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I. Expsito J. F. Simancas F. Gonzlez Lodeiro F. Bea P. Montero K. Salman 《Journal of Structural Geology》2003,25(12):2077-2087
The high-temperature metamorphism recorded in the Valuengo and Monesterio areas constitutes a rare occurrence in the Ossa-Morena Zone of Southwest Iberia, where low-grade metamorphism dominates. The metamorphism of the Valuengo area has been previously considered either Cadomian or Variscan in age, whereas that of Monesterio has been interpreted as a Cadomian imprint. However, these areas share important metamorphic and structural features that point towards a common tectonometamorphic evolution. The metamorphism of the Valuengo and Monesterio areas affects Late Proterozoic and Early Cambrian rocks, and is syn-kinematic with a top-to-the-north mylonitic foliation, which was subsequently deformed by early Variscan folds and thrusts. The U–Pb zircon age (480±7 Ma) we have obtained for an undeformed granite of the Valuengo area is consistent with our geological observations constraining the age of the metamorphism. We propose that this high-temperature metamorphic imprint along a NW–SE ductile extensional shear zone is related to the crustal extension that occurred in the Ossa-Morena Zone during the Cambro-Ordovician rifting. In the same way, the tectonothermal effect of the preorogenic rifting stage may have been wrongly attributed to orogenic processes in other regions as well as in this one. 相似文献
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Pressure-Dependence of Rare Earth Element Distribution in Amphibolite- and Granulite- Grade Garnets. A LA-ICP-MS Study 总被引：4，自引：0，他引：4
Fernando Bea Pilar Montero Giorgio Garuti Federica Zacharini 《Geostandards and Geoanalytical Research》1997,21(2):253-270
Using an excimer (KrF) laser ablation ICP-MS system, we studied the distribution of REE in garnets from metapelites and metabasites from Ivrea-Verbano (Western Alps, Italy) and from the Peña Negra Anatectic Complex (Central Iberia), finding systematic variations that correlate well with the metamorphic grade. Chondrite-normalized REE patterns of garnets from amphibolite-grade metapelites have lower-than-chondrite levels from La to Sm, a very small or no Eu anomaly, and a steep rise in the abundance of heavy REE as the atomic number increases. Metapelitic garnets from the amphibolite-granulite transition have a marked Eu negative anomaly and are enriched in MREE such that Sm is 10-15 times chondrite and the pattern is almost flat from Dy to Yb-Lu. In garnets from granulite-grade metapelites, the intensity of the Eu anomaly and the relative concentration of Nd, Sm, Gd and Tb increase, with almost flat chondrite-normalized patterns from Sm to Lu. Garnets from mafic granulites are remarkably similar to those of metapelitic garnets equilibrated at the same pressure, except for the Eu anomaly. The apparent paradox of enhanced uptake of larger REE ions with increasing pressure is attributed to the 3M2+ 2REE3++ vacancy substitution, which produces a net decrease in the dimensions of the unit-cell of garnet. Variations in REE patterns depend essentially on the pressure and have little dependence on either temperature, bulk-composition of garnet, or REE whole-rock composition, so they could represent a new approach for geobarometric studies. The best numerical parameter to express pressure-related variations of REE distribution in garnets is the Gd/Dy ratio which does not seem perceptibly affected by disequilibrium partitioning. The regression equation between GASP pressure and the average Gd/Dygarnet is P = 3.6 + 5.6 Gd/Dy. This equation seems to be reliable for garnets: (1)equilibrated within a pressure range of 4-9 kbar, (2) coexisting with modal monazite; and (3) with unit-cell dimensions under 11.46 Å. 相似文献
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Summary The granites of the Sistema Central Espanol are richer in ammonium than those of most other regions, and have a mean NH4
+ content of 84 ppm (range = 1–243 ppm). Among the possible causes for the high level of ammonium, a high proportion of organic-rich pelitic protolith and reducing conditions during anatexis are considered to be the most significant. The behaviour of the ammonium ion during magmatic differentiation is discussed by reference to its distribution in the Pedrobernardo layered intrusion: ammonium is depleted in the final liquid fraction, but there is no relative fractionation of NH4
+ and K+. The depletion of the melt in NH4
+ during crystallization is attributed to its removal by biotite and to a lesser extent by K-feldspar. The behaviour of the ammonium ion during anatexis is discussed with reference to the Peña Negra migmatite complex. It is shown that large amounts of NH4
+ are present in these high grade metamorphic rocks, and that NH4
+ is preferentially partitioned into the restite fraction during partial melting. These relationships are attributed to the preferential incorporation of NH4
+ into potassic host minerals in the order: biotite > muscovite > K-feldspar.
