摘要:

AbstractThe isotope characteristics of interbedded fine‐grained sedimentary rocks and pebbles from an Ashgill sequence in the Welsh Basin show that they have different provenance. Gondwana‐derived continental crustal material dominates the Nd‐Sr isotope signatures of the fine‐grained rocks whereas the pebbles sample the Avalonian basement. Detritus from Gondwana and Avalonia accounts for the isotopic composition of most of the lower Palaeozoic sedimentary rocks of Southern Britain and this suggests that any contribution from the reworking of Lower Palaeozoic volcanic rock is

ISSN:0072-1050    

DOI:10.1002/gj.3350290102

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractHercynian gabbroic, dioritic and tonalitic rocks crop out in the neighbourhood of Rovale (Sila Grande, Calabria). They make up a crude rectangular outcrop with the western part consisting of gabbroic rocks and the eastern of dioritic and tonalitic rocks. They come into contact with medium to high grade metapelites on the western side and with heterogeneous granodiorites on the other sides. In the gabbroic body both opx ± ol bearing cumulates and amphibole differentiates occur and are characterized by the widespread presence of brown pargasite. Sporadic magmatic to subsolidus corona textures between olivine and plagioclase or orthopyroxene and plagioclase can be observed and their preservation clearly suggests a post‐tectonic emplacement for the gabbroic magma. Diorites and tonalites display hypidiomorphic textures free of olivine and orthopyroxene and bearing green Mg‐hornblende. The granitoids, on the basis of chemical data, display orogenic features of the continent‐continent collision type. The gabbroic rocks have high Al tholeiitic composition and fractionation of orthopyroxene and plagioclase played an important part in their evolution.The Rb/Sr isochron method did not give a precise emplacement age for the granitoids as a whole. Initial87Sr/86Sr ratios (at 290 Ma) are higher in the gabbroic body (0.7091–0.7095) than in diorites and tonalites (0.7083–0.7092). Thus gabbroic rocks appear more displaced than diorites and tonalites towards crustal isotopic composition. The eNd data seem to confirm this feature, thus suggesting that the gabbroic rocks and diorites derived from distinct mantle magma batches. Interestingly, small isotropic gabbroic masses occur within the diorites and show general features that allow them to be considered as possibly parental with respect to the host diorites. The evolution to the dioritic composition might have occurred through fractionation and minor mixing with a more acidic component such as the northern granodiorites.Geochemical, Sr and Nd isotopic data indicate a scenario of a composite plutonic body formed by distinct magma batches of mixed crust and man

ISSN:0072-1050    

DOI:10.1002/gj.3350290103

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe La Hague region of northwest France exposes Palaeo‐Proterozoic Icartian gneisses which were reworked and intruded by calc‐alkaline plutonic rocks during the Cadomian Orogeny (about 700–500 Ma).40Ar/39Ar mineral cooling ages have been determined to clarify the timing of the regional metamorphism of orthogneisses and the emplacement of quartz diorite plutons in this region. Metamorphic amphiboles within Icartian gneisses display discordant40Ar/39Ar apparent age spectra interpreted to result from limited Variscan (about 350–300 Ma) overprinting of intracrystalline argon systems which initially cooled through post‐metamorphic hornblende closure temperatures during the Cadomian at about 600 Ma. Igneous hornblendes from the weakly foliated Jardeheu and Moulinet quartz diorites record isotope correlation ages of 599 ± 2 and 561 ± 2 Ma, respectively. Igneous hornblende and biotite from foliated quartz diorite on the nearby Channel Island of Alderney record isotope correlation ages of about 560 Ma. The results imply that metamorphic and plutonic events in the La Hague‐Alderney region were approximately contemporaneous with those recorded on Guernsey and Sark, which are thus likely to have formed part of the same tectonic block during the Cad

ISSN:0072-1050    

DOI:10.1002/gj.3350290104

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Calabrian–Peloritan Hercynian Range includes three weakly metamorphosed Palaeozoic sequences cropping out in north‐eastern Sila (Bocchigliero sequence), southern Sila, Serre and Aspromonte (Stilo sequence), and in the Peloritan Mountains (Peloritan sequence). The work reported here considers the Bocchigliero sequence and comprises part of a geological, petrological and geochemical research programme on the Palaeozoic evolution of the Calabrian–Peloritan Arc.The Bocchigliero sequence constitutes the lower tectonic unit of the Hercynian Caiabrian–Peloritan Range and is overthrusted by the metamorphic Mandatoriccio Unit. The Bocchigliero sequence is a terrigenous–carbonate–volcanic association, is affected byclow grade metamorphism, contains Cambro‐Ordovician fossils and extends in age from the Cambrian to the Devonian. The terrigenous material is represented by meta‐arenites and metapelites (Cambrian–Devonian); the volcanics include metatuffites (Cambrian and Ordovician), metabasalts (Cambro‐Ordovician), metaandesites and metarhyolites (Ordovician and Siluro‐Devonian); limestone beds are present in the Devonian. It is believed that the Palaeozoic Bocchigliero basin formed in the Cambrian on a continental crust in which the rocks constituting today's Mandatoriccio Unit were located at 3–8 km depth. The crustal thinning in the Cambro‐Ordovician led to fracturing and upwelling of alkaline within‐plate basaltic magmas, whereas in the Ordovician the thinning took place under conditions of higher plasticity. In this latter period an increase in temperature resulting from mantle upwelling produced crustal partial melts of andesite and rhyolite composition. In addition, this thermal uprise was responsible for regional metamorphism characterized by low pressures and by the absence of penetrative deformation. The effects of this metamorphism are well developed in the rocks of the Mandatoriccio Unit. In the Silurian and Devonian, progressive closing of the basin took place. The Palaeozoic sequence was then subjected to Variscan low pressure–low temperature metamo

ISSN:0072-1050    

DOI:10.1002/gj.3350290105

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo granitoid series have been distinguished in the Tribeč Mountains (Western Carpathians) on the basis of the contrasting petrological behaviour of their accessory minerals. The allanite–magnetite‐bearing (AM)tonalite–granodiorite–granite series typically contains dark magmatic enclaves and is produced from oxidizing, more hydrous (about 5.2 wt.% water) melts that were emplaced at depths equivalent to 350 ± 100 MPa. The monazite‐bearing (M) tonalite–granodiorite–granite series contains only metamorphic xenoliths and comes from reduced and drier (about 2.3 wt.% water) melts that were probably emplaced at a shallower depth. The inferred magma properties probably reflect source rock effects. The mineralogical discrimination scheme between the AM and M series corresponds broadly to I‐ and S‐type subdivision and may be useful not only for the granitoid bodies in the Western Carpathians but also for the whole Var

ISSN:0072-1050    

DOI:10.1002/gj.3350290106

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290107

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290108

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290110

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290112

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290113

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY