I welcome the comment from Dewey and Ryan on my paper (Searle, 2021), and the chance to clarify some conflicting Caledonian tectonic models and new ideas. As outlined in the paper, my review was based on the geology of Scotland, not Ireland, Newfoundland or the rest of the Caledonian orogeny beyond, mainly because of length constraints, and the fact that my personal field experience lies mainly in Scotland. The Great Glen fault and the Moine Supergroup are not exposed at all in Ireland, so critical parts, and half of the Caledonian orogeny are missing in Ireland. I argue that the Caledonian geology of Scotland can be explained by a Laurentia – Midland valley arc-microcontinent collision, progressing from NW-directed ophiolite obduction in the Late Cambrian to crustal thickening and regional metamorphism during the Ordovician and Silurian, across the Dalradian and Moine metamorphic rocks. Caledonian structures do continue north into Greenland, as summarized by Leslie et al. (2008), but the geological evolution of the Scottish Caledonides does not require any collision with Baltica. The Dewey and Ryan comment raises major tectonic questions, which this reply addresses.

The Abu Kharif area in the Northern Eastern Desert consists of contrasting granitic magma suites: a Cryogenian granodiorite suite (850–635 Ma), an Ediacaran monzogranite suite (635–541 Ma) and a Cambrian alkali riebeckite granite suite (541–485 Ma). Tungsten mineralization occurs within W-bearing quartz veins and a disseminated type confined to the monzogranite.

Whole-rock geochemical data classify the granodiorite as a late-orogenic I-type with calc-alkaline affinity, while the monzogranite and alkali riebeckite granite represent respectively a post-orogenic highly fractionated I-type with calc-alkaline affinity and an anorogenic A1-subtype with alkaline affinity. Geochemical modelling indicates that the three intrusions represent separate magmatic pulses where the granodiorite was generated by ∼75 % batch partial melting of an amphibolitic source followed by fractional crystallization of hornblende, biotite, apatite and titanite. The monzogranite was formed by 62 % batch partial melting of the normal ‘non-metasomatized’ Pan-African crust of calc-alkaline granite composition followed by fractional crystallization of plagioclase, biotite, K-feldspar, magnetite, ilmenite, with minor apatite and titanite. The alkali riebeckite granite was generated by 65 % batch partial melting of metasomatized Pan-African granite source followed by fractional crystallization of plagioclase, K-feldspar, amphibole and biotite with minor magnetite, apatite and titanite. In general, the parent magmas of the three intrusions were originally enriched in W, but with different concentrations. This W-enrichment would be caused by magmatic-related hydrothermal volatile-rich fluids and concentrated within the monzogranite.

The orogenic process and crustal growth of the Changning–Menglian Palaeo-Tethys orogenic belt in the southeastern Tibetan Plateau is not fully understood. Triassic Caojian rhyolites and granites occur extensively in this orogenic belt and represent important constraints for this issue. This study aims to examine the relationships between the Triassic Caojian rhyolites and granites and to gain a better understanding of their possible petrogenesis. The study used zircon U–Pb geochronology, trace element analyses and Sr–Nd–Hf isotope data to better understand the relationships and possible origin of the rhyolites and granites. Recent zircon U–Pb ages indicated that the Caojian rhyolites were emplaced at 227.2 Ma, whereas age estimates for Caojian granites were slightly older (233.4–236.9 Ma). The Caojian rhyolites are enriched in large-ion lithophile elements and high-field-strength elements, with elevated FeOtot/MgO and Ga/Al ratios. However, they are significantly depleted in Ba, Sr, Eu, P and Ti. These geochemical characteristics indicate that they have an A-type affinity. Furthermore, the Caojian granites comprise biotite monzogranites and granodiorites and show unfractionated composition. Mineralogically, the Caojian granites were found to contain diagnostic I-type minerals such as hornblende. Geochemical data suggest that the petrogenesis of the Triassic Caojian rhyolites is characterized by rejuvenation of crystal mush represented by the Triassic Caojian granites. The necessary thermal input was supplied by mafic magma. This magmatic evolution was likely related to lithospheric delamination and upwelling of the asthenosphere during the Mid- to Late Triassic, forming post-collisional I-type granites and A-type volcanics in the Changning–Menglian Palaeo-Tethys orogenic belt.

