Transition from eclogite to amphibolite-facies metamorphism in the Austroalpine Ulten Zone

Summary The Ulten Zone of the Austroalpine crystalline basement south-west of Meran (Italy) contains metapelitic schists and granoblastic paragneisses, leucocratic orthogneisses, migmatites (in both gneiss-lithologies), metabasites and ultramafic lenses. Metamorphic textures of the metapelitic schists and granoblastic paragneisses indicate two different metamorphic events, characterized by two mineral assemblages, which differ in mineral chemistry: (1) an eclogite facies mineral assemblage (M1) comprising Grt-Ky I-Bt. Ms-Kfs-PI-Qtz-Rt, and (2) an amphibolite facies mineral assemblage (M2) comprising Grt-KyII-Bt-Ms-PI-Qtz-Ilm±St. For the M1 event, pressures of at least 15kbar and temperatures of about 700°±50°C can be estimated. The later amphibolite facies overprint occurred at pressures of 6 to 8kbar and about 600°±50°C. The M1 and M2 assemblages belong to a continuous clockwise metamorphic evolution during the Variscan orogeny. Evidence for Alpine metamorphism can only be detected by sericite rims around kyanite and reset biotite ages. The migmatites, which contribute about 15–30vol.% of all rocks in the investigated area, were formed on the prograde path during the M1 event. Dissolution of H₂O in the melted part of the migmatites resulted in a CO₂dominated fluid, which was trapped in primary kyanite (M1) fluid inclusions. Secondary H₂O-rich fluid inclusions are found in quartz grains and may represent the fluid which enabled a pervasive equilibration during M2.

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Übergang von eklogit-zu amphibolitfazieller Matamorphose in der austroalpinen Ultenzone

Zusammenfassung Die Ulten Zone, ein Teil des ostalpinen kristallinen basements, südwestlich von Meran, wird aus Metapeliten and granoblastischen Paragneisen, leukokraten Orthogneisen, Migmatiten (in beiden Lithologien), Metabasiten and ultramafischen Linsen aufgebaut. Metamorphe Texturen der Metapelite und granoblastischen Paragneise lassen auf zwei verschiedene metamorphe Ereignisse schließen, die durch unterschiedliche Mineral-chemismen und Paragenesen charakterisiert sind: (1) eine eklogitfazielle Paragenese (M1), bestehend aus Grt-KyI-Bt-Ms-Kfs-P1-Qtz-Rt und (2) eine amphibolitfazielle Paragenese (M2), bestehend aus Grt-KyII-Bt-Ms-P1-Qtz-Ilm±St. Für M1 konnten Minimaldrucke von 15kbar und Temperaturen von 700°±50°C abgeleitet werden. Die spätere amphibolitfazielle Überprägung fand bei 6 bis 8kbar und 600°±50°C statt. M1 und M2 gehören einer kontinuierlichen Metamorphoseentwicklung während der variszischen Orogenese an.Die Migmatite, ungefähr 15–30vol.% der Gesteine im untersuchten Gebiet, wurden am prograden Pfad während des M1 Ereignisses gebildet. Aufgrund der höheren Löslichkeit von H₂0 in der Schmelze, blieb ein CO₂, reiches Fluid zurück, das im primären Kyanit (M1) eingeschlossen wurde. Wässrige Flüssigkeitseinschlüsse können in Quarzkörnern gefunden werden. Dieses Fluid ist wahrscheinlich für die Reequilibrierung zu amphibolitfaziellen Bedingungen verantwortlich.

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With 5 Figures     

基于波动方程的广义屏叠前深度偏移

地震波传播算子的计算效率和精度是制约三维叠前深度偏移的关键因素. 广义屏传播算子(GSP, Generalized Screen Propagator)是一种在双域中实现的广角单程波传播算子. 这一方法略去了在非均匀体之间发生的交混回响,但它可以正确处理包括聚焦、衍射、折射和干涉在内的各种多次前向散射现象. 通过背景速度下的相移和扰动速度下的陡倾角校正,广义屏算子能够适应地层速度的强烈横向变化. 这种算子可以直接应用于炮集叠前偏移,通过将广义屏算子作用于双平方根方程,还可以获得一种高效率、高精度的炮检距域叠前深度偏移方法,用于二维共炮检距道集和三维共方位角道集的深度域成像. 本文首先简述了炮检距域广义屏传播算子的理论,进而讨论了共照射角成像(CAI, Common Angle Imaging)条件,由此给出各个不同照射角(炮检距射线参数)下的成像结果,进而得到共照射角像集. 由于照射角和炮检距的对应关系,共照射角像集又为偏移速度分析和AVO(振幅随炮检距变化)分析等提供了有力工具.     

