Formation of sapphirine during retrogression of a basic high-pressure granulite,Roan, Western Gneiss Region,Norway

Sapphirine-bearing rocks occur in the northern part of the Western Gneiss Region, Vestranden, central Norway. The sapphirine-bearing rocks are characterized by a high MgO/(MgO + FeO) ratio, high Al₂O₃, MgO and CaO, and low SiO₂ contents. These rocks form layers within larger complexes which originated as layered magmatic rocks. High PT-metamorphism produced a cpx+ky+gt assemblage. The P and T estimates are P = 14.5±2 kbar and T= 870±50° C. During retrogression, the high-P granulite assemblage broke down to form an intermediate-P granulite mineralogy comprising orthopyroxene, spinel, anorthite, andesine, sapphirine and corundum. Textural relationships suggest that sapphirine formed by the reaction: spinel+kyanite sapphirine+corundum, and probably also by a reaction between corundum, spinel and orthopyroxene. All reactions took place within the stability field of kyanite. Textural and micro-chemical relationships indicate equilibrium, conditions during the peak metamorphism, whereas pronounced disequilibrium characterizes the mineral associations formed during the early retrogression at low P _H2O. The investigation shows that parts of the northern segment of the Western Gneiss Region underwent a metamorphic evolution similar to the Caledonian one recorded from eclogite/granulite terrains further south.     

New Insights into Crustal Contributions to Large-volume Rhyolite Generation in the Mid-Tertiary Sierra Madre Occidental Province, Mexico, Revealed by U Pb Geochronology

Voluminous (3·9 x 10⁵ km³), prolonged (18 Myr) explosivesilicic volcanism makes the mid-Tertiary Sierra Madre Occidentalprovince of Mexico one of the largest intact silicic volcanicprovinces known. Previous models have proposed an assimilation–fractionalcrystallization origin for the rhyolites involving closed-systemfractional crystallization from crustally contaminated andesiticparental magmas, with <20% crustal contributions. The lackof isotopic variation among the lower crustal xenoliths inferredto represent the crustal contaminants and coeval Sierra MadreOccidental rhyolite and basaltic andesite to andesite volcanicrocks has constrained interpretations for larger crustal contributions.Here, we use zircon age populations as probes to assess crustalinvolvement in Sierra Madre Occidental silicic magmatism. Laserablation-inductively coupled plasma-mass spectrometry analysesof zircons from rhyolitic ignimbrites from the northeasternand southwestern sectors of the province yield U–Pb agesthat show significant age discrepancies of 1–4 Myr comparedwith previously determined K/Ar and ⁴⁰Ar/³⁹Ar ages from thesame ignimbrites; the age differences are greater than the errorsattributable to analytical uncertainty. Zircon xenocrysts withnew overgrowths in the Late Eocene to earliest Oligocene rhyoliteignimbrites from the northeastern sector provide direct evidencefor some involvement of Proterozoic crustal materials, and,potentially more importantly, the derivation of zircon fromMesozoic and Eocene age, isotopically primitive, subduction-relatedigneous basement. The youngest rhyolitic ignimbrites from thesouthwestern sector show even stronger evidence for inheritancein the age spectra, but lack old inherited zircon (i.e. Eoceneor older). Instead, these Early Miocene ignimbrites are dominatedby antecrystic zircons, representing >33 to 100% of the datedpopulation; most antecrysts range in age between 20 and 32 Ma.A sub-population of the antecrystic zircons is chemically distinctin terms of their high U (>1000 ppm to 1·3 wt %) andheavy REE contents; these are not present in the Oligocene ignimbritesin the northeastern sector of the Sierra Madre Occidental. Thecombination of antecryst zircon U–Pb ages and chemistrysuggests that much of the zircon in the youngest rhyolites wasderived by remelting of partially molten to solidified igneousrocks formed during preceding phases of Sierra Madre Occidentalvolcanism. Strong Zr undersaturation, and estimations for veryrapid dissolution rates of entrained zircons, preclude coevalmafic magmas being parental to the rhyolite magmas by a processof lower crustal assimilation followed by closed-system crystalfractionation as interpreted in previous studies of the SierraMadre Occidental rhyolites. Mafic magmas were more probablyimportant in providing a long-lived heat and material flux intothe crust, resulting in the remelting and recycling of oldercrust and newly formed igneous materials related to Sierra MadreOccidental magmatism. KEY WORDS: ignimbrite; rhyolite; Sierra Madre Occidental; Tertiary; U–Pb geochronology; zircon; antecryst; crustal melting     

Multimillion year thermal history of a porphyry copper deposit: application of U–Pb, 40Ar/39Ar and (U–Th)/He chronometers, Bajo de la Alumbrera copper–gold deposit, Argentina

