Deglacial pattern of circulation and marine productivity in the upwelling region off central-south Chile

A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36°S off central-south Chile (GeoB 7165-1, 36°33′S, 73°40′W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30°–41°S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling. Marine productivity augmented rather abruptly at 13–14 ka, well after the oceanographic changes. We suggest that the late deglacial increase in paleoproductivity off central-south Chile reflects the onset of an active upwelling system bringing nutrient-rich, oxygen-poor Equatorial Subsurface Water to the euphotic zone, and a relatively higher nutrient load of the Antarctic Circumpolar Current. During the Last Glacial Maximum, when the Southern Westerlies were located further north, productivity off central-south Chile, in contrast to off northern Chile, was reduced due to direct onshore-blowing winds that prevented coastal upwelling and export production.     

The role of governance in community adaptation to climate change

The capacity to adapt to challenges such as climate change can be seen as largely determined by socioeconomic context or social vulnerability. This article examines the adaptive capacity of local actors in response to globalization and climate change, asking: how much of the desirable adaptation can be undertaken at a local level, and how much is determined by actors at other levels, for instance, when resource conflicts occur? Drawing on case studies of fishing in northern Norway and north-west Russia, the paper shows that adaptive capacity beyond the immediate economic adaptations available to local actors is, to a considerable extent, politically determined within larger governance networks.     

Devonian F-rich peraluminous A-type magmatism in the proto-Andean foreland (Sierras Pampeanas,Argentina): geochemical constraints and petrogenesis from the western-central region of the Achala batholith

A new LA-ICP-MS crystallization age of 370?±?8 Ma is presented for monzogranite from the Achala batholith, the largest Devonian igneous body in the Sierras Pampeanas, confirming previous U-Pb zircon ages and indicating emplacement within a relatively short episode. Granitic rocks from the central area of the batholith display restricted high SiO₂ contents (69.8–74.5 wt.%). Major element plots show ferroan and alkaline-calcic to calc-alkaline compositions with an A-type signature. High concentrations of the high field-strength elements such as Y, Nb, Ga, Ta, U, Th, and flat REE patterns with significant negative Eu anomalies, are also typical of A-type granites. The aluminium saturation index (1.10–1.37) indicates aluminous parent magmas which are further characterised by high FeO/MgO ratios (2.6–3.3) and F contents of igneous biotites (0.9–1.5 wt%), as well as relatively high Al^IV (2.39–2.58 a.p.f.u.) in biotites and the occurrence of primary muscovite. Petrogenetic modelling supports a source enriched in plagioclase and progressive fractional crystallization of feldspar. The central area of the batholith displays small-scale bodies composed predominantly of biotite (80 %), muscovite (10 %) and apatite (10 %), yielding rock compositions with 2.3–5.4 wt. % P₂O₅, and 6–7 wt.% F, together with anomalous contents of U (88–1,866 ppm), Zr (1081–2,581 ppm), Nb (257–1,395 ppm) and ΣREE (1,443–4,492 ppm). Previous studies rule out an origin of these bodies as metasedimentary xenoliths and they have been interpreted as cumulates from the granitic magma. An alternative flow segregation process is discussed here.     

Cumulate and Cumulative Granites and Associated Rocks

Abstract. Processes that move crystals relative to melt, that is crystal fractionation, are of major importance in producing variations that are observed within cogenetic suites of granites. In low‐temperature granite suites, crystal fractionation initially involves the progressive separation of crystals residual from partial melting from that partial melt. Once separation of those crystals, or restite, has been completed, further fractionation may occur through the separation of crystals that had precipitated from the melt, the process known as fractional crystallization. High‐temperature granite magmas are largely or completely molten and elements such as Ca, Mg and Fe, and their associated minor elements, are in that case dissolved in the melt. Such magmas, particularly those that are more potassic and hence contain a higher fraction of low temperature melt, may evolve compositionally through fractional crystallization. Cumulate rocks result, comprising a framework of cumulus minerals with interstitial melt. In this process some of the melt is also displaced to form more felsic rocks. Such cumulate rocks may have distinctive chemical compositions, but that is often not the case. Distinctive features include SiC>2 contents near or below 50 % in rocks that are transitional in the field to more felsic granites, very high Cr and Ni, very low K, P, Ba, Rb and Zr, and anomalous abundances of the anorthite components Ca and Al. These rocks may also have positive Eu anomalies. Cumulate rocks do not necessarily have distinctive textures, at least as such features are understood at this time. Fractional crystallization can also involve the movement of precipitated crystals relative to melt. We refer to rocks as cumulative when formed from the fractions in which the abundance of crystals has increased. The production of cumulative granites typically occurs at more felsic melt compositions than is the case for cumulate granites, and this process may have its greatest significance in the fractional crystallization of the felsic haplogranites. Relative to felsic granites of broadly similar compositions lying on a liquid line of descent, cumulative granites contain more Ca, reflecting the addition from elsewhere of plagioclase crystals with solidus compositions. The abundances of Sr and Ba may be high to very high, and sometimes there are positive Eu anomalies. Cumulative I‐type granites may have low abundances of Y and the heavy REE, while the S‐type granites can be very distinctive with anomalously high abundances of Th and the heavy REE resulting from the concentrating of monazite. Generally, but not always, those who propose fractional crystallization as a mechanism for producing compositional variation within a suite of granites do not state whether the rocks in that particular case are thought to lie on a liquid line of descent or are cumulates/cumulative, although it is generally presumed that they were melts. Our experiences in eastern Australia have shown that the mechanism of fractional crystallization was quantitatively not as important during granite evolution as many workers would expect. However, there are some excellent examples of that process, most notably the Boggy Plain Supersuite. Overall in eastern Australia, varying degrees of separation of restite is a much more common mode of crystal fractionation, and that may also be seen to be the case for some other granite provinces if they are examined with that possibility in mind.     

菲律宾及其邻近地区的地磁场模型研究

根据2001~2007年期间在菲律宾境内测量的74个点的地磁场数据,利用球冠谐和、泰勒多项式两种方法建立了2005.0菲律宾及周边地区地磁基本场模型,得到了菲律宾地区X、Y、Z、D、I、H、F七个分量的分布.两种模型反映的同一地区的地磁场分布形态基本类似,只在拐点的舒缓度、等值线平滑度等方面存在区别.在8°N左右,X、H、F出现系统的拐点,同纬度的X、H、F东低西高.D、Y零线分布于8°N左右呈东西展布,北侧为负,南侧为正,等值线沿经度分布的同时,在纬度上有不同程度的小起伏.Z、I空间分布呈现更加规则均匀的东西向分布特征.零线分布在7.5°N左右,零线北部是正值区域,南部是负值区域.两种模型与IGRF的差值的分布形态有很大的不同,球冠谐模型与IGRF模型差值的正负异常区域呈现正负异常相间的分布特征,且各分量的正负异常最大值分布在低纬度地区.而泰勒多项式与IGRF差值的正负异常分布却相对完整.