The Mogok metamorphic belt (MMB) extends for over 1,000 km along central Burma from the Andaman Sea to the East Himalayan syntaxis and represents exhumed lower and middle crustal metamorphic rocks of the Sibumasu plate. In the Mogok valley region, the MMB consists of regional high-grade marbles containing calcite + phlogopite + spinel + apatite ± diopside ± olivine and hosts world class ruby and sapphire gemstones. The coarse-grained marbles have been intruded by orthopyroxene-and clinopyroxene-bearing charnockite-syenite sheet-like intrusions that have skarns around the margins. Syenites range from hornblende-to quartz-bearing and frequently show layering that could be a primary igneous texture or a later metamorphic overprint. Calc-silicate skarns contain both rubies and blue sapphires with large biotites. Rubies occur in marbles with scapolite, phlogopite, graphite, occasional diopside, and blue apatite. Both marbles and syenites have been intruded by the Miocene Kabaing garnet-muscovite-biotite peraluminous leucogranite. New mapping and structural observations combined with U-Th-Pb zircon, monazite, and titanite geochronology from syenites, charnockites, leucogranites, meta-rhyolite-tuffs, and skarns have revealed a complex multiphase igneous and metamorphic history for the MMB. U-Pb zircon ages of the charnockite-syenites fall into three categories, Jurassic (170-168 Ma), latest Cretaceous to early Paleocene (~68-63 Ma), and late Eocene-Oligocene (44-21 Ma). New ages from five samples suggest that metamorphism in the presence of garnet and melt occurred between~45 and 24 Ma. U-Pb titanite ages from the ruby marbles and meta-skarns at Le Oo mine in the Mogok valley are 21 Ma, similar to titanite ages from an adjacent syenite (22 Ma). U-Th-Pb dating shows that all the metamorphic ages are Late Cretaceous-early Miocene and related to the India-Sibumasu collision.

The Du-Ku Highway traverses the Tian Shan from the cities of Dushanzi to Kuqa in western China and provides a section across the full width of this Paleozoic orogen.The north Tian Shan consists of an accretionary complex of deformed ophiolite, arc volcanic assemblages, and siliciclastic sedimentary rocks derived mainly from volcanic arcs. The central Tian Shan is underlain by Precambrian basement covered mainly by Carboniferous andesitic tuff, Paleozoic marine carbonate and siliciclastic strata, and abundant Carboniferous-Early Permian granitoids. The south Tian Shan features continuous sequences of Silurian to Lower Carboniferous carbonate, chert, and siliciclastic strata of the deformed Paleozoic passive continental margin of the Tarim block.A high pressure-temperature (P-T) blueschist belt, parallel to and south of the Nikolaev line, which bounds the central and south Tian Shan, is exposed to the west of the Du-Ku Highway. Previously published radiometric ages bracket the blueschist metamorphism of the blueschist belt as 415-315 Ma. A paired coeval magmatic belt to the north was active from at least 400 Ma to ca. 330 Ma. Radiolarian fossils from chert associated with the north Tian Shan ophiolite, and Lower to Middle Carboniferous lithic turbidites structurally imbricated with ophiolite and tuff in the north Tian Shan, indicate that subduction-accretion along the north Tian Shan lasted at least through the end of the Early Carboniferous. Plutonism in the Borohoro arc along the northern margin of the central Tian Shan block culminated during Late Carboniferous-Early Permian time based on radiometric dating.We infer that amalgamation of the Tian Shan proceeded in two steps: (1) accretion of the central Tian Shan block to the northwest margin of the Tarim block by the Middle Carboniferous, with attendant cessation of arc magmatism and high P-T subduction metamorphism; (2) accretion of the Junggar arc complex and the

[1] Analysis of a strike-slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high-strain fault core. We focus on the Ennstal segment of the 400-km-long Salzach-Ennstal-Mariazell-Puchberg (SEMP) strike-slip fault system in the Eastern Alps, which accommodated $60 km of left lateral displacement during Oligo-Miocene time. Macroscopic and microscopic observations reveal a zoned fault featuring a high-strain core at least 10 m wide within a fault zone that is at least 150 m wide. Grain-size distribution analysis shows how the Ennstal segment of the SEMP evolved. Our data reveal a 10-m-wide high-strain fault core (characterized by a power law relationship of grain sizes, D 2 % 2.0) bordered by a 54-m-wide ''transition zone'' where the largest and smallest grains are characterized by two power law relationships (D 2 % 2.0 and 1.6, respectively). This zone is in turn bordered by a region with grain sizes that show a single low-strain power law relationship of D 2 % 1.6. We interpret these relationships to be the result of concentrated shear overprinting an initial low-strain, power law grain-size distribution before strain localized to the core. This is consistent with the theory that faults mature by smoothing geometrical complexities, forming a highly localized, high-strain fault core. The data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture, although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure.Citation: Frost, E., J. Dolan, C. Sammis, B. Hacker, J. Cole, and L. Ratschbacher (2009), Progressive strain localization in a major strike-slip fault exhumed from midseismogenic depths: Structural observations from the Salzach-Ennstal-Mariazell-Puchberg fault system, Austria,

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The most conspicuous and spectacular volcanic features on Earth are the graceful volcanic arcs that parallel the deep oceanic trenches where cold and strong surface plates descend into the Earth's mantle. More than three‐quarters of the volcanos that erupt above sea level are found at these regions, called subduction zones. Inclined bands of earthquakes trace the descent of plates into trenches, beneath the arc volcanos, and ultimately down to depths as great as 690 km. Earthquakes at depths below about 40–60 km represent seismic failure within the sinking plate rather than the slipping motion between plates. Some of those earthquakes have been large and very damaging, and future quakes of this type pose a significant seismic hazard in northwest Washington state, Central America, and elsewhere. Most earlier studies have emphasized the role of the sinking force that accompanies the cold thermal structure, as well as the resultant higher density of descending plates in producing stresses that lead to seismic failure of the plate.