Classic tectonic models for the Caledonian orogeny in Scotland involve Ordovician collision of Laurentia–Midland Valley arc (Grampian orogeny), followed by middle Silurian collision of Laurentia–Baltica (Scandian orogeny) and 500–700 km of sinistral displacement along the Great Glen fault separating the Northern Highlands (Moine Supergroup) from the Grampian Highlands (Dalradian Supergroup). A review of the timing of magmatic and metamorphic rocks across Scotland allows a simpler explanation that fits with a classic Himalayan-style continent–island arc–continent collision. Late Cambrian – Early Ordovician NW-directed ophiolite obduction (Highland Border complex) coincided with the ending of stable continental shelf sedimentation along the eastern margin of Laurentia. Following collision between Laurentia and the Midland Valley arc–microcontinent in Early Ordovician time, crustal thickening and shortening led to almost continuous regional metamorphism from c. 470 to 420 Ma, rather than two discrete ‘orogenies’ (Grampian, Scandian). U–Pb monazite and garnet growth ages indicating prograde metamorphism, and S-type granites related to melting of crustal protoliths are coeval in the Grampian and Northern Highlands terranes. There is no evidence that the Great Glen fault was a terrane boundary, and strike-slip shearing post-dated emplacement of Silurian – Early Devonian granites. Late orogenic alkaline granites (c. 430–405 Ma) in both Moine and Dalradian terranes are not associated with subduction. They are instead closely related to regional alkaline appinite–lamprophyric magmatism resulting from simultaneous melting of lower crust and enriched lithospheric mantle. Caledonian deformation and metamorphism in northern Scotland, with continuous SE-directed subduction, show geometry and time scales that are comparable to the Cenozoic India–Kohistan arc–Asia collisional Himalayan orogeny.

High temperature microthermometry and Scanning Electron Microprobe (SEM) analyses were used to study natural magmatic remnants in quartz crystals in granitoids from the Timna Igneous Complex, southern Israel, and to constrain physicochemical parameters during their crystallization. For the porphyritic granite, alkali granite and quartz monzodiorite, liquidus temperatures are 710–770, 770–830 and 770–840°C, respectively; solidus temperatures are 690–770, 710–790 and 770°C, respectively. Pressures during crystallization and water content in the magmas were determined using the phase diagram of the modal granite system. The determined P-T-conditions are typical for water-saturated granitoid magmas (>4–8 wt.%) generated and crystallized at a shallow crustal level.

SEM data on melt inclusions support conclusions of previous investigations on two types of granitoid magmas exposed in the Timna Igneous Complex: the porphyritic and alkali granites. Different trends of crystallization are proposed for these granites. Crystallization of the porphyritic granite started with cotectic crystallization of plagioclase and terminated in residual K-feldspar-rich crystallization; crystallization of the alkali granite took place at higher temperatures, starting with K-rich alkali-feldspar crystallization and terminating in residual Na-rich eutectic crystallization.

Parameters not available from other sources — temperature and pressure of the liquidus and solidus stages, water content, trends of crystallization — were obtained for the porphyritic and alkali granites.

In this paper we present new petrological and geochemical data for two peraluminous granite batholiths (Nisa Alburquerque and Jalama batholiths) representative of the ‘Araya-type’ granites of the Central-Iberian Zone. Both granites are composite with several facies (monzogranites and leucogranites) that can be grouped into two main granite units: the external units and central units. Intrusive relationships and lack of geochemical coherence between the central and external units indicate that they are not comagmatic but represent different pulses. The central units of both batholiths are petrologically and geochemically different. On the other hand, external units show a lot of similarities and are the main object of this study. The main characteristics of the external granites can be interpreted in terms of an incomplete fractional crystallization process of early mineral phases (plg + Kf + bt) which probably took place at the level of emplacement. Other possible mechanisms of magmatic differentiation (magma mixing, restite unmixing, sequential melting) can be discarded based on field, petrography and geochemical data. We propose that the ‘Araya-type’ granites are formed by the intrusion of distinct magma pulses (central and external). Further evolution within each pulse can be due to incomplete fractional crystallization possibly taking place at the emplacement level.

