Proterozoic metamorphosed sequences are identified in the Transversal Zone (TZ) domain of the Borborema geological province, Northeast Brazil. This TZ domain is located between the well-known E–W Patos and Pernambuco continental shear zones. In its eastern part, in the Taquaritinga region, a large mass of augen gneisses with a conspicuous horizontal to subhorizontal tectonic foliation forms one of the most important rock types in the region that displays U–Pb zircon ages ca. 1.52Ga. Paleoproterozoic orthogneisses dated by U–Pb on zircon at ca. 1.97Ga and older paragneisses and banded gneisses represent basement rocks, which were cross-cut by these Mesoproterozoic augen gneisses, and have been in turn intruded by plutonic rocks in upper Neoproterozoic (U–Pb and Rb–Sr, ca. 0.6Ga) times.

Large volumes of granitoids were emplaced in the Hercynian Central Iberian Zone during the last ductile deformation phase (D3, 300-320 Ma). The biotite-rich granitoids are the most abundant: (1) syn-D3 granodiorites-monzogranites (313-319 Ma) with calc-alkaline and aluminopotassic affinities; (2) late-D3 granodiorites-monzogranites (306-311 Ma), related to subalkaline and aluminopotassic series. These granitoids are associated with coeval gabbro-norite to granodiorite bodies and/or mafic microgranular enclaves. Both granitoids and basic-intermediate rocks show petrological, geochemical and isotopic evidence of interaction between felsic and mafic magmas.The mantle-derived melts, represented by shoshonitic gabbro-norites, were probably derived from an enriched and isotopically homogeneous source (Sr-i = 0.7049 to 0.7053, epsilon(Nd) = -2.1 to -2.5). In some syn- and late-D3 plutons there are evidences of essentially crustal granites, represented by moderately peraluminous monzogranites of aluminopotassic affinity. They have similar Nd model ages (1.4 Ga) but different isotopic compositions (Sr-i = 0.7089 to 0.7106, epsilon(Nd) = -5.6 to -6.8), revealing a heterogeneous crust. Potential protoliths are metasedimentary (immature sediments) and/or felsic meta-igneous lower crust materials. Large amounts of hybrid magmas were generated by the interaction of these coeval mantle- and crust-derived liquids, giving rise to slightly peraluminous monzogranites/granodiorites of calc-alkaline and subalkaline affinities, which display more depleted isotopic compositions than the crustal end-members (Sr-i = 0.7064 to 0.7085, epsilon(Nd) = -4.4 to -6.2). Petrogenetic processes involving mingling and/or mixing and fractional crystallization (at variable degrees) in multiple reservoirs are suggested.A major crustal growth event occurred in late-Hercynian times (similar to305-320 Ma) related to the input of juvenile mantle magmas and leading to the genesis of composite calc-alkaline and subalkaline plutons, largely represented in the Central Iberian Zone.

The U-Pb age of a metagranophyre from the Val de Rhemes (Brianconnais basement of the Aosta Valley) of 511 +/- 9 Ma suggests that the micaschists which dominate the pre-alpine basement of the Grand-Saint-Bernard Nappe are, in part, of Early Paleozoic age. The Brianconnais domain is characterized by a Cambrian to Ordovician alkaline to subalkaline (monozonitic) magmatism, similar in age to orthogneisses known in other parts of the Variscan belt and generally interpreted as related to an extensional event. (C) Academie des Sciences / Editions scientifiques et medicales Elsevier SAS.

