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Article

Geochronological and Geochemical Characterization of Triassic Felsic Volcanics in the Youjiang Basin, Southwest China: Implications for Tectonic Evolution of Eastern Tethyan Geodynamics

by
Kai Dong
1,
Zhuoyang Li
1,*,
Xiaoli Fei
2,
Yongqing Wang
1,* and
Xiaohu Deng
3
1
School of Natural Resources and Surveying, Nanning Normal University, Nanning 530001, China
2
Guangxi Land and Resources Planning and Design Group Co., Ltd., Nanning 530001, China
3
School of Physics and Engineering Technology, Minzu Normal University of Xingyi, Xingyi 562400, China
*
Authors to whom correspondence should be addressed.
Minerals 2025, 15(4), 398; https://doi.org/10.3390/min15040398
Submission received: 2 March 2025 / Revised: 5 April 2025 / Accepted: 7 April 2025 / Published: 9 April 2025
(This article belongs to the Special Issue Magmatic Evolution through Time of Volcanic Zones: Evidence from Isotopic, Geochemical and Geochronological Data of Eruption Products)
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Abstract

:
The Youjiang Basin is situated at the junction between the Tethyan and Pacific tectonic domains, and its Permian–Triassic volcanic rocks provide important geological archives recording the tectonic evolution and collisional interactions between the South China and Indochina blocks. This study employed LA-ICP-MS zircon U-Pb geochronology and whole-rock geochemistry to investigate interbedded Triassic felsic volcanics. Felsic volcanic rocks in Youjiang Basin were erupted during the Early–Middle Triassic period (ca. 241~251 Ma) and are situated within the strata of the Beisi, Baifeng, and Banba Formations. These rocks in the Daqingshan area are rich in SiO2 (66.8~72.7 wt%), K2O (1.4~5.1 wt%), U (5.2~6.7 ppm), and Th (26~32.1 ppm). Conversely, they are depleted in MgO (0.6~1.4 wt%), TiO2 (0.5~0.9 wt%), Cr (13.1~19.7 ppm), Ni (7.3~10.1 ppm), and negative Eu anomalies (Eu/Eu* = 0.41~0.52), and they also exhibit negative zircon εHf(t) values. It is inferred that these Triassic felsic volcanics originated from the partial melting of crustal rocks in high-pressure environments such as the garnet stability zone within the deep mantle. These felsic volcanic rocks were likely generated during the transitional stage from island arc subduction to syn-collisional settings. Notably, the syn-collisional interaction between South China and Indochina blocks exerted significantly greater tectonic control on the Youjiang Basin than oceanic subduction.

1. Introduction

The Paleo-Tethys Ocean was an ocean that existed between Gondwana and Laurasia from the Early Paleozoic to the Early Mesozoic [1,2,3,4]. Researchers have preserved some of the most complete geological records of the eastern Paleo-Tethys Ocean’s tectonic evolution [5,6,7,8]. Southeast Asia consists of a series of allochthonous continental blocks that originally rifted from the Gondwana continent during the Paleozoic and accreted to the Eurasian continent during the Mesozoic Era [3,7,9,10]. The South China Block (SCB) and Indochina Block (ICB) are thought to have collided during the Triassic period, with the Jinshajiang–Ailaoshan suture zone in southwestern Yunnan and the Bangxi–Henxing suture zone on Hainan Island marking their western and eastern boundaries, respectively (Figure 1a) [7,8,9,11]. However, the connection between Dian–Qiong and Song Ma suture zones remains a subject of debate. Some geologists have proposed the Dian–Qiong suture zone as the boundary, citing sporadic occurrences of ophiolites and diverse basaltic lithologies within Late Paleozoic deep-marine sequences from Babu to Napo and Pingxiang [5,6]. Others have considered the Song Ma suture zone to be the boundary based on Permian–Triassic dismembered ophiolitic fragments and associated arc igneous rocks along the zone [9,10,11,12]. Meanwhile, the polarity of subduction between the SCB and ICB during the Permian–Triassic also remains contentious. Some researchers support the northeastward subduction of the ICB beneath the SCB, citing evidence from Mesozoic mineralization, whereas others suggest the southwestward subduction of the SCB beneath the ICB, supported by the occurrence of numerous Permian arc-like igneous rocks in the southwestern Song Ma region [12,13]. The SCB and ICB exhibit distinct basement compositions and contrasting pre-Triassic tectonic histories, reflecting in the geochemical diversity of their felsic volcanics [6,10,11].
The Youjiang Basin is located in the western South China Block (SCB). Permian-to-Triassic felsic igneous rocks are mainly concentrated in the southern part of the basin [11,13,14,15]. The Youjiang Basin initially rifted during the Devonian and was subsequently filled with deep-water siliciclastic rocks during the Early-to-Middle Triassic period. The tectonic nature of the Youjiang Basin during those period remains a topic of debate, with interpretations ranging from a rift basin, a passive continental margin rift basin, a back-arc rift basin, and a back-arc basin to an oceanic basin [14,15]. Regarding the basin’s characteristics during the Indosinian period (Early–Middle Triassic), most researchers agree that the Youjiang Basin underwent a transition from an extensional basin to a compressional basin [11,12]. However, there is no consensus on whether the basin represents a remnant basin, a foreland basin, a retroarc foreland basin, or a peripheral foreland basin [16,17]. Furthermore, the discussion around subduction polarity has implications for the Permian–Triassic tectonic framework of the Youjiang Basin, which is closely tied to the convergence of the South China and Indochina blocks [11,12,17]. Those volcanic rocks preserved within the sedimentary strata may provide crucial insights into the tectonic framework of the Youjiang Basin and its underlying crustal composition [4,7,10,11]. This research focuses on the geochronology and geochemical characterization of Triassic felsic volcanic rocks in the Youjiang Basin to elucidate the timing and processes of felsic volcanism in the region. It aims to deepen our understanding of Triassic magmatic processes and to provide insights into the broader tectonic evolution of Eastern Tethyan geodynamics.