Studies of the mafic mineralogy of the Mulanje granite-quartz-syenite-syenite Massif of southern Malawi delineate two mineralogically distinct complexes—the Main complex and the Chambe complex. Each complex is associated with its own trend of pyroxene evolution. The Main complex pyroxenes exhibit initial enrichment in hedenbergite before subsequent enrichment in acmite (i.e. sodic-salite-sodic-hedenbergite-aegirine-hedenbergite-aegirine), whereas the Chambe pyroxenes display constantly increasing acmite content with no significant enrichment in hedenbergite (i.e. sodic-salite-aegirine-augite-aegirine). This phenomenon is also reflected in the more Mg-rich amphiboles and biotites of the Chambe rocks when compared to those of the Main complex.

The general evolutionary trend of the Main complex amphiboles is katophorite → ferroricherite → arfvedsonite which broadly correlates with a change in rock type from syenite to granite. Superimposed on this trend is an essentially similar, yet less extensive trend of the more Mg-rich Chambe amphiboles. The micas of both complexes show a general evolution to more iron-rich compositions with relatively constant Al content. Those of the Main complex, however, display extreme iron enrichment with ultimate formation of essentially pure ferrous annite.

Aenigmatite, astrophyllite, fayalite, chevkinite, yttrofluorite, and unidentified RE minerals are characteristic of the Main complex rocks but totally absent from those of the Chambe complex. Ilmenite constitutes the only iron oxide phase in the Main complex rocks whereas titaniferous magnetite (now unmixed) and ilmenite are both present in the rocks of Chambe.

The differences between the two complexes are explained in terms of oxygen fugacity, silica activity, crystallization interval, and the relative rates of development of peralkalinity. In essence, the Chambe magmas are considered to have crystallized under high fO2 conditions with an earlier development of peralkaline tendencies when compared to those of the Main complex magmas. Moreover, a lower initial silica activity, a smaller alkali to alumina ratio, and a correspondingly smaller crystallization interval could account for the lack of highly evolved granitic magmas in the Chambe complex, whereas such magmas are integral in the evolution of the Main complex.

This paper presents the results of an experimental study of muscovite solid solutions in the system K2O-M2+O-Al2O3-SiO2-H2O-(HF), with M2+ = Mg2+ or Fe2+ in the temperature range 300-700°C under 2 kbar PH2O. Muscovite solid solutions can be described, in this system, as the result of two substitutions. One is the phengitic substitution (x), which preserves the pure dioctahedral character of the mica; the second is the biotitic substitution (y), which leads to trioctahedral micas and does not change the composition of the tetrahedral layer Si3Al. The general formula of muscovite in this system is K(Al2−x−2y∕3M2+x+y□1−y∕3)(Si3+xAl1−x)O10(OH,F)2. Both substitutions x and y are more extensive at lower temperatures. The extent of solid solution decreases drastically with increasing temperature.

For T > 600°C, the phengitic substitution (x) becomes negligible, but some biotitic substitution (y) persists. This unsymmetrical decrease of the solid solution of muscovite with increasing temperature is similar to that previously observed in phlogopite, the micas with a tetrahedral layer composition of Si3Al being the most stable. The behaviour of muscovite solid solutions in the ferrous system is qualitatively identical to that observed in the magnesian one, but the extent of solid solution is smaller than with Mg2+. Fluorine neither changes the size nor the shape of the solid solution fields but increases their stability by about 50°C.

A comparison of these experimental results with data on natural muscovites is presented. Most natural primary (magmatic) granitic muscovites lie very close to the muscovite end member, in agreement with their high-temperature origin. Low-temperature muscovites (300–400°C), typically muscovites from hydrothermally altered granitic rocks, can have high x and y values. The rate of the biotitic substitution y can reach 0.6, which corresponds to an octahedral occupancy of 2.2 atoms per formula unit (based on 11 oxygens), consistent with the experimental data.