Metamorphic petrology and zircon geochronology of high-grade rocks from the central Mozambique Belt of Tanzania: crustal recycling of Archean and Palaeoproterozoic material during the Pan-African orogeny

New data on the metamorphic petrology and zircon geochronology of high‐grade rocks in the central Mozambique Belt (MB) of Tanzania show that this part of the orogen consists of Archean and Palaeoproterozoic material that was structurally reworked during the Pan‐African event. The metamorphic rocks are characterized by a clockwise P–T path, followed by strong decompression, and the time of peak granulite facies metamorphism is similar to other granulite terranes in Tanzania. The predominant rock types are mafic to intermediate granulites, migmatites, granitoid orthogneisses and kyanite/sillimanite‐bearing metapelites. The meta‐granitoid rocks are of calc‐alkaline composition, range in age from late Archean to Neoproterozoic, and their protoliths were probably derived from magmatic arcs during collisional processes. Mafic to intermediate granulites consist of the mineral assemblage garnet–clinopyroxene–plagioclase–quartz–biotite–amphibole ± K‐feldspar ± orthopyroxene ± oxides. Metapelites are composed of garnet‐biotite‐plagioclase ± K‐feldspar ± kyanite/sillimanite ± oxides. Estimated values for peak granulite facies metamorphism are 12–13 kbar and 750–800 °C. Pressures of 5–8 kbar and temperatures of 550–700 °C characterize subsequent retrogression to amphibolite facies conditions. Evidence for a clockwise P–T path is provided by late growth of sillimanite after kyanite in metapelites. Zircon ages indicate that most of the central part of the MB in Tanzania consists of reworked ancient crust as shown by Archean (c. 2970–2500 Ma) and Palaeoproterozoic (c. 2124–1837 Ma) protolith ages. Metamorphic zircon from metapelites and granitoid orthogneisses yielded ages of c. 640 Ma which are considered to date peak regional granulite facies metamorphism during the Pan‐African orogenic event. However, the available zircon ages for the entire MB in East Africa and Madagascar also document that peak metamorphic conditions were reached at different times in different places. Large parts of the MB in central Tanzania consist of Archean and Palaeoproterozoic material that was reworked during the Pan‐African event and that may have been part of the Tanzania Craton and Usagaran domain farther to the west.     

In situ sampling reveals rapid uptake and depuration of polycyclic aromatic hydrocarbons by surf clams (Paphies subtriangulata) affected by the Rena oil spill

ABSTRACT

To investigate the uptake and depuration of polycyclic aromatic hydrocarbons associated with the Rena oil spill we sampled the surf clam Paphies subtriangulata at two open coast locations (6?km apart) just prior to oil coming ashore (7 October 2011), then at 1–3 week intervals for the next 4 months. Total polycyclic aromatic hydrocarbons (tPAH) increased at both sites from 1 to 96–124?µg?kg^?1 (wet weight) by 18 October before declining to low levels (<4?µg?kg^?1) by February 2012. Ongoing sampling throughout 2012–2014 included three additional sites to the north east (up to 30?km away) and a site 5?km to the south east revealing tPAH levels generally <10?µg?kg^?1 except in October 2013 where levels ranged between 39–45?µg?kg^?1 at all sites. A comparison of PAH component profiles with oil-contaminated beach sediment indicated that the high levels observed in surf clams between October–December 2011 were clearly associated with the Rena spill. However, the October 2013 peak had a PAH profile inconsistent with weathered Rena oil, suggesting an alternative source of contamination. Our results highlight the potential for P. subtriangulata as a PAH monitoring tool but recognise more study is needed to better quantify baseline levels and uptake and depuration dynamics.     

Back to the future: reflections and directions of South African marine bioinvasion research

Biological invasions continue to increase around the world, with impacts on many coastal marine systems. Here we review the South African marine invasion literature which, despite the field being relatively new, has grown to have significant presence in both the local and international arenas. Of the 79 papers reviewed, 70% focused on the establishment and spread of alien species, with modes of transport and introduction largely overlooked. An emphasis was also apparent towards field studies, in particular survey work, with few experimental studies. The overwhelming majority of papers focused on a single species, the Mediterranean mussel Mytilus galloprovincialis, reflecting the scale of this invasion and the tractable nature of rocky shores as study systems. With the exception of this one species, the impacts of marine alien species have rarely been quantified. We suggest that future research extends the taxonomic coverage of present work and develops a better understanding of the mechanisms of introduction, establishment and spread of marine alien species. Through an experimental approach, the drivers of altered ecological patterns and processes resulting from invasions should be addressed, providing insight into associated impacts. This approach will maintain the local applicability and international relevance of South African marine invasion research.     