2. Geological Setting and Sample Description

2.1. Regional Geology

The Youjiang Basin is located in the southwestern part of the South China block, marking the junction of the Tethys and the Pacific tectonic domains (Figure 1a) [10,11,12,18]. This basin exhibits a rhomboid geometry bounded by four major faults. Specifically, it is bounded to the northeast by the Ziyun–Nandan Fault, connected to the Shiwandashan Basin to the southeast via the Pingxiang–Nanning Fault, separated from the Indochina Block to the southwest by the Honghe Fault, and linked to the Kangdian Terrane to the northwest through the Shizong–Mile Fault. (Figure 1a) [16,17,18,19,20]. The Youjiang Basin was developed on an early Paleozoic basement and then underwent intense rifting during the Early Devonian, which resulted in a paleogeographic framework characterized by graben basins bounded by normal faults. The sedimentary successions in the graben and carbonate platform domains exhibit distinct depositional architectures, characterized by deep-marine pelites, cherts, and limestone accumulations in the former, contrasting with shallow-water carbonate-dominated facies associations in the latter. This basin configuration remained stable until the Early Triassic, preceding Middle–Late Triassic basin infilling with thick turbidite successions in the Youjiang Basin. Strata corresponding to the Mesoproterozoic–Lower Cambrian and Ordovician–Lower Devonian intervals are conspicuously absent in this basin. Widespread exposures include Devonian, Carboniferous, Permian, and Triassic strata while Jurassic, Upper Cretaceous, Tertiary, and Quaternary strata are sporadically distributed. Middle-to-Late Cambrian strata are relatively infrequent in this basin.
The Youjiang Basin underwent intense magmatic activity during the Mesozoic Era. Mafic igneous rocks are primarily exposed in the northwestern part of the basin, notably in Longlin–Bama, Napo–Jingxi–Pingxiang, Babu, and Funing, as well as in Gaoping and Nui Chua in northeastern Vietnam (Figure 1b). Early-to-Middle Triassic intermediate-to-acid volcanic rocks mainly occur in the Beisi and Banna Formations; the volcanic samples analyzed in this study were collected from these areas. These volcanic rocks are distributed along the northwestern side of the Qin–Fang tectonic belt, particularly in Dongzhong, Banba, and Fulong, and on both sides of the Pingxiang–Nanning Fault in Pingxiang, Longzhou, and Chongzuo. The volcanic rocks of the Beisi Formation can be divided into two volcanic cycles. The first cycle predominantly comprises volcaniclastic rocks and lava assemblages, featuring multiple volcanic rhythms (sub-cycles) transitioning from volcaniclastic rocks to lavas. The lavas are predominantly tholeiitic basalt, andesite, and rhyolite while the volcaniclastic rocks consist of block lavas, breccia lavas, tuff lavas, welded breccia tuffs, and welded tuffs. The thickness of the volcanic layers in the Pingxiang–Chongzuo area varies significantly, ranging from approximately 600 to 1900 m. The second cycle, characterized by a rhyolite-ash tuff assemblage, is separated from the first cycle by an 8 m thick mudstone layer. Its lithologies include rhyolite, breccia lavas, pumice lavas, and ash tuffs, with thicknesses ranging from 500 to 800 m. The Middle Triassic Banna Formation primarily consists of sedimentary ash tuffs and tuffaceous sandstones (siltstones and mudstones), with thicknesses ranging from 20 to 120 m. The felsic volcanic rocks of the Banba Formation are mainly distributed in the southeastern areas of Dongzhong, Banba, and Fulong. They are dominated by rhyolitic lithologies, featuring flow-banded pumice, ash lavas, block lavas, and rhyolitic ash tuffs, with thicknesses ranging from 170 to 500 m.

2.2. Sample Description

The dacitic samples in this study were collected from the first volcanic cycle of the Beisi Formation in the northern Daqingshan area. Their main lithology was rhyolite, displaying a gray-to-dark-gray color, porphyritic texture, and massive structure. The matrix is largely composed of microcrystalline quartz and volcanic glass components, featuring a spherulitic–microlitic or microlitic texture (Figure 2). The phenocrysts included quartz (25%), alkali feldspar (15%), plagioclase (15%), and opaque minerals (5%). The mineral surfaces were smooth and clean under polarized light. The alkali feldspar was colorless and transparent, appearing as euhedral platy or angular crystals with long axes measuring approximately 0.5~1.0 mm, whose surfaces exhibited slight clay alteration under cross-polarized light. The plagioclase was euhedral to subhedral and prismatic with long axes of approximately 0.5~1.0 mm. It displayed significant alteration to sericite under cross-polarized light. The opaque minerals were black and granular, likely consisting of magnetite or ilmenite.

3. Analytical Methods

This study analyzed six fresh samples from the Daqingshan area in the Beisi Formation for major and trace elements, with two selected for zircon U-Pb and Hf isotopic analyses at Wuhan SampleSolution Analytical Technology Co., Ltd. (Wuhan, China) Data for Banba felsic igneous rocks in the Banba Formation for major and trace element were referenced from [11] while major trace elements and Hf isotopes for Nazhen, Fengle, Baihe, and Madong felsic igneous rocks in the Beisi Formation were referenced from [10,21].

3.1. Zircon U–Pb Isotope Analysis

Zircon crystals were separated via heavy liquid and magnetic separation, followed by hand-picking. They were mounted in epoxy resin, polished to half-thickness, and imaged using cathodoluminescence (CL) with a Gatan MonoCL4+ spectrometer attached to an FEI Quanta 450 FEG SEM to reveal internal structures and select U–Pb analysis spots [22,23]. U-Pb dating and trace element analysis were performed simultaneously using LA-ICP-MS at Wuhan SampleSolution Analytical Technology Co., Ltd. The GeolasPro laser ablation system, equipped with a COMPexPro 102 ArF excimer laser (193 nm, 200 mJ), and an Agilent 7900 ICP-MS were used, with helium as the carrier gas and argon as the make-up gas. Zircon 91,500 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration [24,25]. Data reduction, including background correction and calibration, was processed using ICPMSDataCal, and results were visualized with Isoplot/Ex_ver3 [26].

3.2. In Situ Zircon Hf Isotope Analyses

The Hf isotope analyses were performed using a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Waltham, MA USA) coupled with a Geolas HD excimer ArF laser ablation system at Wuhan Sample Solution Analytical Technology Co., Ltd. A “wire” signal smoothing device ensured stable signals even at low repetition rates (1 Hz). Helium was used as the carrier gas, mixed with argon as makeup gas, with nitrogen added to enhance Hf isotope sensitivity [27,28]. The addition of nitrogen, combined with an X skimmer cone and Jet sample cone, increased the signal intensity of Hf, Yb, and Lu by factors of 5.3, 4.0, and 2.4, respectively. Analyses were conducted in single-spot mode (44 μm−7.0 J/cm2). Each measurement included 20 s of background and 50 s of ablation signal acquisition. Zircon standards Plešovice, 91500, and GJ-1 were analyzed for external calibration and quality monitoring, with external precision better than 0.000020. High Yb/Hf zircon data were validated using the Temora 2 standard. Results aligned with recommended values [29,30]. At the same time, in order to monitor the test data of the high Yb/Hf ratio zircon, the internationally used high Yb/Hf ratio standard sample Jilin was used to monitor the test data of the high Yb/Hf ratio zircon [24]. The Hf isotopic compositions of Plešovice, 91500, and GJ-1 have been reported by [30].

