The western belt of the southern Albanian ophiolites consists of six major ophiolite massifs (Voskopoja, Rehove, Morava, Devolli, Vallamara, Shpati) and two smaller ones (Luniku and Stravaj). Each massif has a distinct sequence of mantle tectonites, ultramafic cumulates (plagioclase-bearing peridotites and wehrlites), cumulate gabbros, troctolites and isotropic gabbros. Voskopoja, Rehove and Morava have predominantly lherzolites as mantle tectonites, Shpati lherzolites and harzburgites, and Devolli and Vallamara almost exclusively harzburgites. A volcanic section together with volcanogenic sediments occurs only in the Voskopoja and Rehove massifs as well as in the smaller Luniku and Stravaj massifs. Whole-rock geochemistry and mineral chemistry suggest a mid-ocean ridge setting for the origin of the cumulates and gabbros from the Voskopoja, Rehove and Morava massifs, with only a minor suprasubduction zone (SSZ) influence. The Shpati massif and the small Luniku massif show mid-ocean ridge (MOR) and SSZ signatures in their plutonic sequences. Cumulates and gabbros from Devolli and Vallamara formed in an SSZ setting. The predominance of MOR-generated crustal rocks and the relatively minor occurrence of SSZ-generated plutonic rocks together with the volcanogenic sediments in the Voskopoja and Rehove massifs are indicative of a back-arc basin origin of the western belt ophiolites above a westward-dipping subduction zone.

Elevated P contents of up to 0.086 apfu (1.21 wt.% P2O5) were found in garnet from leucocratic granitic rocks (orthogneisses, granites, barren to highly evolved pegmatites) in the Moldanubicum and Silesicum, Czech Republic, and in complex granitic pegmatites from southern California, USA, and Australia. Minor concentrations (0.15–0.55 wt.% P2O5) appear ubiquitous in garnet from leucocratic granitic rocks of different origins and degrees of fractionation. Concentrations of P are not related to Mn/(Mn + Fe) that vary from 0.12–0.86 and to textural types of garnet (i.e., isolated anhedral to euhedral grains and nodules, graphic and random garnet–quartz aggregates, subsolidus veins of fine-grained garnet). Garnet compositions exhibit negative correlations for P/Si and P/R2+ where R2+ = Fe + Mn + Mg + Ca, while Al is constant at ∼2.05 apfu. Concentrations of Na are largely below 0.02 apfu but positively correlate with P. The main substitution may involve A-site vacancy and/or the presence of some light element(s) in the crystal structure. The substitution □P2 R2+ −1Si−2 and/or alluaudite-type Na□P3 R2+ −1Si−3 seem the most likely P-incorporating mechanisms. The partitioning of P among garnet and associated minerals in granitic systems remains unclear; however, it directly affects the distribution of Y and REEs.

Andalusite occurs as an accessory mineral in many types of peraluminous felsic igneous rocks, including rhyolites, aplites, granites, pegmatites, and anatectic migmatites. Some published stability curves for And = Sil and the water-saturated granite solidus permit a small stability field for andalusite in equilibrium with felsic melts. We examine 108 samples of andalusite-bearing felsic rocks from more than 40 localities world-wide. Our purpose is to determine the origin of andalusite, including the T-P-X controls on andalusite formation, using eight textural and chemical criteria: size-compatibility with grain sizes of igneous minerals in the same rock; shape-ranging from euhedral to anhedral, with no simple correlation with origin; state of aggregation-single grains or clusters of grains; association with muscovite-with or without rims of monocrystalline or polycrystalline muscovite; inclusions-rare mineral inclusions and melt inclusions; chemical composition-andalusite with little significant chemical variation, except in iron content (0.08-1.71 wt % FeO); compositional zoning-concentric, sector, patchy, oscillatory zoning cryptically reflect growth conditions; compositions of coexisting phases-biotites with high siderophyllite-eastonite contents (Al-iv approximate to 2.68 +/- 0.07 atoms per formula unit), muscovites with 0.57-4.01 wt % FeO and 0.02-2.85 wt % TiO2, and apatites with 3.53 +/- 0.18 wt % F. Coexisting muscovite-biotite pairs have a wide range of F contents, and F-Bt = 1.612F(Ms) + 0.015. Most coexisting minerals have compositions consistent with equilibration at magmatic conditions. The three principal genetic types of andalusite in felsic igneous rocks are: Type 1 Metamorphic-(a) prograde metamorphic (in thermally metamorphosed peraluminous granites), (b) retrograde metamorphic (inversion from sillimanite of unspecified origin), (c) xenocrystic (derivation from local country rocks), and (d) restitic (derivation from source regions); Type 2 Magmatic-(a) peritectic (water-undersaturated, Tup arrow) associated with leucosomes in migmatites, (b) peritectic (water-undersaturated, Tdown arrow), as reaction rims on garnet or cordierite, (c) cotectic (water-undersaturated, Tdown arrow) direct crystallization from a silicate melt, and (d) pegmatitic (water-saturated, Tdown arrow), associated with aplite-pegmatite contacts or pegmatitic portion alone; Type 3 Metasomatic-(water-saturated, magma-absent), spatially related to structural discontinuities in host, replacement of feldspar and/or biotite, intergrowths with quartz. The great majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin. Of the many possible controls on the formation of andalusite (excess Al2O3, water concentration and fluid evolution, high Be-B-Li-P, high F, high Fe-Mn-Ti, and kinetic considerations), the two most important factors appear to be excess Al2O3 and the effect of releasing water (either to strip alkalis from the melt or to reduce alumina solubility in the melt). Of particular importance is the evidence for magmatic andalusite in granites showing no significant depression of the solidus, suggesting that the And = Sil equilibrium must cross the granite solidus rather than lie below it. Magmatic andalusite, however formed, is susceptible to supra- or sub-solidus reaction to produce muscovite.In many cases, textural evidence of this reaction remains, but in other cases muscovite may completely replace andalusite leaving little or no evidence of its former existence.

