Next Article in Journal
Natural Frequency of Monopile Supported Offshore Wind Turbine Structures Under Long-Term Cyclic Loading
Previous Article in Journal
Colorectal Cancer Detection Tool Developed with Neural Networks
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Applied Sciences
Volume 15
Issue 15
10.3390/app15158145
applsci-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Tectonic Characteristics and Geological Significance of the Yeba Volcanic Arc in the Southern Lhasa Terrane

by
Zhengzhe Fan
1,2,*,
Zhengren Yuan
1,3,
Minghui Chen
2 and
Genhou Wang
4
1
State Key Laboratory of Continental Shale Oil, Northeast Petroleum University, Daqing 163318, China
2
School of Earth Sciences, Northeast Petroleum University, Daqing 163318, China
3
Policy Research Office, Daqing Oilfield Limited Company, Daqing 163453, China
4
School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(15), 8145; https://doi.org/10.3390/app15158145
Submission received: 11 June 2025 / Revised: 12 July 2025 / Accepted: 13 July 2025 / Published: 22 July 2025
Browse Figures
Versions Notes

Abstract

The Southern Lhasa Terrane, as the southernmost tectonic unit of the Eurasian continent, has long been a focal area in global geoscientific research due to its complex evolutionary history. The Yeba Formation exposed in this terrane comprises an Early–Middle Jurassic volcanic–sedimentary sequence that records multiphase tectonic deformation. This study applies structural analysis to identify three distinct phases of tectonic deformation in the Yeba Formation of the Southern Lhasa Terrane. The D1 deformation is characterized by brittle–ductile shearing, as evidenced by the development of E-W-trending regional shear foliation (S1). S1 planes dip northward at angles of 27–87°, accompanied by steeply plunging stretching lineations (85–105°). Both south- and north-directed shear-rotated porphyroclasts are observed in the hanging wall. 40Ar-39Ar dating results suggest that the D1 deformation occurred at ~79 Ma and may represent an extrusion-related structure formed under a back-arc compressional regime induced by the low-angle subduction of the Neo-Tethys Ocean plate. The D2 deformation is marked by the folding of the pre-existing shear foliation (S1), generating an axial planar cleavage (S2). S2 planes dip north or south with angles of 40–70° and fold hinges plunge westward or NWW. Based on regional tectonic evolution, it is inferred that the deformation may have resulted from sustained north–south compressional stress during the Late Cretaceous (79–70 Ma), which caused the overall upward extrusion of the southern Gangdese back-arc basin, leading to upper crustal shortening and thickening and subsequently initiating folding. The D3 deformation is dominated by E-W-striking ductile shear zones. The regional shear foliation (S3) exhibits a preferred orientation of 347°∠75°. Outcrop-scale ductile deformation indicators reveal a top-to-the-NW shear sense. Combined with regional tectonic evolution, the third-phase (D3) deformation is interpreted as a combined product of the transition from compression to lateral extension within the Lhasa terrane, associated with the activation of the Gangdese Central Thrust (GCT) and the uplift of the Gangdese batholith since ~25 Ma.

1. Introduction

The integrated study of lithostratigraphic characterization, deformation–metamorphism processes, and geochronology within orogenic belts has become both a major focus and a challenging frontier in current Earth science research [1,2,3]. The Southern Lhasa Terrane, as the southernmost tectonic unit of the Eurasian continent, has long been a focal point of research in the international geoscience community [1,2,3]. Previous studies have defined the Early–Middle Jurassic volcanic–sedimentary sequence exposed in this terrane as the Yeba Volcanic Arc, based on lithological associations and geochronological constraints [4,5]. This sequence has attracted considerable attention due to recording the early subduction and consumption of the Tethys Ocean [6]. The magmatic rocks of the Yeba Formation are mainly distributed between Lhasa City and Gongbo’gyamda County, extending in the east–west direction for approximately 399 km and spanning ~30 km in the north–south direction [7,8]. This region is characterized by several NWW-trending thrust nappe systems, resulting from the subduction and subsequent collision between the Indian and Eurasian plates [9,10]. The southernmost structure is the Pongduo Thrust Nappe System, where Middle Jurassic–Early Cretaceous sedimentary strata form a compressional detachment belt in the southern frontal zone of this nappe system [11].
The Yeba Formation has experienced multiple phases of complex ductile and brittle deformation, with each event closely linked to specific tectonic settings, including the subduction of the Neo-Tethys Ocean and the India–Asia collision. Previous studies on the deformation history and genesis of the Yeba Formation have been limited and remain highly contentious. For instance, Zhong et al. (2012, 2013) [12,13] suggested that the Yeba Formation experienced two distinct ductile deformation phases, accompanied by multiple episodes of ductile–brittle deformation. The first phase was interpreted as being related to the northward subduction of the Neo-Tethys Ocean (94–85 Ma), while the second was attributed to the India–Asia collision (60–50 Ma).
Ma (2016) [14] proposed that the Yeba Formation underwent two phases of folding events. In contrast, Ma (2017) [15] identified three distinct deformation phases in the Yeba Formation: phase 1 (D1), dated to ~85–69 Ma, is associated with retroarc detachment structures formed under the subduction-related setting of the Neo-Tethys Ocean; phase 2 (D2), spanning ~65–50 Ma, reflects the emplacement of collision-related granites during the India–Asia convergence, contributing to the development of the Lhasa Dome; phase 3 (D3), around ~42 Ma, was dominated by the reactivation of the Qulong-Sangri-Woka Thrust Fault Zone, generating large-scale thrust structures through compressional overprinting.
In summary, previous studies on the tectonic deformation of the Yeba Group remain relatively sparse and controversial. Therefore, this study systematically investigates the meso- and microstructural features of the Yeba Formation to delineate its deformation phases, applies 40Ar-39Ar geochronology to constrain the timing of these tectonic events, and integrates regional tectonic evolution to interpret the dynamic setting and unravel the tectonic evolution of the formation. These findings provide critical insights into the structural evolution of the Yeba Group and its geodynamic significance within the broader regional context.