3.3. Whole-Rock Major and Trace Element Analyses

The sample discs for whole-rock major element analysis were made by melting method. The flux was a mixture of lithium tetraborate, lithium metaborate, and lithium fluoride (45:10:5). Ammonium nitrate and lithium bromide were used as oxidant and release agent, respectively. The melting temperature was 1050 °C and the melting time was 15 min. Trace element analysis was conducted on an Agilent 7700e ICP-MS at Wuhan SampleSolution Analytical Technology Co., Ltd. The digestion process involved the following: (1) drying 200-mesh sample powder at 105 °C for 12 h; (2) weighing 50 mg powder into a Teflon bomb; (3) adding 1 mL HNO3 and 1 mL HF; (4) sealing in a stainless-steel jacket and heating at 190 °C for >24 h; (5) evaporating to dryness at 140 °C, and repeating with HNO3; (6) adding HNO3, MQ water, and 1 ppm in internal standard; and (7) resealing, heating at 190 °C for >12 h, and diluting to 100 g with 2% HNO3.

4. Results

4.1. Zircon U-Pb Dating

Two rhyolitic samples (PX3 and PX8) from the Daqingshan area in the Youjiang Basin were selected for zircon U-Pb isotopic dating. The results are presented in Table 1, with representative zircon cathodoluminescence (CL) images and U-Pb Concordia diagrams shown in Figure 3 and Figure 4. Zircon grains from the felsic igneous rocks were euhedral or subhedral, showed oscillatory zoning, and had 60~253 ppm Th and 135~560 ppm U, with Th/U ratios of 0.18~0.71, which implies a magmatic origin [7,8]. Sample PX03 yielded a weighted mean 206Pb/238U age of 250.7 ± 1.3 Ma (MSWD = 0.8, n = 15) (Figure 4a,b). Sample PX08 had a weighted mean 206Pb/238U ages of 246.2 ± 2.1 Ma (MSWD = 1.3, n = 14) (Figure 4c,d). These ages constrained the eruption age of volcanism in the Daqingshan area to 246~251 Ma.

4.2. Zircon Hf Isotopes

The Hf isotopic compositions of zircon grains from samples PX3 and PX8 were determined in this study and the zircon U-Pb weighted mean ages of sample PX3 (251 Ma) and PX8 (242 Ma) were used to calculate the corresponding zircon εHf(t) values (Table 2). Zircons from the sample PX03 yielded 176Hf/177Hf and 176Lu/177Hf ratios of 0.281713~0.282617 and 0.001072~0.002488, which corresponded to εHf(t) values of −2.6~−1; zircons from the sample PX08 yielded 176Hf/177Hf and 176Lu/177Hf ratios of 0.281416~0.282432 and 0.000746~0.001880, which corresponded to εHf(t) values of −43.2~−7 (Figure 5).
Previous studies had documented similar zircon Lu–Hf isotopic signatures; zircons from felsic igneous rocks in the Nazhen area yielded initial εHf(t) values ranging from −34.7 to −24.1 [10]; zircons from felsic igneous rock samples in Fengle area yielded initial εHf(t) values ranging from −12.6 to −0.2 [10]; zircons from felsic igneous rock samples in Baihe area yielded initial εHf(t) values ranging from −14.5 to −7.8 [10]; zircons from felsic igneous rock samples in Madong area yielded initial εHf(t) values ranging from −26.8 to −6.1 [21]. The zircon εHf(t) values of the sample predominantly fell within the evolutionary zone of the southern South China Block (SCB) basement crust, as depicted in Figure 5a, and lay within the lower or upper crust evolution zone in Figure 5b. This observation was consistent with the characteristics of SCB basement crustal rocks as revealed by zircon Lu-Hf isotopic dating studies.

4.3. Major and Trace Element Compositions

Major and trace element concentrations for Triassic felsic volcanics in the Daqingshan area (DQS-1~DQS-6) from Youjiang Basin are presented in Table 3. These rocks display geochemical characteristics consistent with other Triassic felsic volcanics within the Youjiang Basin, such as those exposed in the Nazhen, Baihe, Fengle, Banba, and Madong area. The Triassic felsic volcanics of the Daqingshan area have low loss-on-ignition (LOI) contents (<2.4 wt%), and major oxides used in the description and diagrams below are normalized to 100% on an LOI-free basis. The felsic volcanic samples are rhyodacite/dacite in composition (Figure 6a and Table 3) and characterized by high SiO2 (66~73 wt%) and K2O (1.37~5.06 wt%) and low MgO (0.62~1.42 wt%), Al2O3 (12.40~14.56 wt%), CaO (0.73~3.16 wt%), and P2O5 (0.11~0.21 wt%). They are mainly plotted in the high-K calc-alkaline field in Co-Th and A.R.-SiO2 diagrams (Figure 6b,c). The samples were marked by high A/CNK values ranging from 0.95 to 1.23 with peraluminous affinities (Figure 6d). In addition, they mainly were classified as alkalic-to-calcic series on an Na2O + K2O–CaO vs. SiO2 diagram (Figure 6e). Plotting the samples on a K2O vs. SiO2 diagram indicated that they were either high-K calc-alkaline or shoshonitic (Figure 6f).
The Triassic felsic volcanics of the Daqingshan area are marked by enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSE) with significant Nb, Ta, Ti, and Eu negative anomalies (Figure 7a–c). They are enriched in light REE (LREE) with flat heavy REE (HREE) patterns and remarkable Eu negative anomalies (Eu/Eu* = 0.41~0.52) (Figure 7b,d). (La/Yb)CN and (Dy/Yb)CN ratios of the samples ranged from 5.54 to 6.82 and 1.08 to 1.25, respectively (Figure 7). Such multi-element and REE normalized patterns were similar to those of other Triassic felsic volcanics within the Youjiang Basin.

5. Discussion

5.1. The Age of the Triassic Felsic Volcanics from Youjiang Basin

The Triassic felsic volcanic rocks in the Youjiang Basin predominantly occur within the Middle-to-Lower Triassic Beisi and Banba Formations, which are spatially restricted to specific localities (Figure 1) [10,11,27]. New zircon U–Pb dating results from this study further suggest an eruption age of ~251~246 Ma for rhyolites from the Beisi Formation in the Daqingshan area. The Zircon U-Pb dating of rhyolites from the Banba Formation in the Fulong area yielded an age of ~250 Ma whereas dacites from the Beisi Formation in the Pingxiang area were dated at ~246 Ma [11]. Similarly, dacites and rhyolites from the Beisi Formation in the Nazhen and Fengle areas have been dated at ~245~241 Ma and rhyolites and dacites from the Baifeng Formation in the Baihe area at ~240 Ma [7,11]. Additionally, the zircon U-Pb dating of rhyolites from the Banba Formation in the Madong area indicates an eruption age of ~251~250 Ma [21]. Available geochronological data indicate that the Triassic felsic volcanics from the Beisi, Baifeng, and Banba Formations erupted during the Early–Middle Triassic period (ca. 241~251 Ma).

5.2. The Petrogenesis of Triassic Felsic Volcanics in the Youjiang Basin

Petrographic observations reveal that most Triassic felsic volcanic rocks from the Daqingshan area in the Youjiang Basin are relatively fresh, characterized by well-preserved flow-banding textures and predominantly fresh feldspar phenocrysts (Figure 2). These samples exhibited low loss-on-ignition (LOI) values (LOI < 2.0 wt%), with only one sample showing slightly higher LOI values (3.33 wt%) (Table 1). The similarity in primitive mantle- and chondrite-normalized elemental patterns suggests that high field strength elements (HFSEs) and large ion lithophile elements (LILEs) were not significantly affected by alteration, implying negligible alteration effects on the geochemical dataset, which is therefore suitable for petrogenetic discussions. These data can be used to jointly discuss the petrogenesis and tectonic background of Triassic felsic volcanics in the Youjiang Basin.
The petrogenesis of these felsic volcanic rocks can be attributed to (1) the fractional crystallization (FC) and assimilation-fractional crystallization (AFC) of a mantle-derived mafic magma or (2) the partial melting of crustal rocks [38,39,40,41,42,43,44,45,46]. The Triassic felsic volcanics in the study area have relatively high A/CNK (1.50~1.71) and K2O (1.37~5.06 wt%) contents, which suggests an Al- and K-rich source. The vast majority of volcanic samples in the Daqingshan area showed high CaO/Na2O (>0.3) contents, consistent with the volcanic samples in the Daqingshan, Banba, Madong, Nazhen and Baihe areas, suggesting that they were derived from the partial melting of psammitic rocks [10,11,21].
The felsic volcanic samples had zircon Hf isotopic compositions similar to those of the basement rocks of the SCB, supporting a crust-dominant source. They were characterized by low εHf(t) (−0.2~−34.7), similar to those of the South China Block Triassic granitoids that were interpreted as having been derived from the partial melting of metasedimentary rocks (Figure 5) [10,47,48,49,50]. On the La-La/Sm and La-La/Yb diagrams, the Triassic felsic volcanics follow a trend inconsistent with partial melting, and cannot fully explain the observed fractionation history (Figure 8a,b). On the Zr/Nb-Nb/La diagrams, these felsic volcanic rocks exhibit a crustal contamination trend. As a result, these features suggest that Early–Middle Triassic felsic volcanics in the Youjiang Basin could not have been derived from the asthenosphere, the lithospheric mantle, or the parent magmas of basalts via crustal contamination, fractional crystallization, or assimilation crustal contamination processes. In addition, the Triassic felsic volcanics have low Cr, and Ni contents, which are plotted along the fractionation trend approach to slab-derived melts (Figure 8d). Moreover, the negative correlations of SiO2 with the Nb/Zr and Nb/La of the felsic volcanic samples were not observed (Figure 8e,f), which was suggesting insignificant crustal contamination. Thus, these Early–Middle Triassic felsic volcanic rocks in the Youjiang Basin were mainly the products of the partial melting of crustal rocks.
The negative correlations among CaO, FeOT, and SiO2 suggest clinopyroxene and Fe oxide fractionation during magma evolution (Figure 9a,b) [43,48,49,50,51]. The extent of crystal differentiation for clinopyroxene is indicated by the Daqingshan, Nazhen, Banba, Baihe, Fengle, and Madong areas in descending order. The iron oxides exhibit a crystallization trend, with differentiation increasing across the Daqingshan, Nazhen, Fengle, Baihe, Madong, and Banba areas. These felsic volcanic rocks show evidence of plagioclase fractionation, which is consistent with the positive correlations between Sr and Ba, Eu/Eu* versus Ba, and Sr and Ba/Sr (Figure 9c, e) in log–log diagrams. This is because plagioclase is enriched in Eu and Sr [52,53].
The presence of U-shaped patterns in the chondrite-normalized REE patterns (Figure 6) also indicates hornblende fractionation, given that hornblende is the primary host mineral of middle REEs. The positive linear correlation between Er and Dy in the rhyolitic magma (Figure 9g) provides additional evidence for hornblende fractionation during magma evolution [51,54]. The negative anomalies of Nb, Ta, and Ti in the primitive mantle-normalized trace element diagram (Figure 6) can be attributed to the fractionation of Ti-bearing phases. Furthermore, the trends observed on the (La/Yb)CN vs. La diagram (Figure 9f) are predominantly influenced by the fractionation of monazite and allanite, with apatite playing a minor role. It is also evident that zircon fractionation led to a decrease in Zr contents and Zr/Hf ratios (Figure 9h). Consequently, the rhyolites exhibited significant compositional variations, which were likely due to the fractionation of clinopyroxene, plagioclase, hornblende, and Ti-bearing minerals, as well as accessory minerals such as apatite, allanite, monazite, and zircon.
In the chondrite-normalized REE patterns, the Triassic felsic volcanics of the Youjiang Basin exhibited relatively flat REE configurations, coupled with a moderate enrichment in LREEs (4.82 < (La/Yb)CN < 10.21) and elevated (Tb/Yb)CN ratios (1.01~1.57). The presence of garnet in the source area, during the partial melting of certain thickened lower crust layers, can disrupt the heat source dynamics of melting and the fractionation of rare earth elements. This disturbance can result in a high (La/Yb)CN phenomenon [53,55]. When garnets remain in the magma source area, Yb in the melt is significantly retained within the residual phase. This retention leads to a Yb deficit in the melt, subsequently increasing the Tb/Yb ratio, which often indicates partial melting in high-pressure environments (such as the garnet stability field deep within the mantle) [55,56]. Therefore, the rhyolite magma source regions of the Youjiang Basin likely originated from partial melting in a high-pressure environment, such as the garnet stability field in the deep mantle. The rhyolites under analysis also exhibit a notable feature of K-rich source, which took place either in the original magma source or during later stages of magmatic evolution [17,57]. This enrichment resulted in elevated K2O contents and high K2O/Na2O ratios. However, these rhyolites did not undergo chemical alteration post magmatic crystallization, suggesting that the K-enrichment might be indicative of a specific magmatic process in the source. While Meen (1987) argued that orthopyroxene-dominated fractionation produces ultrapotassic magmas [53,57,58], the absence of orthopyroxene phenocrysts and the consistent K2O and MgO trend suggest that this fractionation mechanism was not the primary cause for the K-enrichment in the Triassic felsic volcanics of the Youjiang Basin. Instead, the K-enrichment should be derived from partial melting.