There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian–Zambezi belt in Zambia and Zimbabwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercontinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model. We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma Gneiss and felsic metavolcanic rocks from the Lufilian–Zambezi belt in Zambian, in order to evaluate their chemical characteristics and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this study, are the Mesoproterozoic Munali Hills Granite and associated amphibolites and the Mpande Gneiss. The Neoproterozoic rocks have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements (HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested. On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoproterozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Lufilian–Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be inherited from calcalkaline sources. The Mesoproterozoic Munali Hills Granite and Mpande Gneiss have trace element features e.g., Nb–Ta depletions, which indicate that that these gneisses were emplaced in a convergent-margin setting. The MORB-normalised spider diagram of co-magmatic amphibolites exhibit a fractionated LILE/HFSE pattern recognized in subduction zones. This inference is consistent with remnants of ocean crust, juvenile Island arcs and ophiolites elsewhere in the Mesoproterozoic Irumide belt in Zambia and Zimbabwe. In addition, we report the first U–Pb zircon age of 1090.1 ± 1.3 Ma for the Munali Hills Granite. The age for the Munali Hills Granite provides new constraints on correlation and tectono-thermal activity in the Lufilian–Zambezi belt. The age of the Munali Hills Granite indicates that some supracrustal rocks in the Zambezi belt of Zambia, which were previously thought to be Neoproterozoic and correlated with the Katanga Supergroup in the Lufilian belt, are Mesoproterozoic or older. Consequently, previous regional lithostratigraphic correlations in the Lufilian–Zambezi belt would require revision.

Within the Austroalpine Grobgneiss Unit metagabbros are quite common. Several individual intrusions with an Alpine metamorphic overprint of ~520°C/~11 kbar were recently investigated. They range from olivine gabbro to gabbronorite. Some of them show a preserved magmatic textures and mineral assemblages with a well defined Permian intrusion age and a subsequent cooling history. The stable isotope data define a progressive crustal contamination from olivine gabbro to the normal gabbros.

The Albanian ophiolites are part of a large ophiolitic belt ranging from Croatia to Greece. In south Albania three subunits called Voskopoja s. str., Morava and Rehove were recently investigated. In contrast to north Albania with a clear subdivision into a eastern belt with MOR character and in a western belt formed above a supra-subduction zone (SSZ). In the investigated south Albanian ophiolites the basalts show a transitions between a MOR and a SSZ environment.

