Geochemistry and Intrusive History of the Ashland Pluton, Klamath Mountains, California and Oregon

The Ashland pluton is a calc-alkaline plutonic complex thatintruded the western Paleozoic and Triassic belt of the KlamathMountains in late Middle Jurassic time. The pluton comprisesa series of compositionally distinct magma pulses. The oldestrocks are hornblende gabbro and two-pyroxene quartz gabbro withinitial ⁸⁷Sr/⁸⁶Sr = 0{dot}7044, ¹⁸O = 8{dot}7%, and REE patternswith chondrite normalized La/Lu = 7. These units were followedby a suite of tonalitic rocks (La_N/Lu_N = 7) and then by a suiteof K₂O- and P₂O₅ rocks of quartz monzodioritic affinity (La_N/Lu_N= 13–21; La_N/Sm_N = 2{dot}4–3{dot}) The quartz monzodioriticrocks were then intruded by biotite granodiorite and granitewith lower REE abundances but more fractionated LREE(La_N/Lu_N= 13–19; La_N/Sm_N = 4{dot}3–6 and they, in turn,were host to dikes and bosses of hornblende diorite. The latestintrusive activity consisted of aplitic and granitic dikes.Combined phase equilibria and mineral composition data, indicateemplacement conditions of approximately P_total = 2{dot}3kb,P_H2O between 1{dot}5 and 2{dot}2 kb, and f_O2 between the nickel-nickeloxide and hematite-magnetite buffers. Successive pulses of magma display increasing SiO₂ togetherwith increasing ¹⁸O and decreasing initial ⁸⁷Sr/⁸⁶Sr. The isotopicdata are consistent with either (1) combined fractional crystallizationof andesitic magma and concurrent assimilation of crustal materialcharacterized by low Sr₁ and high (¹⁸O or, more probably, (2)a series of partial melting events in which sources were successivelyless radiogenic but richer in ¹⁸O Each intrusive stage displaysevidence for some degree of crystal accumulation and/or fractionalcrystallization but neither process adequately accounts fortheir compositional differences. Consequently, each stage appearsto represent a distinct partial melting or assimilation event. The P₂O₅-rich nature of the quartz monzodiorite suite suggestsaccumulation of apatite. However, the suite contains abundantmafic microgranitoid enclaves and most apatite in the suiteis acicular. These observations suggest that magma mixing affectedthe compositional variation of the quartz monzodiorite suite.Mass balance calculations are consistent with a simple mixingprocess in which P₂O₅-rich alkalic basalt magma (representedby the mafic microgranitoid enclaves) was combined with a crystal-poorfelsic magma (represented by the tonalite suite), yielding aquartz monzodioritic magma that then underwent differentiationby crystal fractionation and accumulation.     

Stability relations of Mn–Fe–Al piemontite

Abstract Comparison of the stability relations of Fe-piemontite, Pm₁₇Ps₁₇Cz₆₆ (Ca₂Al₂Mn_0.5 Fe_0.5Si₃O₁₂(OH)), with similar experimentally determined results on Pm₃₃Cz₆₇ suggests that, at moderate f_o2, addition of Fe to piemontite raises its thermal stability and slightly decreases its sensitivity to oxygen fugacity. Reversal study of the reaction: Fe-piemontite + quartz = garnet (Gr₃₃Sp₂₇And₄₀) + anorthite + fluid at P_fluid= 2 kbar in cold-seal apparatus using solid oxygen buffers was completed. The data indicated breakdown of Pm₁₇Ps₁₇Cz₆₆ at 645°± 10° C along the Cu₂O–CuO buffer, 477°± 10° C along the Cu–Cu₂O buffer, and 365°± 10° C for the hematite-magnetite buffer. Mn-free clinozoisite and epidote have been shown to be stable to much higher temperatures than piemontite at moderate f_o2 (< Cu–Cu₂O). At very high f_o2, however, the presence of Mn⁺³ in a distorted octahedral site may permit persistence of piemontite to higher temperatures than Mn-poor epidote minerals. The compositional range of natural Fe–Mn–Al piemontites supports these results. Cation partitioning from piemontite-bearing parageneses also indicates crystallization at high f_o2, but application of the cited results should be made with caution. Synthetic phases were too fine-grained for optical or microprobe analysis, and reaction was often incomplete. The assumption that all Fe + Mn was contained in piemontite and garnet, respectively, in the low- and high-temperature assemblages is supported by the cell dimensions for these synthetic minerals, which are close to predicted values. The reaction is pseudo-univariant, as solid solution in garnet and piemontite would be f_o2-dependent in a more complex chemical system. Although bulk rock and fluid compositions may also have a marked effect on the stability of natural epidote–piemontite, f_o2 is the major control on Fe : Mn : Al in epidote minerals.     

INTERSTITIAL STORIES: THE PLACES BETWEEN THEORY AND LURKING

Editors' note: Larry Ford, who taught geography at San Diego State University from 1971 to 2009, was to deliver a version of this essay at the Association of Pacific Coast Geographers Annual Meeting in San Diego, California, 30 September–3 October 2009, but he passed away on 17 September 2009. To honor Larry, Richard Fusch, a professor of geography at Ohio Wesleyan University, read his deceased colleague's paper at that meeting. Prior to the meeting and subsequent to it, Janice Ford, Larry's wife, and Dr. Fusch edited the paper for submission to the Geographical Review, the journal in which Larry had published most frequently and for which he had a great deal of respect. This is that edited version.     

ETHNIC NEIGHBORHOODS AND URBAN REVITALIZATION: CAN EUROPE USE THE AMERICAN MODEL?

ABSTRACT. Ethnic neighborhoods have long been used to facilitate urban revitalization in older, inner‐city neighborhoods in American cities, but this strategy is much less common in European cities. This is especially surprising because immigrants make up a significant percentage of the population in a large number of those cities. This article explores the role that a largely invented Little Italy has played in revitalizing a section of downtown San Diego in contrast to the difficulty of creating such districts in European cities. The question posed here is, Will this contrast in approaches and outcomes remain indefinitely, or will the use of ethnically themed revitalization strategies become more alike as globalization and the expansion of the European Union serve to lessen historic ethnic tensions and increase the number of distinctive immigrant districts in Europe?     

Architecture and sedimentology of the Kerinitis Gilbert‐type fan delta,Corinth Rift,Greece

The Kerinitis Delta in the Corinth Rift, Greece, is a footwall derived, coarse‐grained, Gilbert‐type fan delta deposited in the hangingwall of a linked normal fault system. This giant Gilbert‐type delta (radius 3·8 km, thickness > 600 m) was supplied by an antecedent river and built into a brackish to marine basin. Although as yet poorly dated, correlation with neighbouring deltas suggests that the Kerinitis Delta was deposited during a period of 500 to 800 ka in the Early to early Middle Pleistocene. Facies characterizing a range of depositional processes are assigned to four facies associations (topset, foreset, bottomset and prodelta). The dominantly fluvial topset facies association has locally developed shallow marine (limestone) and fluvial‐shoreface sub‐associations. This delta represents a subsidence‐dominated system in which high fault displacement overwhelmed base‐level falls (creation of accommodation predominantly ≥ 0). Stratal geometries and facies stacking patterns were used to identify 11 key stratal surfaces separating 11 stratal units. Each key stratal surface records a landward shift in the topset breakpoint path, indicating a rapid increase in accommodation/sediment supply. Each stratal unit records a gradual decrease in accommodation/sediment supply during deposition. The cyclic stratal units and key stratal surfaces are interpreted as recording eustatic falls and rises, respectively. A 30 m thick package of foresets below the main delta records the nucleation of a small Proto‐delta probably on an early relay ramp. Based on changes in stratal unit geometries, the main delta is divided into three packages, interpreted as recording the initiation, growth and death of the controlling fault system. The Lower delta comprises stacked, relatively thin, progradational stratal units recording low displacement on the young fault system (relay ramp). The Middle delta comprises vertically stacked stratal units, each recording initial aggradation–progradation followed by progradation; their aggradational component increases up through the Middle delta, which records the main phase of increasing rate of fault displacement. The Upper delta records pure progradation, recording abrupt cessation of movement on the fault. A major erosion surface incising basinward 120 m through the Lower and Middle delta records an exceptional submarine erosion process (canyon or delta collapse).     

How Accurate are Disaster Loss Data? The Case of U.S. Flood Damage

Policy makers need accurate disaster loss data for decisions about disaster assistance, policy evaluation, and scientific research priorities. But loss estimation is difficult in a disaster situation, and initial loss estimates are seldom evaluated in comparison with actual costs. This paper uses the example of historical flood damage data in the U.S. to evaluate disaster loss data. It evaluates the accuracy of historical flood damage estimates from two federal agencies. The U.S. National Weather Service (NWS) has compiled annual flood loss estimates for each state since 1955. Comparison of the NWS data with similar estimates from five state emergency management agencies reveals substantial disagreement between estimates from different sources. The Federal Emergency Management Agency (FEMA) began in the 1990s to systematically collect damage estimates and cost data associated with its disaster assistance programs. Comparison of early damage estimates with actual expenditures in a California flood disaster reveals large errors in some estimates for individual counties, but no statistically significant tendency to underestimate or overestimate. Positive and negative errors tend to average out and the total damage estimate for the state approximates the final expenditures. Both comparisons indicate that damage estimates for small events or local jurisdictions often are extremely inaccurate. On the other hand, estimates aggregated over large areas or long time periods appear to be reasonably reliable; that is, this study finds that independent estimates for events with losses greater than $500 million disagree by less than 40. The paper suggests ways of interpreting and using such loss estimates to reduce the likelihood of misinterpretation.The National Center for Atmospheric Research is sponsored by the National Science Foundation.