Cenozoic Multiphasic Activity and Mesozoic Basin-Control Role of the Dingri–Gangba Fault, Southern Tibet: An Integrated Study of Structural Analysis, Stratigraphic Correlation, and ESR Geochronology

Abstract

The Dingri–Gangba fault, a major structure within the Himalayan Orogenic Belt, records significant geological events, including the tectonic evolution of the northern margin of the Indian plate and the uplift of the Tibetan Plateau. However, its geometry, kinematics, and tectonic characteristics remain debated. To constrain the tectonic evolution of the Dingri–Gangba fault, this study integrates detailed field investigations and structural analysis with Electron Spin Resonance (ESR) dating to characterize its three-dimensional architecture and quantify the timing of its deformation phases. The results show that the fault trends nearly E–W and exhibits multi-phase structural superimposition, including thrusting (60–40 Ma), normal faulting (35–11 Ma), and strike-slip shear (18–6.8 Ma). These phases reflect a multi-stage tectonic evolution following the India–Eurasia collision. Stratigraphic comparisons reveal that during the Mesozoic, the Dingri–Gangba fault played a significant basin-controlling role, marked by variations in sedimentary thickness, soft-sediment deformation, and volcanic activity. The sedimentary evolution alternated between periods of “differentiation” and “uniformity”. A comprehensive analysis suggests that the tectonic evolution of the Dingri–Gangba fault is closely linked to the dynamic transition of the Tethys Himalaya from a passive continental margin to a collision orogeny, also reflecting changes in the tectonic stress field following the India–Eurasia collision. These findings provide valuable insights into the tectono–sedimentary–magmatic coupling along the southern margin of the Tibetan Plateau.

1. Introduction

The Himalayan Orogenic Belt archives two major phases of tectonic history. First, it records the rapid uplift and crustal shortening associated with the Cenozoic India–Eurasia collision. Second, it preserves evidence of earlier Mesozoic processes, including Tethyan oceanic subduction, passive margin evolution, and subsequent intracontinental deformation [1,2,3]. During this period, several large E–W trending fault systems developed, which played a critical role in controlling regional sedimentary and tectonic evolution [4]. The Dingri–Gangba fault (DGF) is an important component of this tectonic system and extends approximately 800 km. It was first recognized as a regional fault by Huang and Ren (1980) [5]. This fault has significantly influenced the Mesozoic–Cenozoic sedimentary formation and basin filling of the Tethys Himalaya (TH). Its tectonic evolution is closely associated with contemporaneous magmatism and has remained highly responsive during the Cenozoic India–Eurasia collision [6,7]. Therefore, the DGF records a series of main tectonic events, from passive continental margin to foreland basin, and to plateau uplift, providing valuable insights into the tectonic evolution of the northern Indian plate and the mechanisms of Tibetan Plateau uplift and crustal shortening.

Current research on the DGF reveals its characteristics as a long-active, complex regional fault system. However, the geometry, kinematics, and tectonic affiliation of the DGF remain contentious. These discrepancies essentially reflect an insufficient understanding of its multi-phase spatiotemporal evolution and the superimposition and cross-cutting relationships between different structural phases. Some scholars, based on field relationships where Paleozoic–Mesozoic strata from the northern block are overthrust onto Eocene marine deposits on the southern block, interpret it as a north-dipping thrust fault [8]. However, more studies have revealed significant spatiotemporal variations in its kinematic characteristics, demonstrating extensional or strike-slip behaviors during different geological periods. For example, Zhu et al. (2005) proposed that the fault acted as a syn-sedimentary normal fault controlling basin development during the Late Jurassic [9]; Li et al. (2008) further documented its left-lateral strike-slip activity since the Miocene in the Kangmar region [10]. These seemingly contradictory observations suggest a complex evolutionary sequence: from Late Mesozoic passive margin extension (basin control), through main collisional phase thrusting, to post-collisional strike-slip and extensional adjustments. Regarding its tectonic affinity, a body of research associates the DGF with the South Tibetan Detachment System (STDS), interpreting it as either an integral part of this low-angle detachment system or its eastern structural manifestation rather than an independent tectonic unit [1,11,12]. The resolution of this longstanding controversy hinges on precisely determining both the spatial and temporal relationships between the two structures—specifically, whether the high-angle DGF cuts the low-angle STDS detachment surface—and constraining their relative timing of activity. Resolving this issue is pivotal for understanding the transition between compressional and extensional tectonic regimes during the evolution of the Himalayan orogen.

Beyond the controversies over geometry and kinematics, there are also differing interpretations regarding the fault’s mechanisms for controlling basin evolution and deep processes. Some studies suggest it long-controlled sedimentary differences between the northern and southern sides, with the northern side being bathyal–basinal facies and the southern side being stable littoral–neritic facies [2,13]. Other studies propose that it served as a conduit for magma ascent during the Miocene (17–31 Ma) [14]. The realization of these different functions likely corresponds to the differential activity of the fault during different evolutionary stages (e.g., Mesozoic basin control, Cenozoic magma control). The precise timing of this transition and its dynamic background are precisely the weak points in current research. In summary, the persistent controversies surrounding the DGF primarily stem from the absence of a comprehensive spatiotemporal model that can coherently integrate its multi-phase tectonic history, including potential Late Mesozoic extension, Paleogene thrusting, and Miocene strike-slip or extensional overprinting. Constructing such a model necessitates the systematic delineation of cross-cutting relationships among diverse structural elements—such as thrust planes, normal faults, and strike-slip shear zones—through detailed field-based structural analysis. This geometric framework must be rigorously calibrated with high-precision geochronology to constrain the absolute timing of each deformation phase. Resolving this fundamental problem constitutes the primary objective of this study.

Despite its critical role in the TH, research on the DGF remains limited. A lack of systematic structural analysis has hindered the clarification of its geometry and kinematics. Although multi-stage activity has been recorded sporadically, precise chronological constraints are still lacking, leaving the timing and driving mechanisms unclear. Furthermore, limited research has been conducted on the fault’s control over basin filling and structural styles, resulting in an unclear understanding of its role in regional tectonic evolution. These have constrained a deeper understanding of the tectonic evolution of the TH. To address these issues, this study systematically investigates the geometry, kinematics, multi-stage activity, and basin-controlling effects of the DGF through detailed geological mapping and structural analysis in the Dingri area, combined with stratigraphic comparisons and ESR geochronology. Based on these results, a revised fault evolution model is proposed, aiming to enhance the understanding of the tectonic–sedimentary–magmatic coupling mechanisms in the TH and provide a new perspective on fault–basin interactions within the Himalayan Orogenic Belt.

2. Geological Background

The Himalayan Orogenic Belt, formed by the ongoing Cenozoic collision between the Indian and Eurasian plates, is the world’s youngest and still active continental orogen [1,11,15]. To the north, it is separated from the Lhasa Terrane by the Yarlung–Zangbo Suture Zone (YZSZ) (Figure 1a), and to the south, it borders the Indian Plate along the Main Frontal Thrust (MFT). From north to south, the belt is subdivided into four major tectono–stratigraphic units: the Tethys Himalaya Sequence (THS), Greater Himalayan Sequence (GHS), Lesser Himalayan Sequence (LHS), and Sub-Himalaya Sequence (SHS) (Figure 1b). These units are bounded by large-scale fault belts, including the STDS, Main Central Thrust (MCT), and Main Boundary Thrust (MBT) [16,17].

Figure 1. (a) Simplified tectonic map of the Tibetan Plateau (modified after [18]). (b) Simplified geological map of the Himalayan Orogenic Belt (modified after [19]). (c) Simplified geological map of the Dingri area. Abbreviations: AKMSZ = Ayimaqing–Kunlun–Muztagh Suture Zone; JSSZ = Jinshajiang Suture Zone; BNSZ = Bangong–Nujiang Suture Zone; YZSZ = Yarlung–Zangbo Suture Zone; STDS = South Tibet Detachment System; DGF = Dingri–Gangba Fault; MCT = Main Central Thrust; MBT = Main Boundary Thrust; MFT = Main Frontal Thrust.

The TH preserves the most complete geological records of passive continental margin evolution and subsequent collision orogeny. Extending over 1500 km from east to west, this belt is bounded to the south by the STDS and to the north by the YZSZ [1,20]. Its sedimentary sequences, spanning from the Cambrian to the Eocene, are categorized into four supersequences: pre-rift deposits from the Cambrian to Early Carboniferous, syn-rift deposits from Early Carboniferous to Early Permian, post-rift deposits from Middle Permian to Paleocene, and syn-collision deposits from Paleocene to Eocene [15,21,22]. Extensive studies have shown that the primary provenance of the TH is from the Gondwana supercontinent [23,24,25,26,27,28,29,30,31,32]. The DGF is widely regarded as the boundary separating the northern and southern sub-belts within the TH. The northern sub-belt is characterized by Mesozoic to Paleogene deep-water outer shelf and slope sediments, consisting of sandstone–mudstone sequences interlayered with limestone and siliceous rocks, exhibiting intense structural deformation [33,34,35,36]. In contrast, the southern sub-belt preserves a continuous sequence of Paleozoic to Cenozoic littoral–neritic and platform clastic and carbonate rocks, indicative of relatively stable passive margin sedimentation [22]. Additionally, several Cenozoic granitic plutons are exposed within the TH [37,38,39].

The DGF is the largest and most influential fault belt within the TH, extending approximately 800 km from east of Purang, through Gyirong, Dingri, Gangba, and Lhoza, to the east of Cuona, where it intersects the STDS near Jiayu. Previous studies indicate that this fault exhibits multi-phase structural characteristics: an early stage of north-dipping reverse thrust, followed by extensional detachment. Some extensional fault surfaces have reactivated earlier reverse fault planes, indicating significant structural inheritance [8,13]. As the boundary between the stable Phanerozoic platform sediments in the southern sub-belt and the Mesozoic deep-water slope sediments in the northern sub-belt, the DGF has played a crucial role in controlling basin distribution and filling processes. Its two sides display distinctly different stratigraphic sequences, lithofacies, metamorphic grades, and magmatic characteristics [2]. Therefore, the DGF is not only a regional tectono–stratigraphic boundary but also an important window for understanding the sedimentary–tectonic–magmatic coupling evolution within the TH.

The Dingri area, located in the western segment of the DGF, provides an ideal natural laboratory for investigating the fault’s structural characteristic and evolutionary history. This area exposes Mesozoic Triassic–Cretaceous, Cenozoic Paleogene, and Quaternary strata. The northern sub-belt is primarily characterized by Upper Jurassic Weimei Formation (Fm.) and Lower Cretaceous Jiabula Fm., while the southern sub-belt preserves a continuous marine sequence spanning from the Paleozoic to the Early Cenozoic (Figure 1c). Mesozoic volcanic rocks, primarily basalt, tuff, and tuffaceous sandstone, are widely developed. Intrusive rocks mainly consist of Cretaceous diabase dikes and Cenozoic leucogranites. Regional metamorphic grade is generally low, characterized by rocks such as slate, metamorphic sandstone, and crystalline limestone. However, within the northern sub-belt, stringer-like domes expose medium- to high-grade metamorphic basements, including gneiss, schist, and granulite.

3. ESR Dating

3.1. Sample Collection

This study collected seven representative quartz vein samples from the DGF in Kema Township, Dingri County (28°46′1″ N, 86°40′28″ E). Sampling focused on fresh outcrops within the fault core to avoid weathered or altered surfaces. Based on the occurrence and structural relationships of the veins, the samples were classified into three genetic types:

First type (reverse thrust-related): Quartz breccias (samples NGL1-2, NGL1-4; 4–8 cm thick) aligned with the structural foliation, exhibiting porphyroclastic or lensoidal textures. These formed in a reverse thrust fault zone, where hydrothermal fluids precipitated along fracture surfaces under cooling and decompression, followed by subsequent shear modification.

Second type (normal fault-related): Quartz veins and breccias (samples NGL1-5, KMX1-1, NGL2-2, KMX3-1; 2–5 cm thick) originating from extensional joints and brittle fracture zones. These veins obliquely offset across the foliation, extending for short distances with tapered ends, representing SiO₂ dissolution and infilling during rock rupture.

Third type (strike-slip-related): Quartz slickenlines (sample NGL1-3), 1–2 cm thick, occurring along fault or shear surfaces. These are straight and extensive, and clearly crosscut the structural foliation and earlier veins, indicating hydrothermal infilling associated with strike-slip shearing.

3.2. Methodology: Principles, Experimental Procedures, and Limitations

3.2.1. Rationale for Method Selection

Electron Spin Resonance (ESR) dating was selected due to its unique applicability for dating shallow brittle faults. ESR directly determines the formation age of fault-related quartz veins, which serve as direct mineralogical records of fault activity. The paramagnetic centers (e.g., Ge centers) in quartz exhibit excellent thermal stability below ~70–80 °C, which is ideal for low-temperature fault zones [40]. ESR provides a dating range from thousands to millions of years, offering significant advantages for dating Cenozoic tectonic events.

3.2.2. Experimental Procedures and Closed-System Behavior

ESR experiments were conducted at the Sichuan Provincial Key Laboratory of Nuclear Techniques in Earth Sciences, Chengdu University of Technology. Following pretreatment, natural α and γ radioactivity were measured using a KJD-2000N low-background gamma spectrometer (Xinxingda, Chengdu, China) coupled with a microcomputer data acquisition system, with simultaneous corrections performed [41]. Each sample underwent single-mineral thermal activation treatment using a mass of approximately 120 mg per sample. After one week of cooling, the concentrations of paramagnetic centers were measured using an ER-2000D-SRC ESR spectrometer (Bruker, Karlsruhe, Germany). Uranium-equivalent content was calculated from the saturated α count rate, with a relative measurement error of less than 1%. The equivalent dose (DE) was determined by fitting dose–response curves. The annual dose rate (D) was calculated based on U, Th (measured by low-background gamma spectrometry), and K (measured by XRF) contents, incorporating cosmic ray corrections. The ESR age was calculated using the formula: Age = DE/D. The ESR dating results for the quartz veins are presented in Table 1.

Table 1. ESR dating results of quartz veins in the Dingri–Gangba fault zone in Dingri area.

