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The Eastern Himalayan Syntaxis (EHS) serves as a natural laboratory for the study of intense continental collision and lateral extrusion tectonics. By aiming at the intricate tectonic dynamics south and southeast of the EHS, we integrate seismic data from new broadband stations in central Myanmar with permanent stations in southeastern Tibet to establish a high‐resolution 3‐D shear wave velocity model through ambient noise surface wave tomography. Our imaging results reveal distinct differences in crustal seismic velocity structures between the West Burma Block, Chuan‐Dian Block, and the Shan Plateau, highlighting the extent of oblique subduction and restricted crustal extrusion. Notably, two north‐south oriented low‐velocity zones in the mid‐to‐lower crust of southeastern Tibet are mainly confined within the Chuan‐Dian Block and terminate near the Red River Fault, with limited extension into the Shan Plateau. Plain Language Summary: The Eastern Himalayan Syntaxis (EHS) marks the point where the Indian and Asian plates collide most intensely in the eastern Himalayas. Geoscientists have observed significant mountain‐building activities around the EHS extending into southeastern Tibet (SE Tibet), driven by the intense collision of these continental plates. In SE Tibet, materials are squeezed sideways, a process known as lateral extrusion due to the collision of these plates. This is evident from seismic studies showing slower wave speeds in two distinct regions of the middle to lower crust. We analyzed seismic data from new stations in central Myanmar and permanent stations in SE Tibet to better understand the zone transitioning from intracontinental collision to lateral extrusion. Using a technique called ambient noise tomography, we developed a high‐resolution 3‐D model of the crust and uppermost mantle. Our findings reveal significant differences in the crust's structure between areas of subduction, extrusion, and transition, enhancing our understanding of the geodynamic processes beneath the EHS and its surrounding areas. Particularly, two slow‐speed belts related to the lateral extrusion are confined within SE Tibet, supporting a model of limited crustal extrusion. Key Points: We obtain an integrated 3‐D Versus model by ambient noise tomography based on the data from both central Myanmar and southeastern TibetDistinct crustal structures in the West Burma Block, southeastern Tibet, and the Shan Plateau coincide with distinct tectonic responsesTwo north‐south low‐velocity zones in mid‐to‐lower crust end near Red River Fault, indicating restricted crustal extrusion [ABSTRACT FROM AUTHOR]

Continental‐scale shear zones in Indochina record Cenozoic tectonic processes in SE Asia. Previous extrusion models link these shear zones to northward indentation of the Indian continent and conflict with distributed Oligocene conjugate strike‐slip pairs, formed by E‐W‐directed compression (present coordinates). This paper presents evidence of Oligocene shearing along the Mogok Metamorphic Belt in Myanmar, the western boundary of the Indochina block. The Kyanigan quarry at northern Mogok Metamorphic Belt exposes paragneiss, marble and quartzite schist with E‐W striking, which would be dragged from N‐S striking foliations of the main Mogok Metamorphic Belt by right‐lateral shearing of the brittle Sagaing Fault. After restoration, right‐lateral shearing 'σ' structures, cored with garnet, in paragneiss in the Kyanigan quarry are consistent with 'σ' and 'δ' structures in the Moulmein granitic mylonite to the south. U–Pb ages of metamorphic zircon of a sheared paragneiss and a leucogranite, cross‐cutting shear foliation in the Kyanigan quarry, and a biotite 39Ar‐40Ar age of mylonite at Moulmein constrain dextral shearing to 33–25.4 Ma, coeval with other 31–24.5 Ma shear zones in Indochina. The eleven NW‐striking left‐lateral shear zones and N‐S to NE‐striking right‐lateral shear zones define Oligocene conjugate fault patterns in Indochina. After restoration of ~80–45° clockwise rotation, these Oligocene conjugate shear zones, coupled with the anticlinal configuration of the Xuelongshan and Doi Inthanon‐Doi Suthep domes, reflect approximate N–S‐directed shortening. These structures to the north with coeval Myanmar‐Sumatra magmatic arc to the south demonstrate that they correspond to back‐arc contraction during northward subduction of the Indian Ocean. Oligocene continental‐scale intra‐continental shearing may be triggered by syn‐subduction compression in SE Asia. [ABSTRACT FROM AUTHOR]

Myanmar bears a high risk of destructive earthquakes, yet detailed seismicity catalogs are rare. We designed a deep‐learning‐based data processing pipeline and applied it to the data recorded by a large‐aperture (∼400 km) seismic array in central Myanmar to produce a high‐resolution earthquake catalog. We precisely located 1891 earthquakes at shallow (<50 km) depth, a 2‐fold increase compared to the traditional procedures. The new catalog reveals the Kabaw Fault seismicity disappears south of ∼22.8°N, where the deeper (20–40 km) seismicity appears west of the southern Kabaw Fault. Such seismicity contrast along the strike of the Kabaw Fault possibly implies an along‐strike change of deformation responses to the shortening process by the India plate oblique subduction. The middle segment of the Sagaing Fault is likely locked and prone to hosting large earthquakes according to the derived low b‐value. Plain Language Summary: Myanmar is a highly seismically active region, yet fault geometry and activities remain poorly understood because of limited modern seismological investigations. Here, we designed a set of machine‐learning algorithms to detect small earthquakes and determine their locations precisely. The seismic data are recorded by a temporary seismic network deployed in central Myanmar. We obtained twice as many earthquakes as the previous research used the regular procedure. Our improved earthquake data set unveils seismic activity changes along the Kabaw Fault through the changes in earthquake locations, depths, and magnitude‐frequency relations. Kabaw Fault is an import boundary fault in the subduction system of the Indo‐Burma Range. This subtle change was not previously observed but means a significant alternation in deformation style along the subduction strike. Moreover, our improved data set indicates that the Sagaing Fault, the most active fault in Myanmar, is prone to generating large earthquakes in the future. This implication warns the nearby populated cities, like Mandalay, of a significant megaquake threat. Key Points: We detect 1891 shallow earthquakes in Myanmar with a deep‐learning‐empowered pipeline, a 2‐fold increase against the routine procedureN‐S seismicity discrepancy is observed near the Kabaw Fault and may imply different responses to E‐W shortening by the Indian subductionLow b‐value derived from the new catalog on the middle Sagaing Fault indicates a high risk of destructive earthquakes [ABSTRACT FROM AUTHOR]

