TY - JOUR A1 - Lorenz, Melanie A1 - Altenberger, Uwe A1 - Trumbull, Robert B. A1 - Lira, Raul A1 - Lopez de Luchi, Monica Graciela A1 - Günter, Christina A1 - Eidner, Sascha T1 - Chemical and textural relations of britholite- and apatite-group minerals from hydrothermal REE mineralization at the Rodeo de los Molles deposit, Central Argentina JF - American mineralogist : an international journal of earth and planetary materials N2 - Britholite group minerals (REE,Ca)(5)[(Si,P)O-4](3)(OH,F) are widespread rare-earth minerals in alkaline rocks and their associated metasomatic zones, where they usually are minor accessory phases. An exception is the REE deposit Rodeo de los Molles, Central Argentina, where fluorbritholite-(Ce) (FBri) is the main carrier of REE and is closely intergrown with fluorapatite (FAp). These minerals reach an abundance of locally up to 75 modal% (FBri) and 20 modal% (FAp) in the vein mineralizations. The Rodeo de los Molles deposit is hosted by a fenitized monzogranite of the Middle Devonian Las Chacras-Potrerillos batholith. The REE mineralization consists of fluorbritholite-(Ce), britholite-(Ce), fluorapatite, allanite-(Ce), and REE fluorcarbonates, and is associated with hydrothermal fluorite, quartz, albite, zircon, and titanite. The REE assemblage takes two forms: irregular patchy shaped REE-rich composites and discrete cross-cutting veins. The irregular composites are more common, but here fluorbritholite-(Ce) is mostly replaced by REE carbonates. The vein mineralization has more abundant and better-preserved britholite phases. The majority of britholite grains at Rodeo de los Molles are hydrothermally altered, and alteration is strongly enhanced by metamictization, which is indicated by darkening of the mineral, loss of birefringence, porosity, and volume changes leading to polygonal cracks in and around altered grains. A detailed electron microprobe study of apatite-britholite minerals from Rodeo de los Molles revealed compositional variations in fluorapatite and fluorbritholite-(Ce) consistent with the coupled substitution of REE3+ + Si4+ = Ca2+ + P5+ and a compositional gap of similar to 4 apfu between the two phases, which we interpret as a miscibility gap. Micrometer-scale intergrowths of fluorapatite in fluorbritholite-(Ce) minerals and vice versa are chemically characterized here for the first time and interpreted as exsolution textures that formed during cooling below the proposed solvus. KW - Britholite KW - apatite KW - exsolution textures KW - miscibility gap KW - compositional gap KW - REE KW - fenite KW - alkaline granites KW - hydrothermal alteration Y1 - 2019 U6 - https://doi.org/10.2138/am-2019-6969 SN - 0003-004X SN - 1945-3027 VL - 104 IS - 12 SP - 1840 EP - 1850 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Anderson, Robert F. A1 - Hayes, Christopher T. A1 - McGee, David A1 - Machalett, Bjoern A1 - Ren, Haojia A1 - Straub, Susanne M. A1 - Gersonde, Rainer A1 - Haug, Gerald H. T1 - Eolian dust input to the Subarctic North Pacific JF - Earth & planetary science letters N2 - Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, He-4, Th-232 and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at similar to 4 mu m. Applying the Th-230-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1-2 g/m(2)/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2-4 g/m(2)/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45 degrees N and west of 165 degrees E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5-1 g/m(2)/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific. KW - eolian dust KW - Subarctic North Pacific KW - INOPEX KW - helium-4 KW - Th-232 KW - REE Y1 - 2014 U6 - https://doi.org/10.1016/j.epsl.2013.11.008 SN - 0012-821X SN - 1385-013X VL - 387 SP - 252 EP - 263 PB - Elsevier CY - Amsterdam ER -