This study documents the textures and chemical evolution of igneous quartz (Qz) in granite from the Oslo Rift (Norway) during the magmatic-hydrothermal transition. Contrary to the other major igneous phases, primary quartz is well preserved. SEM-CL imaging documents four types of quartz (Qz1— Qz4). Qz1: bright primary magmatic quartz that grew under H2O-undersaturated conditions and developed a conspicuous sector zoning. Qz2: light grey luminescent secondary quartz that surrounds Qz1 and altered Qz1 in a ‘non-destructive’ process. Qz3: is usually darker than Qz2 and intersects Qz1 and Qz2. It is formed by dissolution/recrystallization processes involving saline deuteric fluids. Qz4: found in narrow cracks and patches of black quartz intersecting all the other types. EPMA in situ analyses of the different quartz generations confirm that the intensity of luminescence of quartz is positively correlated with the Ti content of the quartz. Aluminium and K are mostly incorporated in quartz in the form of [AlO4/K+]0 centre defects. In the Drammen granite, the Ti and Al contents of Qz1 averages 200 ppm and 80 ppm respectively. Titanium in Qz1 varies from 50 to 95 ppm in the peralkaline granite known as ekerite, whereas Al is irregular and ranges between 100 ppm and values below the limit of detection (LODAl at 2σ = 14 ppm). In all samples, Qz2 and Qz3 are strongly depleted in Ti and Al compared to Qz1. Either the Ti content in Qz2 is falling gradually towards Qz1 or more abruptly, whereas it is sharp from Qz3 towards Qz1 and Qz2. Potassium is variable in all four quartz types and samples, and ranges from values below the detection limit (LODk, at 2σ = 8 ppm) to 120 ppm. Grains in Qz4, being only 1–2µm wide, could not be resolved with the EPMA beam. In all granites, quartz crystallized from haplogranitic melts at P ~1.5 kbar and T = 700—750°C. SEM-CL and EPMA studies of igneous Oslo Rift quartz illustrate vividly the complex chemical and physical processes that characterize the magmatic-hydrothermal transition in shallow granitic systems and show that the chemistry of primary aqueous fluids is strongly modified from its primary igneous composition before eventually being expelled from the granitic system and perhaps incorporated in ore-forming hydrothermal convection systems.

The geochemical evolution of tin-tungsten deposits and their associated sulphides can be discussed in terms of four sequential processes: acquisition of the ore-forming elements (OFEs) by the granitic magma, emplacement of these elements in minerals and residual melt of the crystallizing granite, release of the OFEs to the circulating hydrothermal fluids and transport to the depositional sites, and finally, deposition of ore minerals through interaction of these fluids with the wall rock. Based on their crystallographic behaviour, it is useful to distinguish three principal classes of OFEs, here identified as BOC, LHC, and ALC elements. BOC (bivalent octahedral cation) elements are similar to ferrous iron and here are represented mainly by Zn, Mn, and perhaps Cu. Li also belongs to this class, although it is monovalent. LHC (large highly charged cations) elements encompass As, Nb, Mo, Sn, Sb, Ta, and W and they are similar to ferric iron or titanium in their crystallographic role. ALC (alkali-like cations) are capable of occupying alkali positions and are represented mainly by Pb, Ag, and Hg.

LHCs are rejected from the polymerized silicate liquid network and become enriched in the roof of the acid magma chamber, where more non-bridging oxygens are available. Transport to the roof may be enhanced by the formation of hydrous complexes, as is the pronounced enrichment of Na and Li. BOCs, along with Cl, F, and B, fractionate strongly into the vapour phase during vesiculation. HCl in the ore fluid is crucial for the alteration process and can be produced during boiling by a hydrolysis reaction of the NaCl dissolved or immiscibly present in the silicate magma.

Considerable laboratory information is available concerning release mechanisms of the OFEs to hydrothermal fluids. We can distinguish congruent and incongruent dissolution, both in response to acid buildup, as well as congruent and incongruent exchange not involving HCl. Melt-fluid fractionation is also thought to be important, though the physical mechanisms are not well understood. Any of these release mechanisms may be coupled with reduction or oxidation reactions. LHC, BOC, and ALC elements respond differently to each of these mechanisms, and these differences may in part be responsible for the observed separation of ore minerals in space and time. It is suggested that LHC elements are released preferentially during acid, non-oxidizing conditions typical of early stages, while BOC elements respond more readily to later acid-oxidizing environments, as well as exchange reactions with or without oxidation.

Depositional reactions have been formulated with respect to two contrasting types of country rocks: carbonates and schists. Differences are related to the process of neutralization of the HCl produced by ore deposition: carbonate dissolution on one hand and feldspar-muscovite or biotite-muscovite conversion on the other. In carbonate rocks, evaporite-related sulphates may provide the H2S necessary for sulphide precipitation, while in schists disseminated sulphides and organic matter may be important sulphur reservoirs in addition to the sulphur liberated from the granite. A variety of situations can be envisaged with respect to the sources of the OFEs and the sulphur species required for ore deposition, including granite and wall rocks. Chloride is recognized as the crucial anion for OFE release, transport, and deposition, although F and B play a role yet to be evaluated. Final HCl neutralization is an essential step in the reactions responsible for the deposition of ore minerals.

The ultimate sources of the OFEs must be related to the continental material involved in the process of melt production by partial melting. Oxidized sediments provide sources for LHC and ALC elements in the form of heavy minerals and clastic feldspars and micas. Organic-rich reduced sediments are hosts to BOC and LHC elements as sulphides and ALC elements in organic matter. Remelting of igneous and metamorphic rocks can enrich LHC, BOC, and ALC elements in the melt by extraction from opaques, Fe-Mg silicates, feldspars, and micas.

Uraninite is widespread as an accessory mineral in the Erzgebirge granites. It occurs throughout the entire comagmatic series of strongly peraluminous S-type Li-mica granites and has been discovered in more evolved transitional I-S type biotite and two-mica granites, but is rare in those of A-type affinity. Textural relationships and chemical ages imply that uraninite is of magmatic origin. Its composition is variable with a proportion of U plus radiogenic Pb between 71 and 99 mol.%. Uraninite has incorporated Th, Y, and the REE in total amounts between 1 and 29 mol.%. Elements such as P, Si, Al, Ca, and Fe are subordinate. Uraninite from two-mica and Li-mica granites is low in ThO2 (0.8–6.5 wt.%), Y2O3 (0–0.8 wt.%) and REE2O3 (0.1–0.6 wt.%). In contrast, biotite granites from the Kirchberg pluton contain uraninite which is enriched in these components (in wt.%) (ThO2 = 5.6–11.0, Y2O3 = 0.6–5.5, Ce2O3 = 0.1–0.6, Dy2O3 = 0.2–1.1). Commonly, the lanthanide and actinide contents in uraninite correlate poorly with those in the host granite. In S-type Li-mica granites as well as fractionated two-mica and biotite granites, uraninite is the dominant contributor to the bulk-rock U content. Here the proportion of U approaches 80–90%.

Trioctahedral micas in the Karlovy Vary pluton range in composition from Fe-biotites in the granites of the Older Intrusive Complex (OIC) through siderophyllite and lithian siderophyllite to zinnwaldite in the granites of the Younger Intrusive Complex (YIC). Li + AlVI + Si would appear to substitute for Fe2+ + AlIV in biotite with a formula similar to that given in Henderson et al. (1989), but Li + Si appears to substitute for Fe2+ + AlIV in the Li-micas. In mica vs. host rock plots, Rb and F show positive linear covariation except for the Li-mica granites, but femic constituents and tFeO/(tFeO + MgO) have separate trends for OIC and YIC granites and micas. Further differences between OIC and YIC granite micas are seen in their Ti and Mg contents and in plots like V vs. SiO2, AlIVvs. Fe/(Fe+Mg) and Li vs. total iron as Fe2+ and in the results of discriminant analysis. These reveal a geochemical hiatus between OIC and YIC granite micas that coincides with a major temporal hiatus.