5.3. Tectonic Setting and Geodynamic Implications

The Youjiang Basin, situated near the Ailaoshan–Song Ma suture zone between the South China and Indochina Blocks, preserves a detailed record of the Paleo-Tethys Ocean’s tectonic evolution (Figure 1) [2,10,59,60]. This record encompasses subduction, closure, and post-collisional stages, with studies demonstrating that the basin evolved from an active continental margin during the Early-to-Middle Mesozoic to a back-arc extensional regime. Such evolution provides critical insights into the timing, mechanisms, and dynamics of post-collisional extension following the South China–Indochina Block collision [10,21,61]. Regional geological evidence reveals that the Paleozoic–Mesozoic ophiolite suite (420~240 Ma), high-pressure blueschists (440~390 Ma), and arc volcanic rocks (300~240 Ma) within the Ailaoshan–Song Ma suture zone collectively elucidate the dynamic processes of the Paleo-Tethys Ocean from Carboniferous subduction initiation to Triassic closure [10,11,21,59,62].
The Triassic acidic volcanic rocks in the Youjiang Basin are indicative of the Permian–Triassic subduction and closure processes of the Paleo-Tethys Ocean [10,11,59,60,61,62,63]. However, the tectonic origin of these rocks remains a subject of debate. One hypothesis attribute these volcanic rocks to an active continental margin setting. For instance, Early Triassic intermediate-acidic volcanic rocks in the Pingxiang region (Banba Formation) are interpreted as products of Paleo-Tethyan slab subduction and rollback during the Indosinian orogeny, forming a magmatic arc. This interpretation is substantiated by geochemical signatures and volcanic rock characteristics [10,11,63]. Conversely, an alternative hypothesis proposes a post-collisional extensional origin. Triassic acidic volcanic rocks in southwestern Guangxi exhibit peraluminous affinities and high-K calc-alkaline compositions, consistent with crustal melting in a post-collisional extensional regime [10,59,60,61]. These contrasting interpretations reflect divergent views on the timing and mechanisms of tectonic evolution. Multidisciplinary evidence from petrogeochemistry, detrital zircon geochronology, and structural analyses revealed the basin’s complex staged evolution, offering key constraints on South China–Indochina interactions. To evaluate these hypotheses, tectonic discrimination diagrams were employed. The samples were found to cluster in volcanic arc and active continental margin fields when the Ta vs. Th [64] and Hf vs. Rb/30 vs. 3Ta [65] diagrams were utilized (Figure 10a,b). In contrast, the Yb vs. Ta [65,66] and R1-R2 [67] diagrams exhibited syn-collisional characteristics (Figure 10c,d), a finding further substantiated by Ca + Al vs. 3Al + 2(Na + K) vs. Al + (Na + K) plots (Figure 10e) [68]. These results suggest that Triassic felsic volcanism occurred in a transitional setting combining Tethys oceanic crust subduction and syn-collisional convergence.
Previous studies indicated that Permian–Early Triassic volcanic rocks in the Youjiang Basin exhibited geochemical characteristics of island arc volcanic rocks, consistent with compressional subduction during South China–Indochina convergence [2,3,60,69,70]. However, Early–Middle Triassic felsic volcanic rocks in the basin display geochemical affinities with A-type granites, characterized by crustal remelting signatures rather than mantle-derived inputs. This contrasts with the expected tectonic framework of southwestward subduction, instead suggesting syn-collisional extensional environments [4,47,62]. Continuous sedimentation from the Early to the Middle Triassic is evidenced by initial graben-platform deposits transitioning to turbiditic sequences without a stratigraphic hiatus [18,19,71]. This implies that the basin transitioned from an active continental margin undergoing subduction termination and collisional orogeny to a passive margin during the Early–Middle Triassic [21,58]. The felsic volcanism likely occurred during the arc-continent collision transition, spatially distal from the oceanic trench, with South China–Indochina collision exerting dominant control over basin evolution compared to oceanic subduction [4,15,72]. The provenance analysis of Triassic sedimentary rocks demonstrates predominant southwestern sediment sources, suggesting the Youjiang Basin likely constitutes a peripheral foreland basin, and syn-collisional extension between the Indochina and South China Blocks, coupled with orogenic uplift, supplied substantial detritus to the basin [72,73,74].

6. Conclusions

  • The Triassic felsic volcanics from the Beisi, Baifeng, and Banba Formations erupted during the Early–Middle Triassic period (ca. 241~251 Ma).
  • The Early–Middle Triassic felsic volcanic rocks in the Youjiang Basin were predominantly formed from the partial melting of crustal rocks. These rocks likely originated from partial melting processes occurring within high-pressure environments, such as the garnet stability field within the deep mantle.
  • These felsic volcanic rocks likely originated during the transition from Tethys oceanic crust subduction to syn-collisional settings. Notably, the syn-collisional interactions between the South China and Indochina blocks exerted a significantly greater tectonic impact on the Youjiang Basin compared to oceanic subduction.

Author Contributions

K.D. and Z.L. conceived and designed the experiments; K.D., X.F. and Y.W. took part in the discussion; K.D., X.D. and Z.L. took part in the field campaigns; K.D. wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially funded by the Guangxi Science and Technology Base and Talent Project (project number: AD21220157; AD23026271) and the Guangxi Natural Science Foundation Project (project number: 2025GXNSFAA069450; 2025GXNSFAA069320).

Data Availability Statement

The data presented in this study are available on request from the corresponding authors.

Acknowledgments

We would like to sincerely thank the peer reviewers and the editorial team for their valuable and constructive comments on this paper. We also express our gratitude to Wuhan Sample Solution Analytical Technology Co., Ltd. for their support and assistance with the isotope-dating analysis and rock geochemical analysis experiments.

Conflicts of Interest

The authors declare no conflicts of interest. Among them, Authors Xiaoli Fei are employees of Guangxi Land and Resources Planning and Design Group Co., Ltd. The paper reflects the views of the scientists and not the company.

