Straddling the tholeiitic/calc-alkaline transition: the effects of modest amounts of water on magmatic differentiation at Newberry Volcano,Oregon     

Ben?E.?MandlerEmail author  Julie?M.?Donnelly-Nolan  Timothy?L.?Grove 《Contributions to Mineralogy and Petrology》2014,168(4):1066

Melting experiments have been performed at 1 bar (anhydrous) and 1- and 2-kbar H₂O-saturated conditions to study the effect of water on the differentiation of a basaltic andesite. The starting material was a mafic pumice from the compositionally zoned tuff deposited during the ~75 ka caldera-forming eruption of Newberry Volcano, a rear-arc volcanic center in the central Oregon Cascades. Pumices in the tuff of Newberry caldera (TNC) span a continuous silica range from 53 to 74 wt% and feature an unusually high-Na₂O content of 6.5 wt% at 67 wt% SiO₂. This wide range of magmatic compositions erupted in a single event makes the TNC an excellent natural laboratory in which to study the conditions of magmatic differentiation. Our experimental results and mineral–melt hygrometers/thermometers yield similar estimates of pre-eruptive H₂O contents and temperatures of the TNC liquids. The most primitive (mafic) basaltic andesites record a pre-eruptive H₂O content of 1.5 wt% and a liquidus temperature of 1,060–1,070 °C at upper crustal pressure. This modest H₂O content produces a distinctive fractionation trend that is much more enriched in Na, Fe, and Ti than the calc-alkaline trend typical of wetter arc magmas, but slightly less enriched in Fe and Ti than the tholeiitic trend of dry magmas. Modest H₂O contents might be expected at Newberry Volcano given its location in the Cascade rear arc, and the same fractionation trend is also observed in the rim andesites of the rear-arc Medicine Lake volcano in the southern Cascades. However, the Na–Fe–Ti enrichment characteristic of modest H₂O (1–2 wt%) is also observed to the west of Newberry in magmas erupted from the arc axis, such as the Shevlin Park Tuff and several lava flows from the Three Sisters. This shows that modest-H₂O magmas are being generated directly beneath the arc axis as well as in the rear arc. Because liquid lines of descent are particularly sensitive to water content in the range of 0–3 wt% H₂O, they provide a quantitative and reliable tool for precisely determining pre-eruptive H₂O content using major-element data from pumices or lava flows. Coupled enrichment in Na, Fe, and Ti relative to the calc-alkaline trend is a general feature of fractional crystallization in the presence of modest amounts of H₂O, which may be used to look for “damp” fractionation sequences elsewhere.  相似文献   

A two-stage fluid history for the Orocopia Schist and associated rocks related to flat subduction and exhumation,southeastern California     

Gregory J. Holk  Marty Grove  Carl E. Jacobson  Gordon B. Haxel 《International Geology Review》2017,59(5-6):639-663

ABSTRACT

Stable isotopes combined with pre-existing ⁴⁰Ar/³⁹Ar thermochronology at the Gavilan Hills and Orocopia Mountains in southeastern California record two stages of fluid–rock interaction: (1) Stage 1 is related to prograde metamorphism as Orocopia Schist was accreted to the base of the crust during late Cretaceous–early Cenozoic Laramide flat subduction. (2) Stage 2 affected the Orocopia Schist and is related to middle Cenozoic exhumation along detachment faults. There is no local evidence that schist-derived fluids infiltrated structurally overlying continental rocks. Mineral δ¹⁸O values from Orocopia Schist in the lower plate of the Chocolate Mountains fault and Gatuna normal fault in the Gavilan Hills are in equilibrium at 490–580°C with metamorphic water (δ¹⁸O = 7–11‰). Phengite and biotite δD values from the Orocopia Schist and upper plate suggest metamorphic fluids (δD ~ –40‰). In contrast, final exhumation of the schist along the Orocopia Mountains detachment fault (OMDF) in the Orocopia Mountains was associated with alteration of prograde biotite and amphibole to chlorite (T ~ 350–400°C) and the influx of meteoric-hydrothermal fluids at 24–20 Ma. Phengites from a thin mylonite zone at the top of the Orocopia Schist and alteration chlorites have the lowest fluid δD values, suggesting that these faults were an enhanced zone of meteoric fluid (δD < –70‰) circulation. Variable δD values in Orocopia Schist from structurally lower chlorite and biotite zones indicate a lesser degree of interaction with meteoric-hydrothermal fluids. High fluid δ¹⁸O values (6–12‰) indicate low water–rock ratios for the OMDF. A steep thermal gradient developed across the OMDF at the onset of middle Cenozoic slip likely drove a more vigorous hydrothermal system within the Orocopia Mountains relative to the equivalent age Gatuna fault in the Gavilan Hills.  相似文献   

The C₃₇ alkenone record of seawater temperature during seasonal thermocline stratification     

I. Bentaleb  J. O. Grimalt  F. Vidussi  J. -C. Marty  V. Martin  M. Denis  C. Hatt  M. Fontugne 《Marine Chemistry》1999,64(4):255

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WORLD ATLAS OF DESERTIFICATION, 2nd edition,edited by N. J. Middleton and D. S. G. Thomas,Arnold, London, 1997. No. of pages: x + 182. Price: £145.00 (hb). ISBN 0-340-69166-2.     

A. T. Grove 《地球表面变化过程与地形》1999,24(3):280-280

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Using 3D Printing to Create a Robust and Compact Peristaltic Field Pump: An Update to the Montana Drill Pump          下载免费PDF全文

Jordyn B. Miller  Marty D. Frisbee 《Ground Water Monitoring & Remediation》2018,38(3):75-78

The collection of water samples from springs, streams, and wells is a critical component of field hydrogeological studies. Fieldwork, especially in mountainous terrain, often involves hiking to remote springs and streams. It is logistically and physically difficult to carry bulky, heavy sampling equipment such as large peristaltic pumps with built‐in batteries in these areas. To address this problem, researchers at the University of Montana designed the Montana Drill Pump (MDP) roughly 30 years ago to provide a compact, low‐cost and portable option for sampling with a peristaltic pump in the backcountry (Woessner 2007 ). Although the MDP is popular, with the advent of 3D printing techniques, a more robust and precise fitting pump design can be inexpensively created that can be quickly assembled in the lab or field. This new pump design was tested on multiple backpacking sampling campaigns in the Panamint Mountains of southern California, Mount Hood in Oregon, and Glacier National Park in northern Montana during the summer of 2017. The design was proven to be easy to use and durable in the field and offers a rugged, updated, more precisely fitting option to the MDP.  相似文献