2. Regional Geological Background

The Lhasa Terrane, also referred to as the Gangdese Belt, is a major magmatic–tectonic belt bounded to the south by the Indus–Yarlung Zangbo Suture Zone (IYS) and to the north by the Bangong–Nujiang Suture Zone (BNS). It extends approximately 2500 km in an east–west direction, with a width of 100–300 km from north to south. The Southern Lhasa Terrane is bounded to the north by the Luobadui–Milashan Fault (LMF) and to the south by the Yarlung Zangbo Suture Zone (YZSZ) [16]. It represents the region of most intense magmatic activity, characterized by the east–west-trending Gangdese batholiths, which extend for over 1500 km. The Southern Lhasa Terrane, as the southernmost tectonic unit of the Eurasian continent, has been interpreted as a Mesozoic Andean-type active continental margin, formed by the prolonged northward subduction of the Neo-Tethys Ocean. It has also been regarded as the leading edge of the Cenozoic India–Eurasia collisional orogeny [17,18]. The Early–Middle Jurassic Yeba Volcanic Arc investigated in this study is primarily situated within the southern Gangdese magmatic belt (Figure 1a).
The study area lies within the Southern Lhasa Terrane, part of the Lhasa–Chayu Stratigraphic Subzone [16]. The stratigraphic sequence spans from the Jurassic to the Paleogene systems, with the Jurassic and Cretaceous strata being predominant. The exposed stratigraphic units include the Lower–Middle Jurassic Yeba Group (J1-2y), the Upper Jurassic Duodigou Formation (J3d), the Upper Jurassic–Lower Cretaceous Linbuzong Formation (J3K1l), the Lower Cretaceous Chumulong Formation (K1ch), the Lower Cretaceous Takena Formation (K1t), the Upper Cretaceous Shexing Formation (K2s), the Paleocene Dianzhong Formation (E1d), and the Pana Formation (E2p). These stratigraphic units exhibit pervasive deformation, characterized by a dominant NWW-trending structural orientation (Figure 1b).
The volcanic rocks of the Lower–Middle Jurassic Yeba Formation (J1-2y) are mainly distributed in the area between Dagzê, Maizhokunggar, and Gongbo’gyamda [19,20]. The Yeba Formation (J1-2y) comprises a polygenetic volcanic–sedimentary–metamorphic complex, dominated by intermediate-acid volcanic rocks including dacite, andesite, and tuffaceous to basaltic volcanic breccia lavas. Tuff interlayers are widely developed, with localized occurrences of mafic (basalt) to felsic (rhyolite) volcanic rocks. The alternating pyroclastic rocks (e.g., volcanic breccia) and lavas reflect cyclic alternations between explosive and effusive phases of volcanism. Additionally, the formation is intercalated with sedimentary–metamorphic strata, including limestone, clastic rocks, and tectonically overprinted phyllite/schist. Notably, limestone blocks are mainly concentrated in the central part of the formation [21]. Duodigou Formation (J3d): Predominantly composed of shallow-marine platform carbonates interbedded with minor clastic rocks, this formation exhibits well-developed superposed folds. It is tectonically juxtaposed against the underlying Yeba Formation along a thrust detachment fault system. Linbuzong Formation (J3K1l): Characterized by a lithological assemblage of silty slate, carbonaceous slate intercalated with quartz sandstone, and calcareous sandstone. Similarly, superposed folds are prevalent within this formation. It maintains conformable contact with the underlying Duodigou Formation. Chumulong Formation (K1c): Composed primarily of shoreface-facies clastic rocks that have undergone low-grade metamorphism. Takena Formation (K1t): Dominated by carbonate rocks such as limestone and marl, interbedded with sandstone and mudstone/shale. It maintains conformable contacts with the underlying Chumulong Formation and the overlying Shexing Formation. Shexing Formation (K2s): Consists of purplish red continental siliciclastic rocks, including quartz sandstone, siltstone, and mudstone. While conformable with the underlying Takena Formation, its upper part is unconformably overlain by Paleocene Dianzhong Formation volcanic rocks. Dianzhong Formation (E1d) and Pana Formation (E2p): Both represent typical continental volcanic–sedimentary sequences. The Dianzhong Formation is dominated by andesite, dacite, andesitic breccia, and lithic–crystal tuff, whereas the Pana Formation comprises rhyolitic tuff, rhyolite, and welded tuff, occasionally intercalated with clastic sedimentary rocks. These two formations are in contact via an eruptive unconformity [22].
Applsci 15 08145 g001
Figure 1. Simplified geological map of the study area. (a) Tectonic framework map of the Qinghai–Tibet Plateau (redrawn from [23]). (b) Simplified geological map of the Yeba Rock Group in Dazi and Mozhugongka Counties, Southern Gangdese. The abbreviations shown in the figure are as follows: BNS = Bangong–Nujiang Suture Zone; HFTB = Himalayan Fold-and-Thrust Belt; IYS = Indus–Yarlung Zangbo Suture Zone; MBT = Main Boundary Thrust; STDS = South Tibetan Detachment System; LMF = Luobadui–Milashan Fault Zone.
Figure 1. Simplified geological map of the study area. (a) Tectonic framework map of the Qinghai–Tibet Plateau (redrawn from [23]). (b) Simplified geological map of the Yeba Rock Group in Dazi and Mozhugongka Counties, Southern Gangdese. The abbreviations shown in the figure are as follows: BNS = Bangong–Nujiang Suture Zone; HFTB = Himalayan Fold-and-Thrust Belt; IYS = Indus–Yarlung Zangbo Suture Zone; MBT = Main Boundary Thrust; STDS = South Tibetan Detachment System; LMF = Luobadui–Milashan Fault Zone.
Applsci 15 08145 g001

3. Structural Deformation Characteristics

3.1. D1 Deformation

The D1-phase shear foliation is widely developed in the study area, primarily occurring within various lithostratigraphic units of the Yeba Group. Among them, profile Pm01 is particularly representative of this phase of tectonic deformation (Figure 2).
The phase 1 (D1) deformation is regionally distributed and is characterized by an east–west-trending S1 shear foliation formed under brittle–ductile shearing conditions. The foliation predominantly dips northward, with dipping angles ranging from 27° to 87°. Stereographic projection analysis reveals a dominant orientation of 20°∠75°. Numerous quartz veins subparallel to the S1 foliation are observed (Figure 3b,c). Some of the veins have been sheared, producing σ-type and δ-type porphyroclasts (Figure 3a,e–g). Additionally, mineral stretching lineations are identified on the S1 shear foliation, with plunge directions of 85–105° and plunge angles of 70–85°. The dominant orientation is 90°∠78° (Figure 3i).
Notably, shear sense indicators on the S1 foliation exhibit widespread opposite kinematics, with both south-directed and north-directed hanging-wall shear observed on the same shear plane. These reverse shear senses display a spatially alternating pattern along a roughly N-S trend. Kinematic evidence indicates the coexistence of both sinistral and dextral shear-related rotated porphyroclasts (Figure 3d,h). However, no cross-cutting relationships between these two shear directions have been observed, either at the outcrop scale in the field or under the microscope. Given the absence of evidence for two distinct shear phases within the S1 foliation in the study area, we interpret these opposing senses of rotation as coexisting σ-type and δ-type porphyroclasts formed under the same phase of brittle–ductile shear deformation conditions (Figure 3j).

3.2. D2 Deformation

The phase 2 (D2) deformation is marked by the folding of the S1 shear foliation, accompanied by the development of an axial planar foliation, designated as S2 (Figure 4). The fold axial planes predominantly strike 351–20° and dip at 40–70°, while a minor subset strikes 170–192° with similar dip angles (40–70°). The hinge lines of these folds plunge westward or northwest–west (NWW). Incompetent lithologies, including mica schist, phyllite, and siltstone, are typified by tight to isoclinal folds (Figure 4k,l) and overturned fold geometries (Figure 4a–c), as well as the localized development of rounded folds (Figure 4i), angular folds (Figure 4d,j), and the intense transposition of foliations (Figure 4e). In competent lithologies such as dacite and andesite, a distinct overprinting relationship between S2 and S1 foliations is observed (Figure 4f). Additionally, outcrop-scale, layer-parallel superimposed folds are well developed, attributed to interlayer slip during the folding process (Figure 4g,h). The axial planar cleavage (S2) generally trends 0–20° and dips at angles of 40–70°, with fold limbs dipping either southward or northward. The hinge lines plunge westward or northwest–west (NWW), indicating that the D2-phase longitudinal bending folds resulted from near-N-S-oriented compressional stress. This study interprets the pervasive folding observed within the Yeba Group and Duodigou Formation as the result of N-S-directed compression during a collisional orogenic phase, characterized by a predominantly south-verging imbricate fold system (Figure 4m).

