Contribution of Local Seismic Networks To The Regional Velocity Model of The Bohemian Massif     

Růžek  Bohuslav  Zedník  Jan  Klíma  Karel  Ruprechtová  Libuše 《Studia Geophysica et Geodaetica》2000,44(2):175-187

The routine location of regional seismic events using data from the Czech National Seismological Network (CNSN) is based on Pn, Pg, Sn, Sg phases. A simple velocity model derived from Kárník's (1953) interpretation of an earthquake in Northern Hungary in 1951 has hitherto been used. At present, numerous local seismic networks record and locate local events, which are occasionally recorded at regional distances as well. Due to the relatively small dimensions of local networks, hypocenters (and origin times) determined by a local network might be considered as nearly exact from the point of view of regional-scale CNSN. The comparison of common locations performed by CNSN and by a local network enables us to estimate the accuracy of CNSN locations, as well as to optimize a simple velocity model. The joint interpretation of the CNSN bulletin and the catalogues of four local seismic networks WEBNET, OSTRAVA, KLADNO and LUBIN produced a new ID velocity model. The most frequent epicentral error in this model is less than 5 km, and most foci lie up to 15 km from the true position. The performed analysis indicates bimodal distribution of Sn residuals.  相似文献   

Petrology and geothermometry of retrograded Hercynian charnockites and host gneisses, Agly Massif, French Pyrenees     

JACQUES PAQUET 《Journal of Metamorphic Geology》1985,3(1):43-58

Abstract A Hercynian charnockite occurs within high-grade gneisses in the Agly Massif, French Pyrenees. Its thermal history has been evaluated using the Fe-Mg distribution coefticient ( K _D) between garnet and biotite. These minerals have different origins but similar compositions in the charnockites and host gneisses. In the charnockite, the Bi–Ga pairs are the retrograde products of Opx alteration. This Opx reaction with feldspar can be written. Opx + PI + Fluid 1(H₂O + Al + K + Fe + Ti) = Bi + Ga + Q + Fluid 2(H₂O + Na). The garnets are relatively Ca poor (4–2.5% grossular); they are automorphic and zoned in the gneisses and poikiloblastic in the charnockites. Both types show a retrograde rim (of few hundred microns'width) across which Fe and Mn increase as Mg decreases. The biotites show a good correlation between the octahedral cations (Ti⁴⁺+ Fe²⁺) and (Mg²⁺+ Al³⁺_VI); Ti and Fe both increase, whereas Mg and Al_VI decrease. There is an inverse linear correlation between Fe²⁺ and Mg²⁺ and the Fe/Mg ratio increases as Ti increases. The relation between Ti and K ^Ga-Bi_DFe-Mg is less clear: it seems that K _D slightly decreases as Ti increases. The equilibration temperatures of Ga–Bi pairs are discussed: the charnockite Ga-Bi pairs have equilibrated between 550°C and 600°C; whereas those of the gneisses have equilibrated between 550°C and 650°C. Two main thermal steps appear: one in the gneisses between 600-650°C and a second one in both the gneisses and the charnockites between 550°C and 600°C.  相似文献   

东北牡丹江地区"黑龙江群"中斜长角闪岩与花岗岩的锆石SHRIMP U-Pb定年及其地质学意义   总被引：25，自引：15，他引：10  

颉颃强  张福勤  苗来成  陈福坤  刘敦一 《岩石学报》2008,24(6):1237-1250

佳木斯地块南缘牡丹江地区的岩石学和地球化学研究表明,"黑龙江群"中存在洋壳残片,为形成于古大陆边缘环境的一套造山建造.牡丹江地区东北部的"麻山群"为佳木斯地块南缘的陆壳基底;其南侧的"黑龙江群"属造山建造,包括阿尔卑斯型超基性岩和具有MORB特征的斜长角闪片岩等.对"黑龙江群"中的斜长角闪片岩以及其南边具有同碰撞特征的钾长花岗岩进行了锆石SHRIMP U-Pb定年.结果表明:斜长角闪片岩具有777±18Ma的结晶年龄,并受到437±7Ma的变质作用的影响;同碰撞的钾长花岗岩形成年龄为461±6Ma.据此指出佳木斯地块南缘的黑龙江群中存在新元古代的洋壳残片并推断牡丹江地区存在早古生代的碰撞事件.  相似文献   

Late-orogenic Sveconorwegian massif anorthosite in the Jotun Nappe Complex,SW Norway,and causes of repeated AMCG magmatism along the Baltoscandian margin     