With 5 Figures 相似文献
Ammonium in Zentralspanischen Graniten, und das Verhalten des Ammonium-Ions während Anatexis und fraktionierter Kristallisation
Zusammenfassung Die Granite des Sistema Central Espanol sind reicher an Ammonium als die der meisten anderen Regionen, und haben einen durchschnittlichen NH4 + Gehalt von 84 ppm (von 1-243 ppm). Der hohe Ammoniumgehalt könme auf einen hohen Anteil peiitischer Ausgangsgesteine, die reich an organischen Material sind, and auf reduzierende Bedingungen während der Anatexis zurückgehen. Das Verhalten des Ammonium-Ions während magmatischer Differentiation wind in Hinblick seiner Verteilung in der geschichteten Intrusion von Pedrobernardo diskutiert: Ammonium ist in der finalen Schmelzfraktion angereichert, aber es gibt keine relative Fraktionierung von NH4 + and K+. Die Verarmung der Schmelze an NH4 + wahrend der Kristallisation geht darauf zurück, daß NH4 + von Biotit and in einem geringen Ausmaß von K-Feldspat aufgenommen wird. Das Verhalten des Ammonium-Ions während der Anatexis wird am Peña Negra Migmatit-Komplex diskutiert. Es zeigt rich, daß große Mengen von NH4 + in diesen hochgradig metamorphen Gesteinen vorkommen, and das NH4 + während teilweiser Aufschmelzung vorzugsweise in der Restit-Fraktion angereichert wird. Diese Beziehungen gehen auf die vorzugsweise Aufnahme von NH4 + in Kali-führenden Gastmineralen zurück, and zwar in folgender Ordnung: Biotit > Muskovit > K-Feldspat.
With 5 Figures 相似文献
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Owing to an error in a computer program, some of the LA—ICP—MSdata for yttrium presented in Tables 3, 4, 5, 6, 12 and 13 ofBea (1996) are incorrect. The following changes should be made: 相似文献
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Anomalous alkaline rocks of Soustov, Kola: evidence of mantle-derived metasomatic fluids affecting crustal materials 总被引：13，自引：0，他引：13
F. Bea A. Arzamastsev P. Montero L. Arzamastseva 《Contributions to Mineralogy and Petrology》2001,140(5):554-566
The intrusive complexes of Gremiakha-Vyrmes and Soustov represent the two extremes of the Early Proterozoic alkaline plutons of Kola, predominantly composed of feldespathoidal syenites. Gremiakha-Vyrmes rocks (zircon age: 1,884Lj Ma) have trace-element and isotope signatures (87Sr/86SrtƸ.704, )Ndt,-3-1.3) compatible with an ultimate mantle origin. Soustov syenites (zircon age: 1,872NJ Ma) are totally different and show an acute crustal imprint. They have sodaline and analcite instead of nepheline, contain a plethora of REE-HFSE-rich accessories, and are characterised by elevated contents of F, Cl, REE, Y, Th, U, Zr, Hf, Nb, Ta, Sn, Be, Li, Rb, Tl, Pb and Cs, negative Eu anomalies, K/Rb겞-160, Nd/Thƻ, and Nb/Taᄼ, with extremely high 87Sr/86Srt (>0.720) and, at the same time, relatively high )Ndt (,-1.6-1.7). In this paper, we explore the idea that the anomalous features of Soustov syenites can be explained if we assume they are derived from a metasomatic agent, initially an H2O-CO2 supercritical fluid released by alkaline mafic magmas, that was profoundly contaminated during percolation through crustal materials. As percolation advanced, the bulk composition of the fluid solute changed from alkali halides and carbonates to a silica-undersaturated alkaline melt. When the fluid cooled to a temperature of ~550-600 °C, it reached the point at which vapor and melt were no longer miscible and split into two components, a vapour phase and a Cl- and F-rich silica-undersaturated silicate melt that crystallised to produce Soustov syenites. To study this process, we have developed a numerical method for modelling