time influence of groundwater.

Late Paleozoic pillow basalts are well preserved in the Youjiang Basin of SW China. In this study, we conducted geochemical and Sr−Nd isotopic study on the Late Devonian and Late Carboniferous basalts in Napo area, Youjiang Basin. The analyzed samples comprise moderate SiO 2 , TiO 2 , Mg#, and REE contents, with slightly positive or negative Eu anomalies, similar to the chemical nature of OIB (Oceanic island basalt). All basalts show low ( 143 Nd/ 144 Nd) i and ( 87 Sr/ 86 Sr) i values, close to EMI-type (I-type Enriched Mantle) magma source. Late Carboniferous basalts display higher ( 87 Sr/ 86 Sr) i , Nb/Th, and lower ε Nd ( t ), Zr/Nb values than those of the Late Devonian basalts, implying progressively decreased enrichment components in the magma source processes. Such evolution trend reflects a continuous lithospheric thinning event, supporting a progressive rifting setting of the Youjiang Basin along the southwestern margin of the Yangtze Block in Late Paleozoic. Combined with regional geological background, the Youjiang Basin is viewed as a continental rift basin related to the opening of the Paleo-Tethys Ocean in Late Devonian and became a passive continental margin basin in Carboniferous. The Paleo-Tethys branch ocean probably extended further to the southern Youjiang Basin, likely corresponding to the Song Ma suture zone.

The Qilian Orogen records early Paleozoic collisional suturing of the Qaidam Block and the Central Qilian Block to the North China Craton. The composition and U-Pb age of detrital zircons and the composition of Cr-spinels from the Early Silurian Lujiaogou and Angzanggou formations in the northern part of orogen indicate derivation from evolving oceanic and continental source terranes. Heavy-mineral chemistry indicates the incorporation of suprasubduction zone-type ophiolitic detritus in addition to continent-derived material. Integrating these chemical and age data with regional data on the duration of subduction-related magmatic activity, syn- and postcollisional granitic rocks, and high-pressure metamorphic rocks constrains the transformation from oceanic subduction to continental collision to 450-440 Ma. The collision resulted in a flood of detritus into the northern part of the orogen from the Central Qilian Block, which masked input from the intervening magmatic arc, implying rapid exposure of the block

The Nanhua Basin of South China recorded complete Cryogenian stratigraphic sequence from the Sturtian Glaciation (~717–660 Ma) to the Marinoan Glaciation (~654–635 Ma). The interglacial Datangpo Fm in the Nanhua Basin is divided into two members, and the first member consists of the Mn-carbonate unit and the overlying black shale unit, containing a series of large and superlarge manganese deposits. The metallogenic process of manganese deposits is not clear, and the Mn-carbonates formed through the precursor of Mn-oxide/oxyhydroxide reduction or directly precipitated from an anoxic water column. Moreover, the redox conditions in the deep Nanhua Basin during the precipitation of manganese deposits are also controversial. In this study, the high-resolution nitrogen contents (TN), isotope compositions, carbon isotope compositions of organic and inorganic matter from the first member of the Datangpo Fm are analyzed. The δ 15 N values of the Mn-carbonate unit (+1.53‰ to +5.26‰, mean +3.36‰) are higher than those of the overlying black shale unit (−3.74‰ to +3.54‰, mean +0.89‰). The Mn contents show a negative relationship with TN but a positive relationship with δ 15 N in the Mn-carbonate unit, implying that the formation of Mn-carbonates is related to redox variations. The relatively higher δ 15 N values in the Mn-carbonate unit indicated oxic conditions, and NH 4 + can be released and partially oxidized during the mineralization of organic matter, resulting in the residual 15 N-enriched NH 4 + being transferred into clay minerals. Meanwhile, the lower δ 15 N values in the black shale unit indicated anoxic conditions, which recorded primary N isotope signals. The Mn-carbonate unit is characterized by negative δ 13 C carb values (−11.17‰ to −5.22‰, mean −8.30‰), which show a positive relationship with δ 13 C org , but a negative relationship with Mn contents, implying that the negative δ 13 C carb excursions were related to the organic matter degradation during Mn-carbonate formation. The findings of this study indicated that the metallogenesis of manganese deposits in the Cryogenian Nanhua Basin was constrained mainly by the oxic interval in the deep basin. The nitrogen and carbon cycling process can provide new insights into geochemical cycling after the Sturtian Glaciation.

Continual deep-water sediments from the late Early Devonian to the Late Permian extended in wide areas of western Guangxi. We analyzed the major, trace, and rare earth elements of the Upper Paleozoic cherts in Badu, western Guangxi. High non-terrigenous SiO2 contents （Sinon_ter/Sibulk（%）〉 80%） and pure chert components （〉 70%） indicate a large extent of silicifi- cation in the Upper Paleozoic cherts, except for the Upper Devonian-Lower Carboniferous Luzhai Formation cherts, which have lower non-terrigenous SiO2 contents （avg. 71.8%） and pure chert components （40%-70%）. The Al/（AI＋Fe＋Mn） ratios and Feter/Febulk（%） values of samples from the lowest horizon of the Pingen Formation are 0.05-0.26, 13.1%-14.5%, respec- tively, indicating hydrothermal origins. All other samples show high Al/（Al＋Fe＋Mn） ratios （0.39±0.81） and high Feter/Febulk（%） values （23.1%-186.8%）, indicating non-hydrothermal origins. The Pingen Formation and Liujiang Formation cherts show slightly-moderately negative Ce anomalies （0.71±0.07, 0.81±0.08, respectively） and higher Y/Ho ratios （33.49±1.27, 36.10±2.05, respectively） than PAAS. This suggests that these cherts were deposited in the open marine basin, rather than in the intracontinental rift basin as previously assumed. The Luzhai Formation cherts may be deposited near the seamount or sea- floor plateaus with no negative Ce anomalies （1.09±0.07） and no significant Y-Ho fractionation （Y/Ho=28.60±1.25）. The Nandan Formation and Sidazhai Formation cherts were deposited in the open-ocean basin with moderately negative Ce anom- alies （0.67±0.08, 0.73±0.11, respectively） and high Y/Ho ratios （36.01±1.00, 32.00±2.25, respectively）. On the basis of our studies about cherts, we conclude that the Youjiang Basin originated as part of the Paleo-Tethys that controlled the deposition- al environments of cherts during late Paleozoic. The rift of the Youjiang Basin had occurred at least since the Early-Middle Devonian. The basin had a trend of evolving into an open-ocean basin during the Early-Middle Permian.