Sample ID	Sampling Location	Characteristics	Relative Position	Paramagnetic Center Concentration (1015 Sp/g)	U Content (μg/g)	Age
NGL1-3	Naigulin	Left-lateral strike-slip fault	Secondary fault, quartz striation mirror	0.227	0.359	18 ± 2 Ma
NGL1-5	Naigulin	North-dipping normal fault	Secondary fault, quartz tectonic breccia	0.486	1.059	29 ± 5 Ma
KMX1-1	Kema	North-dipping normal fault	North boundary of fault, quartz vein within the fractured zone	0.248	0.559	32 ± 5 Ma
NGL2-2	Naigulin	North-dipping normal fault	South boundary of fault, quartz breccia in brittle fractured zone	0.261	0.919	33 ± 6 Ma
KMX3-1	Kema	North-dipping normal fault	South boundary of fault, quartz vein within the tectonic fold	0.196	0.779	35 ± 5 Ma
NGL1-4	Naigulin	NNE-dipping reverse fault	Secondary fault, shear-induced quartz clasts	0.154	0.954	45 ± 6 Ma
NGL1-2	Naigulin	North-dipping reverse fault	North boundary of fault, shear-induced quartz lens	0.105	1.059	46 ± 8 Ma

All samples exhibited massive, fine-grained textures without evidence of recrystallization or late-stage fluid alteration under microscopy, supporting the stability of uranium content and confirming closed-system behavior for ESR dating.

3.2.3. Assessment of Dating Uncertainties

The reported age uncertainties (±2–8 Ma, 1σ) primarily stem from two sources: first, DE determination errors (±5–10%), arising from dose–response curve fitting; and second, dose rate estimation errors, particularly U content measurement errors (<1%) and the selection of the α efficiency factor (k-value).

Despite these uncertainties, the temporal relationships of the ages effectively distinguish three main tectonic phases. The reverse thrusting phase (46 ± 8 Ma, 45 ± 6 Ma) and the normal faulting phase (35 ± 5 Ma to 29 ± 5 Ma) are separated by >10 Ma, far exceeding the uncertainty ranges. The strike-slip phase (18 ± 2 Ma) shows high precision and aligns with regional tectonic events (e.g., South Tibet Detachment System activity), further supporting its independence.

3.3. Results and Interpretation

The ESR ages of the different quartz vein types are highly consistent with their respective structural characteristics:

The first type of quartz veins, formed during north-dipping reverse faulting, yielded ages of 45 ± 6–46 ± 8 Ma, indicating that reverse compressional activity occurred during the Middle Eocene.

The second type, consisting of quartz veins that obliquely offset the first-phase structures, yielded ages ranging from 29 ± 5 to 35 ± 5 Ma, representing ductile–brittle extensional deformation during the Late Eocene to Early Oligocene.

The third type, including quartz veins that superimposed and modified the products of the second-phase structures, yielded an age of 18 ± 2 Ma, reflecting left-lateral strike-slip activity during the Early Miocene.

A comprehensive analysis shows that the DGF has undergone three major structural phases since the Cenozoic: reverse compressive thrusting, extensional deformation, and strike-slip shear. The ESR dating results provide critical chronological constraints for understanding the multi-phase structural evolution of the DGF.

4. Field Geological Characteristics

4.1. Structural Deformation Characteristics

The DGF in the Dingri area is continuously well-exposed, trending approximately east–west. It appears as a brittle-ductile shear zone with a width of about 0.5 to 2 km, which is interpreted as an exhumed structure originating from the mid-crustal brittle-ductile transition zone. This present-day exposure is attributed to the profound Cenozoic tectonic exhumation associated with the uplift of the Tibetan Plateau. Following the fault zone architectural model [42,43], the fault zone comprises a fault core and a surrounding damage zone. The fault comprises sedimentary fault blocks from different stratigraphic units, with some displaced by NE-trending strike-slip faults. Field investigations indicate that it can be subdivided into four typical segments: the Kema, Nanmujia, Naigulin, and Maiduozha segments. These segments exhibit structural characteristics such as fault-bounded blocks, tectonic breccia zones within the fault core, and cleavage zones.

4.1.1. Geological Characteristics of the Kema Segment

The Kema segment, located in the western part of the DGF, generally trends E–W with a gentle northward bulge near Yundong village. This segment mainly exhibits a brittle–ductile deformation zone formed by reverse thrusting and fault-bounded blocks, showing multi-phase structural superposition (Figure 2a). The fault blocks are mostly wedge-shaped and consist of the Jiabula Fm. from the northern sub-belt, and the Chaqiela and Gangbacunkou Fms. from the southern sub-belt (Figure 2b).

Figure 2. Structural characteristics of the Kema segment within the Dingri–Gangba fault. (a) Surface map. (b) Cross-sectional profile. (c–e) Representative field photographs of outcrop-scale deformation characteristics.

The northern boundary fault exhibits a steeply dipping plane (fault: 15°/68°), with localized fault scarps and significant offset in the quartz sandstone of the Jiabula Fm. (Figure 2c). Tectonic breccias, which are components of the fault core, and striation lineations are widely distributed, indicating two phases of tectonic activity (reverse thrusting followed by normal faulting), with a displacement of about 2–3 m.

Numerous secondary faults are widely developed within the damage zone, containing multiple sedimentary fault blocks and recording multi-phase superposition, including reverse thrusting, normal faulting, and left-lateral shearing (Figure 2d). Locally, shale of the Chaqiela Fm. in the southern sub-belt, with a gentle dip (fault: 42°/15°), overrides the quartz sandstone of the Jiabula Fm. in the northern sub-belt. The shale in the hanging wall exhibits penetrative cleavage, while the sandstone in the footwall forms complex drag folds. The faulted layers, drag folds, and cleavage structures consistently indicate reverse thrusting. The fault core commonly shows striation lineations, fault steps, tectonic breccias and cataclastic rocks (following the classification of Woodcock and Mort, 2008) [44], and en-echelon tension joints. Steps and striation lineations reveal three superimposed deformation phases: early left-lateral reverse faulting (lineation: 352°/22°), later right-lateral normal faulting (lineation: 33°/21°), and late left-lateral strike-slip (lineation: 70°/1°).

The southern boundary fault comprises a several-meter-wide fault core (fault: 149°/65°), characterized by tectonic lenses, fracture cleavage, cataclastic rocks and tectonic breccias, exhibiting brittle–ductile deformation (Figure 2e). Field observations indicate at least two phases of deformation: an early N–S compressional reverse thrusting, with the Chaqiela Fm. from the southern sub-belt overthrusting the fault core, forming S-type tight folds; and a later extensional deformation, with drag folds and tectonic breccia in the footwall and penetrative cleavage in the hanging wall. Some tectonic lenses are aligned linearly, reflecting normal faulting characteristics.

4.1.2. Geological Characteristics of the Nanmujia Segment

The Nanmujia segment is located in the middle section of the DGF, with a width of 1.6–2 km. It is the most complex segment in terms of both lithology and structural style. The fault belt in this segment gently dips to the north (Figure 3a).

Figure 3. Structural characteristics of the Nanmujia segment within the Dingri–Gangba fault. (a) Cross-sectional profile. (b–d) Representative field photographs of outcrop-scale deformation characteristics.

The northern boundary fault is exposed as a fault core characterized by a breccia zone (fault: 37°/35°), intersecting the shale of the Jiabula Fm. in the northern sub-belt at a low angle. The fault plane contains tectonic breccias, asymmetric folds, striation lineations, and penetrative cleavage. Sandstone layers commonly exhibit Z-type folds, and fault breccias exhibit δ-type porphyroclasts, indicating transpressional deformation. A later phase of extensional activity produced a northward-dipping normal fault that offsets sandstone lenses and early folds, with associated drag cleavage in the hanging wall.