the solute composition of the fluid during the infiltration metasomatism. Our results, using the LREE abundances and the Sr and Nd isotope composition of a Gremiakha-Vyrmes pegmatite as the starting solute composition of the fluid, and the mode and mineral trace-element and isotope composition of a common Kola gneiss as representative of percolated materials, indicate that the fluid would have acquired a signature closely matching Soustov's, even in the case of Nd isotopes, if the gneiss age is 2.9 Ga, near its real age. This model is still a mere working hypothesis that needs further refinements, but may represent a reasonable explanation of the genesis of anomalous alkaline rocks with high 87Sr/86Srt and )Ndt̾, either saturated or undersaturated, which are difficult to understand in terms of magmatic fractionation/contamination. 相似文献
7.
A.?GerdesEmail author P.?Montero F.?Bea G.?Fershater N.?Borodina T.?Osipova G.?Shardakova 《International Journal of Earth Sciences》2002,91(1):3-19
Murzinka and Dzhabyk are continental-type batholiths of the middle and southern East Uralian domain. They comprise mainly undeformed peraluminous K-rich granites whose elemental composition is similar to some late-Variscan granites of western Europe, but with much more primitive Sr and Nd isotope ratios. Murzinka (254±5 Ma) is composed of silica-rich granites forming two different rock series with a 87Sr/86Srinit of 0.709 and 0.704, respectively. Both series have enormous variations in εNd255 (–11.9 to –0.1 and –8.9 to +4.1) that reveal derivation from heterogeneous sources. Dzhabyk (291±4 Ma) also comprises two coeval magmas which yielded voluminous granites and quartz-monzonites, respectively, with smaller differences in 87Sr/86Srinit and εNd290 (~0.7043, +0.8 to +1.6 and ~0.7049, 0.0 to +0.8). Despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle-derived parental magma. Moreover, we suggest that Dzhabyk granitoids were generated by polybaric partial melting of Paleozoic island-arc material, whereas Murzinka granitoids derived from an extremely heterogeneous source consisting mainly of Paleozoic and Proterozoic metagreywackes. This implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the Urals. Since there is neither evidence of significant extension, nor a direct link with subduction, we suggest that the main cause for late-orogenic anatexis was elevated heat production and fertility in the protolith, perhaps combined with some additional heat from unexposed mafic intrusions. 相似文献
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In this paper we report the results of the analysis of rare earth (REE), large-ion lithophile (LILE), and high field strength (HFSE) elements in minerals from the alkaline lamprophyre dikes of the Kola region and the Kaiserstuhl province by the local method of laser ablation inductively coupled plasma mass spectrometry. The contents of Y, Li, Rb, Ba, Th, U, Ta, Nb, Sr, Hf, Zr, Pb, Be, Sc, V, Cr, Ni, Co, Cu, Zn, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu were measured in olivine, melilite, clinopyroxene, amphibole, phlogopite, nepheline, apatite, perovskite, and the host fine-grained groundmass. The obtained data on trace element partitioning among the mineral phases of the alkaline ultrabasic rocks of the dike series indicate that the main mineral hosts for the HFSEs and REEs in alkaline picrites, olivine melanephelinites, and melilitites are perovskite and apatite comprising more than 90% of these elements. Among major rock-forming minerals, melilite, clinopyroxene, and highly magnesian amphibole make a significant contribution to the balance of