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Minerals 15 00398 g001
Figure 1. (a) Simplified sketch map of the South China and Indochina blocks showing the location of the Youjiang Basin (modified after [8,10]). (b) Simplified geological map of southern Youjiang Basin and its surrounding areas (modified after [11]). JA represents Jinshajiang–Ailaoshan suture zone; SM represents Song Ma suture zone; BC: Bangxi represents Chenxing suture zone; DQ represents Dian–Qiong suture zone; DBPF represents Dian Bien Phu Fault; RRF represents Red River Fault; MSF represents Mile–Shizong Fault; ZNF represents Ziyun–Nandan Fault; PNF represents Pingxiang–Nanning Fault; NPJ represents Nanpanjiang Fault; XLF represents Xialei and represents Lingma Fault; WMF represents Wenshan–Malipo Fault; FNF represents Funing–Napo Fault; YJF represents Youjiang Fault.
Figure 1. (a) Simplified sketch map of the South China and Indochina blocks showing the location of the Youjiang Basin (modified after [8,10]). (b) Simplified geological map of southern Youjiang Basin and its surrounding areas (modified after [11]). JA represents Jinshajiang–Ailaoshan suture zone; SM represents Song Ma suture zone; BC: Bangxi represents Chenxing suture zone; DQ represents Dian–Qiong suture zone; DBPF represents Dian Bien Phu Fault; RRF represents Red River Fault; MSF represents Mile–Shizong Fault; ZNF represents Ziyun–Nandan Fault; PNF represents Pingxiang–Nanning Fault; NPJ represents Nanpanjiang Fault; XLF represents Xialei and represents Lingma Fault; WMF represents Wenshan–Malipo Fault; FNF represents Funing–Napo Fault; YJF represents Youjiang Fault.
Minerals 15 00398 g001
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Figure 2. Representative field and microscope photos of the Triassic felsic volcanics from Daqingshan area in Youjiang Basin. (a) macroscopic outcrop of felsic volcanics (sample DQS-1); (b,c) microscopic characteristics (sample DQS-1); (d) macroscopic outcrop of felsic volcanics (sample DQS-3); (e,f) microscopic characteristics (sample DQS-3; (g) macroscopic outcrop of felsic volcanics (sample DQS-4); (h,i) microscopic characteristics (sample DQS-4); (j) hand specimens of felsic volcanics (sample DQS-6); (k,l) microscopic characteristics (sample DQS-6). Qz—quartz; Pl—plagioclase; Chl—chlorite; Ser—sericite.
Figure 2. Representative field and microscope photos of the Triassic felsic volcanics from Daqingshan area in Youjiang Basin. (a) macroscopic outcrop of felsic volcanics (sample DQS-1); (b,c) microscopic characteristics (sample DQS-1); (d) macroscopic outcrop of felsic volcanics (sample DQS-3); (e,f) microscopic characteristics (sample DQS-3; (g) macroscopic outcrop of felsic volcanics (sample DQS-4); (h,i) microscopic characteristics (sample DQS-4); (j) hand specimens of felsic volcanics (sample DQS-6); (k,l) microscopic characteristics (sample DQS-6). Qz—quartz; Pl—plagioclase; Chl—chlorite; Ser—sericite.
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Figure 3. Zircon cathodoluminescence images of the samples PX3 (a) and PX8 (b) for Triassic felsic volcanics of Daqingshan area in the Youjiang Basin. Analyses areas and values of εHf(t) and U-Pb age are given in the yellow and red circles, respectively.
Figure 3. Zircon cathodoluminescence images of the samples PX3 (a) and PX8 (b) for Triassic felsic volcanics of Daqingshan area in the Youjiang Basin. Analyses areas and values of εHf(t) and U-Pb age are given in the yellow and red circles, respectively.
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Figure 4. LA-ICP-MS zircon U-Pb Concordia diagrams and weighted mean 206Pb/238U ages for zircon from felsic volcanics samples PX3 (a,b) and PX8 (c,d) of Daqingshan area in the Youjiang Basin.
Figure 4. LA-ICP-MS zircon U-Pb Concordia diagrams and weighted mean 206Pb/238U ages for zircon from felsic volcanics samples PX3 (a,b) and PX8 (c,d) of Daqingshan area in the Youjiang Basin.
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Figure 5. Age (Ma)-εHf(t) (a) and age (Ma)-176Hf/177Hf (b) diagrams for Triassic felsic volcanics of Daqingshan area in the Youjiang Basin (after [31]). The field of the South China Block (SCB) basement crustal rocks is from [5]. CHUR—chondritic uniform reservoir. The data for felsic igneous rocks in Daqingshan area were taken from this study. The data for felsic igneous rocks in Nazhen, Fengle, and Baihe areas have been quoted from [10]; the felsic igneous rock samples in Madong area have been quoted from [21].
Figure 5. Age (Ma)-εHf(t) (a) and age (Ma)-176Hf/177Hf (b) diagrams for Triassic felsic volcanics of Daqingshan area in the Youjiang Basin (after [31]). The field of the South China Block (SCB) basement crustal rocks is from [5]. CHUR—chondritic uniform reservoir. The data for felsic igneous rocks in Daqingshan area were taken from this study. The data for felsic igneous rocks in Nazhen, Fengle, and Baihe areas have been quoted from [10]; the felsic igneous rock samples in Madong area have been quoted from [21].
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Figure 6. (a) Nb/Y vs. SiO2 (after [32]); (b) Co vs. Th (after [33]); (c) A.R. (Alkalinity Ratio = [Al2O3 + CaO + (Na2O + K2O)]/[Al2O3 + CaO–(Na2O + K2O)]–SiO2; (d) A/CNK-A/NK (after [34]); (e) SiO2 vs. K2O+Na2O–CaO (after [35]); (f) K2O vs. SiO2 (after [36]) diagrams for Triassic felsic volcanics in the Youjiang Basin. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
Figure 6. (a) Nb/Y vs. SiO2 (after [32]); (b) Co vs. Th (after [33]); (c) A.R. (Alkalinity Ratio = [Al2O3 + CaO + (Na2O + K2O)]/[Al2O3 + CaO–(Na2O + K2O)]–SiO2; (d) A/CNK-A/NK (after [34]); (e) SiO2 vs. K2O+Na2O–CaO (after [35]); (f) K2O vs. SiO2 (after [36]) diagrams for Triassic felsic volcanics in the Youjiang Basin. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
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Figure 7. Primitive-mantle and chondrite normalized diagrams for Triassic felsic volcanics in the Youjiang Basin. (a,b) Daqingshan, Nazhen, and Baihe rhyodacite/dacite; (c,d) Fengle, Banba, and Madong rhyodacite/dacite. Chondrite normalization values from [37]. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