3.3. D3 Deformation

The phase 3 (D3) deformation is primarily developed in the south–central Woka area and is manifested by the ductile deformation of granitic mylonites, granitic protomylonites, mylonitized andesites, and dacites. These lithologies collectively define an E-W-trending ductile shear zone, approximately 145 km long and ~2 km wide. The regionally developed S3 shear foliation exhibits a dominant orientation of 347°∠75°. Additionally, mineral stretching lineations exhibit a preferred plunge orientation of 291°∠62°. Feldspar rotated porphyroclasts, predominantly σ-type at the outcrop scale (Figure 5a), are aligned parallel to the S3 foliation. Composed mainly of plagioclase and potassic feldspar, these porphyroclasts exhibit fine-grained groundmass tails that extend along the C-plane. S-C fabrics are well developed within the mylonite zones (Figure 5b), where feldspar and quartz aggregates rotate during shearing to define the S-planes, while the C-planes are defined by aligned dark minerals such as biotite. The mineral stretching lineations are primarily composed of feldspar, quartz, biotite, and amphibole (Figure 5d). Felsic veins are well developed in the mylonitized zones, forming kinematic indicators such as boudinage structures (Figure 5c), asymmetric folds (Figure 5e), and asymmetric felsic bands (Figure 5f). These outcrop-scale ductile deformation indicators suggest a top-to-the-NW shear sense, characterized by the northwest-directed movement of the hanging wall.
At the microscopic scale, the rotated porphyroclasts in the mylonite zones are predominantly composed of feldspar and quartz, accounting for 35–45% of the rock volume. The groundmass is dominated by fine-grained felsic minerals and dark minerals (e.g., mica and amphibole), constituting 50–55%. In the protomylonite zones, feldspar is the dominant porphyroclastic phase (50–75%), with the groundmass composed mainly of dark minerals. Within the mylonitized zones, the abundance of porphyroclasts increases to 85–95%, primarily derived from fine-grained feldspar, quartz, and chert. The groundmass in these zones is composed predominantly of mica and fine-grained felsic minerals.
Under shearing, quartz, mica, and feldspar exhibit deformation characterized by the formation of kinematic indicators, including quartz ribbons and rotated porphyroclasts. At the microscopic scale, the rotated porphyroclasts are classified into δ-type and σ-type (Figure 5h), predominantly composed of K-feldspar, plagioclase, and quartz. Fine-grained minerals develop tails that wrap around the porphyroclasts. Asymmetric pressure shadows (Figure 5i) are characterized by fibrous quartz tails surrounding feldspar porphyroclasts. The long axes of the feldspar porphyroclasts align parallel to the S-foliation, while their tails extend along the C-foliation.
The microstructural analysis aligns with macrostructural observations, indicating that the kinematic signature of the ductile shear zone is characterized by a top-to-the-NW shear sense (Figure 5j). The D3-phase ductile deformation developed within the Yeba Group in the southern study area overprints and truncates the earlier D1 and D2 deformations.

4. Research Methods and Results

4.1. Research Methods

Two samples of albite–quartz–muscovite schist were collected from the phyllite with well-developed S1 foliation within the Yeba Group in the northwestern part of the study area for 40Ar-39Ar dating analysis. Based on the metamorphic ages of muscovite obtained from these samples, the deformation age corresponding to the D1 tectonic event was inferred. Muscovite separation and purification (purity > 99%) from albite–quartz–muscovite schist were carried out by the China Railway Geophysical Exploration Co., Ltd., Beijing, China. The purified mineral separates were sealed in quartz vials and irradiated with fast neutrons in the Swimming Pool Reactor at the China Institute of Atomic Energy. 40Ar-39Ar dating was performed at the Key Laboratory of Isotope Geology, Ministry of Land and Resources, Chinese Academy of Geological Sciences. Step-heating experiments were conducted using a graphite furnace, with each temperature step held for 10 min, followed by 20 min of gas purification. Gas analyses were carried out on a GV Helix MC multi-collector noble gas mass spectrometer (GV Instruments, Manchester, UK), with 20 data cycles collected per peak. All measured isotopic ratios were corrected for time-zero backgrounds, mass discrimination, atmospheric argon, procedural blanks, and interfering isotopes produced during neutron irradiation. System blanks at m/e 40, 39, 37, and 36 were consistently less than 6 × 10−15 mol, 4 × 10−16 mol, 8 × 10−17 mol, and 2 × 10−17 mol, respectively. Interference correction factors, determined by analyzing irradiated K2SO4 and CaF2, were (36Ar/37Ar)Ca = 0.0002389, (40Ar-39Ar)K = 0.004782, and (39Ar/37Ar)Ca = 0.000806. 37Ar was decay-corrected using the 40K decay constant (λ = 5.543 × 10−10 yr − 1). All ages are reported with 2σ uncertainties. Detailed analytical procedures follow those described in Zhang et al. (2006) [24].

4.2. Results

40Ar-39Ar geochronology of muscovite from albite–mica–quartz schist (QY0807-1 and QY0807-4). Muscovite grains separated from albite–mica–quartz schist samples (QY0807-1 and QY0807-4, corresponding to the quartz fabric analysis samples described earlier) were subjected to 40Ar-39Ar step-heating geochronology. The analytical results are summarized in Table 1. Both samples yielded consistent age spectra, as illustrated by their plateau age diagrams (Figure 6b,d) and inverse isochron plots (Figure 6a,c). For sample QY0807-1, eight heating steps between 840 and 1180 °C defined a well-constrained plateau age of 79.21 ± 1.06 Ma, representing 72.23% of the total 39Ar released. The corresponding 36Ar/40Ar vs. 39Ar/40Ar isochron age is 82.14 ± 2.72 Ma. Similarly, sample QY0807-4 produced a plateau age of 79.65 ± 1.04 Ma (72.63% 39Ar release) over the same temperature range, with an isochron age of 79.73 ± 2.45 Ma. The initial 40Ar/36Ar ratios derived from the isochron regressions are 175.0 ± 101.5 (MSWD = 0.11) and 294.0 ± 57.0 (MSWD = 2.25) for QY0807-1 and QY0807-4, respectively. The weighted mean age of ~79 Ma is interpreted to represent the timing of muscovite crystallization, corresponding to a Late Cretaceous metamorphic event linked to regional tectonism. Microstructural observations reveal that micas (muscovite and sericite) are preferentially aligned to define the S1 foliation. S-C fabric analysis indicates that micas dominate the S-surfaces, while felsic minerals (e.g., quartz and feldspar) define the C-surfaces. Given the low-temperature deformation conditions inferred for this fabric development, the 40Ar-39Ar ages of mica are interpreted as directly recording the timing of syn-tectonic metamorphism and associated ductile deformation.