Within the western belt of the southern Albanian ophiolites, the Voskopoja ophiolite consists of duce subunits: Voskopoja, Morava and Rehove. These are predominantly lherzolites with minor harzburgites and dunites in the mantle section. Above come ultramafic and mafic cumulates including wehrlites, troctolites and olivine gabbros. Gabbronorites are restricted to the Morava subunit. Isotropic clinopyroxene gabbros, extrusives and sediments are present only in Rehove and Voskopoja. The volcanic section is dominated by basaltic breccias, including megablocks with sheeted dykes, pillow lavas and isolated dykes. The basaltic breccias grade upwards into sandstones, in turn, interlayered with argillites and cherts of Jurassic age.The basalts are predominantly clinopyroxene-plagioclase basalts, either aphyric or plagioclase phyric. Geochemically, they are divided into four groups: (1) an intermediate Ti and Zr group with low Ni (hereafter called low-Ni group), (2) an intermediate Ti-Zr group with high Ni (hereafter called high-Ni group), (3) a high-Ti-Zr group and (4) a low-Ti-Zr group. The high-Ni content in group 2 is interpreted as originating from olivine and spinel xenocrysts. Apart from the high-Ni content, groups I and 2 are comparable with the volcanics of the "low- to high-Ti intermediate ophiolites." By contrast, group 3 is more comparable to the high-Ti ophiolitic extrusives in the western ophiolite belt of northern Albania. Group 4 consists SSZ-type basalts and is widespread in the volcanics of the eastern ophiolite belt.Comparison of the ultramafic-mafic cumulates and the basaltic volcanics with those in the northern part of the western belt in Albania and the Pindos ophiolite indicates that there is a systematic variation in petrography and geochemistry from north to south in the western belt, with an increasingly distinct SSZ signature towards the south. Ultramafic and mafic cumulates, as well as basalts from the Shebenik massif in the eastern belt, are similar to those of Voskopoja, implying a genetic relationship. (C) 2002 Elsevier Science B.V. All rights reserved.

In the Eastern Alps, a heterogeneous pile of Pre-Mesozoic and Mesozoic nappes was emplaced during several distinct orogenic events. Ultramafic rocks are preserved in: (1) Pre-Mesozoic basement units of the Penninic Tauern Window and in Austroalpine basement complexes, and (2) in Mesozoic units within Penninic windows and in overlying Austroalpine segments. Geochemical data (major, trace and rare earth elements, REE, of bulk rock samples) of ultramafic rocks from 18 regions covering all the major tectonic units are presented.Metamorphic olivine-rich and clinopyroxene-rich ultramafic rocks and serpentinites from the Cambro-Ordovician Lower Schist cover units of the Tauern Window (Stubach Group, "Greiner Series") are grouped into peridotites (#Mg values = molecular 100 x Mg/(Mg + Fe-tot), 87-92; <2 wt.% Al2O3) and clinopyroxene-rich pyroxenites (#Mg = 80-92; 1-3 wt.% Al2O3). Major and trace element characteristics indicate a residual origin of most peridotites as restites after 10-20% partial melting. Most probably, the pyroxenites arc crystal segregates from a basaltic melt in a mantle transition zone. Small lenses of completely serpentinised ultramafic rocks in the Cambrian Habach Group (#Mg = 90-92) also have residual character, although they are strongly metasomatised. The Stubach and Habach Groups developed in a back arc and volcanic are setting, respectively, along the northern margin of Gondwana.Metamorphic harzburgite and dunite (#Mg = 89-90; 0.5-2.4 wt.% Al2O3) veined by metagabbroic dikes were sampled in the Austroalpine Silvretta nappe (Hochnorderer). The harzburgites represent restites after 12% partial melting in suboceanic mantle, most probably during the Cambrian. In the Austroalpine basement east of the Tauern Window, metamorphosed ultramafic rocks occur in association with amphibolite and eclogite in the Proterozoic (about 750 Ma) Speik Complex. Harzburgite and dunite (#Mg = 89-92; 0.1-0.8 wt.% Al2O3) are highly depleted in incompatible elements (2.6-35 ppb Yb) and are interlayered with small amounts of more fertile peridotite (amphibole-rich harzburgite and lherzolite, #Mg = 89; up to 3.0 wt.% Al2O3), metaclinopyroxenite (#Mg similar to 85) and hornblendite. Coarse-grained orthopyroxenite (#Mg = 89-92; 0.5-0.7 wt.% Al2O3; 19-36 ppb Yb) is present as veins and stocks in the harzburgite-dunite sequence. Chondrite-normalised rare earth element patterns of harzburgite-dunite and orthopyroxenite are characteristically U-shaped. The geochemical data indicate that harzburgites and some dunites are products of multiple melting events. They can be modelled as restites after 20-30% partial melting from already depleted mantle in a suprasubduction zone geotectonic setting. Orthopyroxenites crystallised from high(Si, Mg) melts with a significant crustal component, probably during a Cambrian subduction event.

