Blueschist‐facies metapelites from the Malpica–Tui Unit (NW Iberian Massif): phase equilibria modelling and H2O and Fe2O3 influence in high‐pressure assemblages     

A. LÓPEZ‐CARMONA  P. PITRA  J. ABATI 《Journal of Metamorphic Geology》2013,31(3):263-280

The Malpica–Tui Unit (Galicia, NW Spain) records eclogite‐ and blueschist‐facies metamorphism during the onset of the Variscan orogeny in Europe. Petrological analysis involving pseudosections calculated using thermocalc shows that the Upper Sheet of this unit, the Ceán Schists, recorded a three‐stage metamorphic evolution involving (i) Early subduction‐related medium‐pressure/low‐temperature metamorphism (M₁) constrained at ～350–380 °C, 12–14 kbar, which is only recorded in the basal part (lower metapelites, LM) of the Ceán Schists. (ii) Subduction‐related blueschist facies prograde metamorphism (M₂) going from ～19 kbar, 420 °C to 21 kbar, 460 °C in the LM, and from 16 kbar 430 °C to 21–22 kbar, 520 °C in the structurally upper metapelites (UM). (iii) Exhumation‐related metamorphism (M₃) is characterized by a decompression to 8–10 kbar, 470–490 °C in the LM. This decompression is also recorded in the UM, but it was not possible to estimate precise P–T conditions. The calculations indicate that (i) the prograde evolution in subduction zones may occur in fluid‐undersaturated conditions due to the crystallization of lawsonite, even in metapelitic rocks. This significantly influences phase equilibria and hence the P–T estimates. (ii) The proportion of ferric iron also has a strong influence on phase equilibria, even in metapelites. However, the analysed values of Fe₂O₃ may not reflect the oxidation state during the main metamorphic evolution and are probably easily modified by superficial alteration even in apparently fresh samples. The use of P–T–X(Fe₂O₃) pseudosections together with petrographic observations is then necessary to estimate the real oxidation state of the rocks and correctly evaluate the P–T conditions.  相似文献   

Late Pleistocene to Holocene palaeoenvironmental variability in the north‐west Spanish mountains: insights from a source‐to‐sink environmental magnetic study of Lake Sanabria          下载免费PDF全文

VIOLETA BORRUEL‐ABADÍA  MIRIAM GÓMEZ‐PACCARD  JUAN C. LARRASOAÑA  MAYTE RICO  BLAS VALERO‐GARCÉS  ANA MORENO  MARGARITA JAMBRINA‐ENRÍQUEZ  RUTH SOTO 《第四纪科学杂志》2015,30(3):222-234

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Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake Mývatn,Iceland     

Árni Einarsson  Hlynur Óskarsson  Haflidi Haflidason 《Journal of Paleolimnology》1993,8(1):15-26

Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake Mývatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation.Two periods of relatively high concentrations of myxoxanthophyll coincided with relatively frequent deposition of tephra (volcanic ash) but did neither conform with tectonic activity which might have changed the water level nor the available climatic record. Sediment depth, tephra content and percent undegraded chlorophyll (an indicator of pigment preservation) together could explain 56.7% of the variation in myxoxanthophyll. It is hypothesized that temporary increases in myxoxanthophyll resulted from periodic nutrient enrichment by fresh tephra deposited in the watershed or because tephra increased the erosion of organic soil in the water catchment area.Fluctuations in Cladophora show an inverse relationship with myxoxanthophyll in the uppermost 4 m of the core, and may result from a shading effect of planktonic Cyanobacteria on the phytobenthos or competition for nutrients released by the bottom sediments.  相似文献   

Driftwood as an indicator of relative changes in the influx of Arctic and Atlantic water into the coastal areas of Svalbard     

ÓLAFUR EGGERTSSON 《Polar research》1994,13(2):209-218

A total of 276 driftwood samples from Wijdefjorden on the northern coast of Spitsbergen were den-drochronologically analysed and compared with results from a similar study on driftwood from Isfjorden. The composition and origin of the driftwood from the two places differ. Whereas Larix is almost absent in the Isfjorden driftwood, it comprises 25% of the Wijdefjorden collection. The Isfjorden driftwood has its main origin in the White Sea region and the dates of the driftwood concentrate around the period from 1950 to 1979, with only a few dates from the period 1910 to 1950. The Wijdefjorden driftwood has two main origins: Siberia and the White Sea region. The dates of the White Sea components of the Wijdefjorden driftwood are concentrated mainly in the period 1910-1950. The dates of the Siberian (Yenisey) components of the Wijdefjorden driftwood are concentrated in the period 1950–1979. It can be argued that during the time period from ca. 1910 to 1950 the activity of a warm northerly flowing current along the western coast of Spitsbergen was stronger, transporting White Sea driftwood all the way to the Wijdefjorden area. However, after ca. 1950 the input of White Sea driftwood decreased, and the relative importance of the Siberian component increased. These results fit well with the climatic records from Svalbard, showing a warm regime during the first half of this century due to increased activity of the warm West Spitsbergen Current along the western coast of Spitsbergen. After ca. 1950, the influx of Atlantic Water became weaker, the climate became colder and the relative occurrences of Siberian driftwood transported by the Transpolar Current increased on the northern coast of the Svalbard archipelago.  相似文献   