Central Mindanao was the locus of a Pliocene (4–5Ma old) arc–arc collision event followed by basaltic to dacitic magmatism starting at 2.3Ma, representing the most voluminous volcanic field in the Philippines. Lava compositions range from calc-alkaline to shoshonitic. Adakites and Nb-enriched basalts are among the magmatic products. All the lavas are Na-rich (up to 4.88%), with Na2O/K2O ratios from 2.5 to 6.5. Sr, Nd and Pb isotopic compositions are similar to MORB, except for some shoshonitic lavas that have slightly less radiogenic Nd ratios. K-enrichment in basalts can be related to both fractional crystallization (FC) at moderate pressures and to partial melting of an enriched source. Trace element systematics indicate that the sub-central Mindanao mantle is characterized by the presence of garnet, phlogopite, amphibole, and perhaps some titanate phase. The enrichment of this source is attributed to the interaction of slab-derived melts, i.e., adakites, with the arc mantle. This would explain the presence of Nb-enriched basalts, transitional adakites and high-magnesium andesites, as well as the bulk Na-enrichment and relatively unradiogenic character of the central Mindanao lavas. We envision an ion-exchange type of enrichment, in which the HFSE, LILE and LREE, mobilized during slab melting, are preferentially enriched in the metasomatized mantle, resulting in a diversity of post-collision magma compositions. The MORB-like isotopic signatures of the central Mindanao lavas preclude important contributions of slab-derived hydrous fluids, sediments, continental crust or an OIB-type contaminant. Slab melting after cessation of subduction is deemed possible by thermal rebound of previously depressed geotherms. Initial contributions to mantle enrichment in post-collision sites may thus come from slab melts. In most other cases of post-collision magmatism, however, this signature can be easily masked by enrichments coming from other sources, e.g., the continental lithosphere.

The Alto Pajeu Terrain (APT) is a SW-NE trending fold belt in the Neoproterozoic Borborema Province (NE Brazil), formed by metasedimentary sequences interlayered with metavolcanosedimentary units, both intruded by granitic rocks of different compositions and ages. The tectonic evolution of the APT involves Mesoproterozoic and Neoproterozoic transtensional and contractional tectonic events. In this study, we present U-Pb zircon ages of five granitoids selected according to a generally accepted relative chronology: (a) the Tuparetama granite and Tuparetama migmatitic granite with low angle gneissic foliation represent syn-tangential rocks presumably related to a Transamazonian event; (b) the Amparo granite with high angle gneissic foliation related to the Brazilian/Pan-African event; and (c) the Tabira and Jabitaca post-strike-slip granites. The results obtained do not confirm the generally accepted chronology of events. Granites previously classified in different groups (Tuparetama, Amparo, and Jabitaca) belong to the same orogenic cycle (Brazilian). Large batholiths, previously suspected to have been emplaced after the strike-slip deformation, represent older crustal remnants within them. In each case they consist of particular rock types - an alkaline high-temperature granite (Tabira) and a 'granulite' (Tuparetama migmatitic granite). These older ages imply that pre-Brazilian crust-forming events such as the Transamazonian Orogeny (Tuparetama migmatitic granite estimated at ca. 2050 Ma) and Cariris Velhos event (Tabira granite at ca. 972 Ma) occurred in the APT, and their records survived the intense recycling which characterizes the Brazilian/Pan-African orogeny. (C) 2000 Elsevier Science Ltd. All rights reserved.

Conventional and SHRIMP II U-Pb age determinations are reported for orthogneiss zircons from four basement units of the Internal Western Alps, and for detrital zircons from the Belledonne External Crystalline Massif (ECM). The results lead to a reappraisal of the geotectonic evolution of the Penninic basements (Brianconnais and Piemont) and their pre-Alpine origin. Except for the emplacement of the Cogne granodiorite (Valle d'Aosta) dated at 357 +/- 24 Ma (conventional IDTIMS analyses) and 356 +/- 3 Ma (SHRIMP analyses), little evidence has been found for a Variscan imprint. However, results from the Peclet orthogneiss (482 +/- Ma SHRIMP) and Modane metagranite (452 +/- 5 Ma - SHRIMP) in the Sapey gneiss unit, and the Ambin metarhyolite (500 +/- 8 Ma SHRIMP) from the Ambin massif, show that a major plutonic and tectonic event occurred at 450-500 Ma. Evidence has also been found for a major plutonic event of Permian age (269 +/- 6 Ma SHRIMP age from the Gran Paradise orthogneiss) which suggests important Paleotethyan activity at least in the Piemont basement. SHRIMP dating of detrital zircons from a metasediment of the Belledonne massif (ECM) and zircon cores and xenocrysts found in most of the analysed magmatic rocks show a large Pan-African age component (590-630 Ma) in both the External and Internal Alps. This suggests that there is little difference in the composition of the basement between (1) the ECM, which show a clear continuity with Variscan Europe, (2) the Penninic basements, which may represent allochthonous Alpine terranes, and (3) the Southern Alpine and Austro-Alpine domains, classically attributed to an ''African" indenter. They all belong to Gondwana but differ strongly in their Variscan and Alpine history.