Biotite compositions in the YIC granites are similar to those in the granites of the Cornubian batholith and reveal a similar magmatic evolution and genesis in which later biotites evolve to lithian siderophyllites with some enrichment in trace alkalis and F. It is suggested that the biotite granites in the YIC were derived from the products of partial fusion of the OIC granites. A less well-marked geochemical hiatus exists between YIC biotites and zinnwaldites. In some plots (e.g. Si vs. Li, Li vs. tFe) apparent continuity between biotite and the Li-micas suggests continuous evolution, but in others (e.g. Rb vs. TiO2, Rb(biotite) vs. Rb(rock)), Li-mica data points stand apart from the biotites suggesting, like the whole rock data, a separate evolution. Comparison with the more abundant data for Li-micas of the Cornubian batholith suggests derivation of the Li-mica granites by partial fusion of the OIC/YIC granite residues.

We review the causes, mechanisms and consequences of crustal anatexis during the exhumation of metamorphic terranes, from a petrological perspective. During both prograde and retrograde metamorphism, limited influx of free hydrous fluids may result in small volumes of very hydrous melts, which cannot ascend far (if at all) before reaching their solidus. If thermal conditions for dehydration melting are attained in fertile micaceous crustal layers, much larger volumes of water-undersaturated granitic magmas may result, especially where limited external fluid influx raises water activities above those that may be buffered by dehydrating hydrous phases. Magmas have specific trace element characteristics depending on the reaction which formed them which, combined with accessory phase thermometry, may enable the (P-T) conditions of melting to be ascertained. Small volume-fraction magmas will typically remain as in situ migmatites unless their extraction is assisted by deformation. In turn, deformation will be focused in weaker partially molten zones, so that water-undersaturated magmas may often be mobilized. Once segregated, their ascent is limited by the rate of dyke propagation, and they may reach shallow levels (<2 kbar) before crystallizing. The complex interplay between deformation and melting is exemplified by the Miocene evolution of the central Himalaya, where thrust and normal faulting, melting and exhumation were all simultaneously active processes which were linked by feedback relations. In the Nanga Parbat Massif of the western Himalaya, rapid post-Miocene denudation and vigorous fluid flux enabled rocks to experience more than one episode of melting simultaneously, at different levels of the same exhuming crustal section.

The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- and trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondritenormalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/ trachytic/ phonolitic complexes of the Serra do Mar and elsewhere.

Lithium mineralization is common in the Central Iberian Zone and, to a lesser extent, in the Galizia-Trás-OsMontes Zone of Spain and Portugal, occurring along a ∼500 km-long NNW-SSE striking belt. There are different styles of Li mineralization along this belt; they are mainly associated with aplite-pegmatite bodies and, to a much lesser extent, with veins of quartz and phosphate. Lithium mineralization in the Central Iberian Zone may be classified into four types: aplite-pegmatite dykes occurring in pegmatitic fields, Li mineralization associated with leucogranitic cupolas, beryl-phosphate pegmatites and quartz-montebrasite veins. The main Li minerals of these bodies include Li-mica, spodumene and/or petalite in the pegmatitic fields and leucogranitic cupolas; triphylite–lithiophilite in the beryl-phosphate pegmatites, and amblygonite–montebrasite in the quartz-montebrasite veins. The origin of these different styles of mineralization is considered to be related to differentiation of peraluminous melts, which were generated by partial melting of metasedimentary rocks during the Variscan orogeny. On the basis of paragenesis and chemical composition, the pegmatitic fields and Li mineralization associated with granitic cupolas record the highest fractionation levels, whereas the beryl-phosphate pegmatites and quartz-montebrasite veins show lower degrees of fractionation. There are a number of textural and mineralogical indicators for Li exploration in the Central Iberian Zone and in the Galizia-Trás-Os-Montes Zone, with the highest economic potential for Li being in the pegmatite fields.

