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1. PRE-ERUPTIVE TEMPERATURES AND ERUPTION DYNAMICS OF RHYOLITE LAVA, NIMBIN RHYOLITE DOME COMPLEX, EASTERN AUSTRALIA

   https://doi.org/10.1130/abs/2020NC-348134  

   Campo, Chloe; Knesel, Kurt (January 2020, Geological Society of America Abstracts with Programs)
2. Fracture toughness of schist, amphibolite, and rhyolite from the Sanford Underground Research Facility (SURF), Lead, South Dakota

   https://doi.org/10.1038/s41598-022-20031-y  

   Jahnke, Ben; Ruplinger, Casey; Bate, Charlotte E.; Trzeciak, Maciej; Sone, Hiroki; Wang, Herbert F. (December 2022, Scientific Reports)

   Abstract The Cracked Chevron Notched Brazilian Disc (CCNBD) method was selected for Mode I fracture toughness tests on Poorman schist, Yates amphibolite, and rhyolite dikes from the EGS Collab site at the SURF in Lead, South Dakota. The effects of lithology, anisotropy, and loading rate were investigated. Fracture toughness was greatest in amphibolite, with schist and rhyolite having similar toughness values ( $${K}_{amphibolite}$$ K amphibolite > $${K}_{rhyolite}$$ K rhyolite ≈ $${K}_{schist}$$ K schist ). The effects of anisotropy on fracture toughness were investigated in the foliated schist samples. Schist samples were prepared in three geometries (divider, arrester, and short transverse) which controlled how the fracture would propagate relative to foliations. The divider geometry was strongest and short transverse geometry was the weakest ( $${K}_{divider}$$ K divider > $${K}_{arrester}$$ K arrester > $${K}_{short transverse}$$ K shorttransverse ). Fracture toughness was observed to decrease with decreasing loading rate. Optical and SEM microscopy revealed that for the short transverse geometry, fractures tended to propagate along grain boundaries, whereas in arrester and divider geometries fractures tended to propagate through grains. In foliated samples, the tortuosity of the fracture observed in thin section was greater in arrester and divider geometries than in short transverse geometries. 

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3. Magmatic lulls in the Sierra Nevada captured in zircon from rhyolite of the Mineral King pendant, California

   https://doi.org/10.1130/GES00920.1  

   Klemetti, Erik W; Lackey, Jade Star; Starnes, Jesslyn (February 2014, Geosphere)

   The Mineral King pendant in the Sierra Nevada batholith (California, USA) contains at least four rhyolite units that record high-silica volcanism during magmatic lulls in the Sierran magmatic arc. U-Th-Pb, trace element (single crystal spot analyses via sensitive high-resolution ion microprobe–reverse geometry, SHRIMP-RG), and bulk oxygen isotope analyses of zircon from these units provide a record of the age and compositional properties of the magmas that is not available from whole-rock analysis because of intense hydrothermal alteration of the pendant. U-Pb spot ages reveal that the Mineral King rhyolites are from two periods, the Early Jurassic (197 Ma) and the Early Cretaceous (134–136 Ma). These two rhyolite packages have zircons with distinct compositional trends for trace elements and δ18O; the Early Jurassic rhyolite shows less evidence of crustal influences on the rhyolites and the Early Cretaceous rhyolite shows evidence of increasing crustal influences and crystal recycling. These rhyolites capture evidence of magmatism during two periods of low magmatic flux in the Sierran Arc; however, they still show that magmas were derived from interactions of maturing continental crust, increasing from the Early to Late Jurassic. This finding likely reflects the transition of the North America margin from one of docking island arcs in the Early Jurassic to one of a more mature continental arc in the Early Cretaceous. This also shows the utility in examining zircon spot ages combined with trace element and bulk isotopic composition to unlock the petrogenetic history of altered volcanic rocks. 

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4. Transient rhyolite melt extraction to produce a shallow granitic pluton

   https://doi.org/10.1126/sciadv.abf0604  

   Schaen, Allen J.; Schoene, Blair; Dufek, Josef; Singer, Brad S.; Eddy, Michael P.; Jicha, Brian R.; Cottle, John M. (May 2021, Science Advances)

   Rhyolitic melt that fuels explosive eruptions often originates in the upper crust via extraction from crystal-rich sources, implying an evolutionary link between volcanism and residual plutonism. However, the time scales over which these systems evolve are mainly understood through erupted deposits, limiting confirmation of this connection. Exhumed plutons that preserve a record of high-silica melt segregation provide a critical subvolcanic perspective on rhyolite generation, permitting comparison between time scales of long-term assembly and transient melt extraction events. Here, U-Pb zircon petrochronology and 40 Ar/ 39 Ar thermochronology constrain silicic melt segregation and residual cumulate formation in a ~7 to 6 Ma, shallow (3 to 7 km depth) Andean pluton. Thermo-petrological simulations linked to a zircon saturation model map spatiotemporal melt flux distributions. Our findings suggest that ~50 km 3 of rhyolitic melt was extracted in ~130 ka, transient pluton assembly that indicates the thermal viability of advanced magma differentiation in the upper crust. 

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5. FLOW BANDS AND MICROLITE TEXTURES IN OBSIDIAN, MINYON FALLS RHYOLITE, AUSTRALIA

   https://doi.org/10.1130/abs/2020NC-348340  

   Seitzinger, Zenja; Knesel, Kurt (January 2020, Geological Society of America Abstracts with Programs)