Evidence for geomagnetic excursions recorded in Brunhes and Matuyama Chron lavas from the trans‐Mexican volcanic belt

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Long-lived magnetism on chondrite parent bodies

publisher: Elsevier articletitle: Long-lived magnetism on chondrite parent bodies journaltitle: Earth and Planetary Science Letters articlelink: http://dx.doi.org/10.1016/j.epsl.2017.07.035 content_type: article copyright: © 2017 The Authors. Published by Elsevier B.V.© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article

Fluid release from the subducted Cocos plate and partial melting of the crust deduced from magnetotelluric studies in southern Mexico: implications for the generation of volcanism and subduction dynamics

In order to study electrical conductivity phenomena that are associated with subduction related fluid release and melt production, magnetotelluric (MT) measurements were carried out in southern Mexico along two coast to coast profiles. The conductivity-depth distribution was obtained by simultaneous two-dimensional inversion of the transverse magnetic and transverse electric modes of the magnetotelluric transfer functions. The MT models demonstrate that the plate southern profile shows enhanced conductivity in the deep crust. The northern profile is dominated by an elongated conductive zone extending >250 km below the Trans-Mexican Volcanic Belt (TMVB). The isolated conductivity anomalies in the southern profile are interpreted as slab fluids stored in the overlying deep continental crust. These fluids were released by progressive metamorphic dehydration of the basaltic oceanic crust. The conductivity anomalies may be related to the main dehydration reactions at the zeolite → blueschist → eclogite facies transitions and the breakdown of chlorite. This relation allows the estimation of a geothermal gradient of ∼8.5°C/km for the top of the subducting plate. The same dehydration reactions may be recognized along the northern profile at the same position relative to the depth of the plate, but more inland due to a shallower dip, and merge near the volcanic front due to steep downbending of the plate. When the oceanic crust reaches a depth of 80–90 km, ascending fluids produce basaltic melts in the intervening hot subcontinental mantle wedge that give rise to the volcanic belt. Water-rich basalts may intrude into the lower continental crust leading to partial melting. The elongated highly conductive zone below the TMVB may therefore be caused by partial melts and fluids of various origins, ongoing migmatization, ascending basaltic and granitic melts, growing plutons as well as residual metamorphic fluids. Zones of extremely high conductance (>8000 S) in the continental crust on either MT profile might indicate extinct magmatism

Biomarkers Signal Contaminant Effects on the Organs of English Sole (Parophrys vetulus) from Puget Sound

Fish living in contaminated environments accumulate toxic chemicals in their tissues. Biomarkers are needed to identify the resulting health effects, particularly focusing on early changes at a subcellular level. We used a suite of complementary biomarkers to signal contaminant-induced changes in the DNA structure and cellular physiology of the livers and gills of English sole (Parophrys vetulus). These sediment-dwelling fish were obtained from the industrialized lower Duwamish River (DR) in Seattle, Washington, and from Quartermaster Harbor (QMH), a relatively clean reference site in south Puget Sound. Fourier transform–infrared (FT-IR) spectroscopy, liquid chromatography/mass spectrometry (LC/MS), and gas chromatography/mass spectrometry (GC/MS) identified potentially deleterious alterations in the DNA structure of the DR fish livers and gills, compared with the QMH fish. Expression of CYP1A (a member of the cytochrome P450 multigene family of enzymes) signaled changes in the liver associated with the oxidation of organic xenobiotics, as previously found with the gill. The FT-IR models demonstrated that the liver DNA of the DR fish had a unique structure likely arising from exposure to environmental chemicals. Analysis by LC/MS and GC/MS showed higher concentrations of DNA base lesions in the liver DNA of the DR fish, suggesting that these base modifications contributed to this discrete DNA structure. A comparable analysis by LC/MS and GC/MS of base modifications provided similar results with the gill. The biomarkers described are highly promising for identifying contaminant-induced stresses in fish populations from polluted and reference sites and, in addition, for monitoring the progress of remedial actions