Rethinking Late Weichselian ice-sheet dynamics in coastal NW Svalbard     

JON Y. LANDVIK  ÓLAFUR INGÓLFSSON  JÜRGEN MIENERT  SCOTT J. LEHMAN  ERS SOLHEIM  ERS ELVERHØI  DAG OTTESEN 《Boreas: An International Journal of Quaternary Research》2005,34(1):7-24

New marine geological evidence provides a better understanding of ice-sheet dynamics along the western margin of the last Svalbard/Barents Sea Ice Sheet. A suite of glacial sediments in the Kongsfjordrenna cross-shelf trough can be traced southwards to the shelf west of Prins Karls Forland. A prominent moraine system on the shelf shows minimum Late Weichselian ice extent, indicating that glacial ice also covered the coastal lowlands of northwest Svalbard. Our results suggest that the cross-shelf trough was filled by a fast-flowing ice stream, with sharp boundaries to dynamically less active ice on the adjacent shelves and strandflats. The latter glacial mode favoured the preservation of older geological records adjacent to the main pathway of the Kongsfjorden glacial system. We suggest that the same model may apply to the Late Weichselian glacier drainage along other fjords of northwest Svalbard, as well as the western margin of the Barents Ice Sheet. Such differences in glacier regime may explain the apparent contradictions between the marine and land geological record, and may also serve as a model for glaciation dynamics in other fjord regions.  相似文献   

Zero carbon energy system pathways for Ireland consistent with the Paris Agreement     

James Glynn  Maurizio Gargiulo  Alessandro Chiodi  Paul Deane  Fionn Rogan  Brian Ó Gallachóir 《Climate Policy》2019,19(1):30-42

The Paris Agreement is the last hope to keep global temperature rise below 2°C. The consensus agrees to holding the increase in global average temperature to well below 2°C above pre-industrial levels, and to aim for 1.5°C. Each Party’s successive nationally determined contribution (NDC) will represent a progression beyond the party’s then current NDC, and reflect its highest possible ambition. Using Ireland as a test case, we show that increased mitigation ambition is required to meet the Paris Agreement goals in contrast to current EU policy goals of an 80–95% reduction by 2050. For the 1.5°C consistent carbon budgets, the technically feasible scenarios' abatement costs rise to greater than €8,100/tCO₂ by 2050. The greatest economic impact is in the short term. Annual GDP growth rates in the period to 2020 reduce from 4% to 2.2% in the 1.5°C scenario. While aiming for net zero emissions beyond 2050, investment decisions in the next 5–10 years are critical to prevent carbon lock-in.

Key policy insights

• Economic growth can be maintained in Ireland while rapidly decarbonizing the energy system.

• The social cost of carbon needs to be included as standard in valuation of infrastructure investment planning, both by government finance departments and private investors.

• Technological feasibility is not the limiting factor in achieving rapid deep decarbonization.

• Immediate increased decarbonization ambition over the next 3–5 years is critical to achieve the Paris Agreement goals, acknowledging the current 80–95% reduction target is not consistent with temperature goals of ‘well below’ 2°C and pursuing 1.5°C.

• Applying carbon budgets to the energy system results in non-linear CO₂ emissions reductions over time, which contrast with current EU policy targets, and the implied optimal climate policy and mitigation investment strategy.

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Determination of Surface Precipitation Type Based on the Data Fusion Approach     

Marek PÓŁROLNICZAK  Leszek KOLENDOWICZ  Bartosz CZERNECKI  Mateusz TASZAREK  Gabriella TÓTH 《大气科学进展》2021,38(3):387-399

Hazardous events related to atmospheric precipitation depend not only on the intensity of surface precipitation,but also on its type.Uncertainty related to determination of the precipitation type(PT)leads to financial losses in many areas of human activity,such as the power industry,agriculture,transportation,and many more.In this study,we use machine learning(ML)algorithms with the data fusion approach to more accurately determine surface PT.Based on surface synoptic observations,ERA5 reanalysis,and radar data,we distinguish between liquid,mixed,and solid precipitation types.The study domain considers the entire area of Poland and a period from 2015 to 2017.The purpose of this work is to address the question:“How can ML techniques applied in observational and NWP data help to improve the recognition of the surface PT?”Despite testing 33 parameters,it was found that a combination of the near-surface air temperature and the depth of the warm layer in the 0-1000 m above ground level(AGL)layer contains most of the signal needed to determine surface PT.The accrued probability of detection for liquid,solid,and mixed PTs according to the developed Random Forest model is 98.0%,98.8%,and 67.3%,respectively.The application of the ML technique and data fusion approach allows to significantly improve the robustness of PT prediction compared to commonly used baseline models and provides promising results for operational forecasters.  相似文献   