Studies on carbon isotopes of bulk carbonates from Longan and Baping sections of Lower Carboniferous in Guangxi of China show that the stable carbon isotope compositions in carbonate rocks of the isolated platform and deep slope facies were resistant to the influence of early meteoric diagenesis and late burial diagenesis. Three major positive carbon isotope excursions have been recognized in Lower Carboniferous in South China. The first major positive δ3C shift of 4.19‰ occurred in the middle part of Siphonodella isosticha-upper Siphonodella crenulata zone （Tournaisian）; the second with an amplitude of 4.65‰ occurred near the Tournaisian/Visean boundary; and the third of 2.23‰ in the lower part of Gnathodus bollandensis zone. The three positive shifts of δ3C can be correlated with global carbon isotope excursions and are consistent with the fall in global sea level, indicating that abundant organic carbon burial, lowering of atmospheric CO2, and glaciation may have occurred during these time intervals.

The Biyang Depression, lying in the eastern Nanxiang Basin, has a dustpan-shape with faults developed to the southwest and southeast. The Paleogene Hetaoyuan Formation in this depression hosts one of the oldest soda-deposits, the Anpeng deposit. These sodium carbonate-bearing strata consist of lutites, muddy dolomites, and bedded soda-deposits, which are dominated by nahcolite with little trona, mirabilite, and halite. In the top Unit 3 and lower Unit 2 of Hetaoyuan Formation where the sodium carbonates are concentrated, dolomitic shale, muddy carbonate, and sodium carbonate can be separated based on their distinct A1203, TiO〉 Na20, MgO＋CaO, and LOI （loss on ignition） contents. By using Na20/（MgO＋CaO） ratio as an indicator for the relative concentration of Na carbonates to Mg-Ca carbonates, the muddy dolomites can be classified into two groups. One group with Na20/（MgO＋CaO）〈0.6 exhibits a positive correlation between this ratio and AI203＋TiO2 content, an proxy for ter- rigenous clastic input and the other group with Na20/（MgO＋CaO）〉0.6 presents a negative correlation. As the clastic propor- tion decreases, the former indicates that it tends to form pure Mg-Ca carbonates reflecting evaporation less than or equal to re- plenishment for the lake water in a relative humid climate, and the latter reveals a trend to form sodium carbonates with lake water＇s evaporation more than replenishment in a relatively dry climate. From muddy dolomite to sodium carbonate samples, with Na20/（MgO＋CaO） ratio increasing, the A1 normalized Zr, Ti, La, K, Rb, and Ba tend to be enriched and the post-Archean Average Shale （PAAS） normalized positive Eu anomaly becomes more obvious. Integrated with the high B contents and the report of searlesite in the bedded sodium carbonates and the regional extensional tectonic regime, the above geochemical characteristics were interpreted to signify hydrothermal contribution to forming these soda-deposits through the deep fault systems of basin margins.

Upper Permian to Middle Triassic sedimentary rocks in the Youjiang Basin, SW China, record a change from a within-plate mafic-dominated source to the NW, to a mixed source involving magmatic arc and recycled orogenic detritus that lay to the west and east. Upper Permian and some Lower Triassic sedimentary rocks are characterized by relatively high contents of TiO2 and Nb, and low ratios of Al2O3/TiO2 and Th/Nb. Detrital zircons yield U-Pb ages of c. 260 Ma and have geochemical affinities to those crystallized from the within-plate type magmas. These features, combined with extensive basaltic lithic fragments and plagioclase grains in the sandstones, imply a sedimentary source dominated by the Emeishan Large Igneous Province exposed to the NW of the basin. The Early and Middle Triassic marked a significant change in sediment provenance, with rocks displaying geochemical affinity to upper continental crust. U-Pb ages and trace elements of detrital zircons from this material show input from multiple sedimentary sources including the subduction-collision rocks related to the Indosinian Orogeny to the west of the basin and the recycled Precambrian-early Palaeozoic sedimentary and granitic rocks in the South China hinterland to the east of the basin. The Early Triassic change in the nature of the source supplying detritus to the Youjiang Basin, together with regional sedimentary and tectonothermal events, suggests a tectonic transition from the Emeishan Plume to the Indosinian Orogeny in SW China. Regional stratigraphic correlation and provenance data suggest that the Emeishan basalts provided a large sediment influx for the riverine-littoral-marine systems in the Late Permian. This basaltic particulate and dissolved input may have contributed significant unradiogenic Sr to the Late Permian seawater.