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It has long been debated whether the India-Eurasia collision was a single-stage event that began 60-55 million years ago, or whether it was a two-stage process that involved a collision between India and the Trans-Tethyan Arc before the early Paleocene, and the collision of India with Eurasia during the middle Eocene. Here, we report a late Paleogene angular unconformity (ca. 40-28 Ma) in western Myanmar. This angular unconformity developed around the same time as the Assam unconformity (NE India) but is younger than those found in northern Myanmar. Development of these unconformities indicates that an oblique convergence margin in western Myanmar formed before the middle Eocene, with a major dextral strike-slip fault (proto-Sagaing/Shan Scarp Fault) in the backarc. We interpret this oblique convergence margin to be partial continental collision between the West Myanmar Terrane (WMT) and NE India. In backarc regions, syn-rift successions of the Shwebo sub-basin have formed as a consequence of transtensional tectonics along the proto-Sagaing/Shan Scarp Fault since at least the late Paleocene. The syn-rift successions consist of Asian-derived materials that were not identified in the forearc because of the Wuntho-Popa Arc served as a geographical barrier. The presence of the unconformities and tectonic configuration of the Myanmar backarc sub-basins are inconsistent with the scenario inferred from paleomagnetic data, in which the WMT was part of an intra-oceanic arc at near-equatorial latitudes before the late Oligocene. Instead, we propose that the WMT has been part of continental SE Asia since at least the Paleocene (ca. 60-58 Ma). We reconsider the paleomagnetic data and suggest that the Mawgyi Arc, rather than the WMT, is the oceanic fragment that rifted from the northern Gondwana margin during the Late Jurassic. The Mawgyi Arc collided with continental SE Asia (WMT) during the Late Cretaceous, and then with India during the early Eocene (ca. 51-49 Ma). Our results support the collision between India and Eurasia is a multistage event. • Our findings support a two-stage India-Asia collision scenario. • The unconformities propagated from north to south over western Myanmar during the Paleogene. • Syn-Rift sequences of the Shwebo basin were produced by transtensional faulting. • The West Myanmar Terrane was anchored on SE Asia before the late Paleocene (60-58 Ma). [ABSTRACT FROM AUTHOR]

The Hermyingyi quartz vein–type W–Sn deposit is one of the major tungsten and tin producers in Myanmar. It comprises a series of north-trending wolframite-cassiterite-bearing quartz veins mainly hosted in the Late Cretaceous monzogranite which intruded into Paleozoic metasedimentary rocks. Conventional fluid inclusion and infrared microthermometric results reveal that homogenization temperatures decrease from the wolframite-cassiterite stage (stage I, 239–348 °C) through the sulfide stage (stage II, 222–248 °C) to the barren quartz vein stage (stage III, 174–218 °C), whereas salinities vary in a similar range for stage I (1.4–11.7 wt% NaCl equiv.) and II (1.7–11.3 wt% NaCl equiv.) and are slightly lower in stage III (0.7–5.9 wt% NaCl equiv.). Fluid inclusions in wolframite and cassiterite from stage I have similar salinities but distinctly higher (~ 60 °C) temperatures compared to those in coexisting quartz. The δ18Ofluid (3.3 to 7.0‰) and δD (− 76 to − 61‰) values of quartz, wolframite, and cassiterite indicate a dominantly magmatic fluid in stage I, while decreasing values of quartz in stage II (δ18Ofluid = 1.3 to 1.8‰, δD = − 81 to − 71‰) and III (δ18Ofluid = − 3.1 to − 1.6‰, δD = − 89 to − 73‰) show a trend of cooling and dilution by meteoric water. The negative and increasing δ13Cco2 values (from − 20.5 to − 4.9‰) of quartz fluid inclusions from early to late stages imply that organic carbon was added to the magmatic fluid through fluid-rock interaction in stage I, consumed with time and almost exhausted in stage III. The δ34S values (1.6 to 7.9‰) of sulfides coupled with the comparable Pb isotope data of the monzogranite (206Pb/204Pb = 18.572 − 18.784, 207Pb/204Pb = 15.749 − 15.760, 208Pb/204Pb = 39.265 − 39.333) and sulfides (206Pb/204Pb = 18.655 − 18.749, 207Pb/204Pb = 15.737 − 15.768, 208Pb/204Pb = 39.258 − 39.368) suggest igneous sources of sulfur and lead. By combining these results, we propose that fluid-rock interaction and fluid cooling have been responsible for the deposition of wolframite and cassiterite in the Hermyingyi deposit. [ABSTRACT FROM AUTHOR]

The southern Myanmar tin ore district is an important part of the well-known Southeast Asia tin belt (SATB), and hosts numerous economically important primary tin-tungsten ore deposits. However, the timing of formation of these deposits is unclear due to the scarcity of robust age data. The tectonic setting of tin mineralization in this area also needs to be further constrained. Most of the primary tin-tungsten ore deposits in southern Myanmar are typical hydrothermal quartz vein–type, with cassiterite and wolframite as the main ore minerals. Here, we present in situ U–Pb ages of cassiterite and wolframite from nine granite-related hydrothermal Sn–W deposits in southern Myanmar. Cassiterite samples from the Hermyingyi, Thitkhatoe, Thaling Taung, Kalonta, Taungphila, Pagaye, Bawapin, Kanbauk, and Letha Taung deposits yield common lead-corrected weighted mean 206Pb/238U ages of 61.6 ± 0.8 Ma, 61.9 ± 0.6 Ma, 60.4 ± 0.9 Ma, 63.0 ± 0.6 Ma, 62.9 ± 0.6 Ma, 69.5 ± 0.5 Ma, 63.6 ± 0.6 Ma, 61.3 ± 0.6 Ma, and 84.9 ± 0.5 Ma, respectively. Wolframite samples collected from these deposits also yield consistent ages with the cassiterite samples. These ages, combined with available tin mineralization ages from other deposits in the western part of the SATB, define three epochs of Sn metallogeny related to three contrasting geodynamic settings: (1) Early Cretaceous (~ 125–110 Ma) mineralization is related to post-collision slab break-off after collision between the West Burma terrane and the Sibumasu-Tengchong terrane; (2) Late Cretaceous to Paleocene (~ 90–60 Ma) mineralization developed in an Andean-type accretionary setting during subduction of the Neo-Tethys oceanic lithosphere; (3) Early Eocene (~ 50–40 Ma) mineralization may have formed in a post-collision setting after the India-Asia collision. [ABSTRACT FROM AUTHOR]