5. Discussion

5.1. Phase D1 Deformation: Timing and Dynamical Context

Muscovite 40Ar-39Ar dating was conducted on intensely deformed albite–quartz–mica schist subjected to brittle–ductile shearing. The results yield a deformation age of approximately ~79 Ma. Electron backscatter diffraction (EBSD) analyses of quartz from albite–muscovite–quartz schist and mylonitized dacite within the S1 foliation of the D1 deformation phase have been conducted by previous researchers. The results reveal a deformation temperature ≤ 380 °C, characterized by subgrain rotation recrystallization, and deformation–metamorphism temperatures of 420–350 °C, estimated using the chlorite geothermometer [25]. These data suggest that the obtained age approximately corresponds to the peak stage of brittle–ductile shear deformation. Meanwhile, the overlying Late Jurassic to Late Cretaceous strata deposited above the Yeba Group significantly increased the burial depth, providing suitable pressure–temperature conditions for D1-phase brittle–ductile deformation. The kinematic features of high-angle, westward-plunging mineral stretching lineations indicate the westward extrusion of the Yeba Group as a whole (Figure 3j). Consequently, under a nearly N-S-oriented principal stress field, an extrusion-related structure formed within a transpressional tectonic setting.
Kinematic analyses reveal the coexistence of sinistral and dextral shear-rotated porphyroclasts within the Yeba Group. In the absence of cross-cutting relationships between these shear fabrics, we propose that the coexisting synthetic and antithetic porphyroclasts formed synchronously under a single phase of brittle–ductile shearing within a compressional stress regime [26]. Field observations and regional correlations indicate that phase D1 deformation is well developed in the Lower Jurassic Yeba Formation and the basal Duodigou Formation but notably absent in the overlying Linbuzong Formation and younger units [27]. These observations suggest that the D1 deformation may have occurred during the subduction stage of the Neo-Tethys Ocean, likely after the Early Cretaceous. Additionally, stratigraphic studies of the Cretaceous sequences in the Southern Gangdese region indicate that the area experienced a back-arc compressional setting after approximately ~90 Ma. It is further inferred that large-scale folding and detachment-related structural deformation occurred between ~85 and 69 Ma [15]. The aforementioned studies suggest that this deformation phase was likely initiated post-Early Cretaceous and was governed by Neo-Tethys Ocean subduction. The brittle–ductile shearing fabrics developed under a compressional regime rather than an extensional setting.
During the Late Cretaceous (~90–79 Ma), the Neo-Tethys Ocean subducted northward beneath the Lhasa terrane [28,29], leading to the development of a large-scale Gangdese magmatic arc along the southern margin of the Lhasa terrane. Under the influence of this northward subduction, the Cretaceous Gangdese back-arc basin experienced N-S-directed compressional stress. Based on the 40Ar-39Ar muscovite age of ~79 Ma obtained from phyllite in this study, we infer that, around ~79 Ma, a ductile shear zone developed within the Yeba Group under a transpressional regime, resulting in the D1-phase ductile deformation event (Figure 7a).

5.2. Phase D2 Deformation: Timing and Dynamical Context

At both the outcrop and microstructural scales, D2-phase folding overprints D1-phase shear deformation, expressed as the transposition of S1 fabrics by S2 foliation. Lithological competence contrasts result in diverse fold geometries. D2-phase deformation is characterized by longitudinal flexural folding, during which the folding of the S1 shear foliation produces axial planar cleavage (S2). Subordinate folds with S-shaped, M-shaped, and Z-shaped geometries are ubiquitously developed. This folding event is observed in Jurassic and Cretaceous strata [30] but is absent in strata younger than the Paleocene. Previous studies indicate that the Yeba Formation in the Jiama–Qulong district underwent phase D2 brittle–ductile deformation following phase D1 ductile deformation. Structural analysis indicates that this deformation phase is characterized by top-to-the-south (hanging wall moving southward) shear kinematics, forming a series of north-vergent thrust-related folds [13]. In addition, the folding observed in the Early Cretaceous Takena Formation and the Late Cretaceous Shexing Formation, caused by nearly N-S-directed compression [30], is highly consistent with the D2-phase structural deformation characteristics identified in this study.
During the Early Cenozoic (~65–45 Ma), the collision between the Indian and Eurasian plates triggered widespread magmatism in the Gangdese belt, including the emplacement of extensive Linzizong volcanic rocks and voluminous granitoid intrusions (Figure 7b) [8,31,32,33]. The Linzizong volcanic rocks exposed in the Linzhou Basin, located north of the study area, are predominantly terrestrial volcanic rocks of the Dianzhong Formation (65–58 Ma). These volcanic rocks are essentially undeformed and unconformably overlie the Late Cretaceous Shexing Formation at a high angle (Figure 7b) [22]. Therefore, the corresponding phase of structural deformation must have occurred prior to the deposition of the Paleocene Dianzhong Formation.
It is also noteworthy that the Takena Formation underwent a folding and erosion event during 80–70 Ma [30]. Considering the relative sequence of D1 and D2 deformation phases established in this study, we infer that the D2-phase deformation occurred during ~79–70 Ma. This timing still falls within the tectonic framework of the northward subduction of the Neo-Tethys Ocean beneath the Lhasa terrane [34,35].

5.3. Phase D3 Deformation: Timing and Dynamical Context

The D3-phase deformation is predominantly characterized by NW-directed shearing of the hanging wall within ductile shear zones, which truncated both D1- and D2-phase structures. Previous studies [36,37,38] interpret the Woka ductile shear zone as a northward oblique-slip shear zone that developed during the Early Miocene (21–24 Ma). This deformation was likely triggered by N-S-oriented extensional stress within the Lhasa terrane, resulting from the ongoing India–Asia continental collision during this period.
Furthermore, Feng et al. (2020) [39] reported that high-temperature deformation within the Yeba Group mylonites in the Woka shear zone is dominated by grain boundary migration (GBM) and subgrain rotation (SGR), while low-temperature deformation is characterized by bulging recrystallization (BLG). The late-stage low-temperature deformation features overprint the earlier high-temperature deformation structures. The two stages of the temperature environment studied in this article are the products of different tectofacies of the same stage of a ductile deformation event, and it is also a product of a progressive deformation process. This provides microstructural and kinematic evidence for the tectonic regime transition from the Oligocene to Miocene in the Lhasa terrane, consistent with the crustal rheological layering observed in this region [39].
The central segment of the Gangdese orogenic belt underwent a phase of rapid exhumation during the Early Miocene (~23 Ma), an event that closely coincides with the temporal framework of coeval shear zone activity. Emerging constraints from integrated studies [40,41,42] reveal the multistage Cenozoic exhumation of the central Gangdese orogen: an initial pulse at ~45 Ma (Middle Eocene), followed by two discrete rapid exhumation episodes at ~23 Ma and ~10 Ma. Notably, high-precision geochronological constraints from the Woka ductile shear zone (22.38 ± 0.31 Ma [39]) demonstrate that its tectonic activity was precisely synchronized with the second exhumation pulse. Since the Miocene, in the Gangdese magmatic belt, the tectonic superposition of north–south post-collision extension and east–west extensional collapse has occurred owing to lateral variations in the crust-thickened gradient in the Lhasa terrane. The activity of the Gangdese thrust–reverse fault system (GCT) triggered extensive sedimentation in the overlapping zone between the Lhasa terrane and the Indian plate. This process induced flexural bending and deformation along the southern margin of the Gangdese basement, accelerated crustal uplift, and led to the development of a shear zone in the rear of the basement [39,43]. Therefore, we interpret the D3-phase tectonic deformation as the result of the transition from compressional to lateral extensional regimes in the Lhasa terrane, driven by the combined effects of GCT activity and the uplift of the Gangdese basement (Figure 7c).
In summary, the tectonic evolution of the Yeba Volcanic Arc can be summarized as follows: during the Late Cretaceous (~90–79 Ma), the flat-slab subduction of the Neo-Tethys Ocean generated a compressional back-arc tectonic regime. Under this N-S-directed compressional stress, the Cretaceous Gangdese back-arc basin underwent E-W-trending brittle–ductile shearing, leading to the formation of transpressional ductile shear zones within the Yeba Group. The D1-phase ductile deformation event is constrained to have occurred at ~79 Ma (Figure 7a). During the Late Cretaceous (~79–70 Ma), under a nearly N-S-oriented compressional stress regime, the entire back-arc basin system in the Southern Gangdese—including the Yeba Group and its overlying strata—was extruded upward in response to the subduction of the Neo-Tethyan oceanic lithosphere. This process resulted in upper crustal shortening and thickening in the Southern Gangdese, ultimately leading to the D2-phase folding deformation observed within the Yeba Group (Figure 7b). During the Oligocene to Miocene (~31–15 Ma), the D3-phase deformation is interpreted as the result of a tectonic transition in the Lhasa terrane from compression to lateral extension, driven by the combined effects of activity along the Gangdese thrust–reverse fault system (GCT) and the uplift of the Gangdese basement (Figure 7c).