The zircon and monazite U-Pb minimum age of the Hercynian peraluminous two-mica composite granite pluton of Cabeceiras de Baste (Northern Portugal) is 311+/-1 Ma (2 sigma). This age, well constrained by a concordant monazite of 311 +/- 4 Ma (2 sigma), is in good agreement with the age suggested for the synkynematic, syn-D3, Iberian granites of the Hercynian orogeny (315-305; Pinto et al., 1987). The (Sr-87/Sr-86)(i) and epsilon(Nd) isotopic ratios, calculated for 311 Ma, suggest that the three granite units which constitute the massif may derive from an heterogeneous crustal source dated (upper intercept of the discordia) around 1 200 Ma. (C) Academie des sciences/Elsevier, Paris.

In the Central Iberian Zone (CIZ) of the Iberian Massif large volumes of granitoids were emplaced during the post-collisional stage of the Hercynian orogeny (syn- to post-D3, the last ductile deformation phase). Twelve granitic units and a quartz monzodiorite were selected for a U–Pb zircon and monazite geochronological study. They represent successive stages of the D3 event. The Ucanha-Vilar, Lamego, Sameiro and Refoios do Lima plutons are coeval (313±2 Ma, 319±4 Ma, 316±2 Ma and 314±2 Ma, respectively) and belong to the earliest stage. Later on the Braga massif was emplaced, its different units yielding the same age: 309±3 Ma for the Braga granite, 309±1 Ma for the Gonça granite and 311±5 Ma for a related quartz monzodiorite. The Braga massif is subcontemporaneous with the Agrela and Celeirós plutons (307±3.5 Ma and 306±2 Ma, respectively), in agreement with field data. The Briteiros granite is younger (300±1 Ma), followed by the emplacement of the Peneda–Gerês massif (Gerês, Paufito, Illa and Carris granites). The Gerês granite, emplaced at 296±2 Ma, seems to represent a first magmatic pulse immediately followed by the intrusion of the Paufito granite at 290±2.5 Ma. For the Carris granite a minimum emplacement age of 280±5 Ma was obtained. Based on these results the following chronology is proposed: (1) syn-D3 biotite granitoids, 313–319 Ma; (2) late-D3 biotite-dominant granitoids, 306–311 Ma; (3) late- to post-D3 granitoids, ca. 300 Ma; (4) post-D3 granitoids, 290–296 Ma. These chronological data indicate that successive granitic intrusions were emplaced in the CIZ during a short time span of about 30 Ma that corresponds to the latest stages of the Hercynian orogeny. A rapid and drastic change occurred at about 300 Ma, between a compressive ductile tectonic regime (D3, ca. 300–320 Ma) associated to calc-alkaline, monzonitic and aluminopotassic plutonism and a fragile phase of deformation (D4) which controlled the emplacement of the subalkaline ferro-potassic plutonism at 290–296 Ma.

The zircon and monazite U-Pb minimum age of the Hercynian peraluminous two-mica composite granite pluton of Cabeceiras de Basto (Northern Portugal) is 311±1 Ma (2 σ). This age, well constrained by a concordant monazite of 311±4 Ma (2 σ), is in good agreement with the age suggested for the synkynematic, syn-D3, Iberian granites of the Hercynian orogeny (315-305; Pinto et al., 1987). The ( 87 Sr/ 86 Sr), and eNd isotopic ratios, calculated for 311 Ma, suggest that the three granite units which constitute the massif may derive from an heterogeneous crustal source dated (upper intercept of the discordia) around 1 200 Ma.

