Bruce Nelson - Profile on Academia.edu (original) (raw)

Papers by Bruce Nelson

Biochemical Journal, Dec 21, 2006

The TRPM7 (transient receptor potential melastatin 7) ion channel has been implicated in the upta... more The TRPM7 (transient receptor potential melastatin 7) ion channel has been implicated in the uptake of Mg 2+ into vertebrate cells, as elimination of TRPM7 expression through gene targeting in DT40 B-lymphocytes renders them unable to grow in the absence of supplemental Mg 2+ . However, a residual capacity of TRPM7deficient cells to accumulate Mg 2+ and proliferate when provided with supplemental Mg 2+ suggests the existence of Mg 2+ uptake mechanism(s) other than TRPM7. Evaluation of the expression of several members of the SLC41 (solute carrier family 41) family, which exhibit homology with the MgtE class of prokaryotic putative bivalent-cation transporters, demonstrated that one, SLC41A2 (solute carrier family 41 member 2), is expressed in both wild-type and TRPM7-deficient DT40 cells. Characterization of heterologously expressed SLC41A2 protein indicated that it is a plasma-membrane protein with an N-terminus-outside/ C-terminus-inside 11-TM (transmembrane)-span topology, consistent with its functioning as a trans-plasma-membrane trans-porter. In contrast with a previous report of ion-channel activity associated with SLC41A2 expression in oocytes, investigation of whole cell currents in SLC41A2-expressing DT40 cells revealed no novel currents of any type associated with SLC41A2 expression. However, expression of SLC41A2 in TRPM7-deficient cells under the control of a doxycycline-inducible promoter was able to conditionally enhance their net uptake of 26 Mg 2+ and conditionally and dose-dependently provide them with the capacity to grow in the absence of supplemental Mg 2+ , observations strongly supporting a model whereby SLC41A2 directly mediates transplasma-membrane Mg 2+ transport. Overall, our results suggest that SLC41A2 functions as a plasma-membrane Mg 2+ transporter in vertebrate cells.

Science of The Total Environment, 2019

Two species of moss were used to evaluate atmospheric deposition of major and trace elements. • M... more Two species of moss were used to evaluate atmospheric deposition of major and trace elements. • Major and trace elemental concentrations were higher in urban moss samples than those in rural western Washington. • Pb isotope analyses suggest Seattle mosses receive metals from various industrial sources. • Most trace metal concentrations were correlated with traffic rates.

Lithosphere, 2018

The early Eocene (52-44 Ma) was a time of tectonic reorganization and widespread magmatism in Was... more The early Eocene (52-44 Ma) was a time of tectonic reorganization and widespread magmatism in Washington, Oregon, and British Columbia (west coast of the United States and Canada) that culminated with establishment of the Cascade arc. Details of this tectonic transition remain enigmatic, and diverse scenarios involving ridge-trench interaction, slab breakoff, and/or plume magmatism have been proposed. This study focuses on the ca. 48 Ma Basalt of Summit Creek, a ~1500-m-thick sequence of subaerial lavas that erupted during the interval of time between accretion of the Siletzia terrane to the west and inception of the Cascade arc. The sequence dominantly consists of moderately evolved tholeiitic basalts (9.3-3.1 wt% MgO; Mg# = 0.66-0.29) and scarce rhyolites that erupted in the forearc but are chemically and isotopically similar to oceanic basalts of the Crescent Formation, found ~100 km to the west as part of the Siletzia terrane. Basalt of Summit Creek lavas lack subduction signatures (e.g., high field strength element depletions) and require a mechanism whereby asthenospheric melts were able to reach the surface having undergone little or no chemical interaction with fluids derived from the subducting slab or metasomatized mantle. We suggest that the accretion of Siletzia led to breakoff of the Farallon slab, and that Basalt of Summit Creek lavas formed by decompression melting of mantle that upwelled through the rupture. Slab breakoff typically produces a short-lived linear magmatic belt; the Basalt of Summit Creek appears to be part of such a belt, previously unrecognized, that parallels the Siletzia boundary and formed between 50 and 48 Ma.

Contributions to Mineralogy and Petrology, Sep 30, 2014

Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny a... more Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes, Central Kamchatka Depression The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Kayzar, Theresa M. et al. "Deciphering Petrogenic Processes Using Pb Isotope Ratios from Time-Series Samples at Bezymianny and Klyuchevskoy Volcanoes, Central Kamchatka Depression." Contributions to Mineralogy and Petrology 168.4 (2014): n. pag.

