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The collisional history between Greater India and the Eurasian plate has been well constrained by the study of exhumed Barrovian metamorphic sequence (BMS) rocks in the Himalayan Range. However, in the southeastern Tibetan Plateau, the collisional records have been obscured by intense, regional‐scale strike‐slip overprinting and recrystallization. Here, in BMS rocks from the Ailao Shan–Red River shear zone (ARSZ), we report the first discovery of a >250 km long, high‐pressure (high‐P) granulite belt (>1.0 GPa), identified by the presence of relict kyanite and associated decompression reaction textures. Petrological phase equilibrium modeling showed that exposed micaschists in the region represent exhumed middle crust (20–25 km, 600–670°C), while the high‐P granulite rocks are remnants of thickened lower crust (45–55 km, 800–850°C). This indicates that the northeast edge of the ARSZ experienced an additional ∼25 km of uplift and exhumation compared to the southwest side, facilitated by brittle thrusting/imbrication along the Ailao Shan fault (micaschists) and ductile extrusion along the Red River fault (granulite). Geochronological study shows that the upper portion of the BMS preserves older metamorphic ages (52–34 Ma) than the lower portion (32–29 Ma), which was attributed to spatial variation in cooling rates. Using calculated P–T–t–d paths, we also examined variation in density and seismic wave speeds for BMS in the ARSZ. Our data correlate with fieldwork conducted elsewhere within the Himalayan Range indicating that the kyanite to sillimanite transition zone may serve as a "cap" for the horizontal migration of melt within the lower crust. Plain Language Summary: Clay‐rich rocks exhibit systematic mineralogical transformations during burial to the middle and lower continental crust as temperature and pressure increase. This is often referred as a Barrovian metamorphic sequence (BMS). Exhumed BMS rocks in crustal high‐strain zones provide an excellent opportunity for revealing the dynamic processes that take place during mountain building. In the southeastern Tibetan Plateau, crustal‐scale shear zones accommodated much of the northward‐directed indentation of the Indian plate. Here, we systematically studied BMS rocks in the Ailao Shan–Red River shear zone (ARSZ) and simulated how their physical properties vary with changes of temperature and pressure. Additionally, we report the first discovery of a high‐pressure granulite belt along the northeast edge of the ARSZ that was uplifted from ∼45 to 55 km, marking an additional ∼25 km of exhumation compared to the southwest edge. Moreover, distinct metamorphic peak temperature conditions across the ALS massif may account for uneven exhumation and discrepant cooling rates across the massif. Thermal and physical properties simulation indicate that the kyanite to sillimanite transform zone may serve as a "cap" for the sub‐horizontal melt migration in the lower crust of shear zones. Key Points: High‐pressure granulite belt is reported for the first time from the northeastern Ailao Shan (ALS) massif, southeastern Tibetan PlateauWe develop integrated P‐T‐t‐d paths and ρ‐Vp profiles for Barrovian metamorphic sequence rocks in the ALS massifBulk‐rock densification across the kyanite to sillimanite transition zone may serve as a "cap" for horizontal melt flow in the lower crust [ABSTRACT FROM AUTHOR]

[Display omitted] • Eocene–Miocene magmatism is identified in the SE Tibetan Plateau. • Eocene–Oligocene potassic granitoid was derived from crust-mantle mixed magma. • Source of Miocene syn-kinematic magmatism involved metasediments and metabasites. • Decreasing India-Asia convergent rate led to the Eocene lithospheric extension. • Tectonic reworking led to the extrusion of the SE Tibetan Plateau. The convergence of the Indian Plate and Eurasia shaped the Earth's broadest and highest-elevation collisional system and topographic growth, which is not simply illustrated by ongoing contractional deformation. The Cenozoic magmatism along the Ailao Shan-Red River Shear Zone (ARSZ), linking surface geology with deep lithospheric processes, provides additional information regarding the age and progressive deformation of the India-Asia collision. In this study, we present new zircon U–Pb geochronological, elemental geochemical and zircon Hf isotopic data for the Eocene–Miocene granitoid to resolve the southeastern Tibetan Plateau deformation history. The Jinping granitoids in the southern ARSZ were dated at 37.5–33.6 Ma. They show similar geochemical characteristics (whole-rock major oxides, trace element, Sr–Nd–Pb isotopic and zircon in-situ Hf isotopic data) with respect to coeval potassic granitoids in NW Yunnan, suggesting their origination from partial melting of thickened lower crust with additional contribution from enriched mantle-derived magmas. Leucogranite samples within the ARSZ yielded distinctive zircon U–Pb ages of 28.3 Ma and 18.5 Ma. Geochemical features suggest that they were derived from a heterogeneous crustal source consisting of metasediments and metabasites. Our results, along with those previous studies, suggest that the widespread potassic magmatism in the central and southeastern Tibetan Plateau is related to lithospheric mantle upwelling, which resulted in the partial melting of the thickened lower crust and a short-lived crustal extension during a period of decreased convergence rate. Subsequently, the orogenic-scale sinistral strike-slip movement provided shearing heat for generating leucogranites within the shear zones during the late Oligocene–Miocene. The plateau-wide shift in stress reorganization and tectonic reworking led to the lateral extrusion of the SE Tibetan Plateau and its attainment of modern high elevation. [ABSTRACT FROM AUTHOR]