The "Zone Houillere Brianconnaise" (ZHB) is the westernmost continuous unit of the Pennine domain that overlies the Pennine Front. The ZHB comprises Namurian and Westphalian formations locally overlain by Permian and Triassic cover rocks. As with other basements of the Pennine domain (Brianconnais id France, Grand Saint Bernard in Italy and Switzerland), the ZHB comprises gneissic units, whose age, origin and tectonic significance have been discussed for a long time. This study deals with the Sapey gneisses, defined near Modane (Savoie), and the Costa Citrin metagranites (Valle d'Aosta, Italy). The alpine tectonic evolution of the ZHB involves an early thrusting event that produced a non-penetrative foliation in the Carboniferous formations. This foliation occurs only in the vicinity of tectonic contacts between individual slices. The thrusting event is overprinted by a regional large-scale, eastward-verging, deformation event and then by a partly extensional event. Pre-alpine relict amphibolite-facies mineral assemblages found in the Sapey gneisses confirm that they belong to a poly-metamorphic basement. Ages from U-Pb geochronology on zircons (three samples of different lithology and from different regions) confirm this interpretation. Concordia diagrams evidence that zircons have a Proterozoic inheritance and that minimum ages are older than 360 Ma (lower intercepts with the concordia). By contrast, two samples of the Costa Citrin metagranite yielded well-defined Visean-Namurian ages at 324 +/- 17 MA and 323 +/- 8 Ma. This old basement age (early Hercynian or older) associated with evidences for a Visean-Namurian magmatic event in the ZHB are consistent with the recent reappraisal of the age of the sedimentary formations of the ZHB (now dated of Namurian to Westphalian). These data support the possible "exotism" of a "Brianconnais" terrane with respect to external domains of the Alps. The ages of the basement (pre-Carboniferous), of the sediments (Visean-Namurian) and of the recorded magmatic event (Visean-Namurian) of the ZHB cannot be related to the late orogenic basin formation and magmatic evolution of the Eastern Massif Central or of the External Basement Massifs during Stephanian times. The significance of the Visean-Namurian plutonism of the Costa Citrin is discussed with respect to other parts of the european hercynian belt. It is interpreted either to be a consequence of a late Hercynian "eastern" subduction or rather, to relate to an early extensional stage during the orogeny.

The U-Pb age of a metagranite from southern Vanoise ('Brianconnais' domain) at 479 +/- 4 Ma confirms that the micaschists which dominate this pre-alpine basement are, at least, of Early Paleozoic age. The rare magmatic rocks occurring in Vanoise and showing alkaline affinities, may be compared to the orthogneisses belonging to the Cambrian-Ordovician extensional event well known in other parts of the Varican belt.

The Orós belt is a metamorphosed and deformed supracrustal sequence whose deposition started at ca. 1.8 Ga. The volcanic rocks form an essentially bimodal association with a predominance of felsic volcanics. Mafic volcanics show geochemical and Nd isotopic differences which point to separate origins for each type. The mafic rocks are either chemically similar to EMORBs or are transalkaline types, enriched in LILE and LREE and relatively depleted in HFSE but with different isotopic signatures. One mafic type is associated with dominant andesites in a suite which could have evolved by an AFC process involving a Transamazonian-age source rock which later produced some of the overlying felsic volcanics. The rhyolites have variable geochemical signatures, all typical of anatectic products derived from continental crustal rocks. Sedimentary rocks are dominated by pelitic types of different provenances, accompanied by minor arenites and lesser carbonate rocks and calc-silicates. The depositional environment of the supracrustal sequence was continental, and a number of lines of evidence suggest that a rift environment probably developed during relaxation following the Transamazonian orogeny. The most abundant igneous rocks are felsic plutonics, emplaced nearly 100 Ma after the volcanic activity, but whose geochemical signature is similar to that of most of the rhyolites. These are cut by more alkaline anorogenic intrusives. The volcano-sedimentary sequence was intruded at ca. 0.9 Ga by a mafic-ultramafic sill. All deformation and metamorphism occurred during the Brasiliano orogeny, which was accompanied by the intrusion of syn-tectonic granites.

