P-T-t-deformation paths recorded by kinzigites during diapirism in the western Variscan belt (Golfe du Morbihan, southern Brittany, France)     

C. AUDREN  C. TRIBOULET 《Journal of Metamorphic Geology》1993,11(3):337-356

Abstract The high-grade metamorphic rocks of southern Brittany underwent a complex tectonic evolution under various P-T conditions (high-P, high-T), related to stacking of nappes during Palaeozoic continentcontinent collision. The east to west thrusting observed in the whole belt is strongly perturbed by vertical movements attributed to the ascent of anatectic granites in the high-T area. The field reconstruction of subvertical, closed elliptical structures in gneisses and migmatites, associated with the subhorizontal, doubly radial pattern of stretching lineation in the mica schists, suggests the existence of an elliptical diapiric body buried at depth beneath the present erosion level. Deformation is associated with a complex P-T evolution partly recorded in aluminous gneisses (kinzigites, e.g. morbihanites). A chronology of successive episodes of mineral growth at different compositions is established by detailed studies of the mineral-microstructure relationships in X-Z sections, using the deformation-partitioning concept (low- and high-strain zones). Several thermometric and barometric calibrations are applied to mineral pairs either in contact or not in contact but in equivalent microstructiiral positions with respect to the deformation history. This methodology provides a continuous microstructural control of P-T variations through time and leads to three P-T-t-d paths constructed from numerous successive P-T estimations. Path 1 is a clockwise retrograde path preserved in low-strain zones, which records general exhumation movements after crustal thickening. Paths 2 and 3 are clockwise prograde/retrograde paths from high-strain zones; they are interpreted and discussed in the light of models of crustal anatexis and upward movement of magma (diapirism). Deformation and P-T effects induced by diapirism can be distinguished from the general deformation-metamorphic history of a belt, and would seem to be produced during a late stage of its history. The present microstructural-petrological approach to defining successive mineral equilibria in relation to progressive deformation steps provides a far more accurate evaluation of the metamorphic evolution than is possible by ‘standard’thermobarometry.  相似文献   

商丹断裂构造特征及其演化     

王全庆 《地球科学与环境学报》1992,(1)

商丹断裂带是北秦岭加里东造山带与中秦岭海西造山带的分界断裂,由韧性剪切应变带、逆冲推覆构造带、地堑断陷带及其所夹持的岩块、岩片、构造岩、褶曲等多种地质体组合成复杂的断裂带。其演化历史至少经历晋宁期俯冲、加里东期碰撞、海西—印支期陆内俯冲、燕山期滑脱推覆和喜山期地堑断陷的复杂演化过程而形成今日所见的复杂断裂构造。  相似文献   

Contribution of Sponge Spicules to the Composition of Biogenic Silica in the Ligurian Sea     

Giorgio  Bavestrello  Riccardo  Cattaneo-Vietti  Carlo  Cerrano  Stefania  Cerutti Michele  Sará 《Marine Ecology》1996,17(1-3):41-50

Abstract. The importance of sponge spicules in the turnover of biogenic silica (BSi) in the detritic bottoms of the Eastern Ligurian Riviera was evaluated by studying sediment cores and the detrital matter collected by a trap over a one year period.
This study made evident that: i) Sponge spicules represent the main component of the BSi both in the sediments and in the trapped matter; ii) A correlation exists between the sponge biomass present on the overhanging cliff and the amount of sponge spicules found in the sediment below; iii) Inside the sediments, a superficial layer (10 cm deep) characterized by intensive silica dissolution processes can be observed; and iv) The amount of spicules collected using the trap is not constant throughout the year, but shows a characteristic trend with low values in spring and summer and high values in autumn and winter.  相似文献   

Polycyclic aromatic hydrocarbons in water, seston and copepods in a harbour area in the Western Mediterranean (Ligurian Sea)   总被引：2，自引：0，他引：2  

Luigi Pane  Simona Boccardo  Fabio Bonfiglioli  Gian Luigi Mariottini  Francesca Priano  & Osvaldo Conio 《Marine Ecology》2005,26(2):89-99

Polycyclic aromatic hydrocarbons (PAHs) are widespread carcinogenic, mutagenic and teratogenic pollutants that can significantly affect ecosystems and exert an influence on marine planktonic and benthic communities as well as on higher organisms such as fish and mammals, including humans. In this paper the concentrations of six PAHs in water, seston and copepods were examined in a harbour zone of the Genova Gulf (Ligurian Sea) from November 1997 to June 1998. The importance of freshwater inputs coming from a polluted stream and the influence of seasonal and atmospheric factors were also considered. Highest PAH values were recorded during spring. Fluoranthene, Benzo[b]fluoranthene and Benzo[k]fluoranthene were the most abundant PAHs either in water, seston or copepods. The concentration of total PAHs in seawater was often lower than the detection limit: recorded values ranged between 0.001 and 0.06 ppb. In seston, total PAHs ranged between 0.033 and 6.26 ng·g^?1 and in copepods between 0.01 and 2.34 ng·g^?1. With this study, PAH contamination in the harbour zone of Genova Sestri‐Ponente and the importance of inputs of organic pollutants coming from land and freshwaters have been emphasized.  相似文献   