Application of multiple chronometers (including U–Pb and ⁴⁰Ar/³⁹Ar geochronology and zircon and apatite (U–Th)/He thermochronology) to porphyry intrusions at the Bajo de la Alumbrera porphyry copper–gold deposit, Argentina, reveals a complex history of reheating that spans millions of years. Previous U–Pb geochronology, combined with our new ⁴⁰Ar/³⁹Ar data, shows that the multiple porphyritic intrusions at Bajo de la Alumbrera were emplaced during two episodes, the first at about 8.0 Ma (P2 and associated porphyries) and the second about a million years later (Early and Late P3 porphyries). Complex overprinting alteration events have obscured the earliest hydrothermal history of the deposit. By contrast, ⁴⁰Ar/³⁹Ar data reveal the close temporal relationship of ore-bearing potassic alteration assemblages (7.12 ± 0.13 Ma; biotite) to the emplacement of the P3 intrusions. Consistent with low closure temperatures, younger ages have been determined for associated hydrothermal alkali feldspar (6.82 ± 0.05 Ma and 6.64 ± 0.09 Ma). The temperature-sensitive Ar data also record an unexpected prolonged cooling history (to below 200°C) extending to 5.9 Ma. Our data suggest that the Bajo de la Alumbrera system underwent protracted cooling, after the collapse of the main hydrothermal system, or that one or more low-temperature (~100–200°C) reheating events occurred after emplacement of the porphyritic intrusions at Bajo de la Alumbrera. These have been constrained in part by our new ⁴⁰Ar/³⁹Ar data (including multidomain diffusion modeling) and (U–Th)/He ages. Single-grain (U–Th)/He ages (n = 5) for phenocrystic zircon from P2 and P3 intrusive phases bracket these thermal events to between 6.9 (youngest crystallization of intrusion) and 5.1 Ma. Multidomain modeling of alkali feldspar data (from both igneous and hydrothermal crystals) is consistent with the deposit cooling rapidly from magmatic temperatures to below about 300°C, with a more protracted history down to 150°C. We conclude that the late-stage low-temperature (150 to 200°C) thermal anomaly localized at Bajo de la Alumbrera resulted from radiation of heat and/or fluids sourced from deeper-seated magma bodies, emplaced beneath the deposit. To produce the observed thermal longevity of the porphyry system, magma bodies underlying the Bajo de la Alumbrera deposit must have been repeatedly replenished by new magma batches. Without replenishment, crystallization of the source magma will occur, and heat release will stop, leading to rapid cooling (in less than ten thousand years). The influx of deep-seated magma may have caused the development of late low-temperature hydrothermal alteration assemblages at Bajo de la Alumbrera, at the same time that mineralization formed at Agua Rica, some 25 km away. All available chronologic data for the Bajo de la Alumbrera deposit suggest that the hydrothermal system was active episodically over at least a three-million and possibly up to a four-million-year period. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

God's healing leaves: The colonial quest for medicinal plants in the Torrid Zone

The colonial era witnessed a fevered quest for exotic medicinal plants by European physicians and scientists. This essay explores the geographical principles that oriented the search towards the lands and peoples of the humid tropics. Believing that God had planted botanical cures for diseases in their places of origin, medicinal plant collectors concentrated their efforts in the pestilential equatorial latitudes. Although many subscribed to the ancient Doctrine of Signatures, colonial bioprospectors discovered early that indigenous and diasporic peoples represented storehouses of plant knowledge. Assuming that native knowhow constituted more instinct than intelligence, Europeans employed coercion, bribes, torture, and promises of freedom to extract their ethnomedical secrets. In the case of especially lucrative healing plants, imperial and colonial entities conspired to pilfer and naturalize endemic species in their distant colonies. In response to this legacy of inappropriate exploitation of native peoples and tropical plants during the colonial era, most present day bioprospectors follow established codes of ethnobotanical ethics.     

Managing cropland and rangeland for climate mitigation: an expert elicitation on soil carbon in California

Understanding the magnitude of and uncertainty around soil carbon flux (SCF) is important in light of California’s efforts to increase SCF (from the atmosphere to soils) for climate change mitigation. SCF depends, to a great extent, on how soils are managed. Here, we summarize the results of an elicitation of soil science and carbon cycle experts aiming to characterize understanding of current SCF in California’s cropland and rangeland, and how it may respond to alternative management practices over time. We considered four cropland management practices—biochar, compost, cover crops, and no-till—and two rangeland management practices, compost and high-impact grazing. Results across all management practices reveal underlying uncertainties as well as very modest opportunities for soil carbon management to contribute meaningfully to California’s climate mitigation. Under median scenarios, experts expect all the surveyed management practices to reverse SCF from negative to positive, with direct carbon additions via biochar and compost offering the best potential for boosting the soil carbon pool.     

