Correlating magnetic fabrics with finite strain : comparing results from mudrocks in the Variscan and Appalachian Orogens

New magnetic anisotropy data from Variscan mudstones collected in the Cantabrian Arc, N Spain constrain the corresponding strain (shortening). The results are based on our previous study of mudrocks from the Valley and Ridge Province (Appalachians) where independent strain quantification of pencil structures permitted a correlation between magnetic fabric and tectonic strain. An exponential relationship between the AMS shape parameter T and tectonic shortening was found for the interval of 10-25% shortening: shortening (%)=17*exp(T), relationship that appears to be supported by tectonic strains up to 40%. The T parameter describes the shape of the magnetic susceptibility ellipsoid, which in pelitic rocks appears more sensitive to strain than the degree of anisotropy parameter P (or P'). In mudrocks from the Cantabrian Arc a positive correlation between T parameter and deformation intensity, reflected by cleavage domains spacing, is observed. Using the above relationship, we estimate the range of tectonic shortening for the Cantabrian mudstones. The correlation between strain and AMS offers a robust estimate of strain magnitude of 10-40% in weakly to moderately deformed clay-rich rocks, where other strain indicators are often lacking or are poorly preserved

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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95566/1/eost18856.pd

Locally Derived, Meteoric Fluid Infiltration Was Responsible for Widespread Late Paleozoic Illite Authigenesis in the Appalachian Basin

Isotopic and geochronologic investigation of authigenic, K‐bearing clays in the Appalachian Plateau of the northeastern U.S. Midcontinent yields new insights about the tectonic and diagenetic history of the North American sedimentary cover sequence. In situ texture analysis by High Resolution X‐ray Texture Goniometry indicates preservation of bedding‐parallel diagenetic fabrics with burial depths of 2–5 km, and illite mineralization temperatures are spatially variable, ranging from 80 to 190 °C, correlating to similar depths of 3–6 km. The mineralizing geofluid is surface derived, with δD values ranging from −48‰ to −72‰ (in the range of predicted Pangea meteoric fluid). In addition, we find that mineralizing fluid δD values increase away from the orogenic front, consistent with a rain shadow effect from the high elevation Appalachian orogen. The age of authigenic illite is constrained by 40Ar/39Ar geochronology to 308–318 Ma, reflecting Upper Carboniferous diagenesis. We postulate that far‐field stress transmission from continent‐continent collision created regional permeability pathways for surface fluids, altering the hydrologic architecture of the brittle crust and allowing meteoric fluid infiltration into upper crustal rocks. This interpretation challenges the popular view of tectonically forced, lateral fluid flow from the Appalachian orogen (squeegee hypothesis).Key PointsFar‐field stress due to Alleghanian orogenesis facilitates reorganization of architecture and fluid pathways of the brittle crust and drives regional diagenesisEvidence for locally sourced, surface‐derived fluid challenges popular hypothesis of orogenic fluid expulsionPairing of stable and radiogenic isotope analysis of authigenic illite constrains the relationship between regional diagenesis and tectonismPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156223/2/tect21355.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156223/1/tect21355_am.pd

Thank you reviewers of Earth’s Future in 2016

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137763/1/eft2215.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137763/2/eft2215_am.pd

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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113161/1/eft277.pd

Grain‐scale deformation and the fold test ‐ evaluation of syn‐folding remagnetization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96427/1/grl3496.pd