A. M. Lundmark  F. Corfu 《Contributions to Mineralogy and Petrology》2008,155(2):147-163

The age and tectonometamorphic history of massif anorthosite in the Jotun Nappe Complex, SW Norway, were investigated by zircon and titanite U–Pb ID-TIMS. The anorthosite contains sparse zircons showing complex U–Pb systematics reflecting events dated at 965 ± 4 and 913 ± 2 Ma, and a pronounced Caledonian metamorphic overprint. The oldest age is interpreted as the protolith age of the massif anorthosite. We propose that the Jotun anorthosite is related to 970–960 Ma magmatism in the Western Gneiss Region and coeval, orogen-perpendicular extension. Conversely, a 930 Ma high-grade metamorphic event in the Jotun Nappe Complex and the related Lindås Nappe is likely related to formation of the autochthonous ca. 930 Ma Rogaland anorthosite complex. We suggest that the two late- to post-orogenic AMCG events reflect two instances of lithospheric foundering below the orogen separated by ca. 20–30 my. The 913 ± 2 Ma metamorphic episode appears to date a heating event restricted to the outermost edge of the Western Gneiss Region. Leucosome formation in high-grade gneisses geographically close to the Jotun anorthosite is dated at 892 ± 4 Ma and suggested to reflect CO₂-rich (?) fluid flux along shear zones.  相似文献   

Geochemistry of the Mamil Choique granitoids at Rio Chico, Río Negro, Argentina: Late Paleozoic crustal melting in the North Patagonian Massif     

Mnica G. Lpez de Luchi  María Elena Cerredo 《Journal of South American Earth Sciences》2008,25(4):526-546

  相似文献   

Mafic and Felsic Magma Interaction in Granites: the Hercynian Karkonosze Pluton (Sudetes, Bohemian Massif)   总被引：12，自引：0，他引：12  

Slaby  E.; Martin  H. 《Journal of Petrology》2008,49(2):353-391

The Hercynian, post-collisional Karkonosze pluton contains severallithologies: equigranular and porphyritic granites, hybrid quartzdiorites and granodiorites, microgranular magmatic enclaves,and composite and lamprophyre dykes. Field relationships, mineralogyand major- and trace-element geochemistry show that: (1) theequigranular granite is differentiated and evolved by smalldegrees of fractional crystallization and that it is free ofcontamination by mafic magma; (2) all other components are affectedby mixing. The end-members of the mixing process were a porphyriticgranite and a mafic lamprophyre. The degree of mixing variedwidely depending on both place and time. All of the processesinvolved are assessed quantitatively with the following conclusions.Most of the pluton was affected by mixing, implying that hugevolumes (>75 km³) of mafic magma were available. This maficmagma probably supplied the additional heat necessary to initiatecrustal melting; part of this heat could have also been releasedas latent heat of crystallization. Only a very small part ofthe Karkonosze granite escaped interaction with mafic magma,specifically the equigranular granite and a subordinate partof the porphyritic granite. Minerals from these facies are compositionallyhomogeneous and/or normally zoned, which, together with geochemicalmodelling, indicates that they evolved by small degrees of fractionalcrystallization (<20%). Accessory minerals played an importantrole during magmatic differentiation and, thus, the fractionalcrystallization history is better recorded by trace rather thanby major elements. The interactions between mafic and felsicmagmas reflect their viscosity contrast. With increasing viscositycontrast, the magmatic relationships change from homogeneous,hybrid quartz diorites–granodiorites, to rounded magmaticenclaves, to composite dykes and finally to dykes with chilledmargins. These relationships indicate that injection of maficmagma into the granite took place over the whole crystallizationhistory. Consequently, a long-lived mafic source coexisted togetherwith the granite magma. Mafic magmas were derived either directlyfrom the mantle or via one or more crustal storage reservoirs.Compatible element abundances (e.g. Ni) show that the maficmagmas that interacted with the granite were progressively poorerin Ni in the order hybrid quartz diorites—granodiorites—enclaves—compositedykes. This indicates that the felsic and mafic magmas evolvedindependently, which, in the case of the Karkonosze granite,favours a deep-seated magma chamber rather than a continuousflux from mantle. Two magma sources (mantle and crust) coexisted,and melted almost contemporaneously; the two reservoirs evolvedindependently by fractional crystallization. However, maficmagma was continuously being intruded into the crystallizinggranite, with more or less complete mixing. Several lines ofevidence (e.g. magmatic flux structures, incorporation of granitefeldspars into mafic magma, feldspar zoning with fluctuatingtrace element patterns reflecting rapid changes in magma composition)indicate that, during its emplacement and crystallization, thegranite body was affected by strong internal movements. Thesewould favour more complete and efficient mixing. The systematicspatial–temporal association of lamprophyres with crustalmagmas is interpreted as indicating that their mantle sourceis a fertile peridotite, possibly enriched (metasomatized) byearlier subduction processes. KEY WORDS: Bohemian Massif; fractional crystallization; geochemical modelling; hybridization; Karkonosze  相似文献   