The role of social capital for farmers’ climate change adaptation in Lancang River basin in China

This paper distinguishes between bridging and bonding social capital to assess their roles for individual farmers’ adaptation strategies taken through technology adoption. Based on primary data collected in Langcang River (LCR) basin area in southwestern China, the paper finds: (1) adaptation measures have been widely taken by surveyed households, but non-infrastructure-based measures are more prevalent than infrastructure-based measures and (2) surveyed households have strong social capital while having weak bridging social capital. Their bonding social capital has significantly positive relationship with their adaptation decisions, but bridging social capital does not have such statistically significant relationship. It recommends that the governments contemplate carefully how to help the poor to get a good combination of bonding and bridging social capital when designing policies to help the rural poor to improve their long-term adaptive capacity and achieve sustainable rural development.     

Study of Stratus-Lowering Marine-Fog Events Observed During C-FOG

Boundary-Layer Meteorology - Two stratus-lowering marine fog events observed on 28 September and 4 October 2018 during the Coastal Fog (C-Fog) field campaign that took place offshore of eastern...     

Factors controlling stratal pattern and facies distribution of fluvio‐lacustrine sedimentation in the Sivas mini‐basins,Oligocene (Turkey)

The Sivas Basin, located in the Central Anatolian Plateau of Turkey, is a foreland basin that records a complex interaction between sedimentation, salt tectonics and regional shortening during the Oligo‐Miocene leading to the formation of numerous mini‐basins. The Oligocene sedimentary infill of the mini‐basins consists of a thick continental succession, the Karayün Formation, comprising a vertical succession of three main sub‐environments: (i) playa‐lake, (ii) fluvial braided, and (iii) saline lacustrine. These sub‐environments are seen as forming a large Distributive Fluvial System (DFS) modified through time as a function of sediment supply and accommodation related to regional changes in climate and tectonic regime. Within neighbouring mini‐basins and despite a similar vertical stratigraphic succession, subtle variations in facies assemblages and thickness are observed in stratigraphic units of equivalent age, thus demonstrating the local control exerted by halokinesis. Stratigraphic and stratal patterns reveal in great detail the complex interaction between salt tectonics and sedimentation including different types of halokinetic structures such as hooks, wedges and halokinetic folds. The regional variations of accommodation/sediment supply led to coeval changes in the architectural patterns recorded in the mini‐basins. The type of accommodation regime produces several changes in the sedimentary record: (i) a regime dominated by regional accommodation limits the impact of halokinesis, which is recorded as very small variations in stratigraphic thickness and facies distribution within and between mini‐basins; (ii) a regime dominated by localized salt‐induced accommodation linked to the subsidence of each individual mini‐basin enhances the facies heterogeneity within the DFS, causing sharp changes in stratigraphic thickness and facies assemblages within and between mini‐basins.     

Managed Temporary Labour Migration of Pacific Islanders to Australia and New Zealand in the Early Twenty-first Century

ABSTRACT

Circular migration was one of several enduring themes in Graeme Hugo’s highly productive research career. Although his specialist field was Asian population movement, during the 2000s he became increasingly interested in labour migration in the Pacific Islands. This paper reviews the development of two managed circular migration schemes targeting Pacific labour that emerged following the UN High-level Dialogue on International Migration and Development in 2006. New Zealand’s Recognised Seasonal Employer (RSE) scheme and Australia’s Seasonal Worker Program (SWP) have attracted international attention as the kind of ‘best practice’ temporary labour migration schemes that Hugo had in mind when he emphasised the positive contributions that circular forms of mobility could make to development in both source and destination countries. The two schemes have transformed mobility between the participating countries and have played a major role in the negotiations over a free-trade agreement between Pacific Forum countries, including Australia and New Zealand. Although the schemes have been in operation for almost 10 years, this paper argues that they are not becoming ‘business as usual’; they embody complex systems of relationships between multiple stakeholders that require ongoing management to ensure that they do not become traps for low-skilled, low-paid ‘permanent’ temporary workers.     

渤海湾与莱州湾西部毛虾定置网渔获物组成的初步分析

渤海湾与莱州湾西部,定置网的主要渔获物种类,挂子网50余种,樯张网40余种。主要捕捞对象是毛虾,其他种类大多都在2％以下。其中占0.1％以上的经济幼鱼、幼虾有鳓、青鳞、斑鰶、黄鲫、鲻、梭鱼、鲈、梅童鱼、小黄鱼、黄姑鱼、银鲳、半滑舌鳎和幼对虾等。毛虾等经济虾类和经济鱼类的主要出现时间,挂子网为7月11日—8月20日;樯张网为7月6日—8月25日。夏一世代毛虾产卵群体的主要死亡时间在8月中、下旬。经济幼鱼和幼对虾,挂子网从6月21日,樯张网从5月21日开始逐日增多,至8月20日以后出现的数量都很少。为合理利用毛虾资源,保护经济幼鱼、幼虾资源,根据调查结果并参看毛虾生殖期等有关文献资料,建议这两个海区的毛虾生产期,春汛挂子网应于6月20日,樯张网于5月20日结束,秋汛应于8月21日开捕为宜。禁渔期,挂子网应由原来的7月1日—8月31日调整为6月21日—8月20日;樯张网由原来的6月10日—8月31日调整为5月21日—8月20日较为合理。