6. Conclusions

(1)
Three distinct deformation phases are identified within the Yeba Group: the D1 phase—characterized by E-W-trending regional shear foliation (S1) formed through brittle–ductile shearing, associated with steeply plunging stretching lineations (plunge directions: 85–105°); coexisting hanging walls south-directed and north-directed shear-rotated porphyroclasts are observed; the D2 phase—marked by axial planar cleavage (S2) resulting from the folding of S1; S2 planes dip north or south with angles of 40–70°, and fold hinges plunge westward or NWW, indicating N-S-directed compression; and the D3 phase—represented by E-W-striking ductile shear zones that overprint both D1 and D2 structures, displaying hanging wall movement toward the NW.
(2)
During the Late Cretaceous (~90–79 Ma), driven by the northward subduction of the Neo-Tethys Ocean, the Cretaceous Gangdese retroarc basin experienced N-S compression. This tectonic regime triggered the development of a transpressional ductile shear zone within the Yeba Group at ~79 Ma, corresponding to the D1-phase deformation event. During the Late Cretaceous (~79–70 Ma), under a nearly N-S-oriented compressional stress regime, the subduction of the Neo-Tethyan oceanic lithosphere induced the overall upward extrusion of the Southern Gangdese back-arc basin, including the Yeba Group and its overlying strata. This process resulted in crustal shortening and the thickening of the upper crust in the Southern Gangdese, ultimately leading to the D2-phase folding deformation within the Yeba Group. During the Oligocene to Miocene (~31–15 Ma), the D3-phase deformation was a product of the tectonic transition of the Lhasa terrane from compression to lateral extension, driven by the combined effects of activity along the Gangdese thrust–reverse fault system (GCT) and the uplift of the Gangdese basement.

Author Contributions

Conceptualization, Z.F. and Z.Y.; methodology, Z.Y.; software, M.C.; validation, Z.F., Z.Y. and M.C.; formal analysis, Z.F.; investigation, M.C.; resources, G.W.; data curation, G.W.; writing—original draft preparation, Z.F., Z.Y. and M.C.; writing—review and editing, Z.F., Z.Y. and M.C.; visualization, Z.F.; supervision, G.W.; project administration, Z.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We are very grateful to the reviewers and editors for their contributions to improving this paper.