The fault belt contains various fault blocks, with the northern part primarily composed of the Jiabula Fm. from the northern sub-belt, intermixed with small amounts of the Chaqiela and Gangbacunkou Fms. from the southern sub-belt. The southern part is mainly composed of large fault blocks of the Chaqiela, Gangbacunkou, and Gangbadongshan Fms. from the southern sub-belt. The segment exhibits multi-phase superimposed deformation, preserving early N–S reverse thrusting and later brittle extension and left-lateral strike-slip. Typical deformation features include: (1) Compound anticline folds in the Chaqiela Fm., with an S-shaped northern limb and a Z-shaped southern limb, indicating southward reverse thrusting (Figure 3b); (2) A fault core expressed as a breccia zone between the Jiabula and Gangbacunkou Fms., where the Jiabula Fm. is thrust over the Gangbacunkou Fm. Tectonic breccias and drag folds indicate N–S reverse thrusting, while a later extensional fault offsets the earlier thrust surface, exhibiting a displacement of up to 5 m; (3) A normal fault zone within the damage zone, with 27 steep normal faults with displacements ranging from 0.1 to 5 m. Some faults reactivate earlier reverse fault planes and intersect to form Y-type structures (Figure 3c). The zone contains quartz breccias, striation lineations, and en-echelon joints, with local NE-trending left-lateral strike-slip offset and evident superimposed striation phenomena (Figure 3d).

The southern boundary fault is a low-angle structure (fault: 24°/34°), where the Chaqiela Fm. in the hanging wall is thrust over the Gangbadongshan Fm. in the footwall. The fault core contains tectonic breccias, structural lenses, and cataclastic rocks, with some quartz sandstone lenses arranged in an en-echelon pattern. Striations record three phases of superimposed lineation characteristics: NW-trending lineations indicating N–S reverse thrusting, normal fault lineations indicating extensional activity, and E–W lineations showing left-lateral strike-slip deformation.

4.1.3. Geological Characteristics of the Naigulin Segment

The Naigulin segment is located in the central–eastern part of the DGF, with a width of approximately 80–90 m. The fault blocks are narrow and wedge-shaped (Figure 4a).

Figure 4. Structural characteristics of the Naigulin segment within the Dingri–Gangba fault. (a) Cross-sectional profile. (b–d) Representative field photographs of outcrop-scale deformation characteristics.

The northern side of the segment exhibits a distinct fault block collage with a gentle dip, composed of an intermixed sequence of the Jiabula and Gangbacunkou Fms. Both sides of the fault exhibit penetrative cleavage, with tectonic breccias showing a preferred orientation, and the fault blocks displaying rotation and fracturing. This segment records multi-phase superimposed deformation: during N–S compressive deformation, penetrative cleavage zones, asymmetric folds in the hanging wall traditionally interpreted as drag folds, and block rotation fractures developed. Subsequent deformation reactivated the earlier fault plane, forming analogous asymmetric folds and en-echelon tension joints in the footwall. While the geometry of these folds is consistent with the classic drag fold model, we consider that their formation could also be attributed to heterogeneous simple shear or the development of flanking structures in a non-coaxial strain field [45], particularly given the multi-phase reactivation of the fault zone.

The southern boundary fault is a 1–2 m wide fault core dipping steeply northward (fault: 350°/50°) (Figure 4b). Within the zone, weak layers such as shale and siltstone exhibit intense cleavage, while harder layers, such as quartz sandstone, show folds and tectonic lenses. Sandstone fault planes are marked by widespread striation lineations, with local rotational porphyroclasts, and right-lateral shear en-echelon tension joints. This fault core records both early reverse thrusting and later extensional normal faulting, with fault blocks arranged in imbricate structures exhibiting a double-thrust structure.

Overall, the Naigulin segment preserves a record of both N–S compressional thrusting and later brittle extension. Under reverse thrusting, sandstone layers commonly develop m-type folds, asymmetric folds, and thrust-related folds (Figure 4c), accompanied by cleavage zones and fault breccia. Quartz tectonic breccias show σ-type rotational porphyroclasts (long axis: 155°/35°). Later extensional deformation modifies the early structural planes, offsetting or stretching fold limbs into lensoidal shapes. Striation lineations are linearly developed on fault planes. Shales and siltstones exhibit curved cleavage and drag folds (Figure 4d), with striations and steps consistently indicating normal fault activity.

4.1.4. Geological Characteristics of the Maiduozha Segment

The Maiduozha segment is located in the eastern part of the DGF, with the fault plane dipping northward (fault: 349°/62°). The segment is primarily composed of a strong cleavage zone within the damage zone and a tectonic breccia zone constituting the fault core (Figure 5a).

Figure 5. Outcrop-scale deformation characteristics of the Maiduozha segment within the Dingri–Gangba fault. (a) Panoramic view of the Maiduozha segment. (b–d) Representative field photographs of outcrop-scale deformation characteristics.

On the northern side of the cleavage zone, shales of the Jiabula Fm. exhibit intense penetrative cleavage. The bedding and cleavage intersect at a small angle, and the acute angle indicates right-lateral shear. To the south, the Chaqiela Fm. forms a strong cleavage zone (Figure 5b), with cleavage spacing ranging from 0.5 to 2 cm and showing both crenulation cleavage and fracture cleavage. Near the fault core (tectonic breccia zone), penetrative cleavage is intensely developed, resembling an S–C fabric. The shale exhibits multiple joint sets, including shear joints oriented at 15° and en-echelon tension joints at 45°, reflecting a nearly N–S oriented compressional principal stress.

The fault core (tectonic breccia zone) consists of weakly deformed quartz sandstone and breccia, displaying widespread brecciation and cataclasis (Figure 5c), along with striation lineations and steps. The breccia is primarily composed of quartz breccias, with a tightly cemented cataclastic matrix. The fault plane shows large-scale striation lineations, with both positive and reverse steps (Figure 5d). Field structural evidence indicates three phases of superimposed deformation. The early phase is characterized by striation lineations associated with normal steps, with plunge directions ranging from NW (301–347°) to NE (10–69°) and angles of 23–89°, indicating southward reverse thrusting. The intermediate phase is characterized by N–S extensional lineations and steps that record normal fault activity, with plunge directions mainly toward the NNE (11–32°) to NNW (296–340°) at angles of 34–84°. The late phase displays NW-SE to nearly E–W trending lineations that superimposed and modified earlier lineations, reflecting left-lateral strike-slip shear.

4.2. Deformation Characteristics of Different Stratigraphic Units

Stratigraphic units on both sides of the DGF show significant differences in structural style. The northern sub-belt is characterized by open folds with relatively few faults, whereas the southern sub-belt displays isoclinal folds combined with reverse thrusting, further superimposed extensional and strike-slip deformation. Thus, the DGF not only controls sedimentary formations but also forms distinct contrasts in both the style and intensity of structural deformation on both sides.

4.2.1. Structural Deformation of the Northern Sub-Belt

The northern sub-belt is characterized by fold deformation, with types ranging from medium- to large-scale gentle folds, open folds, isoclinal folds, and locally small tight folds (Figure 6). Faults are relatively scarce and mainly consist of conjugate strike-slip systems with NE-trending left-lateral and NW-trending right-lateral motion; E–W-trending faults are limited in scale. Influenced by dome structures, the northern sub-belt shows significantly stronger metamorphism and deformation compared to the southern sub-belt, displaying ductile–brittle and brittle deformation. Siltstones and mudstones of the Jiabula Fm. exhibit widespread cleavage and complex crenulation, with localized late-stage shear overprinting. Limestones of the Weimei Fm. generally exhibit penetrative foliation, plastic deformation, sheath folds, and multiple superimposed structural characteristics.