The giant Shilu Fe-Cu-Co deposit in Hainan Island, South China, which was structurally and hydrothermally superimposed, is mainly hosted in highly metasomatized dolostones/marbles of the ~ 900 Ma Shilu Group. This study confirmed that the ore bodies are originally strata-bound and epigenetic, but do not have spatial relations with any coeval intrusions. In this study, the paragenetic sequence of the pre-deformation mineralization is refined and consists of early Ca-silicate alteration (I), Fe (II), and Cu-Co (III) mineralization stages, followed by multiple overprints and/or undeformed veins (stage IV). Our new oxygen and in situ Pb–S isotopic results for stages I to III show that the mineralizing fluids were initially magmatic-hydrothermal but have undergone variable degrees of interaction with country rocks during mineralization. On the other hand, stage IV fluids have in situ Pb–S isotopic compositions indicative of significant contributions of early-stage components through secondary re-mobilization. These features, in combination with chemical compositions of Fe oxides (e.g., elevated Ti in hematite), strongly argue that the Shilu deposit does not belong to BIF as previously considered, but is typical of magmatic-hydrothermal IOCG deposits. New sulfide Re-Os isotopic data show that the major Fe-Cu-Co mineralization formed at 780 ± 24 Ma (MSWD = 0.62). The deposit is confirmed to be broadly comparable to Neoproterozoic IOCG deposits in the Ailao Shan-Red River shear zone in terms of timing and nature of mineralization. Given that the shear zone likely extends to Hainan Island, the Shilu deposit is considered to be part of the same IOCG metallogenic belt and similar mineralization along the shear zone may be more widespread than previously thought. [ABSTRACT FROM AUTHOR]

Whether there is a relationship between widespread Cenozoic igneous rocks and the activated Ailao Shan–Red River shear zone (ASRR) in western Yunnan, SE Tibet, remains highly controversial. New geochronological, and geochemical data derived from Cenozoic igneous rocks both within and far from the ASRR offers answers. Although these coeval felsic rocks (36.9–33.5 Ma) are enriched in large‐ion lithophile elements relative to high field strength elements, they also display some special geochemical features, such as high Y and Yb values of syenitic porphyries, which contrast with the high Sr and low Y contents of monzoporphyries and granitic porphyries. The syenitic porphyries exhibit geochemical characteristics similar to those of coeval mafic magmas, e.g., high K2O, Y, and Yb contents, indicating that the former were probably generated by fractional crystallization of the latter. However, the high Sr/Y (56.1–109) monzoporphyries and granitic porphyries, combined with their low MgO, and Cr (or Ni) contents, suggest that they were mainly derived from partial melting of a thickened mafic lower crust. Given that these Cenozoic magmatic events exhibiting planar distributions occurred outside of the activation of the ASRR (31–20 Ma), then they were not controlled by the latter. Instead, they were tied to convective removal of a thickened lower lithospheric mantle in western Yunnan during the Paleogene. [ABSTRACT FROM AUTHOR]

Understanding the mountain–basin coupling relationship is fundamental to placing constraints on the tectonic evolution of the Ailao Shan mylonite shear zone, the key feature accommodating relative movement between the Tibetan Plateau and SE Asia, because a contemporary basin, namely Red River, bounds its middle segment on the northeast, along which the shear zone is bent from northwest–southeast to roughly east–west (The Big Bend). The basin comprises two units: the Mubang Breccia and the Lengdun Conglomerate of Early Oligocene and Late Oligocene–Early Miocene age, respectively. This study reveals evidence indicating that the Wubang Breccia marks a high‐strain zone, resulting from top‐to‐north shear (range‐front detachment (RFD), along which the mylonite on the footwall experienced northward bending in the form of creeping. Moreover, the Lengdun Conglomerate on the hanging wall was deposited as growth strata, overlying a thrust belt to the north. The latter marks the southern rim of the Yangtze block, composed of extensional fault blocks, whose northward displacement along the toe of the RFD was synchronized with the north–south extension across the Red River basin. The spatial and temporal relationships between the Red River basin and the Ailao Shan shear zone indicate that basin formation was controlled by the change in geometry of the shear zone. The Red River basin can be viewed as an extensional step‐over in the left‐lateral strike‐slip field, in which all sedimentary and deformation processes were controlled by the extension and subsequent topographic spreading, accommodated by the RFD. This indicates that the extensional crustal materials, including both Langdun Conglomerate and underlying extensional fault blocks, were all shed from the top of the Ailao Shan mylonite belt. The cause of bending of the shear zone is attributed to the northward movement of India with respect to South China and the bending process came to an end as the left‐lateral movement ceased. Plain Language Summary: The Ailao Shan‐Red River shear zone is bent from northwest‐southeast to east‐west along its middle segment, which is bounded by a linear intermountain basin on the northeast. The latter comprises two units: the Mubang Breccia and the Lengdun Conglomerate of Early Oligocene and Late Oligocene‐Early Miocene age. This study reveals evidence indicating that the Wubang Breccia marks a high‐strain zone, resulting from top‐to‐north shear (range‐front detachment [RFD]), along which the mylonite on the footwall experienced northward bending and the Lengdun Conglomerate on the hanging wall was deposited as growth strata, overlying a thrust belt to the north, which is composed of landslide blocks, whose northward displacement was accommodated by the toe of the RFD. The range front of the middle part of the shear zone can be viewed as an extensional step‐over in the left‐lateral strike‐slip field, in which all sedimentary and deformation processes are the manifestation of the gravitational collapse. This indicates that both the landslides and the Langdun Conglomerate were all shed from the top of the Ailao Shan. The cause of bending of the shear zone is attributed to the N‐S right‐lateral shear between India and South China. Key Points: The formation of the Red River basin is correlated with the change in geometry of the Ailao Shan‐Red River shear zoneThe range‐front top‐to‐north shear reflects the gravitational collapse of the Ailao ShanThe change in geometry of the Ailao Shan‐Red River shear zone is caused by the N‐S right‐lateral shear between India and South China [ABSTRACT FROM AUTHOR]