Coupling a two-way nested primitive equation model and a statistical SST predictor of the Ligurian Sea via data assimilation     

A. Barth  A. Alvera-Azcrate  J.-M. Beckers  M. Rixen 《Ocean Modelling》2006,13(3-4):255-270

A primitive equation model and a statistical predictor are coupled by data assimilation in order to combine the strength of both approaches. In this work, the system of two-way nested models centred in the Ligurian Sea and the satellite-based ocean forecasting (SOFT) system predicting the sea surface temperature (SST) are used. The data assimilation scheme is a simplified reduced order Kalman filter based on a constant error space. The assimilation of predicted SST improves the forecast of the hydrodynamic model compared to the forecast obtained by assimilating past SST observations used by the statistical predictor. This study shows that the SST of the SOFT predictor can be used to correct atmospheric heat fluxes. Traditionally this is done by relaxing the model SST towards the climatological SST. Therefore, the assimilation of SOFT SST and climatological SST are also compared.  相似文献   

Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter   总被引：1，自引：0，他引：1  

Albrecht Steck 《Swiss Journal of Geoscience》2008,101(2):515-546

This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:

1.	NW-directed nappe emplacement, starting in the Early Eocene (~50 Ma);
2.	W, SW and S-verging transverse folds;
3.	transpressional movements on the dextral Simplon ductile shear zone since ~32 Ma;
4.	formation of the Bergell – Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31–29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29–25 Ma crustal aplites and pegmatites;
5.	formation of the dextral discrete Rhone-Simplon line and the Centovalli line during the Miocene, accompanied by the pull-apart development of the Lepontine gneiss dome – Dent Blanche (Valpelline) depression.

It is suggested that movements of shortening in fan shaped NW, W and SW directions accompanied the more regular NW- to WNW-directed displacement of the Adriatic indenter during continental collision.

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Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Editorial Handling: Stefan Bucher  相似文献   

北武夷地区逆冲推覆构造的特征及其控矿作用   总被引：3，自引：0，他引：3  

余心起  吴淦国  张达  狄永军  代堰锫 《地质通报》2008,27(10)

北武夷地区成矿地质条件优越,矿产资源分布广泛,而广泛发育的推覆构造深刻影响着矿床的成生与保存。区域性推覆构造是成矿前、成矿期还是成矿后的构造,其精细结构特征如何,是否具有控岩控矿作用,如果是破矿作用,是否造成矿体重复增大或者隐伏、缺失等问题,严重影响着地质找矿的效果。建议开展面积性、追索性的路线地质调查,查明逆冲推覆构造的区域分布、不同单元的产状、构造样式,分别采用40Ar-39Ar和Re-Os定年技术测定推覆构造和矿体的形成时代,结合定量化分析及精细构造解析,研究构造与矿床的成生联系,预测隐伏矿体可能的位置,进而为北武夷地区寻找隐伏矿床和扩大矿床远景提供参考。  相似文献   

福建省大田县广平含煤区推覆构造特征及找煤预测   总被引：1，自引：0，他引：1  

陈开彪 《中国煤田地质》2006,18(2):16-17,70

通过对区内推覆构造及地层等的研究，认为广平含煤区推覆体下蕴藏着丰富的煤炭资源，童子岩组煤系地层埋藏深度主要受发育于童子岩组上部的F1、F2推覆断层控制，并圈定出煤炭资源预测前景较好的3个区作为煤炭勘查后备基地。  相似文献   

青海热水柴达尔井田构造组合型式     

文怀军 《中国煤田地质》2006,18(3):14-16

柴达尔井田构造可分为压缩机制的推覆构造与伸展机制的断块体两类。南北F0为逆冲型的控制性边界断裂，井田内部一系列小型弧形构造为逆掩型浅层断裂；F1、F2、F17，是拉伸作用下的同沉积正断层，切断煤系基底T3地层。其动力机制为印度板块向北推移、西伯利亚板块向南运移发生对挤，脆一韧性剪切变形导致了井用现有的构造组合形式。  相似文献   

大功率激电在双阳煤田找矿应用     

钟立平  关键  孙念仁  陈玉明  华伟 《吉林地质》2003,22(4):29-35

大功率激电法在双阳煤田找煤的应用中,证实了山河推覆构造的存在;在充分研究工作区的地质、地球物理特征前提下,恰当地选用了方法技术,并正确理解异常的地质、地球物理意义,取得了较好的找煤效果,在Ⅰ号剖面的激电异常上经钻探和坑探证实磨盘山组灰岩下存在质量较好的可采煤层。  相似文献