The late tectonic Braga plutonic complex in the “Centro Iberian Zone”, North Portugal, was emplaced during the Hercynian orogeny within a Silurian sedimentary sequence and displays an acid-basic association which consists of three well-defined intrusions: the biotite-dominant Braga granite, minor bodies of gabbro to granodiorite composition and the mildly peraluminous Gonça leucogranite. These three plutonic suites present field relationships indicating a synchronous magmatic emplacement for which a RbSr age of 310±10 Ma is obtained. The distribution of the three plutonic units along regular curves in major and trace element diagrams suggests that the different units can be genetically related. However, the RbSr and SmNd isotopic results do not indicate a unique homogeneous source and a simple fractional crystallization process. The gabbros have chemical characters (high K, Ba, Sr and light rare-earth elements and low Nb, Ti and Zr contents) and isotopic compositions (Sri=0.70497 and ϵNd=−2.5), which suggest an alkaline magmatic affinity of shoshonitic type. They are probably derived from an enriched mantle source. In contrast, the peraluminous Gonça leucogranite (Sri=0.70933 and ϵNd=−6.8) is more likely the result of crustal anatexis. The Braga granite and the evolved members of the basic series have an intermediate isotopic composition (Sri=0.70532 to 0.70733 and ϵNd=−3.0 to −6.2) which can be interpreted in terms of an hybridization process between the two previous end-members. The chemical and SrNd isotopic compositions of the Braga plutonic series can be explained by an assimilation-fractional crystallization (AFC) model between a mantle-derived magma (equivalent to the gabbros) and a crust-derived magma (the Gonça granite).

Diorites previously attributed to an early stage of the ''brasiliano'' plutonic evolution of the Serido belt yielded U-Pb zircon age of 579 +/- 7 Ma. The age of associated granites is slightly younger although a synchronous emplacement of granites and diorites is suggested by field relationships. Such an age difference may result from difficulties to distinguish 'crystallization age' from 'emplacement age'', which is still to be determined precisely.

Numerous drill holes have penetrated close to 1000 m of the volcanic pile of Mururoa atoll. The rocks are a typical example of mildly alkaline intraplate basaltic volcanics ranging from Mg-rich compositions to comenditic trachytes. Evolved basalts and hawaiites are the dominant rock types. Benmoreites and trachytes are relatively uncommon. The available KAr ages indicate a long period of activity between 11.8 and 10.7 Ma. Nevertheless, all the volcanic rocks studied are cogenetic in a broad sense (identical 143Nd144Nd and initial 87Sr86Sr ratios, constancy of ratios of highly incompatible elements). No indications of the occurrence of assimilation or magma mixing have been found. The Mururoa series is thus suitable for the study of fractionation-related processes. Three crystallization/fractionation models have been tested using trace elements, the mineral proportions taken from mass-balance calculations on major elements and individual distribution coefficients determined from trace element data on phenocrysts/host rock pairs. Closed-system fractional crystallization (CSF) is consistent with all of the trace element data. It satisfactorily reproduces the trends observed for compatible and incompatible elements, including the complex behavior of Y and rare-earth elements which are fractionated by kaersutite and apatite in mugearitic and benmoreitic magmas. In situ crystallization and equilibrium crystallization produce trends very close to Rayleigh's law model for most incompatible elements. In contrast, in situ and equilibrium crystallization models produce significant underdepletions (compared to CSF) in compatible elements (Sc, Cr, Co, Ni). The corresponding patterns are not consistent with our analytical data in intermediate and evolved rocks. Cooling calculations indicate, however, that the length of volcanic activity in Mururoa ( ≥ 1 Ma) is hardly compatible with closed-system fractional crystallization of a single magma batch. Various models of open-system fractionation have thus been tested, but generally they do not fit the observed trace element patterns. However, one peculiar case of open-system fractionation in a periodically replenished magma chamber is consistent with the data. In this model, batches of mantle-derived parent liquids filling up the chamber at the beginning of each cycle evolve by fractional crystallization. All the corresponding residual liquids either crystallize or erupt at the end of each cycle, before the next replenishment. Thus, the apparently cogenetic Mururoa series is likely to result from fractional crystallization occurring under similar conditions through time, either in several magma chambers or in a single periodically refilled reservoir.