We present geochronological and geochemical data for eight plutonic rocks from five locations in the Pine Island Bay area of West Antarctica, collected during RV Polarstern expedition ANT-XXIII/4. Ar-Ar laser method dating yielded closure temperatures ages of c. 147–98 Ma for dioritic and granitic plutonic rocks and an age range of c. 97–95 Ma for granitoid and trachyandesitic dykes. Major and trace element compositions indicate that all rocks have an I-type subduction-related chemistry. There are no A-type granitic rocks in our dataset, and none are yet reported from the Pine Island Bay area. Our results confirm earlier models of post 100 Ma subduction on this part of the Gondwana margin.

Trace element abundances in garnet from a polyphase migmatite were measured by secondary ion mass spectrometry (SIMS) in order to identify some of the effective variables on the trace element distribution between garnet and melanosome or leucosome. In general, garnet is zoned with respect to REE, in which garnet cores are enriched by a factor of 2–3 relative to the rims. For an inclusion-rich garnet from the melanosome, equilibrium distribution following a simple Rayleigh fractionation is responsible for the decreasing concentrations in REE from core to rim. Inclusion-poor garnet from the same melanosome located in the vicinity of the leucosomes shows distinct enrichment and depletion patterns for REE from core to rim. These features suggest disequilibrium between garnet and the host rock which, in this case, could have been an in-situ derived melt. This would probably indicate a period of open-system behaviour at a time when the garnet, originally nucleated in the metamorphic environment reacted with the melt. In addition, non-gradual variation in trace element abundances between core and rim may suggest variable garnet growth rates. Inclusion-free garnet from the leucosome, interpreted to have crystallised in the presence of a melt, has a small core with high REE abundances and a broad rim with lower REE abundances. Here, crystal-liquid diffusion-controlled partitioning is a likely process to explain the trace element variation.

The plutons of Cairnsmoor of Fleet (392±2 Ma) and Criffel-Dalbeattie (397±2 Ma, both mineral isochron ages) comprise two of four major post-tectonic granitic complexes emplaced into the Southern Uplands, an Ordovician–Silurian back-arc and foreland basin complex formed at the northern margin of the Iapetus Suture. To expand the palaeomagnetic record of the Southern Uplands we have studied palaeomagnetism and magnetic fabrics in traverses spanning contacts of these intrusions with host mudrocks. A uniform anisotropy of magnetic susceptibility (AMS) fabric across the Cairnsmoor of Fleet contact has been enhanced by recrystallization into hornfels near the contact and records a late Acadian regional stress operative during, or soon after, emplacement of the pluton in Middle Devonian times. Magnetization during slow cooling recorded a dual polarity (‘A’) remanence in granite and hornfels with mean direction D/I = 92/−2° (α95 = 6.5°) yielding a palaeopole (Q = 6) at 2°N, 265°E linked to cooling at c. 392 Ma. Subsidiary magnetizations are overprints imparted during Variscan tectonism (‘B’, D/I = 194/6°) and Jurassic rifting within the adjoining Irish Sea Basin (‘C’, c. 160–140 Ma, D/I = 172/−52°). The Criffel-Dalbeattie pluton has more complex AMS fabrics recording both deformation and emplacement effects. Hematite of secondary hydrothermal origin is a significant feature of the rock magnetic record in the aureole, which is otherwise dominated by paramagnetism. The granodiorite is more strongly magnetized than the country rocks, accounting for a positive aeromagnetic anomaly. A fairly dispersed dual polarity remanence (mean D/I = 115/55°, α95 = 18°) in granodiorite and late tectonic porphyrite dykes is probably the oldest magnetization preserved in this pluton because it correlates with an excursion of Britain into southerly palaeolatitudes at c. 410 Ma and indicates an Early Devonian emplacement age. The palaeofield at c. 397 Ma, the currently accepted isotopic age, is recorded by a minority overprinted remanence (mean D/I = 272/2°, α95 = 12°) similar to the record in the Cairnsmoor of Fleet pluton and granites from the adjoining Lake District terrane. Granite complexes of the Southern Uplands Block collectively record regional rotation and excursion of Britain into southerly latitudes between c. 410 and 390 Ma. Comparable Silurian–Devonian palaeomagnetic poles identify common apparent polar wander (APW) in paratectonic and orthotectonic terranes from the Variscan Front in the south to the Laurentian foreland in the north following climactic Acadian deformation. APW between 430 and 390 Ma embracing the (post-closure) history of the Caledonian orogen is a loop executed at rates much higher than typical rates of plate motion and appears to record a component of true polar wander. The ∼110° arc length is identical to polar shift identified between mid-Silurian and Lower–Middle Devonian poles from Gondwana. The two paths superimpose to show that the western margin of Gondwana was in proximity to the SE margin of Laurentia during Acadian deformation in Early–Middle Devonian times and remote from the Caledonides; the residual Rheic Ocean subsequently closed by a combination of pivotal and left lateral strike-slip motions.

