scholarly journals Migmatite and leucogranite in a continental-scale exhumed strike-slip shear zone: Implications for tectonic evolution and initiation of shearing

2021 ◽  
Author(s):  
Junyu Li ◽  
Shuyun Cao ◽  
Xuemei Cheng ◽  
Franz Neubauer ◽  
Haobo Wang ◽  
...  
Keyword(s):  
Shear Zone ◽  
Thermal State ◽  
Shear Zones ◽  
Strike Slip ◽  
Red River ◽  
Crustal Anatexis ◽  
Plate Convergence ◽  
Continental Scale ◽  
Geological Processes ◽  
Lower Crustal

Plutons within continental strike-slip shear zones bear important geological processes on late-stage plate transpression and continent-continent collision and associated lateral block extrusion. Where, when, and how intrusions and shearing along transpressional strike-slip shear zones respond to plate interactions, however, are often debated. In this study, we investigated migmatite associated leucogranite and pegmatite from the exhumed >1000-km-long Ailao Shan-Red River left-lateral strike-slip shear zone in Southeast Asia that was active during India-Eurasia plate convergence. Most zircons from the migmatites and leucogranitic intrusions present inherited core-rim structure. The depletion of rare earth element patterns and positive Eu anomalies suggest that leucosomes and leucogranites are the result of crustal anatexis. Zircon rims from the foliated migmatites and leucogranites record U-Pb ages of 41−28 Ma, revealing the timing of the Cenozoic crustal anatexis event along this strike-slip shear zone. Ages of the magmatic zircons from the unfoliated pegmatites provide the timing of the termination of a high-temperature tectono-thermal event and ductile left-lateral shearing at 26−23 Ma. The Cenozoic crustal anatexis along the Ailao Shan-Red River strike-slip shear zone indicates that thickened crust underneath the shear zone involved previously subducted crust. We propose that the Cenozoic thermal state has an important effect on the crustal anatexis and thus on the rheological behavior of the lithosphere by thermal weakening, which plays an essential role in localizing the initiation of the deep-seated lower-crustal shear zone.

The Ailao Shan–Red River shear zone revisited: Timing and tectonic implications

2019 ◽  
Vol 132 (5-6) ◽  
pp. 1165-1182 ◽  
Author(s):  
Junlai Liu ◽  
Xiaoyu Chen ◽  
Yuan Tang ◽  
Zhijie Song ◽  
Wei Wang
Keyword(s):  
Shear Zone ◽  
Structural Data ◽  
Shear Zones ◽  
Red River ◽  
Plate Convergence ◽  
Ductile Shearing ◽  
Magma Sources ◽  
T Values ◽  
Tectonic Extrusion ◽  
Lower Crustal

Abstract Continental strike-slip shear zones that may bear important information about the evolution of convergent tectonics often occur to accommodate plate convergence. When and how shearing along the shear zones responds to plate interactions, however, are often debated. In this study, we investigated the Oligocene–Miocene leucocratic dikes from the Ailao Shan–Red River shear zone, which was active during India-Eurasia plate convergence, to constrain the timing and mechanism of ductile shearing along the shear zone. The dikes are structurally grouped into pre-, syn-, and postkinematic types with respect to ductile shearing. Prekinematic dikes from ca. 41 to 30 Ma have low whole-rock 87Sr/86Sr(i) values (0.707–0.710), generally high εNd(t) values (–3.31∼–7.98), and variable εHf(t) values (–7.9∼+5.7). Their magma sources involved high thermal perturbation inducing partial melting of the lower crust, and contributions from the mantle that were possibly related to extensional collapse of the orogenic belt prior to tectonic extrusion of the Sundaland block. Syn- and postkinematic dikes from ca. 28 to 20 Ma dominantly have high whole-rock 87Sr/86Sr(i) (0.707–0.725) and low εNd(t) (–5.83 to –9.76) values, and either negative or positive zircon εHf(t) values (broadly in the range of –12 to + 7.6) for coeval but separate crustal magma sources. The results imply that major shearing accompanying retrograde metamorphism along the Ailao Shan–Red River shear zone was localized to crustal level. A synthesis of regional structural data suggests that Oligocene–Miocene shearing along the Ailao Shan–Red River shear zone and lateral tectonic extrusion of the Sundaland block proceeded in response to progressive India-Eurasia plate convergence. Distributed and inhomogeneous middle- to lower-crustal flow along the boundaries of and within the Sundaland block occurred during the tectonic extrusion.

High–pressure granulite–facies metamorphism and anatexis of deep continental crust: new insights from the Cenozoic Ailaoshan–Red River shear zone, SE Asia

2021 ◽  
Author(s):  
Haobo Wang ◽  
Shuyun Cao ◽  
Franz Neubauer ◽  
Junyu Li ◽  
Xuemei Cheng ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Shear Zone ◽  
Thermal Evolution ◽  
Shear Zones ◽  
Granulite Facies ◽  
Red River ◽  
Crustal Anatexis ◽  
Early Oligocene ◽  
Facies Metamorphism ◽  
T Path

<p>Studies of crustal anatexis have given valuable insights into the evolution of metamorphism–deformation and the tectonic processes at convergent plate margins during orogeny. The transition of metatexite to diatexite migmatite records crucial information about the tectono–thermal evolution and rheology of the deep crust. Along the Ailao Shan–Red River shear zone, metatexite migmatites, diatexite migmatites and leucogranites are widely distributed within the upper amphibolite and granulite facies zones of the Diancang Shan metamorphic complex. The high–pressure granulite–facies metamorphism with mineral assemblage comprising garnet + kyanite + K–feldspar + plagioclase + biotite + quartz + melt is first recognized from the patch metatexite migmatites in the complex. Detailed petrographic evidence and phase diagram reveal that the migmatite underwent nearly isothermal decompression metamorphism, presenting a clockwise P–T path. The peak metamorphic P–T conditions are constrained by phase diagram at ca. 11 kbar and 810 °C, and the amount of melt generated during heating is up to 18 mol%. The extraction and segregation of melts are evidenced by the presence of leucosomes within migmatites and leucogranite dikes, which record the melt flow network through the crust. Zircons and monazites from migmatites record the ages of the melting episode that began at ca. 36 Ma and lasted to ca. 20 Ma. All these results are in accord with orogenic crust thickening accompanied by pervasive anatexis during the Later Eocene to the early Oligocene in the Ailao Shan–Red River shear zone. Combined with available data related to the other continental–exhumed shear zone, we propose that the crustal anatexis has an important effect on the thermal–state of deep–seated shear zones, is thus controlling the rheological behavior of the lithosphere and plays the essential role in the initial localizing of shearing in the lower crust.</p>

scholarly journals The Timing of Strike-Slip Deformation Along the Storstrømmen Shear Zone, Greenland Caledonides: U–Pb Zircon and Titanite Geochronology

2014 ◽  
Vol 41 (1) ◽  
pp. 19 ◽  
Author(s):  
Benjamin W. Hallett ◽  
William C. McClelland ◽  
Jane A. Gilotti
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Fault System ◽  
Oblique Collision ◽  
Plate Convergence ◽  
Ion Probe ◽  
Slip Displacement ◽  
Land Deformation ◽  
Lateral Escape

The Storstrømmen shear zone (SSZ) in the Greenland Caledonides is widely interpreted to have formed in a transpressional regime during sinistral, oblique collision between Baltica and Laurentia in the Silurian to Devonian. New mapping of the SSZ at Sanddal documents a 100 m thick, greenschistfacies mylonite zone cutting the eclogite to amphibolite-facies gneiss complex. We present U–Pb ion probe geochronology on zircon and titanite from a variety of lithologies that shows the SSZ was active from late Devonian to the Carboniferous (at least until 350 Ma). The age of thrusting in the foreland is not well known, but must be younger than the age of eclogite-facies metamorphism at ~400 Ma. It is, therefore, possible that contraction is the same age as strike-slip motion, and that transpression is a viable model. The timing of the SSZ is synchronous with dextral strike-slip displacement on the Germania Land deformation zone. Simultaneous displacement on sinistral and dextral, conjugate shear zones suggests that the SSZ is part of a strikeslip fault system that led to lateral escape of material northward (present day coordinates) during the waning stages of plate convergence between Laurentia and Baltica.SOMMAIRELa zone de cisaillement de Storstrømmen (SSZ) dans les Calédonides du Groenland est généralement comprise comme ayant été formée durant un régime de transpression sénestre lors de la collision oblique entre Baltica et Laurentie, du Silurien au Dévonien.  Une nouvelle cartographie de la SSZ à Sanddal décrit une zone de 100 m d’épaisseur de mylonite au faciès des schistes verts qui recoupe un complexe de gneiss au faciès éclogite à amphibolite.  Notre analyse géochronologique par sonde ionique U-Pb sur zircon et titanite sur diverses lithologies, montre que la SSZ a été active de la fin du Dévonien jusqu’au Carbonifère (au moins jusqu’à 350 Ma).  L’âge du chevauchement dans l’avant-pays n’est pas bien connue, mais il doit être plus jeune que le métamorphisme au faciès d’éclogite à ~400 Ma.  Il est donc possible que la contraction soit du même âge que le mouvement de coulissage, et que la transpression soit un modèle viable.  La chronologie de la SSZ est synchrone au mouvement de coulissage dextre de la zone de déformation de Germania Land.  Les déplacements simultanés, sénestre et dextre, sur des zones de cisaillement conjuguées permettent de penser que la SSZ fait partie d’un système de décrochement qui a engendré une éjection latérale de matériau vers le nord (selon les coordonnées actuelles) durant les stades de convergence des plaques Laurentie et Baltica.

Crustal shear zones and thrust belts: their geometry and continuity in Central Africa

1986 ◽  
Vol 317 (1539) ◽  
pp. 111-128 ◽  
Keyword(s):  
Shear Zone ◽  
Central Africa ◽  
Shear Zones ◽  
Strike Slip ◽  
Thrust Belts ◽  
Ductile Shear Zones ◽  
Displacement Direction ◽  
Crustal Shear Zones ◽  
Orogenic Belts ◽  
Lower Crustal

The Precambrian orogenic belts of Africa are often defined by ductile shear zones which developed in response to large displacements, and which mark orogenic ‘ fronts ’ between mobile and stable parts of the crust. They are thought to represent the major crustal reflectors seen by seismic reflection profiling in younger orogenic belts. These orogenic fronts are connected by shear zones that transfer displacement or accommodate different displacements, between orogenic segments. Smaller shears within an orogenic belt occur as a result of differential movements. These shear zones are seen to pass from flat-lying to steep structures and may have a thrust or strike-slip sense. They compare with the staircase trajectories characteristic of foreland thrust belts. In common with thrust belts, the geometry of the shear zones can be used to estimate displacement direction, as can regional extensional fabrics developed in the associated high-strain tectonites. Central Africa has been previously described as a complex network of late Proterozoic ‘mobile belts’. The recognition of similar displacements and time equivalence in these belts allows their reinterpretation in terms of a linked thrust and strike-slip shear-zone system. An example is the Damaran, Lufilian, Zambezi and Ukingan system. These orogenic belts share a similar displacement picture and broad time equivalence and were apparently linked in a lower crustal shear zone of continental dimensions. This shear zone system appears to have developed under a single tectonic framework

scholarly journals Crustal deformation and exhumation within the India-Eurasia oblique convergence zone: New insights from the Ailao Shan-Red River shear zone

2021 ◽  
Author(s):  
B. Zhang ◽  
S.Y. Chen ◽  
Y. Wang ◽  
P.W. Reiners ◽  
F.L. Cai ◽  
...  
Keyword(s):  
Shear Zone ◽  
Middle Miocene ◽  
Shear Zones ◽  
Strike Slip ◽  
Red River ◽  
Crustal Thickening ◽  
The Core ◽  
Early Oligocene ◽  
Lateral Extrusion ◽  
Tectonic Boundaries

During the collision of India and Eurasia, regional-scale strike-slip shear zones played a key role in accommodating lateral extrusion of blocks, block rotation, and vertical exhumation of metamorphic rocks as presented by deformation on the Ailao Shan-Red River shear zone (ARSZ) in the Eastern Himalayan Syntaxis region and western Yunnan, China. We report structural, mica Ar/Ar, apatite fission-track (AFT), and apatite (U-Th)/He (AHe) data from the Diancangshan massif in the middle segment of the ARSZ. These structural data reveal that the massif forms a region-scale antiform, bordered by two branches of the ARSZ along its eastern and western margins. Structural evidence for partial melting in the horizontal mylonites in the gneiss core document that the gneiss experienced a horizontal shear deformation in the middle crust. Muscovite Ar/Ar ages of 36−29 Ma from the core represent cooling ages. Muscovite Ar/Ar ages of 25 and 17 Ma from greenschist-facies mylonites along the western and southern shear zones, respectively, are interpreted as recording deformation in the ARSZ. The AFT ages, ranging from 15 to 5 Ma, represent a quiescent gap with a slow cooling/exhumation in the massif. AHe results suggest that a rapid cooling and final exhumation episode of the massif could have started before 3.2 Ma, or likely ca. 5 Ma, and continue to the present. The high-temperature horizontal shearing layers of the core were first formed across the Indochina Block, locally antiformed along the tectonic boundaries, and then cooled through the mica Ar-Ar closure temperature during Eocene or early Oligocene, subsequently reworked and further exhumed by sinistral strike-slip movement along the ARSZ during the early Oligocene (ca. 29 Ma), lasting until ca. 17 Ma, then final exhumation of the massif occurred by dextral normal faulting on the Weixi-Qiaohou and Red River faults along the limbs of the ARSZ since ca. 5 Ma. The formation of the antiform could indicate local crustal thickening in an early transpressional setting corresponding to India-Asia convergence. Large-scale sinistral ductile shear along the ARSZ in the shallow crust accommodated lateral extrusion of the Indochina Block, and further contributed to the vertical exhumation of the metamorphic massif from the late Oligocene to the middle Miocene. Furthermore, the change of kinematic reversal and associated cooling episodes along the ARSZ since the middle Miocene or early Pliocene imply a tectonic transfer from strain localization along the major tectonic boundaries to continuous deformation corresponding to plateau growth and expansion.

scholarly journals Geometry, kinematics and regional significance of faulting and related lamprophyric intrusion in the mineralised zone at the Pu Sam Cap complex, Northwest Vietnam

2018 ◽  
Vol 40 (4) ◽  
pp. 320-340 ◽  
Author(s):  
Findlay R. H.
Keyword(s):  
Shear Zone ◽  
South China ◽  
Shear Zones ◽  
Planetary Science ◽  
Strike Slip ◽  
Red River ◽  
Fault System ◽  
Lateral Shear ◽  
Geological Society ◽  
Se Asia

The alkali volcanics and intrusive rocks, dated at around 35-33Ma, are cut by mineralised northeast and east trending faults showing predominant evidence for strike-slip. Mineralisation includes haematite-Au-Cu and is accompanied by iron-rich alteration of the volcanic rocks. Detailed assessment of the geometry of the fault system at Pu Sam Cap suggests that the faults formed as a Riedel shear system during left-lateral slip within the Song Hong-Song Chay shear zone and the numerous contemporaneous northwest trending faults to the south; the northeast trending faults are interpreted as dextral “book-end’’ faults between major northwest trending faults enclosing the Pu Sam Cap massif. As mineralisation is hosted within these faults and is also associated with lamprohyric dykes it confirms a thermal event younger than the alkaline volcanics and syenitic intrusives at Pu Sam Cap, suggesting a hidden, young porphyry system. The age of faulting, and thus the maximum age for this young intrusive event, is attributed to the 23-21Ma period of late-stage left-lateral strike-slip motion across northwest Vietnam.ReferencesAnczkiewicz R., Viola G., Muntener O., Thrirlwall M., Quong N.Q., 2007. Structure and shearing conditions in the Day Nui Con Voi massif: implications for the evolution of the Red River Fault. Tectonics 26: TC2002.Cao Shunyun, Liu Junlai, Leis B., Zhao Chunquiang 2010. New zircon U/Pb geochronology of the post-kinematic granitic plutons in Diancang Shan Massif along the Ailao-Shan-Red River Shear Zone and its geological implications. Acta Geologica Sinica (English Edition), 84, 1474-1487.Chung S.-L., Lee T., Lo C.,  et al., 1997. Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone.Geology, 25, 311-314.Cloos H., 1928. Experimentezurinnern Tektonik.  Zentralblatt fur Mineralogie und Palaeontologie, 1928, 609-621.Findlay R.H., Phan Trong Trinh 1997. The structural setting of the Song Ma region, Vietnam, and the Indochina-South China plate boundary problem. Gondwana Research, 1, 11-33.Jolivet L., Beysasac O., Goffe B., Avigad D., Leprevrier C., Maluski H., Ta Trong Thang, 2001. Oligo-Miocene midcrustal subhorizontal shear in Indochina. Tectonics, 20, 46-57.Khuong The Hung 2010. The complex tectonic events and their influence on formation of mineral deposits in northwest Vietnam. Unpublished PhD Thesis, University of Science and Technology, Cracow, 167p.Leloup P.H., N. Arnau,  R. Lacassin, J.R. Kienast, T.M. Harrison, P.T. Trinh, A. Replumaz and P. Tapponnier, 2001. New constraints on the structure, thermochronology and timing of the Ailao Shan - Red river shear zone, SE Asia, J. G. R., 106, 6657-6671.Leloup  PH.., R. Lacassin, P. Tapponnier, U. Scharer, Zhong Dalai, Liu Xaohan, Zhangshan, Ji Shaocheng and PT.Trinh, 1995. The Ailao Shan - Red river shear zone (Yunnan, China), Tertiary transform boundary of Indochina, Tectonophysics, 251, 3-84. Leprevier C., Maluski H., Nguyen Van Vuong, Roques D., Axente V., Rangin C., 1996. Indosinian NW-trending shear zones within the Truong Son belt, Vietnam: 40Ar-39Ar Triassic ages and Cretaceous to Cenozoic overprints. Tectonophysics, 283, 105-107.Lien-Sheng Zhang, Scharer U. 1999. Age and origin of magmatism along the Cenozoic Red River shear belt, China. Contributions to Mineralogy and Petrology, 134, 67-85.Nagy E.A., Scharer U., Minh N.T., 2000. Oligo-Miocene granitic magmatismin central Vietnam and implications for continental deformation in Indochina. Terra Nova, 12, 67-76.Nguyen Thi Bich Thuy, 2016. Isotop dating U-Pb Zircon of Syenit Formation, Pu Sam Cap. Journal of Geology, A Serie, 356, 30-36. (In Vietnamese).Pei-Long Wang, Ching-Hua Lo, Tung-Yi Lee, Sun-ling Chun, Ching-Yan Lan, Nguyen Trong Yem 1998. Thermochronological evidence for the movement of the Ailo Shan-Red River shear zone, a perspective from Vietnam. Geology, 26, 887-890.Phan Trong Trinh, Nguyen Trong Yem, Herve L.P., Tapponnier P., 1994. Late Cenozoic stress fields in North Vietnam from microtectonic measurements. Proceedings of the International Workshop on Seismotectonics and Seismic Hazard in Southeast Asia. Geological Survey of SR Vietnam, Hanoi, 182-186.Riedel W., 1929. Zur Mechanikgreologischer Brucherscheinungen. Zentralblatt fur Mineralogie und Palaeontologie, Abhandlung B, 354-368.Scharer U., Tapponnier P., Lacassin R., Leloup P.H., Dalai Z., Shaosheng J., 1990. Intraplate tectonics in Asia: a precise age for large-scale Miocene movement along the Ailao Shan-Red River shear zone, China. Earth  and Planetary Science Letters, 97, 65-77.Scharer U., Zhang L.S., Tapponnier P., 1994. Duration of strike-slip movements in large shear zones: the Red River belt, China. Earth and Planetary Science Letters, 126, 379-397.Searle M.P., 2006. Role of the Red River Shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia. Journal of the Geological Society, London, 163, 1025-1036.Searle M.P., Meng-Wan Yeh, Te-Hsien Lin, Sun-Lin Chung, 2010. Structural constraints on the timing of left-lateral shear along the Red River shear zone in the Ailao Shan and Diancang Shan Ranges, Yunnan, SW China. Geosphere, 6, 316-338.Tapponnier P., Lacassin R., Leloup H., Scharer U., Zhong Dalai, Wu Hawei, Liu Ziaohan, Ji Shaocheng, Zhang Lianshang, Zong Jiayou, 1990. The Ailao Shan/ Red River metamorphic belt: Tertiary left-lateral shear between Indochina and south China. Nature, 342, 431-437.Tchalenko J.S., 1970.  Similarities between shear zones of different magnitudes. Bulletin of the Geological Society of America, 81, 1625-1640.Viola G., Anczkiewicz R. 2009. Exhumation history of the Red River shear zone in northern Vietnam:  new insights from zircon and apatite fission-track analysis. Journal of Asian Earth Sciences, 33, 78-90.Yang Yiseng, Hong Qun, Hu Huan-ting, Hieu Pham Trung, Nguyen Thi Bich Thuy, Chen Fu-kun, 2013. Geochemical characteristics and genesis of the Cenozoic porphyry in the Laizhou area, northwestern Vietnam. Acta Petrologica Sinica, 29(3), 899-911. (In Chinese with English abstract, full English version through Google Translate).

scholarly journals The Borborema Strike-Slip Shear Zone System (NE Brazil): Large-Scale Intracontinental Strain Localization in a Heterogeneous Plate

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 6) ◽  
Author(s):  
Sergio P. Neves ◽  
Andréa Tommasi ◽  
Alain Vauchez ◽  
Thais Andressa Carrino
Keyword(s):  
Shear Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Strike Slip ◽  
Northeastern Brazil ◽  
Main Stage ◽  
Plate Boundaries ◽  
Deformation Localization ◽  
Continental Scale ◽  
Dextral Shear

Abstract Large-scale strike-slip faults are fundamental tectonic elements of the continental lithosphere. They constitute plate boundaries (continental transforms), separate terranes with contrasting geological histories within accretionary orogens, or accommodate heterogeneous deformation in intracontinental settings. In ancient orogens, where deeper levels of the crust are exposed, these faults are expressed as shear zones materialized by up to tens of km-wide mylonitic belts. The Borborema shear zone system in northeastern Brazil is one of the largest and best-exposed intracontinental strike-slip shear zone systems in the world, cropping out over 250,000 km2. Here, we review its main geophysical, structural, petrologic, and geochronologic characteristics and discuss the factors controlling its development. This complex continental scale shear zone system is composed of a set of NE- to NNE-trending dextral shear zones from which there are two major E-trending dextral shear zones with horse-tail terminations into the transpressional belt branch, as well as several smaller E-trending dextral and NE-trending dextral and sinistral shear zones. The major shear zones are marked by extensive linear or curvilinear magnetic gradients, implying their continuation at depth. The major shear zones are materialized by migmatite to amphibolite-facies mylonites, but the entire system shows evidence of late deformation at lower temperatures. The system developed during the late stages of the Neoproterozoic Brasiliano (Pan-African) orogeny (mainly from 590 to 560 Ma), postdating by more than 20 Ma the main stage of contractional deformation. Localization of strike-slip shearing in this intraplate setting was controlled by rheological contrasts between blocks with distinct Paleoproterozoic histories, the presence of preorogenic Neoproterozoic rifts, the craton geometry, and zones of enhanced magmatic activity, highlighting the importance of rheological heterogeneity in controlling shear zone nucleation and evolution.

Structure and spatial-temporal relationship of potassic magmatism linked to a continental-scale strike-slip shear zone and post-collisional Cenozoic extension

2021 ◽  
Author(s):  
junyu Li ◽  
shunyun Cao ◽  
Xuemei Cheng ◽  
Haobo Wang ◽  
Wenxuan Li
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Continental Crust ◽  
Red River ◽  
Compositional Variation ◽  
Continental Scale ◽  
Magmatic Rocks ◽  
Western Yunnan ◽  
Potassic Rocks ◽  
Potassic Magmatism

<p>Adakite‐like potassic rocks are widespread in post-collisional settings and provide potential insights into deep crustal or crust-mantle interaction processes including asthenosphere upwelling, partial melting, lower crustal flow, thickening and collapse of the overthickened orogen. However, petrogenesis and compositional variation of these adakite‐like potassic rocks and their implications are still controversial. Potassic magmatic rocks are abundant developed in the Jinshajiang–Ailaoshan tectono-magmatic belt that stretches from eastern Tibet over western Yunnan to Vietnam. Integrated studies of structure, geochronology, mineral compositions and geochemistry indicate adakite-like potassic rocks with different deformation are exposed along the Ailaoshan-Red River shear zone. The potassic felsic rocks formed by mixing and partial melting between enriched mantle-derived ultrapotassic and thickened ancient crust-derived magmas. The mixing of the mafic and felsic melts and their extended fractional crystallization of plagioclase, K-feldspar, hornblende and biotite gave rise to the potassic magmatic rocks. Zircon geochronology provide chronological markers for emplacement at 35–37 Ma of these adakite-like potassic rocks along the shear zone. Temperature and pressure calculated by amphibole-plagioclase thermobarometry range from 3.5 to 5.9 kbar and 650 to 750 ℃, respectively, and average emplacement depths of ca. 18 km for granodiorite within this suite. In combination with the results of the Cenozoic potassic magmatism in the Jinshajiang–Ailaoshan tectono-magmatic belt, we suggest that in addition to partial melting of the thickened ancient continental crust, magma underplating and subsequent crust-mantle mixing beneath the ancient continental crust have also played an important role in crustal reworking and strongly affected the rheological properties and density of rocks. The exhumation underlines the role of lateral motion of the Ailaoshan-Red River shear zone initiation by potassic magma-assisted rheological weakening and exhumation at high ambient temperatures within the shear zone.</p>

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