REEs during the evolution of melanephelinite melts. The partition coefficients of Ni, Co, Cu, Zn, Sc, V, Cr, Ga, Y, Li, Rb, Ba, Th, U, Ta, Nb, Sr, Hf, Zr, Pb, Be, and all of the REEs were calculated for olivine, clinopyroxene, amphibole, phlogopite, nepheline, perovskite, and apatite on the basis of mineral/groundmass ratios. Variations in the composition of complex zoned clinopyroxene phenocrysts reflect the conditions of polybaric crystallization of melanephelinite melt, which began when the magmas arrived at the base of the lower crust and continued during the whole period of their ascent to the surface. The formation of green cores in clinopyroxene is an indicator of mixing between primary melanephelinite melts and phonolite magmas under upper mantle conditions. The estimation of the composition of primary melts for the rocks of the alkaline ultrabasic series of the Kola province indicated a single primary magma for the whole series. This magma produced pyroxene cumulates and complementary melilitolites, foidolites, and nepheline syenites. 相似文献
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Seyed Ali Mazhari Sadraldin Amini Jalil Ghalamghash Fernando Bea 《Arabian Journal of Geosciences》2011,4(7-8):1207-1214
The Naqadeh mafic plutonic rocks are located on a plutonic assemblage and include different granitoid rocks related to ～40 Ma. U-Pb SHRIMP data shows different ages of 96?±?2.3 Ma for mafic rocks. Naqadeh mafic plutonic rocks consist of diorite to diorite-gabbros with relatively high contents of incompatible elements, low Na2O, and $ {\hbox{Mg\# }} = \left[ {{\hbox{molar}}\;{100} \times {\hbox{MgO/}}\left( {{\hbox{MgO}} + {\hbox{FeO}}} \right)} \right] > 44.0 $ . These features suggest that the Naqadeh mafic rocks originate from enriched lithospheric mantle above subducted slab during Neotethys subduction under Iranian plate. 相似文献
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A.I. Grabezhev F. Bea M.P. Montero G.B. Fershtater 《Russian Geology and Geophysics》2013,54(11):1332-1339
The Tomino–Bereznyaki ore field lies in the western part of the East Urals volcanic megazone (20–30 km southwest of Chelyabinsk). The commercial Tomino porphyry (Mo, Au)–Cu deposit is localized in the east of the field, within a small mesoabyssal intrusion of quartz–diorite composition. The epithermal Au–Ag Bereznyaki deposit is confined to subvolcanic dioritic porphyrites in the west of the field. The western and eastern parts of the ore field have a tectonic boundary. Granitoids belong to a single volcanoplutonic complex of K–Na-quartz–diorite composition. The U–Pb concordant age of zircons from the ore-bearing dioritic porphyrite of the Tomino and Bereznyaki deposits is 428 ± 3 Ma (MSWD = 0.9) and 427 ± 6 Ma (MSWD = 1.1), respectively. A Silurian absolute age has been established for the Urals porphyry Cu ore-magmatic system for the first time. The diorites and acid metasomatites of both deposits contain a unique three-mica assemblage (Mu, Pa, and Mu0.36Pa0.64). The metasomatized diorites are of similar isotope-petrogeochemical compositions; they have close total REE contents (24–52 ppm) and REE patterns. Their Zr–Hf, Nb–Ta, and La–Ce diagrams show similar trends. The obtained data indicate the close time of formation of the porphyry and epithermal deposits and their probable genetic unity. The vertical evolution of the porphyry Cu column from meso- and hypabyssal to subvolcanic level includes the isotope (Sr, S, and O) crust–mantle interaction. The deposits formed at different depths expose on the modern surface as a result of the block tectonic processes in the ore field. 相似文献