Figure 6. Structural deformation features of the northern sub-belt in the Dingri area. Colors represent different stratigraphic units (see Figure 1 for the age scheme). Superscript numbers denote members (e.g., ¹ for Member 1). Key to units: Pr, Precambrian basement; J₃w¹⁻³, Weimei Fm.; K_1-2j¹⁻⁴, Jiabula Fm.; ηγN₁, Neogene granite. The Dingri-Gangba Fault is indicated.

4.2.2. Structural Deformation of the Southern Sub-Belt

The southern sub-belt preserves a continuous sedimentary sequence from the Permian to the Eocene and displays a structural style sharply contrasting with that of the northern sub-belt. It is dominated by a fold–thrust system (Figure 7a), characterized by dense faulting and a typical fold–thrust belt. The faults record multi-phase activity: drag folds, striations, tectonic lenses, cleavage zones, and secondary faults reflect reverse thrusting, whereas tectonic breccias, striations, quartz lenses, and bookshelf structures in sandstones indicate subsequent extensional normal faulting. The fold styles are diverse (Figure 7b–d), revealing a polyphase deformation history with at least two significant tectonic events. The first-phase (D1) fold system constitutes the dominant structural framework of the belt, characterized by tight, medium- to large-scale folds with axial trends oriented E–W or NWW–SEE. Their axial planes predominantly dip northward at 40–60°, with undulating hinges and plunge angles of 5–15°. These folds along with the association with regional E–W trending thrust faults, collectively define a typical fold-thrust nappe system, indicating intense N–S compressional contraction. The second-phase (D2) fold system is superimposed upon the D1 structures. It is characterized by relatively open, locally distributed, medium- to small-scale asymmetric plunging folds. This later phase is associated with extensional structures (e.g., extensional fault breccias, quartz lenses), suggesting a localized extensional regime or a tectonic stress field transformation within the overarching compressional setting.

Figure 7. Structural deformation features of the southern sub-belt in the Dingri area. (a) Cross-sectional profile. (b–d) Macrophotographs of different types of folds. Colors represent different stratigraphic units (see Figure 1 for the age scheme). Superscript numbers denote members (e.g., ¹ for Member 1). Key to units in (a): T₃q, Qulonggongba Fm.; T₃d, Derirong Fm.; J₁p¹⁻², Pupuqa Fm.; K₁gc¹⁻², Gucuocun Fm.; K₁gb¹⁻², Gangbadongshan Fm.; K_1-2c¹⁻², Chaqiela Fm.; K₂g¹⁻², Gangbacunkou Fm.; K₂zs¹⁻², Zongshan Fm.; E₁j¹⁻², Jidula Fm.; E₂p¹⁻², Zongpu Fm.

4.3. Multi-Phase Activity Analysis

This study conducted a systematic analysis of the cross-cutting relationships among slickenside lineations from different tectonic phases within the DGF and performed quantitative paleostress inversion using the Win-Tensor software (Version 5.9.3) (Table A1). The inversion is based on the Wallace-Bott hypothesis, which optimizes the stress tensor through iterative calculations to minimize the misfit angle between the observed slickenside lineations and the theoretically predicted shear direction [46]. Key parameters were set during the inversion (e.g., friction coefficient μ = 0.75, with reference to rheological studies of the Tibetan Plateau), and strict quality control criteria (average misfit angle < 15°; tensor stability index > 0.8) were adopted to ensure the reliability of the results. Based on clear field cross-cutting relationships, kinematic indicators, and quantitative inversion results, the measured lineations were classified into three tectonic phases (Table 2). It should be noted that interpreting multi-phase fault activities within the brittle-ductile deformation regime entails inherent uncertainties, such as the reactivation of earlier faults leading to complex slip histories and the incomplete preservation of ancient displacement records due to erosion and overprinting. To mitigate these uncertainties, this study prioritized sampling and analysis of fault surfaces with well-preserved, clearly identifiable slickensides, and ensured that the phase classification was ultimately based on the mutual verification of three lines of evidence: stress field orientation, ESR absolute ages, and field relationships. In conclusion, despite the existing uncertainties, the current tectonic evolution model, supported by multiple evidence chains, is robust.

Table 2. Summary of Paleostress Inversion Results from Slickenside Data along the Dingri–Gangba fault zone in Dingri area.

Tectonic Phase	Number (N)	σ1 Orientation (Mean ± Std Dev)	Stress Ratio (Φ)	Average Misfit Angle	Tensor Stability Index	Displacement (m)	Representative Kinematic Indicator	Dominant Stress Field
Stage 1	24	355° ± 10°	0.45	8.5°	0.92	0.9–5.8	Left-lateral thrust fault	N–S compression
Stage 2	29	82° ± 15°	0.60	11.2°	0.85	1.2–3.9	Left-lateral normal fault	N–S extension
Stage 3	15	93° ± 5°	0.35	9.8°	0.89	0.5–1.3	Left-lateral strike-slip fault	E–W shearing

Note: Data were obtained from field-measured slickensides using paleostress inversion with Win-Tensor software (Version 5.9.3). The stress ratio is defined as Φ = (σ₂ − σ₃)/(σ₁ − σ₃). All data points meet the quality control criteria of an average misfit angle < 15° and a tensor stability index > 0.8.

The first-phase striations are widely distributed and exhibited slickensides, tectonic breccias, or mineral stretching lineations. These striations predominantly display left-lateral reverse characteristics, with some showing right-lateral reverse faulting (Figure 8a). Stress inversion indicates a maximum principal stress (σ₁) orientation of 355° (Figure 8d), consistent with deformation under N–S compression. The second-phase striations are mainly exposed in the Nanmujia and Maiduozha segments, overprinting and reactivating the first-phase structures. These striations mainly indicate left-lateral normal faulting, with some right-lateral normal faulting. Striation plunge angles are steep (Figure 8b). Stress analysis yields a σ₁ direction of 82° (Figure 8e), indicating N–S extension. The third-phase striations are widely distributed in the Kema and Naigulin segments, associated with fault steps, breccias, and cataclasites. These striations predominantly indicate left-lateral strike-slip faulting (Figure 8c), with both normal and reverse characteristics. Stress inversion indicates a σ₁ direction of 93° (Figure 8f), suggesting E–W shear.

Figure 8. Kinematic analysis and paleostress inversion of fault surfaces in the Dingri area. (a–c) Representative field photographs of striated fault surfaces with kinematic indicators. Arrows indicate the sense of motion of the hanging wall. (d–f) Results of quantitative paleostress tensor inversion conducted using the Win-Tensor software (v5.9.3) based on fault striation analysis, showing the orientation of principal stress axes (σ₁, σ₂, σ₃) and the associated stress ratio.

Field investigations and structural analysis indicate that the DGF has experienced three major Cenozoic deformation stages: reverse thrusting, extensional faulting, and strike-slip shearing. These styles provide clear evidence of multi-phase deformation.

4.3.1. Reverse Compressional Stage

Under near N–S compression, the fault developed extensive reverse-related folds and fault structures. In the Kema segment, the Chaqiela Fm. is thrust over the Jiabula Fm. sandstone, with penetrative cleavage in the hanging wall and drag folds in the footwall. The Nanmujia segment exhibits tight isoclinal folds and δ-type porphyroclasts in sandstone, and crenulation in shale. The Naigulin segment preserves m-type folds, double-thrust breccia zones, and first-phase reverse striations. Regionally, these characteristics show a northward-dipping fold–thrust belt within the TH, consistent with Eocene collision orogeny between the Indian and Eurasian plates.