The Maguan (MG) region in the southwestern part of the South China Block contains many Neogene potassic basaltic volcanic rocks along the Ailao Shan–Red River (ASRR) shear zone. These alkaline volcanic rocks contain abundant peridotite xenoliths which are mostly spinel (Spl)-facies lherzolite. We examined xenoliths in young, ~12 Ma, alkaline basalts. Most contain clinopyroxene (Cpx), >15 vol%, and minor xenoliths contain low Cpx, ~10 vol%. Olivine (Ol) shows forsterite components ranging from 88.6 to 90.1 in most lherzolite and from 90.4 to 90.8 in depleted lherzolite, Spl Cr# (=Cr/(Cr + Al)) between 0.08–0.11 for lherzolite and 0.17–0.22 for depleted lherzolite. Platinum group elements (PGE) show a near flat primitive mantle-normalized pattern; the ratios of IPGE/PPGE are 1.3–1.8 for lherzolite and 2.1 for depleted lherzolite. The xenoliths do not contain metasomatic minerals, but Cpx in depleted lherzolite samples is enriched in light rare earth elements (LREE; (La/Sm)N = 0.97–1.74). Two pyroxene geothermometry gives the temperatures ranging from 1029 °C to 1148 °C (average 1087 °C, n = 13). Spl–Ol geothermobarometry yields the oxidation state ranging from FMQ −1.5 to −0.25 with an average value of FMQ −0.59 (n = 13), which is comparable to those of abyssal peridotite and the asthenospheric mantle. The calculated temperatures and oxidation state are similar among samples independent of mineralogy and mineral chemistry, suggesting that partial melting and the cryptic metasomatism did not change the oxidation conditions. The data suggest that the subcontinental lithospheric mantle (SCLM) beneath the region formed from the asthenosphere mantle. Since the South China Block is generally underlain by Proterozoic SCLM, the data obtained this study suggest that the ancient lithosphere was replaced by the asthenospheric mantle in the local extension along the ASRR shear zone. [ABSTRACT FROM AUTHOR]

The rapid uplift of the Tibetan plateau, the intense movement of the Ailao Shan-Red River Shear Zone (ARSZ), and the related climate change during the Cenozoic Indo-Asian collision have been widely studied; however, their timings varied considerably due to different data and methods used. As these events have been documented in the Red River sediment that came from the eastern Tibetan plateau and the Red River region and eventually deposited in the offshore Yinggehai and Qiongdongnan basins, here these events can be explored by calculating and analysing the Red River sediment budget, especially in the Qiongdongnan basin based on dense seismic profiles and wells. Results show that the Red River sediment mainly accumulated in the Yinggehai basin and the west part of the Qiongdongnan basin, and there are three sedimentary accumulation peaks in the Red River sediment budget during ~29.5–21, ~15.5–10.5, and ~5.5–0 Ma. By further comparing with previous studies on the timings of these events, it is inferred that the first sedimentary peak, prior to the onset of the monsoon intensification (~22 Ma), was probably driven by an intense left-lateral movement of the ARSZ in ~29.5–21 Ma. The second peak (~15.5–10.5 Ma), however, reflects a rapid uplift of the Tibetan plateau after the cessation of the left-lateral strike slip of the ARSZ. The third peak (~5.5–0 Ma) is most likely linked with a right-lateral movement of the ARSZ and the related climate change. Overall, the Red River sediment budget from the offshore Yinggehai and Qiongdongnan basins provides an important constraint on the timings of these tectonic events as well as the related climate change during the Cenozoic Indo-Asian collision. [ABSTRACT FROM AUTHOR]

This study investigates the crustal flow within the southeastern orogenic belt of the Tibetan Plateau, with a focus on the Diancang Shan (DCS) complex. As an A-type gneiss dome, the DCS complex offers valuable insights into the deformation and evolution of intra-continental orogenic belts and the flow of deep crustal material. We have identified three main stages of deformation within the DCS complex since the Cenozoic. The initial stage (D 1), spanning 41–30 Ma, was characterized by high-temperature pure shear deformation, which developed penetrative foliations, symmetric folds, and structural lenses. The subsequent major stage (D 2), which shaped the overall architecture of the DCS complex from approximately 27–21 Ma, was primarily influenced by strike-slip stress regimes, resulting in shear fabrics with a top-to-the SE orientation in the releasing bend. The final stage (D 3), initiated around 13 Ma, was marked by retrograde metamorphism at lower temperatures. Kinematic vorticity calculations indicate that the D 1 stage was dominated by pure shear, while the D 2 stage was primarily influenced by simple shear. The deformation temperature for the major deformation stage (D 2) is estimated to range between 450 and 550 °C. During this stage, strain rates lie between 10−13–10−16 s−1 at 450 °C and 10−12–10−14 s−1 at 550 °C, indicating relatively low strain rates within the DCS complex. Our findings suggest that the formation of the DCS dome can be attributed to the ductile extrusion of channel flow, driven by the gravitational collapse of the Tibetan Plateau. Partial melting of the thickened middle and lower crust may have provided the channels and material sources. Furthermore, shear strain analysis (0.15–0.49) indicates that pure shear played a more significant role, contributing ∼ 65 % to the formation of the DCS dome. • The DCS complex is an A-type gneiss dome. • The DCS dome underwent early pure shear and late simple shear deformation. • Sinistral strike-slip shearing ceased ∼ 21 Ma with a strain rate of ∼ 10−15 s−1. • Formation of the DCS dome is attributed to lateral flow mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the structure of the Yinggehai Basin in the offshore Ailao Shan–Red River Shear Zone (ASRRSZ) to obtain a clear understanding of the basin's multiphase development from the Palaeogene to the Miocene, with links to regional tectonic events. The results of our work indicate that the initial rift architecture of the Yinggehai Basin was associated with extensional faults oriented NW–SE to NNW–SSE driven by a NE–SW- to ENE–WSW-trending extensional stress field, likely resulting from the far-field effect of the India–Eurasia collision. The formation of E–W-striking normal faults in the Palaeogene section and the strike-slip movement of pre-existing faults support the occurrence of sinistral strike-slip deformation during the second rifting stage to the early Miocene. In response to the left-lateral shearing of the ASRRSZ, which mostly ended in the early Miocene, flower-like structures, strike-slip faults and associated folds were detected in the northern and southern portions of the basin. Subsequently, middle to late Miocene compression produced a series of folds in the central basin. A series of layer-bound normal faults are present in the middle Miocene section suggesting a compactional or gravitationally driven origin. Although activity on the major faults in the main part of the basin almost ceased at the end of the early Miocene, a greater thickness of post-rift sediment was present inside the basin. This study suggests an extensional origin for the Yinggehai Basin and implies that both multiphase tectonic evolution and post-rift sediment loading played key roles in the Cenozoic development of this basin. • The initial rift architecture at the base of the Cenozoic strata indicates an extensional origin for the Yinggehai Basin. • The left-lateral shearing of the offshore ASRRSZ almost ceased at the end of the early Miocene. • The thick basin centre is likely associated with post-rift sediment loading. • Basin evolution reflects the interaction between Pacific subduction and the collision of India and Australia with Eurasia. [ABSTRACT FROM AUTHOR]