GSA Bulletin

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and pr... more The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and preserves evidence that more than 50% of this orogen represents juvenile crustal growth over an extended period of some 750 million years from ca. 1000 Ma to ca. 250 Ma. However, the mechanism of crustal growth is controversial, as implied by a variety of proposed models ranging from contributions of mantle-derived basaltic underplating in a post-collisional extensional setting to subduction-related processes in an island arc setting. To distinguish among these models, we report petrological, geochemical, whole-rock Sr-Nd isotope and zircon U-Pb and Hf isotope analyses of late Paleozoic felsic igneous rocks from the northern Inner Mongolia region, southeastern CAOB. New zircon U-Pb analyses of three plutonic and extrusive magmatic suites yield Late Carboniferous to Early Permian ages of 319–279 Ma. The Xi Ujimqin granodiorites have low-K tholeiitic to calc-alkaline, metaluminous to weakly ...

Journal of Petrology, 2015

The recent eruptive history on the island of Tenerife is characterized in part by the presence of... more The recent eruptive history on the island of Tenerife is characterized in part by the presence of zoned phonolitic ignimbrites, some of which prominently display two types of juvenile clasts (i.e. light-colored, aphyric pumices alongside darker, more crystal-rich pumices, here dubbed 'crystalpoor' and 'crystal-rich', respectively). Petrographic observation of the crystal-rich pumices reveals intensely resorbed and intergrown mineral textures, consistent with the system reaching a high crystallinity, followed by perturbation and remobilization prior to eruption. Some trace elements show anomalous concentrations in such crystal-rich pumices (e.g. bulk Ba > 2000 ppm alongside low Zr and a positive Eu anomaly) indicative of crystal accumulation (of feldspar 6 biotite). Many biotite and feldspar crystals are reversely zoned, with rim concentrations that are high in Ba but low in Sr, implying crystallization from an 'enriched' melt, potentially derived from remobilization by partial melting of the aforementioned cumulate zones. Given (1) the presence of cumulates in the eruptive record on Tenerife and a bimodality of pumice textures, (2) the presence of three dominant compositions (basanite, phonotephrite, phonolite, separated by compositional gaps) in the volcanic record, and (3) abundant support for crystal fractionation as the dominant drive for magmatic evolution in Tenerife, it is hypothesized that crystal-poor magmas are extracted from mushy reservoirs in both the lower and upper crust. The thermodynamic software MELTS is used to test a polybaric differentiation model whereby phonolites (sensu lato) are generated by extraction of residual liquids from an intermediate-crystallinity phonotephritic mush in the upper crust, which is in turn generated from the residual liquids of an intermediate-crystallinity basanitic mush at deeper levels. Latent heat spikes following crystallization of successive phases in the upper crustal reservoir provide a thermal buffering mechanism to slow down cooling and crystallization, permitting enhanced melt extraction at a particular crystallinity interval (mostly $40-60 vol. % crystals). MELTS modeling typically fits the observed chemical data adequately, although some major elements (mostly Al 2 O 3) also indicate partial 'cannibalization' of feldspar along with some magma mixing (and potentially minor crustal contamination).

Biochemical Journal, 2007

Magmatic rocks and depositional setting of associated volcaniclastic strata along a north-south t... more Magmatic rocks and depositional setting of associated volcaniclastic strata along a north-south traverse spanning the southern Tien Shan and eastern Pamirs of Kyrgyzstan and Tajikistan constrain the tectonics of the Pamirs and Tibet. The northern Pamirs and northwestern Tibet contain the north facing Kunlun suture, the south facing Jinsha suture, and the intervening Carboniferous to Triassic Karakul-Mazar subduction accretion system; the latter is correlated with the Songpan-Garze-Hoh Xi system of Tibet. The Kunlun arc is a composite early Paleozoic to late Paleozoic-Triassic arc. Arc formation in the Pamirs is characterized by 370−320MavolcanismthatprobablycontinueduntiltheTriassic.ThecrypticTanymassutureofthesouthernnorthernPamirsispartoftheJinshasuture.Amassive370-320 Ma volcanism that probably continued until the Triassic. The cryptic Tanymas suture of the southern northern Pamirs is part of the Jinsha suture. A massive 370−320MavolcanismthatprobablycontinueduntiltheTriassic.ThecrypticTanymassutureofthesouthernnorthernPamirsispartoftheJinshasuture.Amassive 227 Ma batholith stitches the Karakul-Mazar complex in the Pamirs. There are striking similarities between the Qiangtang block in the Pamirs and Tibet. Like Tibet, the regional structure of the Pamirs is an anticlinorium that includes the Muskol and Sares domes. Like Tibet, the metamorphic rocks in these domes are equivalents to the Karakul-Mazar-Songpan-Garze system. Granitoids intruding the Qiangtang block yield 200−230MaagesinthePamirsandincentralTibet.ThestratigraphyoftheeasternPshartareainthePamirsissimilartotheBangong−NujiangsuturezoneintheAmdoregionofeasterncentralTibet,butaTriassicoceanbasinsequenceispreservedinthePamirs.Arc−typegranitoidsthatintrudedintotheeasternPshartoceanic−basin−arcsequence(200-230 Ma ages in the Pamirs and in central Tibet. The stratigraphy of the eastern Pshart area in the Pamirs is similar to the Bangong-Nujiang suture zone in the Amdo region of eastern central Tibet, but a Triassic ocean basin sequence is preserved in the Pamirs. Arc-type granitoids that intruded into the eastern Pshart oceanic-basin-arc sequence (200−230MaagesinthePamirsandincentralTibet.ThestratigraphyoftheeasternPshartareainthePamirsissimilartotheBangong−NujiangsuturezoneintheAmdoregionofeasterncentralTibet,butaTriassicoceanbasinsequenceispreservedinthePamirs.Arc−typegranitoidsthatintrudedintotheeasternPshartoceanic−basin−arcsequence(190-160 Ma) and granitoids that cut the southern Qiangtang block ($170-160 Ma) constitute the Rushan-Pshart arc. Cretaceous plutons that intruded the central and southern Pamirs record a long-lasting magmatic history. Their zircons and those from late Miocene xenoliths show that the most distinct magmatic events were Cambro-Ordovician ($410-575 Ma), Triassic ($210-250 Ma; likely due to subduction along the Jinsha suture), Middle Jurassic ($147-195 Ma; subduction along Rushan-Pshart suture), and mainly Cretaceous. Middle and Late Cretaceous magmatism may reflect arc activity in Asia prior to the accretion of the Karakoram block and flat-slab subduction along the Shyok suture north of the Kohistan-Ladakh arc, respectively. Before India and Asia collided, the Pamir region from the Indus-Yarlung to the Jinsha suture was an Andean-style plate margin. Our analysis suggests a relatively simple crustal structure for the Pamirs and Tibet. From the Kunlun arc in the north to the southern Qiangtang block in the south the Pamirs and Tibet likely have a dominantly sedimentary crust, characterized by Karakul-Mazar-Songpan-Garze accretionary wedge rocks. The crust south of the southern Qiangtang block is likely of granodioritic composition, reflecting long-lived subduction, arc formation, and Cretaceous-Cenozoic underthrusting.

Magmatic history of central Myanmar and implications for the evolution of the Burma Terrane

Gondwana Research

High Resolution, Pb Isotope Variability Within Historic Eruptions of the Cumbre Vieja Volcano, La Palma, Canary Islands

The range of time-scales over which ocean island basalt (OIB) magmatism taps different mantle het... more The range of time-scales over which ocean island basalt (OIB) magmatism taps different mantle heterogeneities is a fundamental dynamic of mantle plumes. The variability of long-lived radiogenic isotopes in OIB magmas erupted on time scales less than 100 years has been addressed primarily for Hawaiian magmas (e.g., Pietruszka et al., 2001). Similar data are relatively sparse for hot spots with

Oxygen - Osmium Isotopic Compositions of West Maui Lavas and the Link to Oceanic Lithosphere

Biological Controls on Coral Sr/Ca and delta18O Reconstructions of Sea Surface Temperatures

Science, 1995

Geochemistry Of The Late Eocene Grays River Volcanics, Southwestern Washington And Northwestern Oregon; Evidence For A Slab Window In The Cascadia Forearc

Abstracts With Programs Geological Society of America, 2009

Geochemical Structure of the Plume Beneath Maui Nui, Hawaii

Evidence for Shallow-level Assimilation of the Submarine Volcanic Complex Underlying the NW Rift Zone of Tenerife, Canary Islands

Agu Fall Meeting Abstracts, Dec 1, 2005

Rapid change in strontium isotopic composition of sea-water be-fore the Cretaceous/Tertiary boundary

Nature, 1991

Selenium Biogeochemistry as a Planetary Deep-Time Redox Proxy

Selenium isotope biogeochemistry in combination with sulfur is introduced as a new tool to recons... more Selenium isotope biogeochemistry in combination with sulfur is introduced as a new tool to reconstruct redox changes in Earth's environments through time more precisely.

Spatial and Temporal Isotopic Gradients in the Western Canary Islands

The westernmost Canary Islands (La Gomera, La Palma and El Hierro) are erupted on Jurassic oceani... more The westernmost Canary Islands (La Gomera, La Palma and El Hierro) are erupted on Jurassic oceanic crust away from chemical influence by African continental crust or its sedimentary apron. These islands are in their shield-building or post-shield gap stage of growth, and expose thick volcanic sections that have excellent absolute age constraints. Although on a reconnaissance scale magmas from these

A Multi-Component Geochemical Study of Short-Term Melt and Volatile Evolution in the Kamchatka Volcanic Arc