4.3.2. Extensional Normal Fault Stage

The earlier thrust structures were overprinted by N–S extension. In the Kema segment, second-phase striations and steps indicate normal faulting reactivating reverse faults. The Nanmujia segment contains multiple steep normal fault zones that locally inherited reverse fault surfaces. In the Naigulin segment, fold limb is stretched into lenses; shale and sandstone display curved cleavage and en-echelon joints, and quartz breccias form σ-type porphyroclasts, all indicating normal faulting. These characteristics suggest that extensional deformation not only inherited the early fault planes but also significantly modified them. Regionally, this extension correlates with the initiation of the STDS at ~35 Ma and a shift from thrusting to north-directed detachment [47,48].

4.3.3. Strike-Slip Shear Stage

During the Miocene, E–W strike-slip shear was superimposed on previous structures. The Maiduozha segment contains large-scale left-lateral strike-slip striations and steps. The Naigulin segment shows right-lateral en-echelon joints, and the Nanmujia segment has normal faults offset by NE-trending strike-slip shear. These characteristics suggest that strike-slip shear became the dominant deformation mechanism later. Regionally, this phase corresponds to a shift from N–S extension to E–W left-lateral shear due to continental oblique convergence at 18–13 Ma [49], leading to N–S graben formation in southern Tibet.

In conclusion, the DGF has experienced a three-stage Cenozoic evolution involving thrusting, extension, and strike-slip. This evolution not only shaped complex superimposed structures but also reflects the dynamic evolution of the stress field along the southern margin of the Tibetan Plateau, transitioning from N–S compression to extension and eventually to strike-slip shear since the Eocene.

5. Discussion

5.1. Cenozoic Deformation Phases of the Dingri–Gangba Fault

ESR dating results from the DGF, combined with previous research (Table 3), provide robust chronological constraints for its Cenozoic multi-phase deformation history. However, a critical interpretation of these ages within the regional tectonic framework reveals deeper insights into the evolution of the Himalayan orogenic belt.

Table 3. Compilation of ESR dating results from the Dingri–Gangba fault in the Dingri and Lhozhag areas.

Sample ID	Sampling Location	Sample Composition	Characteristics	Relative Position	Age (Ma)	Period	Genesis Explanation
D011-1	South Gongzhu, Lhozhag	Quartz vein	Thrust fault	North wall	59 ± 5	Early Paleogene	Plate convergence-collision stage, North wall fold belt fill
NGL1-2	Naigulin, Dingri	Quartz breccia	North-dipping thrust fault	Northern boundary of fault	46 ± 8	Eocene	Plate collision stage
NGL1-4	Naigulin, Dingri	Quartz breccia	Nne-dipping thrust fault	Secondary fault	45 ± 6	Eocene	Plate collision stage
S1949-1	Mendang Gully, Lhozhag	Quartz vein	Thrust fault	North wall	40 ± 4	Paleogene	Plate collision stage, North wall fold belt fill
KMX3-1	Kema, Dingri	Quartz vein	North-dipping normal fault	Southern boundary of fault	35 ± 5	Late Eocene	Associated with N-S extension
NGL2-2	Naigulin, Dingri	Quartz breccia	North-dipping normal fault	Southern boundary of fault	33 ± 6	Oligocene	Associated with N-S extension
KMX1-1	Kema, Dingri	Quartz vein	North-dipping normal fault	Northern boundary of fault	32 ± 5	Oligocene	Associated with N-S extension
NGL1-5	Naigulin, Dingri	Quartz breccia	North-dipping normal fault	Secondary fault	29 ± 5	Oligocene	Associated with N-S extension
S420-1	North Naixi, Lhozhag	Quartz vein	Thrust fault	North wall	23 ± 2	Late Paleogene	Plate collision stage, North wall fold belt fill
NGL1-3	Naigulin, Dingri	Quartz vein	Left-lateral strike-slip fault	Secondary fault	18 ± 2	Miocene	Associated with E-W extension
S402-1	North Zhongjue, Lhozhag	Quartz vein	Normal fault	North wall	17 ± 1	Miocene	Associated with detachment-related layer-parallel sliding fill
S337-1	North Qumei, Lhozhag	Quartz vein	Normal fault	North wall	14 ± 1	Miocene	Associated with detachment-related layer-parallel sliding fill
S344-1	North Qumei, Lhozhag	Quartz vein	Normal fault	North wall	13 ± 1	Miocene	Associated with detachment-related layer-parallel sliding fill
S467-2	South Taiba, Lhozhag	Quartz vein	Normal fault	North wall	11 ± 1	Miocene	Associated with detachment-related layer-parallel sliding fill
S1788-2	South Zhamai, Lhozhag	Quartz vein	Normal fault	South wall	11 ± 1	Miocene	Associated with detachment-related layer-parallel sliding fill
S265-1	Dejiangguo, Lhozhag	Quartz vein	Thrust fault	North wall	9 ± 1	Late Miocene	Fill in compressional deformation
S432-1	East Cuomei, Lhozhag	Quartz vein	Right-lateral thrust fault	North wall	6.8 ± 0.6	Late Miocene	Fill in compressional deformation

Data for Lhozhag area after [13].

5.1.1. Reverse Compressional Stage (Paleocene–Middle Eocene)

Two reverse-related samples from the Kema segment yielded ages of 46 ± 8 Ma and 45 ± 6 Ma. Liu et al. (2019) reported reverse compressional ages of 59 ± 5 Ma and 40 ± 4 Ma in the Lhozhag segment [13]. A comprehensive analysis suggests that reverse thrusting initiated in the Middle Paleocene and peaked in the Middle Eocene.

This ~15 Myr duration of reverse faulting suggests sustained compression following the initial India-Eurasia collision (~55–50 Ma). The age progression from Lhozhag (east) to Dingri (west) may indicate along-strike propagation of thrusting, potentially controlled by pre-existing structural gradients. Notably, the peak thrusting period coincides with: (1) This timing aligns with the formation period of collision-related leucogranites in the TH [50,51], and (2) the transition from marine to continental sedimentation in the foreland basin [15]. This temporal association suggests that DGF’s reverse phase represents a critical period of crustal thickening and tectonic reorganization.

5.1.2. Extension and Detachment Stage (Late Eocene–Middle Miocene)

ESR ages for the extensional quartz veins are 35 ± 5 Ma, 33 ± 6 Ma, 32 ± 5 Ma, and 29 ± 5 Ma. Combined with extension ages measured by Liu et al. (2019) in the Lhozhag segment (23 ± 2 Ma–11 ± 1 Ma) [13], it is concluded that extensional deformation began in the Late Eocene, peaked in the Miocene, and continued into the Middle Miocene. At the same time, time series indicate eastward migration or prolonged activity.

This extended extensional phase correlates with: (1) the onset timing of the STDS activity (~35 Ma) [48,49,52,53], (2) the emplacement of extension-related leucogranites (37–18 Ma) [54], and (3) the formation of North Himalayan gneiss domes [55]. The spatiotemporal coexistence of the high-angle normal faulting along DGF and the low-angle STDS within the study area reveals the vertical stratification and spatiotemporal evolution of crustal extension since the Miocene. Specifically, the STDS, as a deep detachment zone, facilitated large-scale low-angle shear deformation, which induced secondary extensional deformation in the upper plate (Tethyan Himalaya). This process led to the reactivation of pre-existing high-angle faults such as the DGF with normal-slip kinematics.