High-pressure–low-temperature metamorphism of metasedimentary rocks, southern Menderes Massif, western Turkey     

Donna L. Whitney  Christian Teyssier  Seth C. Kruckenberg  Valerie L. Morgan  Lindsay J. Iredale 《Lithos》2008,101(3-4):218-232

Kilometer-scale lenses of quartz-rich metasedimentary rocks crop out in a discontinuous belt along the southern margin of the Menderes Massif, Turkey, and preserve evidence for high-pressure–low-temperature (HP–LT) metamorphism related to subduction of a continental margin during Alpine orogeny. Kyanite schist, quartzite, and quartz veins contain kyanite + phengite + Mg-chlorite, and the veins also contain magnesiocarpholite. A deformed carbonate metaconglomerate juxtaposed with the quartzite-dominated unit does not contain HP index minerals, and likely represents the tectonized boundary of the siliceous rocks with adjacent marble. The HP–LT rocks (10–12 kbar, 470–570 °C) record different pressure conditions than the adjacent, apparently lower pressure Menderes metasedimentary sequence. Despite this difference there is disagreement as to whether these HP–LT rocks are part of the Menderes sequence or are related to the tectonically overlying Cycladic blueschist unit. If the former, the entire southern Menderes Massif experienced HP–LT metamorphism but the evidence has been obliterated from most rocks; if the latter, rocks recording different metamorphic-kinematic conditions experienced different tectonic histories and were tectonically juxtaposed during thrusting. Based on observations and data in this study, the second model better accounts for the differences in P–T-deformation histories of the southern Menderes Massif rocks, and suggests that the HP–LT rocks are not part of the Menderes cover sequence.  相似文献   

From orthogneiss to migmatite: Geochemical assessment of the melt infiltration model in the Gföhl Unit (Moldanubian Zone, Bohemian Massif)     

P. Hasalov  V. Janou&#x;ek  K. Schulmann  P. &#x;típsk  V. Erban 《Lithos》2008,102(3-4):508-537

The Gföhl Unit is the largest migmatite terrain of the Variscan orogenic root domain in Europe. Its genesis has been until now attributed to variable degrees of in situ partial melting. In the Rokytná Complex (Gföhl Unit, Czech Republic) there is a well-preserved sequence documenting the entire migmatitization process on both outcrop and regional scales. The sequence starts with (i) banded orthogneiss with distinctly separated monomineralic layers, continuing through (ii) migmatitic mylonitic gneiss, (iii) schlieren migmatite characterised by disappearance of monomineralic layering and finally to (iv) felsic nebulitic migmatite with no relics of the original banding.

While each type of migmatite shows a distinct whole-rock geochemical and Sr–Nd isotopic fingerprint, the whole sequence evolves along regular, more or less smooth trends for most of the elements. Possible mechanisms which could account for such a variation are that the individual migmatite types (i) are genetically unrelated, (ii) originated by equilibrium melting of a single protolith, (iii) formed by disequilibrium melting (with or without a small-scale melt movement) or (iv) were generated by melt infiltration from external source. The first scenario is not in agreement with the field observations and chemistry of the orthogneisses/migmatites. Neither of the remaining hypotheses can be ruled out convincingly solely on whole-rock geochemical grounds. However in light of previously obtained structural, petrologic and microstructural data, this sequence can be interpreted as a result of a process in which the banded orthogneiss was pervasively, along grain boundaries, penetrated by felsic melt derived from an external source.

In terms of this melt infiltration model the individual migmatites can be explained by different degrees of equilibration between the bulk rock and the passing melt. The melt infiltration can be modelled as an open-system process, characterised by changes of the total mass/volume and accompanied by gains/losses in many of the major- and trace elements. The modelling of the mass balance resulted in identification of a component added by a heterogeneous nucleation of feldspars, quartz and apatite from the passing melt. This is in line with the observed presence of new albitic plagioclase, K-feldspar and quartz coatings as well as resorption of relict feldspars. At the most advanced stages (schlieren and nebulitic migmatites) the whole-rock trace-element geochemical variations document an increasing role for fractional crystallization of the K-feldspar and minor plagioclase, with accessory amounts of monazite, zircon and apatite.

