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41.
Herbert W. Fournier James K. W. Lee Alfredo Camacho 《Journal of Metamorphic Geology》2019,37(6):769-793
The determination of the thermal (temperature–time) histories of high‐P metamorphic terranes has been commonly based on the concepts of slow cooling and closure temperatures. In this paper, we find that this approach cannot reconcile a geochronological data set obtained from the amphibolite‐facies allochthonous Leknes Group of the Lofoten islands, Norway, which reveals an extremely complex thermal history. Using detailed results from several different geochronometers such as 40Ar/39Ar, Rb–Sr and U–Pb, we show that a model invoking multiple, short‐lived thermal pulses related to hot‐fluid infiltration channelized by shear zones can reconcile this complicated data set. This model suggests that hot fluids infiltrated throughout basement shear zones and affected the overlying cold allochthon, partially resetting U/Pb rutile and titanite ages, crystallizing new zircon and produced identical 40Ar/39Ar and Rb/Sr ages in muscovite, biotite and amphibole in various rocks throughout the region. This paper shows the enormous potential of coupling laser Ar‐spot data with thermal modelling to identify and constrain the duration of short‐lived events. An optimal P–T–t history has been derived by modelling the age data from a previously dated large muscovite crystal (Hames & Andresen, 1996, Geology, 24 :1005) and using Zr‐in‐rutile thermometry which is consistent with all geochronological data and geological constraints from the basement zones and allochthon cover. This tectonothermal model history suggests that there have been three episodic hot‐fluid and 40Ar‐free infiltration events, resulting in the total resetting of Ar ages during the Scandian (425 Ma) for 1 Ma at 650°C and two reheating events at 415 Ma for 400 ka at 650°C and at 365 Ma for 50 ka at 600°C, which are modelled as thermal spikes above an ambient temperature of 300°C. Independent confirmation of these parameters was provided by Pb‐diffusion modelling in rutile and titanite. The model suggests that the amphibolite facies rocks of the Leknes Group probably remained cold before being exhumed for at least 60 Ma (425–365 Ma) and successfully explains the presence of different minerals that crystallized or were totally/partially reset in the allochthon and in the basement. The migration of hot fluids for short periods of times within conduits extending through the basement and allochthon rock units is likely associated with episodic seismic activity during the Caledonian orogeny. 相似文献
42.
Lidia Romero-Viana Brendan J. Keely Antonio Camacho Eduardo Vicente M. Rosa Miracle 《Journal of Paleolimnology》2010,43(4):771-786
We analysed photosynthetic pigments in annually laminated sediment of meromictic Lake La Cruz, Spain, to cope with the timing
and characterisation of primary productivity changes over the last four centuries. The photosynthetic pigments identified
included chlorophyll a and b (and its derivatives) and specific carotenoids of different algal groups, such as zeaxanthin, lutein, alloxanthin, diadinoxanthin
and diatoxanthin among others. Marker pigments of phototrophic sulfur bacteria were also observed, including bacteriochlorophyll
a derivatives, homologue series of bacteriophaeophytins d and bacterial carotenoids okenone and chlorobactene. We investigated the diagenetic processes of pigment alteration in anoxic
sediments and the possible implications for paleoproductivity reconstruction and interpretation. The lack of systematic down-core
changes in diagenetic indicators suggests that variability of sedimentary pigment concentrations is the result of changes
in lake productivity. The lower concentration of algal photosynthetic pigments in the bottom of sediment sequence corresponds
to the onset of meromictic conditions. Before that, sediment was not continuously anoxic and the preservation of pigments
was reduced. Regarding photosynthetic bacteria, green sulfur bacteria derivatives indicate that population growth was limited
until the settled organic matter was sufficient to provide enough sulphide. Moreover, the presence of bacterioviridine, an
oxidised derivative of bacteriochlorophyll a, suggest the competitive relation among photosynthetic bacteria. The high relative abundance of zeaxanthin indicates the
dominance of picocyanobacteria in the primary productivity over the last centuries. Fluctuations of the pigment signal observed
in the sediment sequence during the meromictic period were well correlated with fluctuations of solar activity. 相似文献
43.
Camacho M Boada LD Orós J Calabuig P Zumbado M Luzardo OP 《Marine pollution bulletin》2012,64(9):1974-1980
Polycyclic aromatic hydrocarbons (PAHs) were measured in plasma samples of 162 juvenile loggerhead sea turtles (Caretta caretta) from Canary Islands, and 205 adult nesting loggerheads from Cape Verde. All the 367 samples showed detectable values of some type of PAH. Phenanthrene was the PAH most frequently detected and at the highest concentration in both populations. Median concentrations of ∑PAHs in the plasma of loggerheads from the Canary Islands and Cape Verde were similar (5.5 and 4.6ng/ml, respectively). Di- and tri-cyclic PAHs were predominant in both populations suggesting petrogenic origin rather than urban sources of PAHs. In the group of turtles from Canary Islands, there was evident an increasing level of contamination over the last few years. The present study represents the first data of contamination by PAHs in sea turtles from the studied areas. 相似文献
44.
45.
Rehabilitation of damaged reefs: Outcome of the use of recently broken coral fragments and healed coral fragments of pocilloporid corals on rocky boulders
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The use of two types of coral transplants on rock boulders was evaluated as a low‐cost alternative for rehabilitation of live coral coverage in localities whose reef structure has been reduced considerably. Transplant success between recently broken coral fragments (BCF) and healed coral fragments (HCF) was compared assuming that initial fragmentation accelerates the attachment of corals by regeneration stimulation. Two sets of both types of transplants were started during the dry and rainy seasons to contrast the effect of environmental stability on transplant survival, vertical growth and horizontal growth over 12 months. The technique provided adequate conditions for coral development, as transplants responded satisfactorily. BCF showed higher success than HCF in attaching to the substrate (up to 98 ± 4% versus 86.4 ± 18.9% after 9 months) during both seasons and also showed a greater increase in height (209.63 ± 43.65% versus 124 ± 15.83%) and diameter (107.26 ± 25.75% versus 99.98 ± 19.74%) during the rainy season. Boat anchorage caused mortality in transplants started during the dry season (less than 10% for BCF versus 37.2% for HCF) while the impact of Hurricane Polo in October 2014 caused higher mortality in transplants started during the rainy season (up to 55%). We conclude that (i) coral transplantation on rock boulders is a good choice to restore damaged coral communities, (ii) BCF seems to be the best source of transplants for pocilloporid corals, and (iii) although high light availability during the rainy season enhances transplant growth, the stable, low energy conditions in the dry season facilitate initial transplant attachment and high survival. 相似文献
46.
47.
S. de la Cruz-Reyna M.A. Armienta V. Zamora F. Jurez 《Journal of Volcanology and Geothermal Research》1989,38(3-4)
Local seismic activity consisting of sharp earthquakes accompanied by thunderous noise was reported starting in late December 1985 around Tacaná volcano (15.13°N, 92.10°W). Portable seismic stations were established in the area by late January 1986 and sampling of the only known thermal spring on the volcano flanks started at the same time. A marked increase in SO42− concentration in the spring water preceded by two months the occurrence of a seismic swarm crisis and a small phreatic explosion. A model involving a crystalline basement fractured by tectonic stresses is proposed to explain the chemical and seismic anomalies, and the consequences on risk of volcanic activity are briefly discussed in terms of the observed behaviour. 相似文献
48.
49.
Carolyn Lampe Kristijan Kornpihl Simone Sciamanna Toms Zapata Gonzalo Zamora Roberto Varad 《Journal of Geochemical Exploration》2006,89(1-3):201
A roughly 30 km 2D section across the Faja Plegada y Corrida del Agrio in the Neuquen Basin, Argentina, is the basis for a petroleum systems study, including structural restoration through time, deposition and erosion, pressure, temperature and migration modeling. Integrating tectonic and petroleum systems modeling proved critical to properly evaluate sub-thrust plays. Multi-dimensional modeling of dynamic processes allows accurate assessment and prediction of the potential of petroleum systems in tectonically complex areas such as the Neuquen Basin. 相似文献
50.
Gravimetric determination of an intrusive complex under the Island of Faial (Azores): some methodological improvements 总被引:2,自引:0,他引:2
Antonio G. Camacho J. Carlos Nunes Esther Ortiz Zilda França Ricardo Vieira 《Geophysical Journal International》2007,171(1):478-494
We present some improvements of a gravity inversion method to determine the geometry of the anomalous bodies for priori density contrasts. The 3-D method is based on an exploratory process applied, not for the global model, but for the steps of a growth approach. The (positive and/or negative) anomalous structure is described by successive aggregation of cells, while its corresponding gravity field remains nearly proportional to the observed one. Moreover, a simple (e.g. linear) regional trend can be simultaneously adjusted. The corresponding program is applied to new gravity data on the volcanic island of Faial (Azores archipelago). The inversion approach shows a subsurface anomalous structure for the island, the main feature being an elongated high-density body. The body is interpreted as a compact sheeted dyke swarm, emplaced along Faial-Pico Fracture Zone, a leaky transform structure that forms the current boundary between Eurasian and African plates in the Azores area. The new results in this paper are (1) a Bouguer gravity anomaly map, (2) several improvements in the inversion process (robust process, optimal balance fitness/model magnitude), (3) a new gravimetric method for estimating the mean terrain density, (4) a 3-D model for subsurface mass anomalies in Faial and (5) some interpretative conclusions about a main intrusive complex detected under the island as a wall-like structure extending from a depth of 0.5 to 6 km b.s.l., with a N100°E trend and corresponding to an early fissural volcanic episode controlled by the regional tectonics. 相似文献