Figure 7. Primitive-mantle and chondrite normalized diagrams for Triassic felsic volcanics in the Youjiang Basin. (a,b) Daqingshan, Nazhen, and Baihe rhyodacite/dacite; (c,d) Fengle, Banba, and Madong rhyodacite/dacite. Chondrite normalization values from [37]. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
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Figure 8. (a) La vs. La/Sm, (b) La vs. La/Yb, (c) Zr/Nb vs. Nb/La, (d) Cr vs. Ni, (e) SiO2 vs. Nb/La, and (f) SiO2 vs. Nb/La diagrams for Triassic felsic volcanics in the Youjiang Basin. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
Figure 8. (a) La vs. La/Sm, (b) La vs. La/Yb, (c) Zr/Nb vs. Nb/La, (d) Cr vs. Ni, (e) SiO2 vs. Nb/La, and (f) SiO2 vs. Nb/La diagrams for Triassic felsic volcanics in the Youjiang Basin. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
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Figure 9. (a) CaO vs. SiO2 [43], (b) FeOT vs. SiO2 [43], (c) Ba vs. Eu/Eu* [17], (d) Ba vs. Sr [17], (e) Ba/Sr vs. Sr [53], (f) (La/Yb)CN vs. La [53], (g) Dy vs. Er [54], and (h) Zr/Hf vs. Zr [54] diagrams showing variations in composition of the Triassic felsic volcanics in the Youjiang Basin. Abbreviations are as for Figure 2 with Kf = K-feldspar, Hb = hornblende, Cpx = clinopyroxene, Opx = orthopyroxene, Mon = monazite, Allan = allanite, Zr = zircon, and Ap = apatite. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
Figure 9. (a) CaO vs. SiO2 [43], (b) FeOT vs. SiO2 [43], (c) Ba vs. Eu/Eu* [17], (d) Ba vs. Sr [17], (e) Ba/Sr vs. Sr [53], (f) (La/Yb)CN vs. La [53], (g) Dy vs. Er [54], and (h) Zr/Hf vs. Zr [54] diagrams showing variations in composition of the Triassic felsic volcanics in the Youjiang Basin. Abbreviations are as for Figure 2 with Kf = K-feldspar, Hb = hornblende, Cpx = clinopyroxene, Opx = orthopyroxene, Mon = monazite, Allan = allanite, Zr = zircon, and Ap = apatite. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
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Figure 10. Geotectonic setting diagrams for Triassic felsic volcanics of Pingxiang area in the Youjiang Basin. (a) Yb vs. Ta diagrams [65,66]; (b) Hf vs. Rb/30 vs. 3Ta diagrams [65,66]; (c) the Ta vs. Th diagram [64]; (d) the R1 vs. R2 diagram (R1 = 4Si–11(Na + K)–2(Fe + Ti), R2 = 6Ca + 2Mg + Al) [67]. (e) The Ca + Al–3Al + 2(Na + K)–Al + (Na + K) diagram [68]. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
Figure 10. Geotectonic setting diagrams for Triassic felsic volcanics of Pingxiang area in the Youjiang Basin. (a) Yb vs. Ta diagrams [65,66]; (b) Hf vs. Rb/30 vs. 3Ta diagrams [65,66]; (c) the Ta vs. Th diagram [64]; (d) the R1 vs. R2 diagram (R1 = 4Si–11(Na + K)–2(Fe + Ti), R2 = 6Ca + 2Mg + Al) [67]. (e) The Ca + Al–3Al + 2(Na + K)–Al + (Na + K) diagram [68]. Data for Daqingshan felsic volcanics (DQS) were from this study; Banba felsic igneous rocks (BB) were from [11]; Nazhen (NZ), Fengle (FL), and Baihe (BH) felsic igneous rocks were from [10]; Madong felsic igneous rocks (MD) were from [21].
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Table 1. LA-ICP-MS zircon U-Pb dating results for felsic igneous rocks from Daqingshan area in Youjiang Basin.
Table 1. LA-ICP-MS zircon U-Pb dating results for felsic igneous rocks from Daqingshan area in Youjiang Basin.
SpotThUTh/U207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238UConcordance
ppmppmRatio1σRatio1σRatio1σAge (Ma)1σAge (Ma)1σAge (Ma)1σ
PX3-011203600.330.051290.001940.283720.01050.040190.00042254872548254399%
PX3-02883310.270.050270.001830.274430.00970.039710.00044206902468251398%
PX3-031004790.210.053490.001590.295010.008940.039820.00033350692637252295%
PX3-04853290.260.052310.001920.287650.010590.03980.00043298882578252397%
PX3-05733060.240.054040.00210.292010.011390.039010.00042372872609247394%
PX3-061063340.320.052260.002080.28060.010710.038990.00043298862519247398%
PX3-071343400.390.057170.002130.318260.011490.040420.00037498882819255290%
PX3-082013940.510.053720.001840.298130.010430.040150.00045367782658254395%
PX3-091434360.330.053260.001810.293010.010060.039790.00037339762618252296%
PX3-101874920.380.05070.001590.275960.008670.039430.00041228722477249399%
PX3-111112800.400.05690.002230.320980.013620.040580.00064878728311256490%
PX3-121002630.380.050870.002440.279220.012930.039910.0004723511125010252399%
PX3-13613400.180.051920.001760.285860.009170.040050.00045283782557253399%
PX3-141163650.320.055510.001960.302280.010260.039560.00036432782688250293%
PX3-151945610.350.053620.001530.288480.008080.0390.00033354582576247295%
PX3-161343250.410.054060.001860.295250.00990.039650.00041372782638251395%
PX3-171324250.310.05150.001680.281030.008810.039750.00041265792527251399%
PX8-012143040.700.053230.001930.286960.010140.039120.00041339832568247396%
PX8-022533950.640.052490.002100.282900.011530.038750.00040306912539245396%
PX8-031432690.530.049140.002170.261780.011690.038410.00048154992369243397%
PX8-041672710.620.052230.002220.277120.011290.038910.00047295982489246399%
PX8-051162410.480.052130.002300.274330.012290.038190.0005030010224610242398%
PX8-061472520.580.052420.002520.283710.013880.039510.0006030210925411250498%
PX8-071472560.570.053980.002790.279660.014730.038140.0006436911725012241496%
PX8-08771350.570.050570.003120.276600.015910.038610.0006822014724813244498%
PX8-091272440.520.052770.002330.277260.012110.038360.0004932010024910243397%
PX8-101311850.710.060210.003070.334080.017370.040300.0006561310929313255486%
PX8-111092040.540.053880.002960.292630.014970.040040.0005436512626112253397%
PX8-121903370.560.050910.002010.271860.010600.038780.00042235912449245399%
PX8-131352760.490.051950.002440.280210.012720.039460.0005328310725110250399%
PX8-141052110.500.050570.002580.271420.013670.039100.0005322012324411247398%
PX8-151292520.510.051270.002580.279240.013700.039930.0005825411725011252499%
