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Exhumed high pressure/low temperature metamorphic belts provide evidence of subduction processes at depth, but the mechanisms by which subduction zones initiate and evolve to steady thermal state remain contested due to a paucity of recovered subduction infancy rocks. The Easton metamorphic suite in northwest Washington is a Jurassic-Cretaceous subduction complex that preserves a high-grade metamorphic sole inferred to have formed during subduction initiation. Near Gee Point, WA, coherent garnet amphibolite, hornblende-bearing white mica quartzose schist, and underlying garnet blueschist are characterized by their proximity to overlying serpentinized peridotite and the presence of blocks and layers of foliated and unfoliated metasomatic rock. These high-grade rocks are exposed in a series of northeast vergent, steeply inclined, tight-isoclinal folds that post-date regional high pressure/low temperature metamorphism. Two shear zones dip steeply to the southwest, concordant to adjacent blueschist-greenschist, quartzose schist, and amphibolite fabrics. Pervasive retrogression from amphibolite to blueschist-greenschist facies from high to low structural levels is documented at the map, outcrop, and micro scale. Amphibolites contain a foliation defined by aligned hornblende, or in places are weakly foliated. Retrogression of amphibolite is associated with a well-developed glaucophane-white mica-chlorite fabric that wraps older garnet and hornblende, with pargasite cores rimmed by glaucophane and chlorite. Both garnet blueschist and quartzose schist preserve at least one younger foliation. Prior 40Ar/39Ar thermochronology and thermobarometry are consistent with a cooling subduction zone, from amphibolite facies conditions of 760C at >167 Ma to <400C at ~163 Ma. Paired garnet 176Lu-176Hf geochronology and 40Ar/39Ar thermochronology samples will elucidate the timing of (1) proposed subduction initiation, (2) early subduction zone cooling rates, and (3) two shear zones that deformed the Easton metamorphic suite.
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This content will become publicly available on March 25, 2026
Unveiling the cold reality of metamorphic proteins
Metamorphic proteins switch reversibly between two differently folded states under a variety of environmental conditions. Their identification and prediction are gaining attention, but the fundamental physicochemical basis for fold switching remains poorly understood. In this Perspective article, we address this problem by surveying the landscape of well-characterized metamorphic proteins and noting that a significant fraction of them display temperature sensitivity. We then make the case that the dependence on temperature, in particular cold-denaturation effects, is likely to be an underlying property of many metamorphic proteins regardless of their ultimate triggering mechanisms, especially those with a single domain. The argument is supported by rigorous analysis of hydrophobic effects in each well-characterized metamorphic protein pair and a description of how these parameters relate to temperature. The conclusion discusses the relevance of these insights to a better understanding of prediction, evolution, and de novo design strategies for metamorphic proteins.
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- PAR ID:
- 10591643
- Publisher / Repository:
- PNAS
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 122
- Issue:
- 12
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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