Rb-Sr ages of Swanson Formation on Edward VII Peninsula, West Antarctica, indicate a late Ordovician age, 421–432 Ma for regional metamorphism. K-Ar ages of 113–440 Ma, reflect a second thermal metamorphism during emplacement of widespread Cretaceous granites. Rb-Sr ages of five monzogranite/syenogranitic plutons of Byrd Coast Granite are in the range 95–105 Ma (initial 87Sr/86Sr ratios 0.710–0.715) and represent stages of crystallization of anorogenic granite (A subtype). These correlate with Byrd Coast Granite (100–110 Ma) farther east in Marie Byrd Land, and with Cretaceous granitoids on the Campbell Plateau and in southern New Zealand. K-Ar mica/hornblende and fission-track apatite/zircon ages indicate that regional cooling began c. 90–100 M.y. ago immediately after granite emplacement. Uplift continued throughout the peninsula during the period 55–100 Ma (late Cretaceous-early Tertiary), associated with regional uplift in the rift-drift stages of Gondwana break-up at the South-west Pacific spreading centre. Apatite fission track ages show that during late Cretaceous-early Tertiary time the peninsula behaved as two blocks. The Alexandra Mountains were exhumed 20 m.y. before the Rockefeller Mountains and are possibly separated by a fault active initially in the mid-Cretaceous or earlier, and later reactivated in the late Cretaceous-early Tertiary. An averaged uplift rate (50–100 Ma) of 0.025 mm yr−1 is characteristic of the inferred intraplate tectonic setting.

Mafic rocks in the Ryoke belt, the Cretaceous granitic province in Southwest Japan, occur in two modes: (1) as mafic dykes and pillow-shaped enclaves, and (2) as isolated kilometresized bodies of gabbroic cumulate. The dykes and pillows have fine-grained textures with thin radiating plagioclase laths, indicative of quenching. The gabbroic cumulates are predominantly coarse-grained and commonly lithologically layered.

SHRIMP zircon U-Pb ages of both types of mafic rocks are in the range 71–86 Ma, late Cretaceous. The mafic rocks become younger eastwards, matching the along-arc age trend of the associated Cretaceous granites (Nakajima et al. 1990). Both types of mafic rocks were apparently generated during the same magmatic event that produced the Ryoke/San-yo granites. The mafic dykes and pillows are aphyric basaltic-andesites to andesites (SiO2 54–60 wt.%), with microphenocrysts of biotite and hornblende. They have a composition which is similar to mafic rocks from the northern Sierra Nevada, and also to medium-K calc-alkaline rocks from present-day arc volcanics. The gabbroic cumulates are mostly pyroxene-hornblende gabbros (SiO2 43–52 wt.%). Their bulk-rock chemical compositions are mostly unlike any magma compositions.

Both types of mafic rocks from the Ryoke belt have relatively high 87Sr/86Sr initial ratios (SrI), 0·7071–0·7097, which are similar to those of the associated granites. The granites were formed either by fractional crystallisation of the mafic magmas, or by partial melting of newly formed mafic rocks at depth. The high SrI indicates that the mafic magmas were derived from enriched mantle or mixed with enriched crustal materials. Even if the mixing occurred between primitive basaltic magma and metasedimentary rocks, then the basaltic andesite–andesite magmas must have contained more than 60% mantle-derived components. The Cretaceous magmatism in Southwest Japan represents a major episode of crustal growth by additions from the upper mantle in an arc setting.