Fluid infiltration into (meta-)carbonate rocks is an important petrologic process that induces metamorphic decarbonation and potential mineralization of metals or nonmetals. The determination of the infiltration time and the compositional features of reactive fluids is essential to understand the mechanism and process of fluid–rock interactions. Zirconolite (ideal formula: CaZrTi 2 O 7) is an important U-bearing accessory mineral that can develop in metasomatized metacarbonate rocks. In this study, we investigate the occurrence, texture, composition, and chronology of various types of zirconolite from fluid-infiltrated reaction zones in dolomite marbles from the Mogok metamorphic belt, Myanmar. Three types of zirconolite are recognized: (1) the first type (Zrl-I) coexists with metasomatic silicate and oxide minerals (forsterite, spinel, phlogopite) and has a homogeneous composition with high contents of UO 2 (21.37 wt %–22.82 wt %) and ThO 2 (0.84 wt %–1.99 wt %). (2) The second type (Zrl-II) has textural characteristics similar to those of Zrl-I. However, Zrl-II shows a core–rim zonation with a slightly higher UO 2 content in the rims (average of 23.5 ± 0.4 wt % (n=8)) than the cores (average of 22.1 ± 0.3 wt % (n=8)). (3) The third type (Zrl-III) typically occurs as coronas around baddeleyite and coexists with polycrystalline quartz. Zrl-III has obviously lower contents of UO 2 (0.88 wt %–5.3 wt %) than those of Zrl-I and Zrl-II. All types of zirconolite have relatively low rare earth element (REE) contents (< 480 µ g g -1 for Σ REE). Microtextures and compositions of the three zirconolite types, in combination with in situ zirconolite U–Pb dating using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), reveal episodic fluid infiltration and element mobilization in the dolomite marbles. The first-stage infiltration occurred at ∼ 35 Ma, leading to the formation of Mg-rich silicates and oxides and accessory minerals (Zrl-I, baddeleyite, and geikielite). The reactive fluid was characterized by high contents of Zr, Ti, U, and Th. After that, some Zrl-I grains underwent a local fluid-assisted dissolution–precipitation process, which produced a core–rim zonation (i.e., the Zrl-II type). The final stage of fluid infiltration, recorded by the growth of Zrl-III after baddeleyite, took place at ∼ 19 Ma. The infiltrating fluid of this stage had relatively lower U contents and higher SiO 2 activities than the first-stage infiltrating fluid. This study illustrates that zirconolite is a powerful mineral that can record repeated episodes (ranging from 35 to 19 Ma) of fluid influx, metasomatic reactions, and Zr–Ti–U mineralization in (meta-)carbonates. This mineral not only provides key information about the timing of fluid flow but also documents the chemical variation in reactive fluids. Thus, zirconolite is expected to play a more important role in characterizing the fluid–carbonate interaction, orogenic CO 2 release, and the transfer and deposition of rare metals. [ABSTRACT FROM AUTHOR]

The cooling history of granulite is crucial to understanding tectonic scenarios of the continental crust. Ti-in-quartz, a useful indicator of temperature, can decipher the thermal evolution of crustal rocks. Here we apply the Ti-in-quartz (TitaniQ) thermometer to ancient ultrahigh-temperature (UHT) granulites from the Khondalite Belt (KB) in the North China Craton (NCC) and young UHT granulites from the Mogok Metamorphic Belt (MMB), Myanmar. Ti content in quartz was analyzed using a highly precise method constructed in a CAMECA SXFive electron probe microanalyzer (EPMA). The granulites from the two localities show different quartz Ti contents with a constant deforced beam of 10 μm. Matrix quartz and quartz inclusions from the NCC granulites have 57–241 ppm and 65–229 ppm, respectively, corresponding to the TitaniQ temperatures of 653–810 °C and 666–807 °C. The calculated temperatures are significantly lower than the peak temperatures (850–1096 °C) obtained by other methods, due to the formation of abundant rutile exsolution rods in quartz during cooling. Thus, the low calculated temperatures for the NCC granulites reflect a cooling state near or after the exsolution of rutile from quartz, most likely caused by a slow cooling process. However, the matrix quartz from the MMB granulites is exsolution-free and records higher Ti contents of 207–260 ppm and higher metamorphic temperatures of 894–926 °C, close to the peak UHT conditions. This feature indicates that the MMB granulites underwent rapid cooling to overcome Ti loss from quartz. Therefore, determining the amount of Ti loss from quartz by diffusion can provide new insight into the cooling behavior of UHT granulites. When a large deforced beam of 50 μm was used to cover the rutile rods, the matrix quartz in the KB granulites could also yield the TitaniQ temperatures above 900 °C. Thus, our new data suggest that the TitaniQ thermometer could be useful for revealing UHT conditions. [ABSTRACT FROM AUTHOR]

The Mogok continental foreland region and Katha-Gangaw range (KGR) are located in the north-central section of the Myanmar plate, which is a component of the Eurasian plate. The origin of KGR, exposed along northern Myanmar (SE Asia), is still up for argument, despite numerous prior studies. Based on the petrography, geochemistry, and detrital zircon U-Pb geochronology of metamorphic rock samples, the current study focuses on the tectonic evolution of the KGR. The study also emphasizes the phenomenon of microcontinents rifting from the Gondwanan supercontinent and their subsequent amalgamation with Asia. Detrital zircon ages from four samples in the southern region of KGR peak at 634 Ma, 525 Ma, 290 Ma, and 248 Ma, and two samples yielded > 40% of the grains of younger than 400 Ma. Similar results were obtained from three samples (out of six) from the central region of the KGR. All of the samples from the northern part of KGR are older than 400 Ma, with the exception of MT-02A, which contains nearly all of the younger grains. These younger peaks are identical to the zircon U-Pb ages of the Indochina block, the Sibumasu block, and the Pane Chaung Formation of the Myanmar plate, as well as the Langjiexue Formation (southeastern Tibet). This similarity raises the possibility of either these units being a source region of strata in northern Myanmar or sharing a similar source. The geochemistry of metamorphic rocks samples from KGR revealed loss-on-ignition (LOI) values of 0.29–4.18 wt%, emphasizing the modest to moderate alteration. The samples are enriched in large-ion lithophile elements (LILEs), and depleted in high-field strength elements (HFSEs). All metamorphic samples are peraluminous, indicating the linkage with collisional orogenies. This result is most comparable to upper continental crustal provenance. Hence, the metamorphic rocks in KGR regions must be associated with the crustal materials. [ABSTRACT FROM AUTHOR]

The Mogok metamorphic belt (MMB) in central Myanmar is well known for its complex tectonics, magmatism, and metamorphism in the framework of Tethyan subduction and India–Asia collision. It is also world renowned due to the gemstone‐class rubies and sapphires. Identification and discrimination of those petrological units in this region therefore are important for understanding the gemstone mineralization. Ultramafic massifs also crop out together with the gemstone‐bearing metamorphic rocks in the MMB. It is still poorly constrained about their origin (i.e., mantle peridotites of Jurassic–Cretaceous ophiolites or cumulate rocks) and their relationship with the gemstone generation. Here, we report petrological and geochemical data for the Mogok ultramafic rocks. Petrographic observations show that they have typical cumulate textures, with a crystallization order of olivine/spinel‐orthopyroxene‐clinopyroxene. They have low whole‐rock Al2O3 and CaO, and extremely high spinel Cr# (=Cr/[Cr + Al]; up to 0.86). Clinopyroxenes of these rocks show light rare earth element enriched patterns when normalized to CI chondrite. The results suggest that the Mogok ultramafic rocks have different compositions, both whole‐rock and mineral, from mantle peridotites of Myanmar ophiolites, such as the Kalaymyo and Myitkyina ophiolites, but resemble typical Alaskan‐type ultramafic cumulates. Therefore, the Mogok ultramafic rocks are cumulates generated by high‐pressure crystallization of hydrous arc melts, probably during the subduction of the Tethyan oceanic slab. We argue that the emplacement of these arc melts may have provided additional heat for the earlier magmatic rocks and regional high‐temperature metamorphism, although there is a need to further constrain the ages of these rocks. This, along with magmatism and metamorphism during post‐collisional extension, probably collectively contributed to the generation of world‐class coloured gemstone mineralization. [ABSTRACT FROM AUTHOR]

This study represents the first campaign‐style teleseismic shear wave splitting (SWS) investigation of central Myanmar, an area that is tectonically controlled by the oblique subduction of the Indian Plate underneath the Eurasian Plate. The resulting 678 well‐defined and 247 null SWS measurements obtained from recently deployed 71 broadband seismic stations show that the Indo‐Burma Ranges (IBR) possess mostly N‐S fast orientations that are parallel to the trend of the depth contours of the subducted slab. Relative to the global average of 1.0 s, extremely large splitting times with station‐averaged values ranging from 1.28 to 2.79 s and an area‐averaged value of 2.09 ± 0.55 s are observed in the IBR. In contrast, the Central Basin (CB) and the Shan Plateau (SP) are characterized by slightly larger than normal splitting times. The fast orientations observed in the CB are mostly NE‐SW in the northern part of the study area, N‐S in the central part, and NW‐SE in the southern part. The fast orientations change from nearly N‐S along the N‐S oriented Sagaing Fault, to NW‐SE in the central and eastern portions of the SP. These observations, together with SWS measurements using local S events, crustal anisotropy measurements using P‐to‐S receiver functions, and the estimated depth of the source of anisotropy using the spatial coherency of the splitting parameters, suggest the presence of a trench‐parallel sub‐slab flow system driven by slab rollback, a trench‐perpendicular corner flow, and a trench‐parallel flow possibly entering the mantle wedge through a slab window or gap. Plain Language Summary: Myanmar is located at the boundary between the Indian Plate and the Eurasian Plate. Here, the Indian Plate moves northward at a rate that is faster than most other tectonic plates on Earth and subducts obliquely beneath the Eurasian Plate. This subduction not only causes a strong deformation of the Earth's surface, forming the approximately 1,250 km long, N–S trending Indo‐Burma Ranges, but also results in pervasive crustal deformation and possibly modulates the mantle flow field in the area. Mostly due to the limited coverage by broadband seismic stations until recently, crustal deformation and mantle flow beneath Myanmar were poorly understood. In this study, we used data from 71 seismic stations that we deployed in central Myanmar to analyze seismic azimuthal anisotropy, that is, the directional dependence of the velocity of seismic waves in a medium, at different depths. Based on the established relationship between seismic anisotropy and mantle flow, we proposed a model to explain the observations. Our model implies the presence of a trench‐parallel mantle flow beneath the subducted Indian Plate. Above the plate, there are two flow systems with trench‐parallel and trench‐orthogonal orientations, respectively, with spatially varying strengths. Key Points: N‐S anisotropy and large XKS splitting times (∼3 s) on the Indo‐Burma Ranges are from trench parallel flow and lithospheric shorteningXKS and local S results indicate trench‐parallel flow and corner flow coexist in the mantle wedge beneath the Central BasinE‐W oriented corner flow explains the splitting measurements in the Shan Plateau [ABSTRACT FROM AUTHOR]

Fluid infiltration into metacarbonates is a key mechanism to induce orogenic decarbonation, which influences the global carbon cycle and long‐term climate evolution. Little is known regarding the fluid pathways during episodic infiltration events and how flow patterns control time‐integrated CO2 outflux. We investigate the "vein‐like" polycrystalline mineral reaction zones (PMRZs) in dolomite marbles (Mogok metamorphic belt, Myanmar), which are formed by metasomatism via the infiltration of Si–Al–K–Ti–Zr‐bearing fluids. The petrographic textures and mineral U–Pb chronology reveal three episodes of fluid influx in a single PMRZ: (1) the initial episode (Stage‐I) transformed most dolomite into Mg‐rich silicates/oxides and calcite at ∼35–36 Ma indicated by baddeleyite cores; (2) baddeleyite rims gave ages of ∼23–24 Ma, representing a subsequent infiltration episode (Stage‐II) that modified Stage‐I minerals via a dissolution–precipitation mechanism; (3) the final episode (Stage‐III) is recorded by zircon replacing baddeleyite, which yielded ages of ∼17 Ma. Stage‐III fluid has a higher SiO2 activity and XCO2 [CO2/(CO2 + H2O)] than Stage‐I/Stage‐II fluids. Thermodynamic and mass‐balance analyses indicate that Stage‐I infiltration causes >62–67% loss of CO2 by both dolomite‐consuming reactions and calcite dissolution, whereas the latter two infiltration episodes induce <12–18% loss of CO2 via calcite dissolution. Our results provide compelling evidence that repeated episodes of infiltration (each separated in time by 7–13 Ma) occurred along a single channel in marbles. The initial infiltration episode may create high‐permeability regions, offering favorable channels for later‐stage fluids that transfer obviously less CO2 than the initial metasomatism. This considerably complicates a quantitative assessment of CO2 liberation from metacarbonates during orogenesis. Key Points: Gem‐bearing reaction zones in Mogok marbles record three episodes of fluid infiltration each separated in time by 7–13 MaInitial fluid infiltration drives dolomite‐consuming reactions and produces high‐permeability zones that channelize later fluid transportEffect of multiple fluid infiltration episodes on metamorphic CO2 release from marbles in orogenic belts is assessed [ABSTRACT FROM AUTHOR]

Linking the India‐Tibet collision to the north and the Andaman oceanic subduction to the south, Myanmar occupies a crucial position in the India‐Eurasia convergence system. Various seismological studies have indicated that the Indian plate is obliquely subducted along the Burma arc. However, the depth extent and continuity of the subducted slab remain enigmatic. With seismic recordings collected from 114 recently deployed seismic stations, we map the topographies of the mantle transition zone (MTZ) boundaries, that is, the 410‐ and 660‐km discontinuities, beneath Myanmar using receiver functions. Regional 3‐D velocity models were adopted to account for the lateral velocity heterogeneity. The 410‐km discontinuity is uplifted by over 15 km within 95°E‐97°E and 21°N‐24°N beneath Myanmar. This feature correlates well with the east‐dipping high‐velocity anomaly in the tomographic models, with a velocity increase of 0.9%–1.2% at the 410‐km discontinuity depth, suggesting that the subducted slab has reached the MTZ. The uplift of the 410‐km discontinuity terminates to the south at ∼21°N, indicating a distinct change in slab geometry. Our results also reveal a depressed 660‐km discontinuity, which is spatially offset to the southwest of the uplifted 410‐km discontinuity. We propose that the offset between the 410‐km discontinuity uplift and the 660‐km discontinuity depression could indicate a slab break‐off and tearing beneath Myanmar, which was triggered by the northward motion of the Indian plate during the eastward subduction. We further speculate that the slab tear could mark the transition from oceanic to continental plate subduction. Plain Language Summary: The complex tectonic activities in Myanmar are largely dominated by highly oblique eastward subduction of the Indian plate. So far, the depth and continuity of the Indian plate that is subducted deeply beneath Myanmar remain unclear. The present work focuses on the mantle transition zone (MTZ) in order to trace the subducting Indian slab. Based on seismic data collected from 114 recently installed broadband stations in Myanmar, we useseismic P‐to‐S converted waves to map the topographies of the MTZ interfaces, that is, the 410‐ and 660‐km discontinuities. We observe a localized uplift of the 410‐ and a depression of the 660‐km discontinuity, and the two anomalies are horizontally offset by ∼120 km. Since the depths of these discontinuities are sensitive to temperature, our observations indicate that the MTZ structure is affected by the cold subducted slab. Integrating with previous studies, we confirm the arrival of the Indian slab into the MTZ beneath Myanmar and further suggest the occurrence of a slab break‐off and tearing during the eastward subduction. Our results provide important constraints on the subduction geometry as well as the fate of the eastward subducted Indian slab. Key Points: Mantle discontinuities beneath Myanmar are imaged using P‐wave receiver functions from dense regional seismic networksDepth variations of the 410 and 660‐km discontinuities indicate interaction of the subducted Indian slab with the mantle transition zoneSpatial offset between the 410‐km discontinuity uplift and the 660‐km discontinuity depression implies slab break‐off and tearing [ABSTRACT FROM AUTHOR]

Magmatic processes that occur during the transition from oceanic to continental subduction and collision in orogens are critical and still poorly resolved. Oceanic slab detachment in particular is hypothesized to mark a fundamental change in magmatism and deformation within an orogen. Here, we report on two Quaternary volcanic centers of Myanmar that may help us better understand the process of slab detachment. The Monywa volcanic rocks are composed of low‐K tholeiitic, medium‐K calk‐alkaline, and high‐K to shoshonitic basalts with arc signatures, while the Singu volcanic rocks show geochemical characteristics similar to asthenosphere‐derived magmas. These volcanic rocks have low Os concentrations but extremely high 187Os/186Osi ratios (0.1498 to 0.3824) due to minor (<4%) crustal contamination. The Monywa arc‐like rocks were generated by small degrees of partial melting of subduction‐modified asthenospheric mantle at variable depths from the spinel to garnet stability fields. Distinct from the Monywa arc‐like rocks (87Sr/86Sri = 0.7043 to 0.7047; εNdi = +2.3 to +4.7), the Singu OIB‐like rocks exhibit higher 87Sr/86Sri (0.7056 to 0.7064) and lower εNdi (+0.8 to +1.6) values. These isotopic characteristics indicate a large contribution of an isotopically enriched asthenosphere layer beneath the Burmese microplate, which possibly flowed from SE Tibet. We interpret that this short‐lived, small‐scale, and low‐degree melting Quaternary volcanism in Myanmar was triggered by its position above a slab window resulting from the tearing of the oceanic lithosphere from buoyant continental lithosphere of the Indian plate. Key Points: Southward tearing of oceanic lithosphere from continental lithosphere of the Indian plate occurred in central MyanmarActive slab detachment triggers both arc‐like and OIB‐like Quaternary basaltic volcanism during highly oblique continental subductionAn exotic asthenosphere layer beneath the Burmese microplate flowed from central and SE Tibet [ABSTRACT FROM AUTHOR]

The tropical Asian regions are particularly prone to catastrophic droughts due to high temperature and evaporation and their sensitivity to variable oceanic‐atmospheric circulation. The extent to which future global warming may intensify droughts in this populous region is a matter of utmost concern. Palaeoclimatic data can help inform scientists learn more about the temporal patterns and drivers of monsoon change over geological timescales. In this paper, we present a new 8,200 year biomarker record preserved in the annually laminated sediments of Maar Lake Twintaung, Myanmar. The δ13C27‐35 sedimentary record is mainly derived from leaf wax lipids in the lake catchment, which is presently dominated by C3 vegetation in the modern lake catchment. The δ13C27‐35 is mainly regulated by plant physiological and biochemical responses to drought stress and, as such, can be used as a proxy of past changes in moisture. The δ13C27–35 record reveals distinct decadal‐to‐centennial‐scale droughts superimposed on a trend of gradually decreasing summer monsoon intensity from the mid‐Holocene to late Holocene. Within the limits of the dating uncertainties, these decadal‐to‐centennial‐scale droughts are found to be well correlated with the southward shift of the Intertropical Convergence Zone. It highlights thepimportance of the Intertropical Convergence Zone shift (tropical monsoon trough) in regulating monsoon rainfall in the region. In addition, most of the droughts are likely to be linked with active volcanism and solar minima and suggest a coupled process between external drivers and internal climate dynamics. Key Points: Leaf wax n‐alkanes record in varved sediment of Maar lake Twintaung, MyanmarThe result indicates distinct decadal‐to‐centennial‐scale droughts over the past 8.2 kaThe drought cycles link with the ITCZ shift, solar and volcanic eruption [ABSTRACT FROM AUTHOR]

Fusuline faunas including 29 species belonging to 19 genera/subgenera are described from the Thitsipin Formation in eight sections/localities on the Shan Plateau in eastern Myanmar. These fusulines broadly indicate a Midian (middle Permian, Guadalupian) age. The lower diversity and the presence of some genera, such as Monodiexodina and Eopolydiexodina, suggest that the Sibumasu Block belonged to the palaeobiogeographic Cimmerian Province during the Midian. Furthermore, quantitative cluster analysis of middle Permian fusulines from the Shan Plateau and adjacent Cimmerian blocks suggests close faunal affinities between the Sibumasu Block and the Baoshan Block in western Yunnan. More importantly, the widespread occurrence of fusulines Eopolydiexodina afghanensis and Jinzhangia shengi on the Shan Plateau is similar to that of contemporaneous fusuline faunas from the Baoshan Block and the South Qiangtang Block but different to that of the Tengchong and Lhasa Blocks, which are dominated by the characteristic Nankinella–Chusenella assemblage. This faunal discrepancy provides strong evidence that the Bangong–Nujiang suture passes through the Gaoligong Orogen in western Yunnan rather than through the Myitkyina ophiolites in northern Myanmar. Additionally, palaeobiogeographical analysis of these fusuline faunas from the Lhasa, Tengchong, South Qiangtang, Baoshan and Sibumasu Blocks implies that the Bangong–Nujiang Ocean might have been present before the Midian. [ABSTRACT FROM AUTHOR]

Myanmar, one of the most active tectonic regions in the world, endures the risk of destructive earthquakes. Based on seismic data recorded at the recently deployed dense array of the China‐Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO), we detect 854 and locate 599 shallow earthquakes with high precision and determine the focal mechanisms of 40 earthquakes. We identify two NW‐SE trending fault zones accommodating dextral strike‐slip earthquakes beneath the Central Basin, indicating potential seismic risk in the region. We also recognize a nearly N‐S trending seismic zone in the overlying Indo‐Burma Ranges (IBR) crust near the Kabaw Fault (KBF). The earthquakes within this seismic zone mostly show thrusting focal mechanisms. Our results suggest that strike‐slip deformation dominates to the east of the KBF, while shortening is mainly confined to the west of the KBF in Central Myanmar. Plain Language Summary: Myanmar in Southeast Asia suffers from disasters resulting from destructive earthquakes. However, the present knowledge on their causative faults is limited due to the deployment of few seismic observation stations in Myanmar. We deployed a seismic observation network containing 71 stations for 1.5 years and tried to identify unknown causative faults and their characteristics by studying the small earthquakes there. Our results suggest that larger areas than previously expected in Myanmar may encounter significant seismic hazards. More attention to mitigating hazards should be paid to the Central Basin and western mountain areas, where densely populated cities are located. Key Points: We detect 854 shallow earthquakes and analyze the focal mechanisms of 40 events based on the data set from a new seismic array in MyanmarWe identify two fault zones in the Central Basin that may accommodate surplus strike‐slip deformations not taken up by the Sagaing FaultWe observe a lower‐crustal seismic zone west of the Kabaw Fault, which is controlled by eastward subduction of the Indian Plate [ABSTRACT FROM AUTHOR]

Indian continental subduction can explain Cenozoic crustal deformation, magmatic activity and uplift of the Tibetan Plateau following the India-Asia collision. In the western Himalayan syntaxis and central Himalaya, subduction or underthrusting of the Indian Plate beneath the Eurasian Plate is well known from seismological studies. However, because information on the deep structure of the eastern Himalayan syntaxis is lacking, the nature of the Indian subduction slab beneath Myanmar and the related tectonic regime remain unclear. Here, we use receiver function common conversion point imaging from a densely spaced seismic array to detect direct structural evidence of present-day Indian continental subduction beneath Asia. The entire subducting Indian crust has an average crustal thickness of ~30 km, dips at an angle of ~19°, and extends to a depth of 100 km under central Myanmar. These results reveal a unique continental subduction regime as a result of Indian-Eurasian continental collision and lateral extrusion. Indian continental subduction can explain crustal deformation, magmatic activity and uplift of the Tibetan Plateau following collision, however, the nature of the Indian subducting slab beneath Myanmar and the related tectonic regime remain unclear. Here, the authors present direct structural evidence of present-day Indian continental subduction beneath Asia. [ABSTRACT FROM AUTHOR]

Subduction zone fluids are critical for transporting materials from subducted slabs to the mantle wedge. Jadeitites from Myanmar record fluid compositions and reactions in the forearc subduction channel. Here we present high‐precision Mg isotope data of the Myanmar jadeitites and associated rocks to understand the Mg isotope composition of subduction zone fluids at forearc depths. Two types of jadeitites (white and green) exhibit distinct Mg isotope compositions. The white jadeitites precipitated from Na‐Al‐Si‐rich fluids and have low δ26Mg values, varying from −1.55‰ to −0.92‰, whereas the green jadeitites have higher δ26Mg values (−0.91‰ to −0.74‰) due to metasomatic reactions between fluids and Cr spinel. The amphibole‐rich blackwall in the contact boundaries between jadeitites and serpentinites also exhibits low δ26Mg values (−1.17‰ to −0.72‰). Therefore, the jadeite‐forming fluids have not only high concentrations of Na‐Al‐Si but also low δ26Mg values. The low δ26Mg signature of the fluids is explained by the dissolution of Ca‐rich carbonate in subducted sediments or altered oceanic crust, which is supported by the negative correlation of δ26Mg with CaO/TiO2, CaO/Al2O3, and Sr in the white jadeitites. Given the common occurrence of Ca‐rich carbonates in the subduction channel, the Mg isotope composition of low‐Mg aqueous fluids would be significantly modified by dissolved carbonates. Metasomatism by such fluids along conduits has the potential to generate centimeter‐scale Mg isotope heterogeneity in the forearc mantle wedge. Therefore, Mg isotopes could be a powerful tracer for recycled carbonates not only in the deep mantle but also in the shallow regions of subduction zones. Key Points: The Myanmar jadeitites have δ26Mg values lower than normal mantleJadeite‐forming fluids have high contents of Na‐Al‐Si and low Mg contents and δ26Mg valuesSubduction zone fluids at forearc depths may have low δ26Mg values due to carbonate dissolution [ABSTRACT FROM AUTHOR]

The provenance of Sibumasu terrane sedimentary rocks and their tectonic relationships with surrounding terranes exposed in Southeast Asia record separation and accretion of Gondwana-derived terranes during Late Paleozoic and Mesozoic time. This paper reports sandstone petrographic and U–Pb detrital zircon geochronologic data from Ordovician to Lower Jurassic strata within the Sibumasu terrane in Shan State, Myanmar. The Ordovician strata are composed of limestone and siltstone. The Lower Silurian Linwe and Upper Silurian Namhism Formations are comprised of limestone, silty sandstone, conglomerate and sandstone, respectively. Sandstones from both Ordovician and Silurian strata are dominated by 567–470 Ma and 982–917 Ma detrital zircons that are interpreted to be sourced from the eastern Gondwana supercontinent. The Carboniferous unit is composed of metasedimentary rocks (phyllite, slate, quartzite, and meta-marl). Sandstones from Carboniferous units show a strong 1165–1070 Ma detrital zircon age peak that is not present in the Ordovician and Silurian strata. These zircon grains were most likely derived from both the Albany–Fraser Province in Southwest Australia and Maud Province in Antarctic. The Upper Triassic to Lower Jurassic, shallow marine Loi-an Group consists of thin- to medium-bedded sandstone and mudstone that unconformably overly the Permian to Middle Triassic Plateau Limestone Group. Sandstones from the Loi-an Group contain abundant Permian to Triassic detrital zircons that are interpreted to have been derived from the Sukhothai Arc of the western Indochina terrane. Formation of this arc is attributed to eastward (present coordinates) subduction of Paleo-Tethyan oceanic lithosphere beneath Indochina. Therefore, we propose that the Sibumasu terrane was juxtaposed against northwestern Australia as part of the Gondwana supercontinent during Paleozoic to Early Permian time. During the Late Triassic and Early Jurassic, Sibumasu strata record an abrupt influx of Permian and Triassic zircon grains, signifying a change in provenance from Gondwana to the Sukhothai Arc. These data are consistent with a tectonic model involving rifting of the Sibumasu terrane from Gondwana and subsequent docking with the Indochina/Simao terranes during Mesozoic time. [ABSTRACT FROM AUTHOR]

Ruby (red corundum) is one of the most prominent colored gemstones in the world. The highest-quality ruby ("pigeon blood" ruby) comes from marbles of the Mogok Stone Tract in central Myanmar. Although Mogok ruby has been exploited since the 6th century AD, the formation time of this gemstone is ambiguous and controversial. In this paper, we describe a mineralogical, geochemical, and geochronological study of ruby and titanite in ruby-bearing marbles obtained from an outcrop in the Mogok Stone Tract, central Myanmar. Petrographic observations have shown that titanite generally occurs in the marble matrix or occurs as inclusions in ruby. These two types of titanite exhibit identical chemical compositions. In situ secondary ion mass spectrometer (SIMS) U–Pb dating of the separated titanite from two representative samples of ruby-bearing marbles yielded lower intercept ages of 25.15 ± 0.24 Ma (MSWD = 0.26) and 25.06 ± 0.22 Ma (MSWD = 0.15), respectively. Because the closure temperature of the U–Pb system in titanite is close to the temperature of ruby growth, the obtained U–Pb ages (~25 Ma) are suggested to represent the timing of the studied ruby formation in Mogok. The acquired ages are in agreement with the timing of post-collisional extension in the Himalaya related to the migration of the eastern Himalayan syntaxis. Combining our dating results with previous geochronological data from the Mogok Stone Tract, we suggest that the formation of the studied ruby is most likely related to the high-temperature metamorphic event in the marbles during the India–Asia collision. Our study not only confirms that texturally constrained titanite could be a precise geochronometer to date the mineralization of different types of ruby, but also provides important geochronological information linking gemstone formation to the India–Asia collision. [ABSTRACT FROM AUTHOR]

Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar, and represent the remnants of the Neotethyan oceanic lithosphere (Sengupta et al., 1990; Mitchell, 1993). These ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet farther northwest (Mitchell, 1993; Fareeduddin and Dilek, 2015), as indicated by their coeval crystallization ages and geochemical compositions (Yang et al., 2012; Liu et al., 2016). The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges (Fig. 1). composition of these ophiolites from the central Tibetan Plateau (CTP) is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs, which is inconsistent with most ophiolites worldwide (Robinson and Zhou, 2008; Zhang et al., 2008). But the generation and tectonic nature of these ophiolites are still controversial. The Kalaymyo peridotites consist mainly of harzburgites, which show typical porphyroclastic or coarse-grained equigranular textures. They are composed of olivine (Fo = 89.8-90.5), orthopyroxene (En86-91Wo1-4Fs8-10; Mg# = 89.6-91.9), clinopyroxene (En46-49Wo47-50Fs3-5; Mg# = 90.9-93.6) and spinel (Mg# = 67.1-78.9; Cr# = 13.5-31.5), and have relatively homogeneous whole-rock compositions with Mg#s of 90.1-90.8 and SiO2 (41.5-43.65 wt.%), Al2O3 (1.66-2.66 wt.%) and CaO (1.45-2.67 wt.%) contents. They display Light Rare Earth Element (LREE)-depleted chondrite-normalized REE patterns with (La/Yb)CN = 0.04-0.21 and (Gd/Yb)CN = 0.40-0.84, and show a slight enrichment from Pr to La with (La/Pr)CN in the range of 0.98-2.36. The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic (Pd/Ir)CN ratios (1.15-2.36). Their calculated oxygen fugacities range between QFM-0.57 and QFM+0.90. These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees (5-15%) of partial melting at a mid-ocean-ridge (MOR) environment. The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts, percolating through these already depleted, residual peridotites. The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges hence represent mid-ocean ridge (MOR)-type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction-accretion system along the eastern margin of India. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Sibumasu Block during the Permian remains controversial, and Permian faunas and their paleobiogeographic affinities provide some insight into its paleogeographic and tectonic evolutionary histories. In this paper, a new brachiopod fauna dominated by Spinomartinia prolificaWaterhouse, 1981 is described from the uppermost part of the Taungnyo Group in the Zwekabin Range, eastern Myanmar. This brachiopod fauna includes 23 species and its age is well constrained as late Kungurian by the associated conodonts, i.e., Vjalovognathus nicolliYuan et al., 2016 and Mesogondolella idahoensis (Youngquist, Hawley, and Miller, 1951), contrary to the late Sakmarian age given to the same brachiopod faunas previously reported from southern Thailand and Malaysia. Based on comprehensive comparisons of the Cisuralian brachiopod faunas and other data in different parts of the Sibumasu Block, we consider that they are better subdivided into two independent stratigraphic assemblages, i.e., the lower (earlier) Bandoproductus monticulus-Spirelytha petaliformis Assemblage of a Sakmarian to probably early Artinskian age, and the upper (younger) Spinomartinia prolifica-Retimarginifera alata Assemblage of a late Kungurian age. The former assemblage is a typical cold-water fauna, mainly composed of Gondwanan-type genera, e.g., BandoproductusJin and Sun, 1981, SpirelythaFredericks, 1924, and SulciplicaWaterhouse, 1968. The latter assemblage is strongly characterized by an admixture of both Cathaysian and Gondwanan elements, as well as some genera restricted to the Cimmerian continents. Notably, the spatial distribution pattern of these two separate brachiopod assemblages varies distinctly. The Sakmarian cold-water brachiopod faunas have been found in association with glacial-marine diamictites throughout the Sibumasu Block including both the Irrawaddy and Sibuma blocks. In contrast, the Kungurian biogeographically mixed brachiopod faunas are only recorded in the Irrawaddy Block, unlike the Sibuma Block that contains a contemporaneous paleotropical Tethyan fusuline fauna. Thus, it appears likely that by the end of Cisuralian (early Permian), the Sibumasu Block comprised the Irrawaddy Block in the south with cool climatic conditions, and the Sibuma Block in the north with a temperate to warm-water environment, separated by the incipient Thai-Myanmar Mesotethys. [ABSTRACT FROM AUTHOR]

Scheelite, which is an important ore of tungsten and colored gemstone, is well developed in the calc-silicate rocks from the Mogok metamorphic belt (MMB), Myanmar. In this study, the textural, mineralogical, and compositional characteristics of scheelite and its associated minerals were systematically investigated to constrain the petrogenesis of scheelite-bearing calc-silicate rocks and the tungsten transfer and mineralization mechanism in a hydrothermal–metasomatic system. The petrological evidence, bulk and mineral geochemical signatures, and mass-transfer calculations indicate that the calc-silicate rocks formed by local metasomatism of marble via the introduction of an externally derived Si–Al–Fe–W–F-bearing, H 2 O-rich fluid phase. The distinct compositional zonations [F, Fe, Ca, and heavy rare earth elements (HREEs)] of garnet in the calc-silicate rocks record a two-stage metasomatic process and significant compositional variation in the associated fluid. The late-stage metasomatic fluid that led to the formation of the F-rich garnet rims, scheelite, and most of the calc-silicate minerals has noticeably higher fluorine activity ( a F − ), oxygen fugacity ( f o 2 ), and HREE content than the early-stage metasomatic fluid responsible for the garnet cores. The MMB scheelite exhibits typical “skarn-type” compositional characteristics with a high La N /Yb N ratio (100–180), a negative Eu anomaly (δEu = 0.3–0.5), and a high Mo content (1100–1330 ppm). These geochemical signatures are primarily controlled by the protolith, metasomatic fluid, redox conditions, and coexisting mineral phases. The enrichment of rare earth elements (REEs) and high field strength elements (HFSEs) in the MMB scheelite was dominated by two substitution reactions: Ca 2+ + W 6+ = REE 3+ + HFSE 5+ and 3Ca 2+ = 2REE 3+ + □Ca (where □Ca is a Ca-site vacancy). Considerable amounts of F and OH in the metasomatic fluid substituted for O in the garnet via the substitute reaction 4(F, OH) − = 4O 2− + Si 4+ , leading to a significant enrichment of F (up to 1.2 wt.%) and OH (up to 0.32 for n OH ) and a negative correlation between F and Si in the garnet. Detailed petrographic observations show that the occurrence of scheelite in the MMB calc-silicate rocks is always associated with the growth of F-rich minerals such as garnet rims (0.8–1.2 wt.% F), vesuvianite (2.4–2.6 wt.% F), fluorite (48–49 wt.% F), apatite (3.9–4.1 wt.% F), and titanite (2.6–3.4 wt.% F). These textural characteristics, combined with the positive correlation of whole-rock F and W (as well as Sn, Mo) contents in the calc-silicate rocks, indicate that the elevated F contents increased the solubility of W in the infiltrating fluid, thereby allowing the W transfer in the hydrothermal–metasomatic system. The mineralization of scheelite was triggered by the crystallization of F-rich minerals during the formation of the calc-silicate rocks, which caused F depletion and consequent saturation of W in the metasomatic fluid. Our results suggest that, in the MMB metasomatic system, F rather than Cl is the key fluxing compound that facilitates the transfer of W and the mineralization of scheelite. [ABSTRACT FROM AUTHOR]

• The Indian continental lithosphere is explored to a depth of 100 km beneath Myanmar. • The underlying Indian lower crust may have experienced partial eclogitization. • A low velocity anomaly beneath the Monywa volcano indicates its latest volcanism. The Indian plate descends obliquely eastward beneath the Eurasian plate along the Burmese arc. Previous tomographic results revealed a high-velocity structure that plunges eastward into the deep mantle beneath Myanmar. However, the shallow structure beneath Myanmar remains unclear due to the lack of local seismic observations. Based on the local seismic data recorded by a newly deployed dense array in Myanmar, we obtain a three-dimensional velocity structure of the crust and lithospheric mantle above 100 km by employing the double-difference tomography method. Our imaging results support the existence of the Indian continental lithosphere to a depth of at least 100 km with a dip angle of ∼25° beneath the Indo-Burma Ranges and the Central Myanmar Basin. At the deep end of the continental slab, the high V P , high Vs and rather low average V P / V S ratio indicate that the lowermost portion of the crust from 80 to 120 km may have experienced partially metamorphic eclogitization. The imaging results also provide direct seismic evidence for the origin of the last Monywa volcanic activity in the Holocene. This subduction-related volcanism is characterized by a prominent low Vs anomaly in the lithospheric mantle, which indicates continental lithosphere dehydration and partial melting in mantle wedge. These findings provide new seismic constraints to understand the continental collision system between India and Eurasia under Myanmar and the related magmatic activities of the Monywa volcano. [ABSTRACT FROM AUTHOR]

• The West Burma Block experienced a significant clockwise rotation of 38.3°±6.9°since 64.4 Ma. • The West Burma Block experienced a counterclockwise rotation of 14.6 ± 4.2°since 26.6 Ma. • Results endorsed lateral extrusion model which predicts escape tectonics developed in SE Asia in Cenozoic. The magnitude and timing of deformation in the form of vertical-axis rotation in the eastern Tibetan Plateau and Southeast Asia during the Cenozoic period are the key to understanding the India-Asia collision and subsequent geological processes. Our new paleomagnetic and geochronological data from Myanmar show that the characteristic remanent magnetization (ChRM) mean directions of sedimentary tuffaceous layers (31 effective specimens) and rhyolites (11 paleomagnetic site-mean directions), which formed at ∼64.4 Ma and ∼26.6 Ma, were D±ΔD/I±ΔI = 50.8°±11.0°/33.1°±9.2° with α 95 = 9.2° and D±ΔD/I±ΔI = 356.8°±6.5°/16.9°±6.2° with α 95 = 6.2°, respectively. These data indicate that the West Burma Block (WBB) has experienced a significant clockwise rotation of 38.3°±6.9° since ∼64.4 Ma and a later counterclockwise rotation of 14.6 ± 4.2° since ∼26.6 Ma with respect to stable Asia. The clockwise rotation of ∼40° of the WBB since 64.4 Ma (early Paleocene) with respect to stable Asia is attributable to the India-Asia collision, and the later counterclockwise rotation of 14.6°±4.2° since 26.6 Ma (late Oligocene) is attributable to the dextral-slip faulting activity of the Sagaing Fault. These paleomagnetic analyses, combined with previously published geological research in SE Asia, are substantially consistent with the predictions of the extrusion model for the SE Asia realm. [ABSTRACT FROM AUTHOR]

Closure of the Neo-Tethyan Ocean is one of the most significant tectonic events of the Cenozoic, forming the longest continental collision belt on Earth and influencing global climate and biodiversity. However, whether late Mesozoic subduction of the Neo-Tethyan Ocean occurred along one single or a double subduction system remains controversial. Here, upper mantle imaging from seismic tomography and waveform modeling in the Myanmar region reveals two prominent, parallel, slab-like structures with high seismic velocities that trend to the north-south and dip to the east. The western high-velocity zone has been observed previously and represents the modern subducting slab. The eastern zone has not been previously reported and exhibits high-velocity anomalies of 1.0 to 2.5% to a depth of ~300 km. This zone likely represents a remnant of another Neo-Tethyan oceanic slab that subducted ~40 million years ago. Double subduction of the Neo-Tethyan Ocean during the late Mesozoic to early Cenozoic requires reevaluation of previous tectonic models.