The Cenozoic deformation of SE Asia is classically related to India‐Asia collision and Tibet Plateau rise, supposedly resulting in the southeastward drift of lithospheric blocks bounded by strike‐slip faults with displacements in the order of 1,000 km. Here we report on the paleomagnetism of 44 Triassic‐Cretaceous red bed sites from the northern Simao, Chuandian, and Lanping "blocks," along both sides of the Ailao Shan‐Red River shear zone (north Indochina). In the Simao domain, remagnetization predates folding and subsequent 48–70° clockwise rotation of three 2–5 km wide subblocks separated by two unrotated blocks. A primary magnetization component from the Lanping domain center suggests variably clockwise rotated (up to 95° ± 24°) sites, interrupted by a 2–6 km wide block that is rotated counterclockwise by 27° ± 6°. Thus, the Lanping and Simao "blocks" are far from being rigid, being made of a mosaic of independently deforming subblocks, whose kinematics and association with documented tectonics are speculative. It is unclear whether both folding and widespread remagnetization were synchronous or diachronous across north Indochina, but (considering previously published results) strike‐slip activity along major shear zones, remagnetization, rotations, and crustal shortening overlapped within the 32–15 Ma time window, thus were likely genetically related. As opposed to previous models, we suggest that in early to mid‐Cenozoic times, north Indochina was under the influence of oblique Neo‐Tethys subduction. Collision between the NE corner of Greater India and Indochina at ~30 Ma yielded ENE‐WSW shortening and strike‐slip reactivation of preexisting faults, in turn fragmenting the crust into small, independently rotating, blocks. Key Points: Paleomagnetism of Triassic‐Cretaceous red beds from the Simao, Chuandian, and Lanping "blocks""Blocks" are in fact brocken in 2‐6 km wide sub‐blocks rotating independently both CW and CCWCrust fragmentation of north Indochina related to collision with Greater India NE corner at ~30 Ma [ABSTRACT FROM AUTHOR]

• Zircon inclusions in rubies have an U-Pb age of 36.2 Ma and phlogopite has Ar-Ar ages of 22.2–22.5 Ma. • The formation of the Yuanjiang ruby deposit was closely linked with the Cenozoic crustal tectonic evolution. • Ruby mineralization in the Ailao Shan-Red River shear zone was triggered by the local continental subduction-collision. • Exhumation of the deposits may have occurred during the later left-lateral shearing. The Yuanjiang marble-hosted ruby deposit in the middle Ailao Shan-Red River (ASRR) shear zone, is the only economic ruby deposit in China. This deposit is hosted in Paleoproterozoic sillimanite gneisses and the ores are found in metamorphosed platform carbonates. Rubies are unevenly distributed within calcite-rich marble layers and mainly associated with phlogopite, scapolite, graphite, pyrite. Rubies contain zircon, rutile, apatite, calcite inclusions. The genesis of the Yuanjiang ruby deposit and its genetic link to the ASRR shear zone remain poorly understood. In this contribution, its formation age has been indirectly constrained by the in-situ LA-ICP-MS U-Pb dating of zircon inclusions in rubies and 40Ar/39Ar dating of syngenetic phlogopite from the ruby-phlogopite bearing marble, which yielded the ages of 36.2 ± 1.1 Ma (MSWD = 1.4, 2σ, n = 4) and 22.2–22.5 Ma, respectively. The 36.2 Ma U-Pb age of metamorphic zircon inclusions falls within the range of local crustal thickening related subduction-collision and coupled with the spatial distribution in which ruby deposits were not restricted in the shear zone, we propose that ruby mineralization was triggered by the local continental subduction-collision rather than the large-scale left-lateral shearing. Due to the estimated closure temperature of the 40Ar-39Ar system is lower than the ore-forming temperature, the obtained phlogopite 40Ar/39Ar ages of 22.2–22.5 Ma represent the minimum ore-forming age of the Yuanjiang ruby deposit. These phlogopite ages reveal a slower cooling rate of ruby deposits within the shear zone (including the Yuanjiang and the Yen Bai ruby deposits) than outside of the shear zone (the Luc Yen deposit), which can be attributed to the additional heat from the left-lateral shearing movement. Therefore, we propose that the left-lateral shearing plays an important role in transporting marble-hosted ruby deposits in the Ailao Shan-Red River shear zone to the subsurface. [ABSTRACT FROM AUTHOR]