The penetrating melt was probably (leuco-) granitic, poor in mafic components, Rb rich, with low Sr, Ba, LREE, Zr, U and Th contents. It probably originated by partial melting of micaceous quartzo-feldspathic rocks.

If true and the studied migmatites indeed originated by a progressive melt infiltration into a single protolith resembling the banded orthogneiss, this until now underappreciated process would have profound implications regarding rheology and chemical development of anatectic regions in collisional orogens.  相似文献   

Age and emplacement of late-Variscan granites of the western Bohemian Massif with main focus on the Hauzenberg granitoids (European Variscides, Germany)     

T. Klein  S. Kiehm  W. Siebel  C.K. Shang  J. Rohrmüller  W. Drr  G. Zulauf 《Lithos》2008,102(3-4):478-507

The Variscan Hauzenberg pluton consists of granite and granodiorite that intruded late- to postkinematically into HT-metamorphic rocks of the Moldanubian unit at the southwestern margin of the Bohemian Massif (Passauer Wald). U–Pb dating of zircon single-grains and monazite fractions, separated from medium- to coarse-grained biotite-muscovite granite (Hauzenberg granite II), yielded concordant ages of 320 ± 3 and 329 ± 7 Ma, interpreted as emplacement age. Zircons extracted from the younger Hauzenberg granodiorite yielded a ²⁰⁷Pb–²⁰⁶Pb mean age of 318.6 ± 4.1 Ma. The Hauzenberg granite I has not been dated. The pressure during solidification of the Hauzenberg granite II was estimated at 4.6 ± 0.6 kbar using phengite barometry on magmatic muscovite, corresponding to an emplacement depth of 16-18 km. The new data are compatible with pre-existing cooling ages of biotite and muscovite which indicate the Hauzenberg pluton to have cooled below T = 250–400 °C in Upper Carboniferous times. A compilation of age data from magmatic and metamorphic rocks of the western margin of the Bohemian Massif suggests a west- to northwestward shift of magmatism and HT/LP metamorphism with time. Both processes started at > 325 Ma within the South Bohemian Pluton and magmatism ceased at ca. 310 Ma in the Bavarian Oberpfalz. The slight different timing of HT metamorphism in northern Austria and the Bavarian Forest is interpreted as being the result of partial delamination of mantle lithosphere or removal of the thermal boundary layer.  相似文献   

The rock magnetic signal of climate change in the maar lake sequence of Lac St Front (France)     

P. Vlag  N. Thouveny  D. Williamson  V. Andrieu  M. Icole  A. J. van  Velzen 《Geophysical Journal International》1997,131(3):724-740

Rock magnetic properties of the maar lake sediments of Lac St Front (Massif Central, France) reflect environmental changes during the last climatic cycle. High magnetic concentrations are measured in the sediments deposited under glacial climatic conditions, while lower concentrations correspond with more temperate climatic periods. Low- and high-temperature measurements indicate that the remanence is carried by (titanium-poor) magnetite. However, some maghemite and haematite is present in sediments deposited under temperate conditions.
Normalized intensities and coercivities of the anhysteretic remanent magnetization (ARM) are clearly higher for the sediments deposited during the temperate climatic periods of the Eemian, St Germain I, II and Mid-glacial than for glacial sediments, but other magnetic parameters hardly differ between these groups. Due to slight differences in magnetic composition and possible effects of grain interactions, it is not straightforward to relate this different ARM behaviour to magnetic grain-size variations. For the Holocene sediments, rock magnetic parameters indicate a larger grain size. This trend is also suggested by granulometric experiments with an optical laser granulometer. Dissolution of smaller grains is the most likely explanation for this larger grain size.
Changes in magnetic composition and grain size are extremely limited for the glacial sediments, but magnetic concentration varies considerably. Magnetic concentration maxima in the glacial sediments of Lac St Front correlate with those of the nearby Lac du Bouchet (Thouveny et al. 1994). Correlating the susceptibility records of these sequences with the δ¹⁸O record of the GRIP ice cores (Thouveny et al. 1994) suggests that magnetic concentration maxima may correspond with short cold climatic episodes, associated with Heinrich events.  相似文献