Metamorphism and kinematics of the early deformation in the Variscan suture of SW Iberia     

C. PONCE  J. F. SIMANCAS  A. AZOR  D. J. MARTÍNEZ POYATOS  G. BOOTH‐REA  I. EXPÓSITO 《Journal of Metamorphic Geology》2012,30(7):625-638

The early (Devonian) collisional stage in SW Iberia has been investigated through the analysis of deformation in the Cubito‐Moura schists, the main lithology of an Allochthonous Complex putatively rooted in the suture between the Ossa‐Morena and South Portuguese zones. The first deformation in these schists (D₁) is recorded as a S₁‐L₁ mylonitic fabric well preserved in early quartz veins. Subsequent D₂ deformation caused the main folds and the main (S₂) foliation. After restoration, the stretching lineation (L₁) trends at a small angle with the Ossa‐Morena/South Portuguese suture. This trend, together with the top‐to‐the‐east kinematics determined from quartz microfabric is indicative of an oblique left‐lateral collisional scenario in SW Iberia. Chlorite–white K‐mica–quartz ± chloritoid multi‐equilibrium calculations yield P–T conditions in the range 0.9–1.2 GPa and 300–400 °C, during the first collisional stage. P–T conditions during D₂ were 0.3–0.8 GPa and 400–450 °C, thus indicating an important stage of exhumation of the Allochthonous Complex during these two collisional events, after subduction of the Ossa‐Morena Zone margin under the South Portuguese Zone continental crust. In the general context of the Variscan orogen, dominated by dextral collision, the left‐lateral convergence in SW Iberia can be explained in terms of the Avalonian salient represented by the South Portuguese Zone, which would impinge between Iberia and Morocco.  相似文献   

Biochronological data inferred from the Early Pleistocene small mammals of the Barranc de la Boella site (Tarragona,north‐eastern Spain)          下载免费PDF全文

IVÁN LOZANO‐FERNÁNDEZ  SANDRA BAÑULS‐CARDONA  HUGUES‐ALEXANDRE BLAIN  JUAN MANUEL LÓPEZ‐GARCÍA  JOSEP VALLVERDÚ  JORDI AGUSTÍ  GLORIA CUENCA‐BESCÓS 《第四纪科学杂志》2014,29(7):722-728

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Formation of a stratified subglacial ‘till’ assemblage by ice‐marginal thrusting and glacier overriding     

COLM Ó COFAIGH  DAVID J. A. EVANS  JOHN F. HIEMSTRA 《Boreas: An International Journal of Quaternary Research》2011,40(1):1-14

Ó Cofaigh, C., Evans, D. J. A. & Hiemstra, J. F. 2010: Formation of a stratified subglacial ‘till’ assemblage by ice‐marginal thrusting and glacier overriding. Boreas, 10.1111/j.1502‐3885.2010.00177.x. ISSN 0300‐9483. A thick sequence of glaciotectonically stacked till and outwash is preserved in a coastal embayment at Feohanagh, southwest Ireland. The sequence contains a variety of diamicton lithofacies, including laminated, stratified and massive components, but stratified diamictons dominate. Stratification/lamination is imparted by the presence of numerous closely spaced subhorizontal and anastomosing partings, which give a fissile appearance to the diamictons. Many partings are the result of sandy or thin gravelly layers within the diamictons. Some diamictons contain interbeds and lenses of sand, mud and gravel, which still preserve the original stratification. The sequence at Feohanagh is the product of a two‐stage depositional process in which initial glaciolacustrine sedimentation in an ice‐dammed lake was followed by glaciotectonic thrusting and overriding, during which the lake sediments were reworked and variably deformed. Similar late Quaternary sequences of glaciotectonically stacked stratified sediments and till have been described from around the coastal margins of Ireland and Britain, where they constitute glaciotectonite–subglacial traction till continuums rather than true lodgement tills as traditionally implied. Thick stratified diamicton assemblages are likely to occur in areas where steep topography provides pinning points for the glacier margin to stabilize and deliver large volumes of sediment into a glaciolacustrine or glaciomarine setting before proglacial and subglacial reworking of the sediment pile. The resulting geological–climatic unit, often defined as ‘till’, will contain a large amount of stratified and variably deformed material (laminated and stratified diamictons will be common), including intact sediment rafts, reflecting low strain rates and short sediment transport distances.  相似文献