Abstract: Extrusion tectonics forced by plate collisions shape continents not only through lateral terrain displacement and mountain building but also through massive rifting and basin development. The rift system underneath the Gulf of Tonkin, Vietnam, constitutes a world‐class example of how extrusion tectonics drives continental rifting and transtensional basin development. Rifting and the Song Hong and Beibuwan Basin evolution are compared with the development of the Ailao Shan‐Red River Shear Zone (ASRRSZ) that accommodated the extrusion of Indochina forced by the Indian‐Eurasia collision. Rifting occurred during later Eocene‐Late Oligocene time forced by ASRRSZ left‐lateral shearing. Latest Oligocene‐earliest Miocene transpression and inversion brought rifting to a halt, after which left‐lateral shearing decreased. Paleogene rift systems extended along the trail of the ASRRSZ now outlined by lower to midcrustal metamorphic core complexes. Most of these rift systems were probably inverted and removed during the latest Oligocene‐earliest Miocene, however. The metamorphic core complexes are suggested to represent the lower to midcrustal roots of these transtensional rift basins exhumed by inversion. Rift termination in the northern Gulf of Tonkin and exhumation of the metamorphic core complexes coincided with cessation of Paleogene rifting along the western South China Sea, and a common causal mechanism is speculated. [ABSTRACT FROM AUTHOR]

Structural and microstructural characteristics, deformation temperatures and flow vorticities of the northern Ailao Shan (ALS) high-grade metamorphic belt provide significant information regarding the nature and tectonic evolution of the Ailao Shan-Red River (ASRR) shear zone. Mineral deformation mechanisms, quartz lattice-preferred orientation (LPO) patterns and the opening angles of quartz c-axis fabrics of samples from the Gasa section indicate that the northern ALS high-grade metamorphic belt has experienced progressive shear deformation. The early stage shearing is characterized by a gradual decrease of deformation temperatures from >650 °C at the northeastern unit to ca. 300 °C at the southwestern unit, that results in the formation of migmatites, mylonitic gneisses, thin bedded mylonites, mylonitic schists and phyllonites from the NE to SW across the strike of the shear zone. The late stage low-temperature (300–400 °C) shearing is superimposed on the early deformation throughout the belt with the formation of discrete, small-scale shear zones, especially in the thin-banded mylonitic rocks along both margins. The kinematic vorticity values estimated by rotated rigid porphyroclast method and oblique grain-shaped/quartz c-axis-fabric method imply that the general shear-dominated flow (0.49–0.77) progressively changed to a simple shear-dominated flow (0.77–1) toward the late stage of ductile deformation. The two stages of shearing are consistent with early shortening-dominated and late extrusion-controlled regional tectonic processes. The transition between them occurred at ca. 27 Ma in the ALS high-grade metamorphic belt along the ASRR shear zone. The large amount of strike-slip displacement along the ASRR shear zone is predominantly attributed to accelerated flow along the shear zone during the late extrusion-controlled tectonic process. [ABSTRACT FROM AUTHOR]

Four metamorphic massifs in southeastern Tibet – the Xuelong Shan (XLS), Diancang Shan (DCS), Ailao Shan (ALS) and Day Nui Con Voi (DNCV) – have been suggested to constitute coherent parts of the Ailao Shan-Red River (ASRR) shear zone. This study details the cooling/exhumation histories of the crustal-scale shear zone by determining the cooling paths of the ALS massif and comparing these paths to those of the DCS massif. We show that the different parts of the ALS massif have experienced two stages of diachronous cooling histories. The two cooling stages of the ALS massif, i.e., an early rapid cooling of ca. 45–715 °C/Myr and a late slow cooling of 10–17 °C/Myr, differ significantly from the cooling of the DCS massif along the same shear zone, which featured an early slow cooling of 11–17 °C/Myr and a late rapid cooling of 30–140 °C/Myr. This study confirms that differing cooling/exhumation histories exist along the same crustal-scale shear zone. From the contrasting cooling/exhumation histories, we would argue that the ALS and DCS massifs are isolated units with different tectono-thermal histories during the Oligo-Miocene tectonic evolution of southeastern Tibet. [ABSTRACT FROM AUTHOR]

Abstract: This paper offers new evidence on whether the Ailao Shan–Red River Shear Zone of NW Vietnam is part of a suture zone between two continental blocks (the IndoChina Block and the South China Block) or whether it is itself of intracontinental origin, developed within the South China margin. To help clarify the role that the Ailao Shan–Red River Shear Zone plays in South China tectonic reconstructions, we gathered new whole-rock geochemistry, structural field data, and zircon U–Pb (SHRIMP) ages from granites, rhyodacites, and migmatites that occur within geological units adjacent to both the SW and NE sides of the Red River Fault Zone, a segment of the larger shear zone. The new zircon ages show that both walls of the Red River Fault Zone contain metamorphic and intraplate A-type granitoid rocks of Late Permian–Early Triassic age (263–240 Ma) and are of Indosinian origin. In the SW wall, the Fan Si Pan complex is a Neoproterozoic basement of metagranites and metasediments that was intruded by Late Permian (∼260Ma), peralkaline, A-type granites and by subalkaline, A-type, biotite granite of Eocene age (∼35Ma), containing xenoliths of gneissified Permian granitoids. The two intrusive episodes were separated by regional tectonic deformations occurring within a transpressional regime of a NW/W-vergent thrusting with a left-lateral oblique component, that was associated with greenschist to amphibolite facies metamorphism, presumably also of Eocene age (∼50–35 Ma), and that may have been related to the left-lateral movement on the Ailao Shan–Red River Shear Zone. In the NE wall, the Lo Gam complex is a Neoproterozoic basement (∼767 Ma) that was repeatedly subjected to tectonothermal activity throughout the Palaeozoic (at ∼450–420 Ma, ∼350 Ma, ∼265 Ma), ending in the Early Triassic (∼248 Ma). There was no thermal overprint during the Cenozoic. In this wall, a significant part of the Permo-Triassic thermotectonism was ductile shearing that was concentrated along dextral, strike-slip NW-trending zones in the vicinity the Ailao Shan–Red River Shear Zone but that became a type of NE/N-ward extensional/contractional, regional movement further away of it. An early shearing on the Ailao Shan–Red River Shear Zone may date back to the Permo-Triassic and we consider that this probably originated in a continental fault zone initiated in the hinterland of the oblique Indosinian collisional zone. [Copyright &y& Elsevier]