Conflicts of Interest

Author Zhengren Yuan was employed by the company Daqing Oilfield Limited. The remaining authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Wu, G.Y. Stratigraphy of orogenic belt: A case study of the Tethys orogenic belt in Sanjiang area. J. Stratigr. 1998, 22, 161–169, (In Chinese with English abstract). [Google Scholar]
  2. Wang, G.H.; Tang, J.X.; Li, D.; Mao, X.C.; Liu, Z.B.; Liang, X.; Song, Y.; Liu, J.Y. Field methods for orogenic belts: A case study of the Bangong Lake-Nujiang/Longmu Co-Shuanghu accretionary orogenic belt. Beijing Geol. Publ. House 2019, 1–203, (In Chinese with English abstract). [Google Scholar]
  3. Zhang, K.; He, W.; Jin, J.S.; Wang, J.; Xu, Y.; Zhang, X.; Yu, Y.; Lin, Q.; Luo, M.; Ji, J.; et al. Application of oceanic plate strata in tectonic stratigraphic division of orogenic belt. Geoscience 2020, 45, 2305–2325, (In Chinese with English abstract). [Google Scholar]
  4. Dong, Y.H.; Xu, J.F.; Zeng, Q.G.; Wang, Q.; Mao, G.Z.; Li, J. Is there an earlier Neo-Tethys subduction record than the Sangri Group arc volcanic rocks? Acta Petrol. Sin. 2006, 22, 661–668, (In Chinese with English abstract). [Google Scholar]
  5. Huang, F.; Xu, J.F.; Chen, J.L.; Kang, Z.Q.; Dong, Y.H. Early Jurassic Yeba Formation and Sangri Group volcanic rocks: Continental margin arc and intra-oceanic arc during the subduction of the Tethys Ocean? Acta Petrol. Sin. 2015, 31, 2089–2100, (In Chinese with English abstract). [Google Scholar]
  6. Zhu, D.C.; Pan, G.T.; Chung, S.L.; Liao, Z.L.; Wang, L.Q.; Li, G.M. SHRIMP zircon age and geochemical constraints on the origin of Lower Jurassic volcanic rocks from the Yeba Formation, southern Gangdese, South Tibet. Int. Geol. Rev. 2008, 50, 442–471. [Google Scholar] [CrossRef]
  7. Pan, G.T.; Mo, X.X.; Hou, Z.Q.; Zhu, D.C.; Wang, L.Q.; Li, G.M.; Zhao, Z.; Geng, Q.; Liao, Z. Space-time structure and evolution of the Gangdese orogenic belt. Acta Petrol. Sin. 2006, 22, 521–533, (In Chinese with English abstract). [Google Scholar]
  8. Xu, Z.Q.; Yang, J.S.; Li, H.B.; Ji, S.C.; Zhang, Z.M.; Liu, Y. India-Asia collision tectonics. Acta Petrol. Sin. 2011, 85, 1–33, (In Chinese with English abstract). [Google Scholar]
  9. Wu, Z.H.; Ye, P.S.; Hu, D.G.; Liu, Q.S. The thrust-nappe tectonic system in the northern Lhasa block. Geol. Rev. 2003, 49, 74–80, (In Chinese with English abstract). [Google Scholar]
  10. Hu, D.G.; Wu, Z.H.; Jiang, W.; Ye, P.S. Study on the metamorphic and deformation chronology of Precambrian gabbro in the western margin of Nam Co, northern Tibet. Acta Petrol. Sin. 2004, 20, 627–632, (In Chinese with English abstract). [Google Scholar]
  11. Ye, P.S.; Wu, Z.H.; Hu, D.G.; Jiang, W.; Yang, X.D. Geochemical characteristics and formation environment of the ophiolite on the west bank of Nam Co, Tibet. Mod. Geol. 2004, 18, 237–243, (In Chinese with English abstract). [Google Scholar]
  12. Zhong, K.H.; Li, L.; Zhou, H.W.; Bai, J.G.; Li, W.; Zhong, W.T.; Zhang, Y.; Lin, J.; Zheng, F.; Huang, X. Characteristics of Jiama-Kajunguo Nappe-Sliding Structural System in Tibet. Acta Geosci. Sin. 2012, 33, 411–423, (In Chinese with English abstract). [Google Scholar]
  13. Zhong, K.H.; Yao, D.; Duo, J.; Zheng, F.S.; Xu, C.H.; Huang, X.Y.; Lu, B.; Lin, J.; Bao, C.; Yan, G. Structural characteristics of Yeba Formation in Jiama-Qulong area, Tibet. Acta Geosci. Sin. 2013, 34, 75–86, (In Chinese with English abstract). [Google Scholar]
  14. Ma, S.W.; Xu, Z.Q.; Zhang, Z.K.; Ma, Y.; Zhao, Z.B.; Pang, X.; Zhao, X.; Wang, H. Structural deformation of Jiama copper polymetallic deposit in southern Tibet and its constraints on mineralization. Acta Petrol. Sin. 2016, 32, 227–245, (In Chinese with English abstract). [Google Scholar]
  15. Ma, Y.; Xu, Z.Q.; Li, G.W.; Ma, S.W.; Ma, X.X.; Chen, X.J.; Zhao, Z. The crustal deformation and the formation of the initial plateau of the Cretaceous back-arc basin in Gangdese, southern Tibet. Acta Petrol. Sin. 2017, 33, 3861–3872, (In Chinese with English abstract). [Google Scholar]
  16. Wang, L.Q. Geological Maps and Instructions of Qinghai-Tibet Plateau and Its Adjacent Areas; Geology Press: Beijing, China, 2013; (In Chinese with English abstract). [Google Scholar]
  17. Mo, X.X.; Dong, G.C.; Zhao, Z.D.; Zhou, S.; Wang, L.L.; Qiu, R.Z.; Zhang, F. Temporal and spatial distribution characteristics and crustal growth and evolution information of granite in Gangdise belt, Tibet. J. Univ. Geol. 2005, 11, 281–290, (In Chinese with English abstract). [Google Scholar]
  18. Mo, X.; Zhao, Z.; Deng, J.; Flower, M.; Yu, X.; Luo, Z.; Li, Y.; Zhou, S.; Dong, G.; Zhu, D.; et al. Petrology and geochemistry of postcollisional volcanic rocks from the Tibetan plateau: Implications for lithosphere heterogeneity and collision-induced asthenospheric mantle flow. In Postcollisional Tectonics and Magmatism in the Mediterranean Region and Asia; GeoScienceWorld: McLean, VA, USA, 2006; pp. 507–530. [Google Scholar] [CrossRef]
  19. Gou, J. A new understanding of the age of the Yeba Formation in Lhasa area. Tibet Geol. 1994, 52, 1–6, (In Chinese with English abstract). [Google Scholar]
  20. Yin, J.R.; Gou, J.; Pei, S.W.; Jiang, G.W. The Middle Jurassic bivalve fauna in the Yeba Formation of Lhasa block and its paleogeographic significance. Reg. Geol. China 1998, 17, 132–136, (In Chinese with English abstract). [Google Scholar]
  21. Mao, G.Z.; Hu, J.R. Characteristics and formation environment of Yeba Formation in Lhasa area. Tibet Geol. 2002, 12–18, (In Chinese with English abstract). [Google Scholar]
  22. Mo, X.; Hou, Z.; Niu, Y.; Dong, G.; Qu, X.; Zhao, Z.; Yang, Z. Mantle contributions to crustal thickening during continental collision: Evidence from Cenozoic igneous rocks in southern Tibet. Lithos 2007, 96, 225–242. [Google Scholar] [CrossRef]
  23. Xu, Z.; Dilek, Y.; Cao, H.; Yang, J.; Robinson, P.; Ma, C.; Chen, X. Paleo-Tethyan evolution of Tibet as recorded in the East Cimmerides and West Cathaysides. J. Asian Earth Sci. 2015, 105, 320–337. [Google Scholar] [CrossRef]
  24. Zhang, Y.; Chen, W.; Chen, K.L.; Liu, X.Y. Study on the Ar-Ar age spectrum and 39Ar core recoil loss mechanism of diagenetic mixed layer (I/S)-Taking the P-T boundary clay rock in Changxing area of Zhejiang Province as an example. Geol. Rev. 2006, 52, 556–561, (In Chinese with English abstract). [Google Scholar]
  25. Tang, Y.; Wang, G.H.; Feng, Y.P. Tectono-Stratigraphic Attributes and Evolution of the Yeba Volcanic Arc in the Southern Gangdese, Tibet. Earth Sci. Front. 2022, 29, 18, (In Chinese with English abstract). [Google Scholar]