5.1.3. Strike-Slip Shear Stage (Miocene)

The ESR age of strike-slip quartz veins yielded an age of 18 ± 2 Ma, indicating left-lateral strike-slip activity. Liu et al. (2019) reported strike-slip activity ages of 9 ± 1 Ma and 6.8 ± 0.6 Ma in the Lhozhag segment [13], suggesting the regional stress field transitioned to lateral extrusion and shear by the Early Miocene. This stage overlapped with the extension and detachment stage and reached a peak of strike-slip activity during the Late Miocene. This timing is consistent with the emplacement of E–W extension-related leucogranites (18–15 Ma) [56].

The study on the Cenozoic activity of the DGF has certain limitations. The uncertainty in ESR ages (error range ±2–8 Ma) necessitates caution when correlating these ages with specific tectonic events. The ESR signals from samples within polyphase deformation zones may have been affected by thermal resetting. Furthermore, as field investigations and geochronological sampling were primarily concentrated on the Dingri and Lhozhag segments, the results may not fully represent the deformation characteristics and activity history of the entire fault zone.

From a regional tectonic perspective, however, the Cenozoic kinematic sequence established for the DGF effectively reflects mid- to late-stage strain partitioning within the Himalayan orogen and correlates well with key regional events. Its evolutionary—from thrusting to extension and subsequently to strike-slip motion—reveals a typical pattern of tectonic regime transformation in collisional orogens. This pattern is comparable to large-scale strike-slip systems such as the Altyn Tagh Fault [57] and the Xianshuihe Fault [58]. The thrust-to-extension transition at ~35 Ma coincides with the gravitational collapse following the crustal thickening of the Tibetan Plateau, while the onset of strike-slip activity at ~18 Ma responded to the lateral escape of crustal blocks under the ongoing India-Eurasia convergence. This complete evolutionary sequence provides temporal constraints for tectonic models of the Himalayan orogen and aligns with mechanisms of intracontinental deformation during the late-stage uplift of the plateau.

5.2. Mesozoic Basin Control by the Dingri–Gangba Fault

Basin evolution is a complex result of the coupling of multiple geological processes, including tectonics, sea-level change, and climate [59]. Due to the scarcity of well-preserved direct evidence for Mesozoic fault activity, this study investigates the basin-controlling role of the DGF by comparing sediment sequences, soft-sediment deformation, and volcanic activity on both sides. In assessing the influence of the fault, we have fully considered potential factors including regional crustal subsidence/uplift, sea-level fluctuations, and basement structure. However, the spatial specificity (concentration of sedimentary differentiation along the fault zone) and temporal synchronicity (correspondence between “differentiation periods” and regional tectonic active phases) observed in this study collectively suggest that the episodic activity of the DGF was likely a key factor responsible for the north–south basin differentiation (e.g., the “deeper north, shallower south” pattern). Analysis reveals that the sedimentary evolution of the area exhibits an alternating rhythm of “differentiation periods” and “uniformity periods,” clearly recording the intermittent activity of the fault (Figure 9).

Figure 9. Stratigraphic correlation and soft-sediment deformation evidence for the basin-controlling role of the Dingri–Gangba fault. (a–d) Field photographs of soft-sediment deformation structure sinterpreted as seismites, providing direct evidence for syndepositional fault activity. These include: (a) sand injections and liquefaction veins in the Kangshare Fm., indicating Early Triassic seismicity; (b) liquefied sandstone veins in the Pupuqa Fm., recording Early Jurassic seismic shaking; (c) a slump fold in the Gucuocun Fm., evidencing Middle Jurassic slope instability; and (d) a slump mass in the Jiabula Fm., reflecting strong syndepositional tectonism during the Late Cretaceous. Color shades in the stratigraphic columns represent depositional facies (warm colors: shallow-water; grey tones: deep-water). Color shades in the stratigraphic columns represent depositional facies (warm colors: shallow-water; grey tones: deep-water). Color shades in the stratigraphic columns represent depositional facies (warm colors: shallow-water; grey tones: deep-water). The columns, based on data from [60,61,62,63], illustrate the contrasting depositional records between the southern and northern sub-belts. Key discrepancies in thickness and facies during the Triassic, Middle-Late Jurassic, and Late Cretaceous correlate with phases of intense fault activity and differential subsidence. Periods of relative uniformity (e.g., Early Jurassic, Early Cretaceous) indicate fault quiescence. Stratigraphic abbreviations (for units not defined in Figure 6 and Figure 7): P₁j–Jilong Fm.; P₂q–Qubu Fm.; P_2-3qb–Quburiga Fm.; T₁k–Kangshare Fm.; T₂l–Laibuxi Fm.; T₃z–Zhamure Fm.; J₂n–Nieniexiongla Fm.; J₂l–Lanongla Fm.; J₃m–Menkadun Fm.; P₁p–Polinpu Fm.; P₁b–Bilong Fm.; P₂k–Kangma Fm.; P_2-3b–Baidingpu Fm.; T_1-2l–Lvchun Fm.; T₃n–Nieru Fm.; J_1-2r–Ridang Fm.; J₂lr–Lure Fm.

5.2.1. Late Paleozoic Uniform Period (~P)

During the Early Paleozoic to Permian, the TH was part of a stable passive continental margin on the northern margin of the Gondwana supercontinent. Sedimentation was dominated by carbonate–clastic rock sequences in shallow marine environments. In the Permian, both northern and southern sub-belts developed glaciomarine conglomerates, shore sandstones, and carbonate–clastic rocks. These consistent sedimentary characteristics suggest that the DGF had not yet developed during this period.

5.2.2. Triassic Differentiation Period (T)

In the Triassic, as the Yarlung Zangbo Ocean expanded, the DGF formed and began to exert basin control. The southern sub-belt recorded a sediment thickness of ~257 m, characterized by mixed shelf deposits with abundant fossils. In contrast, the northern sub-belt accumulated up to 1739 m of deep-water mudstone with abundant pyrite and sparse biota. The sediment thickness ratio between the northern and southern sub-belts exceeded 6:1, indicating significant differences in subsidence. In the Dingri area, the Kangshare Fm. exhibited earthquake-induced fluidized veins, seismites, and fluid escape structures (Figure 9a), reflecting strong syn-sedimentary fault activity. Basaltic and andesitic basaltic eruptions in the Nieru Fm. (northern sub-belt) further attest to magmatic–tectonic coupling [64].

5.2.3. Early Jurassic Uniform Period (J₁)

During the Early Jurassic, fault activity waned. Both the Pupuga Fm. (southern sub-belt) and the Ridang Fm. (northern sub-belt) were deposited in shallow marine environments. However, liquefied sandstone veins in the Pupuga Fm. (Figure 9b) suggest that although the fault has stabilized, it remained capable of triggering seismic events.

5.2.4. Middle to Late Jurassic Differentiation Period (J_2-3)

Fault reactivation during the Middle Jurassic led to significant sedimentary differences between the two sub-belts. The southern sub-belt recorded ~968 m of coastal to shallow shelf deposits, while the northern sub-belt accumulated up to 3502 m of deep-water slope sediments, representing a thickness ratio exceeding 3:1. In the Late Jurassic, the Menkadun Fm. (southern sub-belt) reflects shallow marine conditions, while the Weimei Fm. (northern sub-belt) consists of turbidite fan deposits. Widespread tuff and basalt units during this period indicate that fault activity controlled both sedimentation patterns and volcanic–sedimentary coupling across the fault [14].