Highlights: [•] Epithermal-porphyry Cu–Au mineralization is related to the 40–32Ma high-K alkaline magmatism. [•] The porphyry Cu–Mo–Au and epithermal Au systems have magmatic S and Pb isotopes. [•] Paleotethyan subduction and Indian–Eurasian Plate interaction contributed to mineralization. [ABSTRACT FROM AUTHOR]

Abstract: The relationship between potassic felsic intrusions, cospatial and cotemporal with potassic mafic magmatism, and strike–slip displacement along the Ailao Shan-Red River shear zone in western Yunnan, SW China has been highly controversial. We report 22 new SHRIMP zircon U–Pb ages from 19 potassic felsic intrusions located as far as 150km east and 50km west of the shear zone to constrain temporal relationships. The results show that the felsic intrusions in western Yunnan were emplaced between 36.9±0.3Ma and 32.5±0.3Ma. This age range is significantly shorter than previous dating of 38Ma to 23Ma using K–Ar and Ar–Ar methods from 15 intrusions, indicating that the latter are reset or cooling ages. Potassic felsic intrusions are coeval with potassic mafic volcanic rocks (36.6Ma to 33.4Ma) in the same area, supporting a possible genetic link between the two end members. The dated intrusions occur over a 200km wide zone across the Ailao Shan-Red River shear zone; therefore they are unlikely genetically related to shearing. Rather, potassic mafic magmatism in western Yunnan may be related to delamination and melting of previously subduction-modified mantle lithosphere along the Mesozoic Jinsha suture reactivated in the Eocene–Early Oligocene, following the India-Asia continental collision; potassic felsic magmas were crustal melts hybridized with mafic liquids. Delamination in turn facilitated and localized initiation of the Ailao Shan-Red River shear zone at ca. 32Ma during continental extrusion. [Copyright &y& Elsevier]

Abstract: The structural geology, timing of shearing, and tectonic implications of the ASRR shear zone, one of the most striking lineaments in Southeast Asia, have been the topics of extensive studies over the past few decades. The Xuelong Shan (XLS), Diancang Shan (DCS), Ailao Shan (ALS) and Day Nui Con Voi (DNCV) metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution. Our field structural analysis, detailed microstructural and fabric analysis, as well as the quartz, sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during Cenozoic tectonic evolution in the shear zone. Among the contrasting structural and microstructural associations in the shear zone, D2 structures, which were formed at the brittle to ductile transition during large-scale left-lateral shearing in the second deformation episode, predominate over the structural styles of the other two deformation episodes. Discrete micro-shear zones with intensive grain size reduction compose the characteristic structural style of D2 deformation. In addition, several types of folds (early shearing folds, , and late-shearing folds, ) were formed in the sheared rocks, including discrete to distributed mylonitic foliation, stretching lineation and shear fabrics (e.g., mica fish, domino structures, as well as sigma and delta fabrics). A sequence of microstructures from syn-kinematic magmatic flow, high-temperature solid-state deformation, to brittle–ductile shearing is well-preserved in the syn-kinematic leucocratic intrusions. Deformation structures from the first episode (D1) are characterized by F1 folds and distributed foliations (S1) in rocks due to pure shearing at high temperatures. They are preserved in weakly sheared (D2) rocks along the eastern margin of the ALS belt or in certain low-strain tectonic enclaves within the shear zone. Furthermore, semi-brittle deformation structures, such as hot striae and discrete retrogression zones, are attributed to normal-slip shearing in the third deformation episode (D3), which was probably locally active, along the eastern flank of the DCS range, for example. There are four quartz c-axis fabric patterns in the mylonitic rocks, including type A point maxima, type B Y point maxima with crossed girdles superimposition, type C quadrant maxima, as well as type D point and quadrant maxima combination. They are consistent with microscopic observations of microstructures of high-temperature pure shearing, low-temperature simple shearing and their superimposition. Integrated microstructural analysis and fabric thermometer studies provide information on both high temperature (up to 750°C) and dominant low-temperature (300–600°C) deformations of quartz grains in different rock types. Sillimanite and garnet fabrics, especially the latter, were primarily formed at the peak metamorphism during high-temperature pure shearing. The above structural, microstructural and fabric associations were generated in the tectonic framework of the Indian-Eurasian collision. The low-temperature microstructures and fabrics are attributed to left-lateral shearing along the ASRR shear zone from 27 to 21Ma during the southeastward extrusion of the Indochina block, which postdated high-temperature deformation at the peak metamorphism during the collision. [Copyright &y& Elsevier]

The Diancang Shan metamorphic massif, the northwestern extension of the Ailao Shan Massif, is a typical metamorphic complex situated along the NW–SE-trending Ailao Shan–Red River shear zone. Diancang Shan granitic and amphibolitic mylonites collected from sheared high-grade metamorphic rocks were studied using petrographic and electron-backscatter diffraction techniques. Sensitive high-resolution ion microprobe U–Pb dating of zircon grains from the granitic mylonites constrains the timing of shearing. Macro- and microstructural and textural analysis reveals intense plastic deformation of feldspar, quartz, and amphibole under amphibolite-facies conditions, all consistently document left-lateral shearing. Porphyritic monzogranitic mylonite within the shear zone possesses evidence supporting a sequential, progressive process from crystallization during magma emplacement, through submagmatic flow to solid-state plastic deformation. We suggest that the early-kinematic pluton subsequently underwent strong left-lateral strike–slip shearing. The development of complex textures of quartz, feldspar, and amphibole from the granitic and amphibolitic mylonites apparently records successive variation of conditions attending coherent, solid-state high-temperature ductile deformation during regional left-lateral shearing. All magmatic zircons from the mylonitized porphyritic monzogranite give U–Pb ages of 30.95 ± 0.61 million years for the crystallization of the granite. This age provides the timing of onset of left-lateral shearing along the Ailao Shan–Red River shear zone in the Diancang Shan high-grade metamorphic massif. [ABSTRACT FROM PUBLISHER]

Abstract: The Ailao Shan–Red River (ASRR) shear zone, one of the most prominent geologic strike-slip shear zones in Southeast Asia, consists of high-grade metamorphic complexes that provide a rare opportunity to sample the mid-crustal rocks along the western margin of the Yangtze Block of South China. Here we report combined, in-situ analyses of zircon U–Pb and Lu–Hf isotopes of eight gneisses from the Diancang Shan and Ailao Shan segments of the ASRR shear zone. Our zircon U–Pb data indicate that the rocks contain abundant magmatic zircons ranging in age from 1785 to 25Ma, with peak ages at ca. 770, 350 and 240Ma, suggesting three major periods of protolith formation. The 350-Ma zircons, observed only in an orthogneiss from the Diancang Shan, show uniform initial Hf isotopic ratios marked by high and positive εHf(T) values from +16 to +10. This is in contrast with the other two zircon populations that are more common, occurring in both the Diancang Shan and Ailao Shan, and overall delineate very heterogeneous Hf isotopic compositions, with εHf(T) values ranging from +15 to −16. Many zircons reveal distinctive core-rim age variations. Zircon rims, formed between ca. 34 and 26Ma, show significant variations in Th/U ratios (5–0.01) and εHf(T) values (+14 to −10) that suggest complicated magmatic and metamorphic zircon overgrowth during the Oligocene. The presence of both metamorphic and magmatic overgrowths on zircons suggests that the metamorphism reached upper amphibolite facies, corresponding to mid-crustal level P–T conditions, as also suggested by structural and petrologic data. Our data furthermore suggest that the ASRR gneisses were not produced solely by shear heating during the Tertiary strike-slip faulting, but are uplifted, mid-crustal basement rocks that formed essentially during two major stages of magmatism, represented by the Neoproterozoic Kangding Complex and Late Permian Emeishan large igneous province. As a result of the India–Asia collision, these basement rocks underwent regional magmatic and metamorphic overprinting in the Oligocene that, based on our relevant work (Searle et al., 2010, Geosphere, 6, 1–23), predated the initial left-lateral movement along the ASRR shear zone. The 350-Ma protolith, which requires a dominant depleted-mantle input in the petrogenesis, cannot be linked to any major magmatic events in South China but may be interpreted as part of the Paleotethys remnants that were later incorporated into the ASRR shear zone. [Copyright &y& Elsevier]

Abstract: Exhumation of the high-grade metamorphic rocks from deep to shallow crustal levels in the Diancang Shan (DCS) massif is evident by the temporal transition from shearing and mylonitization at the amphibolite facies in the lower to middle crust, through retrograde ductile–brittle faulting at greenschist facies in the middle crust and brittle faulting near the surface. New 40Ar/39Ar ages of amphibole, muscovite, biotite and K-feldspar, mostly from mylonitic rocks, help constrain the thermal evolution of the massif during its exhumation. The thermochronologic studies have shown at least three stages of exhumation and cooling from late Oligocene to Pliocene, e.g., 28–13Ma, 13–4Ma and 4–0Ma, respectively. The initiation of the unroofing history of the DCS massif resulted from ductile left-lateral shearing along the Ailao Shan-Red River shear zone (ASRR) since the late Oligocene. Diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history of the massif. The first stage of exhumation might have stopped due to the cessation of the left-lateral shearing at ca. 21Ma, although cooling continued until 13Ma ago to relatively low-temperature conditions. The second and third stages of cooling started from 13Ma and lasted until the recent active faulting. The diversity of cooling rates during the second stage from 13 to 4Ma suggests differences in exhumation rates at various localities. Ductile to brittle shearing along the eastern flank retrograde normal shear zone is the best explanation for the exhumation during this stage. The inhomogeneous cooling and exhumation of the lower plate of the normal fault zone possibly resulted from the tilting of the lower plate or differential exhumation of slabs in the lower plate. During the third stage, cooling and exhumation of the DCS massif since 4Ma ago is recognized when higher temperature cooling paths are extended and plotted at a lower temperature of about 16°C, the present day average surface temperature. Therefore, the diachronous cooling and exhumation continuously spanned to the surface. The tectonic exhumation of the DCS massif constitutes a part of the tectono-thermal evolution and diachronous exhumation of the metamorphic complexes in the fan-shaped area bounded broadly in SE Asia by the Red River fault zone and Sagaing fault zone since 36Ma. Extrusion-induced strike-slip shearing and rotation-associated normal faulting, played important roles in the diachronous cooling and exhumation of the DCS massif and other metamorphic complexes in SE Asia. [Copyright &y& Elsevier]

Abstract: The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and post-collisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31Ma, culminated between ca. 27 and 21Ma resulting in high-temperature metamorphic conditions and slowed down at ca. 20Ma at relatively low-temperatures. [Copyright &y& Elsevier]

The Diancang Shan Complex located at the northwestern extension along the Ailao Shan-Red River (ASRR) shear zone is a representative metamorphic complex of the ASRR tectonic belt. This complex is constituted by two units, a central high-grade metamorphic belt and an eastern low-grade superposed metamorphic belt. Structural, microstructural, sub-microstructural and texture analysis of sheared rocks in the high-grade metamorphic rocks reveal that deformation of rocks occurred at high-temperature conditions. The related structures, micro-structures and textures are attributed to left-lateral shearing along the ASRR shear zone, which also helps to constrain the timing of initiation of left-lateral shearing at early Oligocene. [ABSTRACT FROM AUTHOR]

The anisotropy of magnetic susceptibility (AMS) of 351 specimens from 51 sites across the Ailao Shan–Red River shear zone (ASRR) was measured to determine its magnetic fabric. Rocks range westward from core schistose gneiss, through low-grade schist, to Triassic sediment. Magnetic ellipticity analysis shows that 41 of 51 sites have an oblate compressional fabric and the other 10 sites have a prolate fabric. PJ value drops by 22.4% in the low-grade schist and by 27.4% in the Triassic sediment on average with respect to the gneiss, suggesting a rapid decrease of deformational intensity. The directions of principal susceptibilities are closely related to the deformation of the Ailao Shan–Red River shear zone. The susceptibility plane always coincides with the schistosity or cleavage plane. Most of the maximum susceptibility axes trend NW–SE. In the shear zone, the maximum susceptibility axes (Kmax) are parallel to the lineation within the foliation plane. With increasing distance from the shear zone, there is a trend that they become parallel to the down-dip of reverse faults or cleavage. This indicates changes in deformation mode, inside and outside the shear zone. Within the shear zone, horizontal movement is dominant. Outside, shortening prevails. The overall minimum magnetic axes align NE–SW with subhorizontal to low dip angles, suggesting that the dominant shortening is NE–SW directed. Caution should be exercised when AMS is used to determine shear sense in strong shear zones because the angle between the minimum susceptibility axis (Kmin) and pole of foliation is small, and also because the attitude of foliation varies from place to place. They result in unreliable or even wrong shear sense. Another important result is the axial ratio of magnetic susceptibility ellipsoid along the study section. With these data, it is possible to establish an axial ratio relationship between the finite strain ellipsoid and magnetic susceptibility ellipsoid for quantitative calculation of offset. [Copyright &y& Elsevier]

Using cooling curves of K-feldspars obtained by specific40Ar/39Ar step heating procedure and multiple diffusion domain modeling (MDD model), together with results of dating hornblende, biotite, muscovite, and apatite, this research relates the cooling history of 3 areas, from Ejia in NWto Jinping in SE of Ailao Shan-Red River shear zone, and near Hekou (distance about 390 km). The results indicate that the slip distance of Ailao Shan-Red River shear zone is more than 350 km (at least based on the study done within China). And between the end of the left-lateral slip movement and the beginning of the right-lateral slip movement, the uplift of shear zone from SE to NW was homogeneously extended. [ABSTRACT FROM AUTHOR]

• Leucogranites in the ASRR shear zone experienced extensive fractional crystallization. • Sr-Nd-Hf isotope systematics indicate partial melting of amphibolite. • Leucogranite emplacement coincides with slip-strike movement of the ASRR at 27 Ma. We report for the first time the occurrence of leucogranite bodies that intruded the Ailaoshan metamorphic complex along the Ailao Shan-Red River (ASRR) shear zone. Leucogranites in Yuanyang, Southeast Yunnan province, are composed of quartz (~30%), alkali feldspar (~45%), plagioclase (~5%), muscovite (~13%) and biotite (~3%) and other minor silicate minerals (~3%, garnet, tourmaline). U–Pb dating of zircon from leucogranites yields a weighted mean age of 27.4 ± 0.5 Ma, suggesting a late Oligocene anatexis event. These leucogranites are strongly peraluminous with A/CNK values of 1.01–1.19 and have high SiO 2 (73.3–77.0 wt%) and K 2 O + Na 2 O (7.87–10.08 wt%), and low CaO (0.41–0.99 wt%), MgO (0.04–0.21 wt%), TiO 2 (0.01–0.06 wt%) and Fe 2 O 3 T (0.44–0.86 wt%) contents. They are geochemically similar to Himalayan leucogranites and are enriched in large-ion lithophile elements (e.g. Rb), and depleted in high-field-strength elements (e.g. Nb, Zr, and Hf). They have low Zr/Hf (12.3–22.5) and Nb/Ta (2.54–12.73) with negative Eu anomalies (Eu/Eu* = 0.05–0.45), indicative of extensive fractional crystallization of plagioclase and zircon. In addition, these rocks have low 87Sr/86Sr (t) (0.7072–0.7111), high ε Nd (t) (−1.53 to −3.61). They contain zircon grains with ε Hf (−5 to +1.8) and old two-stage Hf model ages of 1.24–1.02 Ga, implying that they were probably derived from partial melting of amphibolite (old crustal material) within the lower crust. In combination with previous studies of metamorphism of the ASRR shear zone, our study demonstrates that the leucogranites may have been generated in a highly dynamic setting involving both extrusion and extension that defined the beginning of left-lateral slip-strike movement of the ASRR shear zone at 27 Ma. [ABSTRACT FROM AUTHOR]