U-Pb on zircon, Nd and Sr isotopic compositions are reported for die Guena gneisses and Mfoubou granite belonging to the Mayumbian belt of South-Western Congo. The belt overthrusts the Archaean basement of the Congo craton; it extends NW-SE from Gabon to Angola and is composed by a Lower-Proterozoic polycyclic basement and a Middle to Upper Proterozoic volcano sedimentary sequence. Tectonic and metamorphic evolution of the belt is believed to have occurred during the Pan-African orogenesis. The U-Pb on zircon age of 2014 +/- 56 Ma for the Guena gneiss confirms its Eburnean age whereas the 1050 +/- 25 Ma emplacement age of the Mfoubou granite and its transitional magmatic affinity are in agreement with the Mid-Proterozoic intracratonic rifting model proposed by Franssen and Andre (1988).Gneiss and granite show similar (T(Nd))DM ages (2.6 - 3 Ga). Their negative initial (e(T))Nd Values (-5 to -6 at 2 Ga for the gneiss and -15 to -16 at 1 Ga for the granite) imply that both are derived from an Archaean protolith including a LREE enriched crustal component. Pan-African metamorphic imprint is shown by Sr isotopic data on biotites and induces opening of Rb-Sr whole rocks system. From these data it is suggested that the polycyclic part of the Mayumbian belt represents essentially recycled material from an Archaean basement with only restricted new injections of mantle material.

The Mururoa volcanic rocks belong to a mildly alkalic magmatic series. They range in composition from oceanites and Mg-rich basalts to peralkaline (comenditic) trachytes. Basalts and hawaiites are the most common types. Petrographic, mineralogical and geochemical data obtained on 248 samples indicate that the petrogenesis of the Mururoa series is controlled by closed system fractional crystallization of basaltic magma originating from a mantle source containing a HIMU component. Sr, Nd, isotopic data are homogeneous and therefore preclude the occurrence of assimilation processes. The available data do not support the occurrence of magma mixing processes; variations in the partial melting degrees of the mantle source have not been detected. The main peculiarities of the fractionation sequence are : (1) important separation of amphibole together with apatite leading to the depletion in rare earth elements of the benmoreitic magmas ; (2) fractionation of sodic plagioclase followed by alkali feldspar, leading to peralkaline residual liquids. Trace element behaviour throughout the suite is best modelled by Rayleigh's law. Alternative models (equilibrium crystallization ; in situ differentiation) are not supported by our data. Fractionation in a periodically replenished magma chamber is considered as a plausible process as far as the corresponding geochemical variations follow Rayleigh's law, i.e. if all the liquids are removed from the magma reservoir before its replenishment.

A dominant feature of the Braga region (Centro-Iberian Zone) is the abundance of syn-to late-tectonic Hercynian granite plutons controlled by the major Vigo-Regua shear zone. They are biotite-dominant aluminous granites defining separate series based on their chemical and mineralogical compositions. The large development of such plutonism along the Iberian domain supports the predominance of crustal recycling during the main Hercynian tectonic phase (F3) and suggests, for the genesis of the magmas, a complex mechanism which may associate different processes such as partial melting of an heterogeneous crust and mixing of magmas.