  26. Dutta, D.; Mukherjee, S. Opposite shear senses: Geneses, global occurrences, numerical simulations and a case study from the Indian western Himalaya. J. Struct. Geol. 2019, 126, 357–392. [Google Scholar] [CrossRef]
  27. Gao, X. Study on Tectonic Deformation and Ore-Controlling Law in Jiama Area, Tibet. Ph.D. Dissertation, China University of Geosciences, Beijing, China, 2019; pp. 1–157, (In Chinese with English abstract). [Google Scholar]
  28. Chu, M.F.; Chung, S.L.; Song, B.; Liu, D.; O’Reilly, S.Y.; Pearson, N.J.; Ji, J.; Wen, D.J. Zircon U-Pb and Hf isotope constraints on the Mesozoic tectonics and crustal evolution of southern Tibet. Geology 2006, 34, 745–748. [Google Scholar] [CrossRef]
  29. Ji, W.Q.; Wu, F.Y.; Zhong, S.L.; Liu, C.Z. Age and petrogenesis of Gangdise batholith granite in southern Tibet. Sci. China Ser. D 2009, 39, 849–871, (In Chinese with English abstract). [Google Scholar]
  30. Wen, D.R.; Chung, S.L.; Song, B.; Iizuka, Y.; Yang, H.J.; Ji, J.; Liu, D.; Gallet, S. Late Cretaceous Gangdese intrusions of adakitic geochemical characteristics, SE Tibet: Petrogenesis and tectonic implications. Lithos 2008, 105, 1–11. [Google Scholar] [CrossRef]
  31. Xu, Z.Q.; Yang, J.S.; Li, H.B.; Zhang, J.X.; Zeng, L.S.; Jiang, M. The deep driving force of the Qinghai-Tibet Plateau and continental dynamics-terrane collision, collision orogeny and plateau uplift. Chin. Geol. 2006, 33, 221–238, (In Chinese with English abstract). [Google Scholar]
  32. Xu, Z.Q.; Yang, J.S.; Hou, Z.Q.; Zhang, Z.M.; Zeng, L.S.; Li, H.B. Some progress in the study of continental dynamics of the Qinghai-Tibet Plateau. Chin. Geol. 2016, 43, 1–42, (In Chinese with English abstract). [Google Scholar]
  33. Zhu, D.C.; Wang, Q.; Zhao, Z.D.; Chung, S.L.; Cawood, P.A.; Niu, Y.; Liu, S.A.; Wu, F.Y.; Mo, X.X. Magmatic record of India-Asia collision. Sci. Rep. 2015, 5, 14289. [Google Scholar] [CrossRef] [PubMed]
  34. Yin, A. Cenozoic tectonic evolution of the himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation. Earth-Sci. Rev. 2006, 76, 1–131, Erratum in Earth-Sci. Rev. 2006, 79, 163–164. [Google Scholar] [CrossRef]
  35. Chen, M.; Niu, F.; Tromp, J.; Lenardic, A.; Lee, C.T.A.; Cao, W.; Ribeiro, J. Lithospheric foundering and underthrusting imaged beneath Tibet. Nat. Commun. 2017, 8, 15659. [Google Scholar] [CrossRef] [PubMed]
  36. Wang, G.H.; Zeng, Q.G. Study on Xietongmen-Wuyu oblique-slip ductile shear zone in Tibet. Tibet Geol. 1995, 93–98, (In Chinese with English abstract). [Google Scholar]
  37. Song, P.F. The Tectonic Deformation Characteristics and Geological Significance of the Xietongmen-Numa Ductile Shear Zone in Lhasa, Tibet. Master’s Thesis, China University of Geosciences, Wuhan, China, 2013. (In Chinese with English abstract). [Google Scholar]
  38. Meng, Y.K.; Xu, Z.Q.; Ma, S.W.; Yang, F.F.; Ma, X.X. The deformation characteristics and geochronological constraints of the Qushui ductile shear zone in the middle part of the Gangdese magmatic belt in southern Tibet. Geoscience 2016, 41, 1081–1098, (In Chinese with English abstract). [Google Scholar]
  39. Feng, Y.; Wang, G.; Meng, Y.; Li, D.; Xu, X.; Lu, Y.; Liu, H. Kinematics, strain patterns, rheology, and geochronology of Woka ductile shear zone: Product of uplift of Gangdese batholith and Great Counter Thrust activity. Geol. J. 2020, 55, 7251–7271. [Google Scholar] [CrossRef]
  40. Li, Y.; Wang, C.; Dai, J.; Xu, G.; Hou, Y.; Li, X. Propagation of the deformation and growth of the Tibetan–Himalayan orogen: A review. Earth-Sci. Rev. 2015, 143, 36–61. [Google Scholar] [CrossRef]
  41. Li, G.; Kohn, B.; Sandiford, M.; Xu, Z.; Seiler, C. Synorogenic morphotectonic evolution of the gangdese batholith, south tibet: Insights from low-temperature thermochronology. Geochemistry 2016, 17, 101–112. [Google Scholar] [CrossRef]
  42. Meng, Y.; Xu, Z.; Santosh, M.; Ma, X.; Chen, X.; Guo, G.; Liu, F. Late Triassic crustal growth in southern Tibet: Evidence from the Gangdese magmatic belt. Gondwana Res. 2016, 37, 449–464. [Google Scholar] [CrossRef]
  43. Wang, E.; Kamp, P.J.; Xu, G.; Hodges, K.V.; Meng, K.; Chen, L.; Wang, G.; Luo, H. Flexural bending of southern Tibet in a retro foreland setting. Sci. Rep. 2015, 5, 12076. [Google Scholar] [CrossRef] [PubMed]
Applsci 15 08145 g002
Figure 2. Typical profile Pm01. (a) Lens; (b) kink band; (c) shear lens.
Figure 2. Typical profile Pm01. (a) Lens; (b) kink band; (c) shear lens.
Applsci 15 08145 g002
Applsci 15 08145 g003
Figure 3. Tectonostratigraphic profile of the Yeba Rock Group. (a) Felsic sigma-type rotated porphyroclast indicating sinistral shear; (b,c) felsic vein showing dextral shear; (d) coexisting rotated porphyroclasts with opposite shear senses, lacking cross-cutting relationships—schematic diagram of shear foliation development; (e) felsic delta-type rotated porphyroclast indicating dextral shear; (f) photomicrograph of plagioclase sigma-type rotated porphyroclast showing sinistral shear in mylonite; (g) photomicrograph of quartz delta-type rotated porphyroclast showing dextral shear in mylonite; (h) rotated porphyroclasts and foliations with opposite shear senses observed under plane-polarized light; (i) lower hemisphere stereographic projection of D1-phase stretching lineations; (j) schematic diagram showing D1-phase ductile shearing and associated S1 foliation.
Figure 3. Tectonostratigraphic profile of the Yeba Rock Group. (a) Felsic sigma-type rotated porphyroclast indicating sinistral shear; (b,c) felsic vein showing dextral shear; (d) coexisting rotated porphyroclasts with opposite shear senses, lacking cross-cutting relationships—schematic diagram of shear foliation development; (e) felsic delta-type rotated porphyroclast indicating dextral shear; (f) photomicrograph of plagioclase sigma-type rotated porphyroclast showing sinistral shear in mylonite; (g) photomicrograph of quartz delta-type rotated porphyroclast showing dextral shear in mylonite; (h) rotated porphyroclasts and foliations with opposite shear senses observed under plane-polarized light; (i) lower hemisphere stereographic projection of D1-phase stretching lineations; (j) schematic diagram showing D1-phase ductile shearing and associated S1 foliation.
Applsci 15 08145 g003
Applsci 15 08145 g004
Figure 4. Characteristics of the D2-phase folding in the Yeba rock group. (a) Inclined fold; (b) tight fold; (c) tight and overturned folds; (d) upright fold; (e) chevron fold; (f,g) intense foliation transposition; (h) superimposed fold; (i) photomicrograph of rounded fold; (j) photomicrograph of chevron fold; (k) photomicrographs of tight folds; (l) photomicrographs of tight folds; (m) schematic diagram showing D2-phase fold characteristics.
Figure 4. Characteristics of the D2-phase folding in the Yeba rock group. (a) Inclined fold; (b) tight fold; (c) tight and overturned folds; (d) upright fold; (e) chevron fold; (f,g) intense foliation transposition; (h) superimposed fold; (i) photomicrograph of rounded fold; (j) photomicrograph of chevron fold; (k) photomicrographs of tight folds; (l) photomicrographs of tight folds; (m) schematic diagram showing D2-phase fold characteristics.
Applsci 15 08145 g004
Applsci 15 08145 g005
Figure 5. Characteristics of the D3-phase stretching in the Yeba rock group. (a) σ-type rotated porphyroclasts; (b) mylonitic S-C fabric; (c) “curved-neck bottle” structure; (d) mineral stretching lineation; (e) asymmetric folds; (f) asymmetric felsic bands—microscopic indicators of ductile shear; (g) δ-type and σ-type rotated porphyroclasts; (h) σ-type rotated porphyroclasts; (i) asymmetric pressure shadows; (j) schematic diagram showing the structural characteristics of D3-phase deformation and its relationship with the D1 and D2 phases; Q = quartz; Pl = plagioclase.
Figure 5. Characteristics of the D3-phase stretching in the Yeba rock group. (a) σ-type rotated porphyroclasts; (b) mylonitic S-C fabric; (c) “curved-neck bottle” structure; (d) mineral stretching lineation; (e) asymmetric folds; (f) asymmetric felsic bands—microscopic indicators of ductile shear; (g) δ-type and σ-type rotated porphyroclasts; (h) σ-type rotated porphyroclasts; (i) asymmetric pressure shadows; (j) schematic diagram showing the structural characteristics of D3-phase deformation and its relationship with the D1 and D2 phases; Q = quartz; Pl = plagioclase.
Applsci 15 08145 g005
Applsci 15 08145 g006
Figure 6. 40Ar-39Ar plateau (a,c) and inverse isochronal (b,d) ages for mica from the quartz samples used in EBSD analysis. All age uncertainties are reported at the 2σ level. tp = plateau age; ti = inverse isochron age; MSWD = mean square of weighted deviates.
Figure 6. 40Ar-39Ar plateau (a,c) and inverse isochronal (b,d) ages for mica from the quartz samples used in EBSD analysis. All age uncertainties are reported at the 2σ level. tp = plateau age; ti = inverse isochron age; MSWD = mean square of weighted deviates.
Applsci 15 08145 g006
Applsci 15 08145 g007
Figure 7. Tectonic evolution model of the Yeba Volcanic Arc. (a) Ductile shear zones developed in the Yeba Rock Group under a transpressional regime during the Late Cretaceous; (b) fold deformation formed in the Yeba Rock Group and Duodigou Formation under N-S compressional settings during the Late Cretaceous; (c) ductile shear zones in the Yeba Rock Group developed due to combined effects of GCT activity and the exhumation of the Gangdese batholith during the Oligocene–Miocene. The abbreviations shown in the figure are as follows: GCT = Gangdese southern marginal back-thrust.
Figure 7. Tectonic evolution model of the Yeba Volcanic Arc. (a) Ductile shear zones developed in the Yeba Rock Group under a transpressional regime during the Late Cretaceous; (b) fold deformation formed in the Yeba Rock Group and Duodigou Formation under N-S compressional settings during the Late Cretaceous; (c) ductile shear zones in the Yeba Rock Group developed due to combined effects of GCT activity and the exhumation of the Gangdese batholith during the Oligocene–Miocene. The abbreviations shown in the figure are as follows: GCT = Gangdese southern marginal back-thrust.
Applsci 15 08145 g007
Table 1. 40Ar-39Ar dating results.
Table 1. 40Ar-39Ar dating results.
T/℃40Ar/39Ar1σ37Ar/39Ar1σ36Ar/39Ar1σ40Ar*/39Ark ± 2σ(Age ± 2σ)/(Ma)
QY-4-08-07-1
65047.87590.29350.00000.03650.13320.00358.5259 ± 2.0056.98 ± 13.13
72032.63120.19550.03770.00520.08010.00208.9536 ± 1.1559.79 ± 7.53
76012.10540.07260.02620.00400.00630.000210.2532 ± 0.1668.31 ± 1.07
80012.07780.07240.00560.00350.00380.000210.9622 ± 0.1672.94 ± 1.04
84012.46250.07470.00480.00210.00290.000111.6004 ± 0.1677.09 ± 1.01
88012.90800.07740.01450.00190.00300.000112.0254 ± 0.1679.86 ± 1.01
92012.98520.07780.00770.00280.00340.000111.9715 ± 0.1679.51 ± 1.06
96013.08250.07850.00000.00570.00420.000211.8372 ± 0.1978.63 ± 1.26
101013.28570.07970.00000.00440.00510.000211.7836 ± 0.2078.28 ± 1.31
106013.52940.08140.00000.00570.00680.000311.5320 ± 0.2176.65 ± 1.39
112013.41620.08050.00000.00550.00730.000311.2494 ± 0.2274.81 ± 1.41
118015.54380.09360.00000.00510.01420.000611.3405 ± 0.3675.40 ± 2.36
140074.01100.45670.08270.02880.19180.004917.3288 ± 2.83113.98 ± 18.04
QY-4-08-07-4
600102.67310.66590.00000.03570.33720.00853.0288 ± 4.8820.24 ± 32.40
68021.16950.12710.00690.00740.04510.00127.8560 ± 0.7052.03 ± 4.55
72032.07970.19290.00000.01230.07610.00199.5996 ± 1.1163.37 ± 7.21
76015.50990.09300.00000.00400.01540.0004 10.9568 ± 0.2872.16 ± 1.78
80013.05710.07820.01970.00420.00570.000211.3624 ± 0.1974.77 ± 1.24
84013.41710.08040.00000.00200.00460.000212.0430 ± 0.1779.16 ± 1.11
88013.37560.08030.00000.00440.00450.000212.0449 ± 0.1879.17 ± 1.17
92013.71780.08220.00090.00150.00470.000112.3181 ± 0.1780.92 ± 1.10
96013.92810.08350.00000.00530.00660.000311.9906 ± 0.2178.82 ± 1.33
102014.34190.08630.00000.01240.00720.000412.2173 ± 0.2780.28 ± 1.74
110015.31010.09180.00030.00310.01080.000312.1103 ± 0.2279.59 ± 1.43
118016.81420.10080.00800.00350.01450.000412.5203 ± 0.2782.22 ± 1.72
126029.34090.18010.00000.03290.04330.001616.5397 ± 0.95107.84 ± 6.03
140057.79730.37970.00000.05840.12530.003520.7632 ± 2.05134.38 ± 12.76
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Fan, Z.; Yuan, Z.; Chen, M.; Wang, G. Tectonic Characteristics and Geological Significance of the Yeba Volcanic Arc in the Southern Lhasa Terrane. Appl. Sci. 2025, 15, 8145. https://doi.org/10.3390/app15158145

AMA Style

Fan Z, Yuan Z, Chen M, Wang G. Tectonic Characteristics and Geological Significance of the Yeba Volcanic Arc in the Southern Lhasa Terrane. Applied Sciences. 2025; 15(15):8145. https://doi.org/10.3390/app15158145

Chicago/Turabian Style

Fan, Zhengzhe, Zhengren Yuan, Minghui Chen, and Genhou Wang. 2025. "Tectonic Characteristics and Geological Significance of the Yeba Volcanic Arc in the Southern Lhasa Terrane" Applied Sciences 15, no. 15: 8145. https://doi.org/10.3390/app15158145

APA Style

Fan, Z., Yuan, Z., Chen, M., & Wang, G. (2025). Tectonic Characteristics and Geological Significance of the Yeba Volcanic Arc in the Southern Lhasa Terrane. Applied Sciences, 15(15), 8145. https://doi.org/10.3390/app15158145

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop