An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.
Abstract Myanmar, the third largest global tin supplier, is an important component of the Southeast Asian tin province. We have conducted laser ablation-inductively coupled plasma-mass spectrometry U-Pb dating of cassiterite, wolframite, and zircon and Re-Os dating of molybdenite from six primary and two placer Sn deposits in Myanmar. A combination of our geochronological data with previous studies revealed that three episodes of Sn mineralization in the Western tin belt of Southeast Asia formed during the closure of multiple Tethys oceans, namely the Late Triassic (~218 Ma) mineralization in a collisional setting after closure of the Paleo-Tethys, the Early Cretaceous (~124–107 Ma) mineralization during subduction of the Meso-Tethys, and the Late Cretaceous to Eocene (~90–42 Ma) mineralization related to the Neo-Tethys subduction. Recurrent Sn mineralization is recorded not only in the Western tin belt but also in the Central and Eastern tin belts in Southeast Asia. Compilation of currently available cassiterite U-Pb ages from all over the world revealed that durations of regional Sn mineralization events are typically in the range of ~5–30 m.y., whereas the Neo-Tethys subduction in Southeast Asia generated prolonged Sn mineralization lasting up to ~50 m.y. The Southeast Asian tin province, as a whole, has the longest cumulative episodes of mineralization, compared to other Sn provinces. The Sn mineralization ceased in the late Eocene when the tectonic setting changed from Neo-Tethys subduction to dextral motion along a series of strike-slip faults and extrusion of the Indochina block in Southeast Asia.
Abstract Despite decades of research, the mechanisms and processes of subduction initiation remain obscure, including the tectonic settings where subduction initiation begins and how magmatism responds. The Cretaceous Mawgyi Volcanics represent the earliest volcanic succession in the Wuntho-Popa arc of western Myanmar. This volcanic unit consists of an exceptionally diverse range of contemporaneously magmatic compositions which are spatially juxtaposed. Our new geochemical data show that the Mawgyi Volcanics comprise massive mid-oceanic ridge basalt (MORB)-like lavas and dikes, and subordinate island arc tholeiite and calc-alkaline lavas. The Mawgyi MORB-like rocks exhibit flat rare earth elements (REEs) patterns and are depleted in REEs, high field strength elements (except for Th) and TiO2 concentrations relative to those of MORBs, resembling the Izu-Bonin-Mariana protoarc basalts. Our geochronological results indicate that the Mawgyi Volcanics formed between 105 and 93 Ma, coincident with formation of many Neotethyan supra-subduction zone ophiolites and intraoceanic arcs along orogenic strike in the eastern Mediterranean, Middle East, Pakistan, and Southeast Asia. Combined with its near-equatorial paleo-latitudes constrained by previous paleomagnetic data, the Wuntho-Popa arc is interpreted as a segment of the north-dipping trans-Neotethyan subduction system during the mid-Cretaceous. Importantly, our restoration with available data provides new evidence supporting the hypothesis of a mid-Cretaceous initiation of this >8000-km-long subduction system formed by inversion of the ∼E-W–trending Neotethyan oceanic spreading ridges, and that this was contemporaneous with the final breakup of Gondwana and an abrupt global plate reorganization.
Abstract 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.
Abstract 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.
Abstract 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.
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.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