A Maunder Minimum Scenario Based on Cross-Hemispheric Coupling and Intermittency

A novel scenario for Maunder minimum-like grand minima epochs of reduced solar activity is proposed, based on diffusive coupling between both solar hemispheres, each susceptible to stochastically-driven intermittent behavior. After introducing cross-hemispheric coupling into a well-validated reduced model of the solar cycle based on the Babcock–Leighton mechanism for poloidal field regeneration, simulations are presented demonstrating that even weak coupling can lead to a high degree of synchronicity between the two hemispheres. This is in qualitative agreement with the similar onset and recovery times of sunspot activity at and around the Maunder minimum. Moreover, even weak coupling manages to greatly reduce the frequency and duration of quiescent episodes, again in qualitative agreement with the relative paucity of grand minima in the sunspot and radioisotope records.     

Neoproterozoic calc‐alkaline peraluminous granitoids of the Deleihimmi pluton,Central Eastern Desert,Egypt: implications for transition from late‐ to post‐collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield

The widely distributed late‐collisional calc‐alkaline granitoids in the northern Arabian–Nubian Shield (ANS) have a geodynamic interest as they represent significant addition of material into the ANS juvenile crust in a short time interval (∼630–590 Ma). The Deleihimmi granitoids in the Egyptian Central Eastern Desert are, therefore, particularly interesting since they form a multiphase pluton composed largely of late‐collisional biotite granitoids enclosing granodiorite microgranular enclaves and intruded by leuco‐ and muscovite granites. Geochemically, different granitoid phases share some features and distinctly vary in others. They display slightly peraluminous (ASI = 1–1.16), non‐alkaline (calc‐alkaline and highly fractionated calc‐alkaline), I‐type affinities. Both biotite granitoids and leucogranites show similar rare earth element (REE) patterns [(La/Lu)_N = 3.04–2.92 and 1.9–1.14; Eu/Eu* = 0.26–0.19 and 0.11–0.08, respectively) and related most likely by closed system crystal fractionation of a common parent. On the other hand, the late phase muscovite granites have distinctive geochemical features typical of rare‐metal granites. They are remarkably depleted in Sr and Ba (4–35 and 13–18 ppm, respectively), and enriched in Rb (381–473 ppm) and many rare metals. Moreover, their REE patterns show a tetrad effect (TE_1,3 = 1.13 and 1.29) and pronounced negative Eu anomalies (Eu/Eu* = 0.07 and 0.08), implying extensive open system fractionation via fluid–rock interaction during the magmatic stage. Origin of the calc‐alkaline granitoids by high degree of partial melting of mafic lower crust with subsequent crystal fractionation is advocated. The broad distribution of late‐collisional calc‐alkaline granitoids in the northern ANS is related most likely to large areal and intensive lithospheric delamination subsequent to slab break‐off and crustal/mantle thickening. Such delamination caused both crustal uplift and partial melting of the remaining mantle lithosphere in response to asthenospheric uprise. The melts produced underplate the lower crust to promote its melting. The presence of microgranular enclaves, resulting from mingling of mantle‐derived mafic magma with felsic crustal‐derived liquid, favours this process. The derivation of the late‐phase rare‐metal granites by open system fractionation via fluid interaction is almost related to the onset of extension above the rising asthenosphere that results in mantle degassing during the switch to post‐collisional stage. Consequently, the switch from late‐ to post‐collisional stage of crustal evolution in the northern ANS could be potentially significant not only geodynamically but also economically. Copyright © 2011 John Wiley & Sons, Ltd.     

钢管混凝土柱带钢板耗能键组合剪力墙抗震研究

提出了连排钢管混凝土柱带钢板耗能键组合剪力墙,它由钢管混凝土连排柱、柱间钢板耗能键、钢板耗能键外包混凝土条带三种单元组合而成。进行了4个不同设计参数试件的低周反复荷载试验研究。分析了各试件的承载力、刚度及其退化过程、滞回特性、延性和破坏特征,探讨了分灾耗能机制。研究表明:连排钢管混凝土柱带钢板耗能键组合剪力墙,承载力较大,后期刚度较稳定;混凝土条带在开裂与闭合过程中消耗地震能量,钢板耗能键通过弯剪变形消耗地震能量,钢管与混凝土条带共同工作协同耗能,具有良好的抗震耗能机制;这种新型组合剪力墙具有较强综合抗震耗能能力。