5.2.5. Early Cretaceous Uniform Period (K₁)

During the Early Cretaceous, regional tectonics stabilized. Both sub-belts developed bathyal–abyssal turbidite deposits. The Gucuocun, Gangbadongshan, and Chaqiela Fms. (southern sub-belt) and the Jiabula Fm. (northern sub-belt), all exhibit Bouma sequence turbidites, with locally developed slump folds (Figure 9c). Markedly reduced differences in sediment thickness indicate a weakened basin-controlling influence of the fault.

5.2.6. Late Cretaceous Differentiation Period (K₂)

The Late Cretaceous saw strong fault reactivation, resulting in a tectonic pattern of high terrain in the south and low terrain in the north. Member 4 of the Jiabula Fm. (northern sub-belt) reached 1719 m in thickness and consists of black shale, grain-flow deposits, and slump blocks (Figure 9d). In contrast, the Gangbacunkou and Zongshan Fms. (southern sub-belt) were only ~197 m thick, representing shelf–platform deposits, with a thickness ratio of nearly 9:1. Tuff and andesitic basalt interbeds within the Jiabula Fm. suggest close links between fault activity and volcanism [65,66]. During this period, the basin-controlling role of the fault was particularly significant, strongly influencing sedimentary patterns and basin architecture.

5.3. Tectonic Evolution and Dynamic Background

The evolution of the DGF clearly records the dynamic transition of the TH from a passive continental margin to a collisional orogenic system. By integrating Mesozoic stratigraphy with Cenozoic ESR geochronological constraints, this study reveals the varying tectonic roles of the DGF at different periods. During the Mesozoic, the fault primarily acted as a basin-controlling fault, driving sedimentary differentiation. During the Cenozoic, it evolved into an inherited fault that accommodated multi-mechanism strain in response to the India–Eurasia collision.

5.3.1. Mesozoic Passive Margin Basin Control

During the Triassic, the DGF formed and began to exert basin control, resulting in significant sedimentary differentiation between the northern and southern sub-belts (Figure 10a). Subsequent reactivations during the Middle–Late Jurassic and Late Cretaceous further established its role as an inherited basin-controlling structure, sustaining strong disparities in subsidence rates and depositional environments, with north–south sediment thickness ratios exceeding 6:1. Soft-sediment deformation structures, such as seismites, liquefied sandstone veins, and slump breccias, record frequent syn-sedimentary tectonic disturbances. Widespread basaltic and andesitic volcanism during these periods further attests to strong magmatic-tectonic-sedimentary coupling [14,65]. In contrast, during the Early Jurassic and Early Cretaceous, both sides of the fault showed similar shallow marine or turbidite deposition, with minimal differential subsidence. This shift reflects stabilization phases of the fault, during which its basin-controlling influence weakened significantly.

Figure 10. Schematic model of the Mesozoic–Cenozoic tectonic evolution of the Dingri–Gangba fault. (a) Late Mesozoic (T-K): The DGF acted as a syn-sedimentary normal fault, controlling the initial basin architecture. (b) Early-Middle Eocene (E₁-E₂): The DGF reactivated as a major north-dipping thrust fault, with the deformation front propagating northward. (c) Late Eocene-Early Miocene (E₃-N₂): The fault was reactivated under N-S extension. (d) Miocene-Present (N): The eastern segment of the DGF became a dominant left-lateral strike-slip fault, offsetting earlier structures.

This alternating rhythm of “differentiation—uniformity” corresponds closely to the evolutionary stages of the Yarlung Zangbo Ocean [1,3,67,68]. During periods of active ocean expansion or subduction (Triassic, Middle to Late Jurassic, Late Cretaceous), the fault experienced intense activity, leading to significant sedimentary differentiation. During periods of slowed expansion or early subduction (Late Paleozoic, Early Jurassic, Early Cretaceous), the fault stabilized, and the sedimentary disparities diminished. Thus, Mesozoic activity of the DGF was characterized by intermittent reactivation driven by the expansion–subduction dynamics of the oceanic basin.

5.3.2. Reactivation During Cenozoic Collisional Orogeny

In the Cenozoic, the tectonic function of the DGF shifted from basin control to inherited reactivation within a collisional setting. ESR dating reveals three main phases of activity. During the Paleocene to Early Eocene (~60–40 Ma), the fault exhibited reverse thrusting, corresponding to the India–Eurasia collision [51]. Stress was transmitted northward and concentrated along the fault belt, producing reverse faults and thrust folds (Figure 10b). During the Late Eocene to the Middle Miocene (~35–11 Ma), the fault underwent extension, reflecting gravitational collapse of thickened crust following continued shortening. This phase aligns temporally and spatially with low-angle detachment along the STDS (Figure 10c) [53]. During the Miocene (~18–6.8 Ma), continued N–S compression induced E–W lateral escape and shear coupling, expressed as near E–W strike-slip motion along the fault [56] (Figure 10d).

Overall, the Cenozoic evolution of the DGF followed a sequence of “compression—extension—strike-slip,” reflecting its multi-stage response as an inherited fault within the collisional orogen.

5.3.3. Regional Dynamic Significance

Regionally, the long-term evolution of the DGF reflects the superposition of two key dynamic mechanisms. First, as a basin-controlling fault along the northern Indian continent, it was intermittently reactivated by oceanic basin expansion and passive margin subsidence throughout the Mesozoic, shaping both the sedimentary system and the tectonic architecture of the region. Second, during the Cenozoic, within the India–Eurasia convergence setting, the fault was reactivated as an inherited fault, responding to the changing regional stress field through reverse thrusting, extensional collapse, and strike-slip adjustments. This multi-stage deformation helped regulate compressional and extensional coupling along the southern margin of the Tibetan Plateau. Therefore, the DGF is not an isolated tectonic unit, but a crucial nexus in the transition of the northern Indian continent from a passive setting to a collisional orogen, and ultimately to intracontinental deformation and plateau uplift. Its episodic activity directly mirrors the deep-time geodynamic processes that underpinned the formation and evolution of the Tibetan Plateau.

6. Conclusions

(1) The Dingri–Gangba fault in the Dingri area trends approximately E–W and comprises sedimentary fault blocks derived from multiple stratigraphic units. It exhibits multi-phase tectonic overprinting, including reverse thrusting, normal faulting, and strike-slip shearing.

(2) ESR dating results indicate that the Dingri–Gangba fault experienced three phases of Cenozoic tectonic evolution: reverse thrusting (~60–40 Ma), extensional deformation (~35–11 Ma), and strike-slip shearing (~18–6.8 Ma). These results provide critical chronological constraints for the multi-phase tectonic evolution following the India–Eurasia collision.

(3) Stratigraphic comparative analysis reveals that during the Mesozoic, the Dingri–Gangba fault played a major basin-controlling role, influencing variations in sediment thickness, soft-sediment deformation, and volcanic activity. The sedimentary evolution followed an alternating rhythm of “differentiation” and “uniform” phases, reflecting a close relationship between the fault activity and magmatic–sedimentary coupling.

(4) The tectonic evolution of the Dingri–Gangba fault records the dynamic transition of the TH from a passive continental margin to a collisional orogenic system. It highlights the genetic relationship between Mesozoic fault activity and the tectonic evolution of the Yarlung Zangbo Ocean, as well as significant changes in the tectonic stress field during the Cenozoic India–Eurasia collision.