Table 2. LA-ICP-MS zircon Lu–Hf isotope dating results for felsic igneous rocks from Daqingshan area in Youjiang Basin.
Table 2. LA-ICP-MS zircon Lu–Hf isotope dating results for felsic igneous rocks from Daqingshan area in Youjiang Basin.
SpotAreaAge (Ma)176Yb/177Hf1σ176Lu/177Hf1σ176Hf/177Hf1σ176Hf/177HfiεHf(t)TDM (Ma)TDMC (Ma)
24K3-01Daqingshan2540.0679970.000960.0016890.0000140.2823550.0000350.282347−9.912901871
24K3-02Daqingshan2520.0897330.000650.0022100.0000090.2824970.0000110.282486−5.011041564
24K3-03Daqingshan2520.0637940.000520.0017020.0000090.2824530.0000110.282445−6.411501654
24K3-04Daqingshan2470.0917880.001910.0023010.0000270.2825300.0002510.282519−3.910581494
24K3-05Daqingshan2470.0678630.000690.0016560.0000170.2824330.0000110.282425−7.211781702
24K3-06Daqingshan2540.0589170.000480.0014360.0000070.2825000.0000110.282493−4.710761548
24K3-07Daqingshan2520.1011110.000400.0024880.0000090.2824460.0000110.282434−6.811861679
24K3-08Daqingshan2530.0763710.002540.0017650.0000270.2817130.0002890.281704−32.622023274
24K3-09Daqingshan2490.0939960.002060.0022370.0000190.2826170.0004420.282606−0.89301298
24K3-10Daqingshan2560.0845630.001840.0020010.0000320.2822800.0001020.282270−12.514092039
24K3-11Daqingshan2520.0416580.000470.0010720.0000050.2822860.0000120.282281−12.213652017
24K3-12Daqingshan2530.0584220.001230.0015690.0000380.2823010.0000330.282293−11.813631990
24K3-13Daqingshan2500.0624040.001500.0015370.0000130.2822250.0000780.282218−14.514692158
24K3-14Daqingshan2470.0663880.000620.0017060.0000170.2823980.0000120.282390−8.512291779
24K3-15Daqingshan2510.0466860.001140.0011680.0000220.2824300.0000100.282425−7.211671701
24K3-16Daqingshan2510.0797430.000780.0019940.0000330.2823610.0000270.282351−9.812931863
24K8-03Daqingshan2470.0504740.001290.0012740.0000360.2823470.0000560.282341−10.212871888
24K8-04Daqingshan2450.0651160.001000.0015740.0000150.2823210.0000550.282314−11.213351950
24K8-05Daqingshan2430.0696960.001850.0016190.0000260.2820580.0002820.282051−20.617082528
24K8-06Daqingshan2480.0347980.000350.0008750.0000060.2824000.0000110.282396−8.211991766
24K8-07Daqingshan2500.0670030.001490.0016460.0000260.2823270.0000200.282320−10.913281934
24K8-08Daqingshan2460.0500040.001100.0013270.0000350.2823330.0000160.282327−10.713081919
24K8-09Daqingshan2420.0312320.000430.0008240.0000150.2823450.0000160.282341−10.312751891
24K8-10Daqingshan2500.0366780.000620.0009470.0000160.2823880.0000120.282384−8.612191793
24K8-11Daqingshan2540.0556970.002240.0015980.0000670.2823720.0000180.282364−9.212631832
24K8-12Daqingshan2410.0714990.003600.0018800.0000880.2819250.0002730.281916−25.419092822
24K8-13Daqingshan2440.0460720.002440.0011620.0000360.2820720.0003200.282067−20.016672492
24K8-14Daqingshan2430.0423280.021070.0007640.0002910.2814160.0276750.281412−43.225493904
24K8-15Daqingshan2530.0280180.000230.0007460.0000030.2824320.0000130.282428−7.011511691
24K8-16Daqingshan2450.0364320.000630.0009660.0000140.2822270.0000660.282222−14.414442151
24K8-17Daqingshan2500.0523680.000230.0013810.0000150.2823970.0000140.282390−8.412201777
Table 3. Major and trace element compositions of felsic igneous rocks from Daqingshan area in Youjiang Basin.
Table 3. Major and trace element compositions of felsic igneous rocks from Daqingshan area in Youjiang Basin.
SampleDQS-1DQS-2DQS-3DQS-4DQS-5DQS-6
SiO267.2671.0866.8268.8668.9372.69
TiO20.80.650.850.880.80.53
Al2O314.5612.913.1913.3913.0812.4
TFe2O36.065.227.66.536.314.63
MnO0.060.060.080.070.10.06
MgO1.320.721.420.930.950.62
CaO1.160.732.771.542.843.16
Na2O5.992.781.772.043.961.45
K2O1.375.063.264.381.923.28
P2O50.190.150.190.210.190.11
LOI1.491.122.451.721.131.36
SUM100.27100.47100.39100.56100.21100.29
V37.729.746.450.052.027.3
Cr16.813.117.519.719.213.8
Co7.779.309.899.969.305.38
Ni7.378.699.4310.108.107.33
Ga19.622.019.921.520.122.3
Rb73.5219149207106160
Sr14492.112013690.3242
Y57.868.863.364.156.073.3
Zr351371354322318415
Nb17.316.517.516.614.020.1
Ba449812602750386942
Lu0.851.020.900.840.831.07
Hf9.7210.49.809.089.0311.8
Ta1.281.221.231.221.121.49
Th27.628.127.626.026.232.1
U5.596.015.635.235.336.74
Zr/Hf36.135. 736.135.535.235.2
Ba/Sr3.128.825.025.514.273.89
Rb/Sr0.512.381.241.521.170.66
U/Th0.200.210.200.200.200.21
Tzr891896898891865899
La53.952.853.355.349.161.3
Ce10510110510495.4120
Pr12.812.51312.911.415.1
Nd45.544.945.646.041.252.9
Sm10.310.210.510.89.512.1
Eu1.371.651.771.851.621.70
Gd10.010.610.611.09.4012.2
Tb1.681.831.731.861.602.10
Dy9.7211.010.410.99.5212.7
Ho2.102.412.202.302.002.65
Er6.047.006.396.445.797.69
Tm0.881.060.910.940.841.14
Yb5.676.845.805.835.307.14
(La/Yb)CN6.825.546.596.806.656.16
(Dy/Yb)CN1.151.081.201.251.201.19
Eu/Eu*0.410.480.510.510.520.42
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Dong, K.; Li, Z.; Fei, X.; Wang, Y.; Deng, X. Geochronological and Geochemical Characterization of Triassic Felsic Volcanics in the Youjiang Basin, Southwest China: Implications for Tectonic Evolution of Eastern Tethyan Geodynamics. Minerals 2025, 15, 398. https://doi.org/10.3390/min15040398

AMA Style

Dong K, Li Z, Fei X, Wang Y, Deng X. Geochronological and Geochemical Characterization of Triassic Felsic Volcanics in the Youjiang Basin, Southwest China: Implications for Tectonic Evolution of Eastern Tethyan Geodynamics. Minerals. 2025; 15(4):398. https://doi.org/10.3390/min15040398

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Dong, Kai, Zhuoyang Li, Xiaoli Fei, Yongqing Wang, and Xiaohu Deng. 2025. "Geochronological and Geochemical Characterization of Triassic Felsic Volcanics in the Youjiang Basin, Southwest China: Implications for Tectonic Evolution of Eastern Tethyan Geodynamics" Minerals 15, no. 4: 398. https://doi.org/10.3390/min15040398

APA Style

Dong, K., Li, Z., Fei, X., Wang, Y., & Deng, X. (2025). Geochronological and Geochemical Characterization of Triassic Felsic Volcanics in the Youjiang Basin, Southwest China: Implications for Tectonic Evolution of Eastern Tethyan Geodynamics. Minerals, 15(4), 398. https://doi.org/10.3390/min15040398

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