Detailed geochemical and petrographic analyses of a lower crustal bimodal sequence near Perdoes/Minas Gerais contribute to the reconstruction of the Archean-Proterozoic evolution of the southern Sao Francisco craton. Trace element patterns of enderbites with tonalitic/trondhjemitic compositions (felsic members) indicate an origin by a two-phase partial melting process from a mantle source at depths, where garnet exists as a residual phase. Gabbroic rocks and mafic-ultramafic cumulates (mafic members) occur as lens-shaped elongated bodies exposed in the felsic complex. The gabbroic rocks are tholeiitic in composition, with rare earth element (REE) patterns indicating generation through relatively high percentages of partial melting from mantle material. Trace element ratios indicate a slightly depleted mantle source for the gabbroic rocks. Charnockites, which occur in the same area, are granitic/granodioritic in composition. The REE patterns indicate magma generation by intracrustal partial melting of tonalitic/trondhjemitic material, which must have occurred at depths of less than 40 km, where plagioclase is a stable residual phase.The whole-rock sequence shows a uniform PT path. The rocks were generated in granulite facies conditions. During exhumation, they underwent a strong retrograde amphibolite facies metamorphism, followed by a weak greenschist facies overprint.The granitic rocks of Perdoes represent a rock association that is characteristic of the transition between Archean and Proterozoic times, during which the continental crust evolved from Archean tonalite-trondhjemite-granodiorite (TTG) suites towards an increased lithologic diversity in Post-Archean time, with greater amounts of more evolved and more potassium-rich granitoids (granodiorite/granite/monzogranite (GGM) suites). (C) 2002 Elsevier Science Ltd. All rights reserved.

The Suqii-Wagga two-mica granite, situated in the western Ethiopian Precambrian, is emplaced in a high-grade migmatitic terrane. It is composed of feldspars + quartz + muscovite + biotite +/- garnet + zircon +/- allanite +/- apatite + Fe-Ti oxides + Fe sulphide. Textural studies and microprobe analyses revealed two generations of almandine-spessartine-rich magmatic garnet. The first is euhedral, fine-grained (300-350,um), commonly occurs as inclusions in plagioclase and alkali feldspars, and exhibits chemical zoning with almandine-rich cores and spessartine-rich rims. In contrast, the second variety is medium- to coarse-grained (1-7 mm) and shows reverse zoning with spessartine-rich cores and almandine-rich rims. Primary and secondary muscovites were discriminated based on the concentrations of Ti, Fe, Mn and Na. Biotite is characterised by a higher alumina saturation index than biotites of other granitoids in the area, suggesting considerable alumina concentration in the source magma.Garnet-biotite thermometry and phengite barometry were used to estimate the P-T conditions of crystallisation for the Suqii-Wagga two-mica granite pluton at similar to 7 kbar and similar to 670 degreesC. Mineral paragenesis, the composition of aluminous minerals and the P-T conditions of crystallisation indicate that samples containing fine-grained garnet crystallised earlier than those containing medium- to coarse-grained garnet. Field and petrographic investigations, mineral chemistry, and whole rock major and trace element studies suggest that the Suqii-Wagga two-mica granite has the characteristics of anatectic granite. Highly variable normative Ab/Or ratios suggested melting under varying a(H2O) conditions and/or source characteristics. The relatively high Rb/Sr, Rb/Ba and low CaO/Na2O (< 0.3) ratios indicate the derivation of the granitic magma from a plagioclase-poor pelitic source. Moreover, pronounced negative Eu anomalies and large ion lithophile element modelling suggested crystal fractionation involving plagioclase. The presence of the Suqii-Wagga Granite Pluton implies a significant contribution of older mature crustal material to the magmatic evolution of the area. (C) 2001 Elsevier Science Limited. All rights reserved.

Crystalline rocks from the western Ethiopian Precambrian terrain comprise two major rock groups: (1) the often migmatised eastern and western high-grade gneisses; and (2) the central low-grade metavolcanosedimentary rocks. Granitoid bodies of different ages and compositions intrude these rocks. Field observations, petrographic investigations, and geochemical features support a two-fold classification of the granitoid rocks. The volcanic are granitoids (VAG) are most common and include the Ujjukka granite and granodiorite, and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites. The second and geographically more restricted group represents within-plate or anorogenic (A-type) granitoids, typified by the Tullu Kapii syenite. Geochemically, the Tullu Kapii syenite is characterised by moderate to high contents of SiO2, total alkalis, Y, Nb, Ta, Hf, Zn, Zr, Ga, Sigma REE, higher ratios of Fe2O3(total)/MgO, Rb/Sr, Rb/Ba, and lower contents of CaO, MgO, Sr, and Ba, compared to the other granitoids. The VAG group shows chondrite-normalised REE patterns with slightly enriched LREE and flat HREE patterns without significant Eu anomalies. In contrast, the Tullu Kapii A-type granitoid is characterised by a nearly horizontal REE pattern with variable negative Eu anomalies. The Ujjukka granite and granodiorite; and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites originated in a two-step process, which involves batch equilibrium melting of basaltic or andesitic material producing tonalitic magma, followed by fractional crystallisation. The Tullu Kapii syenite was the product of partial melting of source rocks enriched in high field strength elements. (C) 2000 Elsevier Science Limited. All rights reserved.

The ReOs and SmNd isotopic systematics of polymetamorphic massif peridotite bodies, which have been described as ophiolites, are examined. The serpentinized mantle rocks from different tectonic units of the Eastern Alps reveal that Os isotopes are robust and provide information that field studies, petrographic and major and trace element studies do not. Presumed Paleozoic (e.g., Kraubath and Hochgrössen) and Mesozoic (e.g., Reckner Complex) bodies have uniform 187Os/188Os ratios that are slightly higher than, but within the range of, abyssal peridotites, which are presumed to represent the depleted mid-ocean ridge basalt source mantle (DMM). One serpentinite from the Penninic unit yields 187Os/188OS much lower than DMM. This mantle rock must have had a source in a long-term Re-depleted reservoir of the upper mantle. Although our understanding of the ReOs isotope system of upper mantle reservoirs is still limited, this system can be used to help constrain the tectonic evolution of diverse terrains.

Major-, trace-, rare-earth-element, and Rb-Sr and Sm-Nd isotope data of the various low-grade metamorphosed magmatic units in the Pan-African Gariep Belt, southwestern Namibia, presented in this paper, provide the basis for the reconstruction of the evolution of the late Proterozoic Adamastor ocean between the South American and Kalahari Cratons. The Gariep Belt is subdivided into two major zones, a para-autochthonous, predominantly sedimentary rift and passive continental margin succession (Port Nolloth Zone, PNZ) and the allochthonous, predominantly mafic Marmora Terrane. The latter has been thrust in southeasterly direction over the former. All of the magmatic activity in the PNZ can be related to lithospheric stretching. The earliest magmatic activity is expressed as bimodal volcanism with continental within-plate affinity along an embryonic rift graben (Posh Pinah Formation) and is found within the older sediment package of the para-autochthonous external zone of the orogen. After similar to 24 Ma, this was followed by the intrusion of mafic, tholeiitic dykes into the basement and the lower parts of the PNZ, heralding the opening of the Gariepian basin at 717 Ma.There is evidence of a series of seamounts, or an aseismic ridge, with oceanic within-plate characteristics in the Marmora Terrane. Such volcanic piles make up most of the Schakalsberge Complex and parts of the Chameis Complex. Both complexes are separated by turbidites (Oranjemund Complex), which are interpreted as continental slope deposits. In the Chameis Complex, metagabbros predominate. Most of them are part of the oceanic seamounts, but some have a markedly different chemistry, indicative of a mid-ocean ridge setting.During Pan-African collision, the Marmora Terrane formed an accretionary wedge that was thrust over the passive continental margin succession. Peak metamorphism in the thickened crust was reached at similar to 545 Ma, with erosion of the orogen having commenced as early as 540 Ma.

In the Nebelstein area, molybdenite-bearing greisens occur together with peraluminous leucogranites. In the compositional change of the granites to the greisens, there is an almost complete loss of Na, combined with a decrease in Ca, Mg, Sr, and Ti concentrations. The progressive alteration is reflected by lower homogenization temperatures and increasing salinity in aqueous fluid inclusions. The fluid regime prior to greisenization was water-dominated with low salt contents, while the early stage of the greisen development was characterized by a mixed fluid containing carbon dioxide and water. This was succeeded by a moderate saline aqueous fluid which caused the mineralization by exchange of metal ions for Na+(Ca2+, K+). A negative correlation between salt content in fluid inclusions and Na2O concentrations in the bulk rocks supports this model. Mass balance calculations for this interaction yield a minimum fluid-rock ratio of approximately 2 : I. Greisenization took place at a minimum pressure of 180 MPa (1.8 kb) and in a temperature range between 200 and < 400 °C.