A growing body of evidence indicates that some, and perhaps most, plutons are highly composite. However, the geometrical forms of increments and the processes by which they are added are poorly known. Magmatic crack-seal probably is an important incremental assembly process, particularly in the upper crust where wall-rock fracture is important. Evidence for magmatic crack-seal is clearest where it is antitaxial, i.e., new fractures form at the contact between wall rock and a growing intrusion. Local deviation of antitaxial cracks into wall rocks isolates wall-rock bodies that therefore mark increment contacts. Wall rock isolated by this process remains in situ and thus is likely to preserve a ghost stratigraphy. Previously described plutons are identified, and interpreted to have grown by antitaxial magmatic crack-seal. In contrast, it remains unclear what observable geological record may remain in plutons formed by syntaxial crack-seal, in which new cracks form in the middle of the growing pluton. Several plutons are identified that preserve possible indirect evidence for growth by syntaxial crack seal, but conclusive identification of a direct record of the process remains elusive. However, plutons with sharp discordant contacts but few xenoliths may have been emplaced incrementally by syntaxial magmatic crack-seal.

The mechanisms by which Cordilleran plutons are emplaced vary widely. However, the present authors have examined a series of plutons ranging from 2-35 km emplacement depth that have many common features, which suggest that downward transport of host rock is the most important mechanism during magma ascent and pluton emplacement. Many of these Cordilleran plutons preserve gently dipping, unfaulted roofs attached to steep walls bordered by narrow ductile aureoles. Flat lying roof strata commonly roll over into steeply dipping rim monoclines and anticlines that young towards and follow the pluton margin. Field observations suggest that such rim monoclines and anticlines formed due to gravitationally driven roof collapse and channel flow along margins. In the examples in this paper, pluton walls are often comprised of narrow steeply dipping ductile aureoles in which the intensity of strain increases downward. Aureole ductile strains are insufficient to account for the volume of magma emplaced, and are typically <40% of pluton volume. However, when aureole strain is combined with minimum estimates of stoping and host rock rotation during rim monoclines formation, sufficient space can be created. The examples suggest that gravitationally driven downward host rock transport by stoping and rigid rotations along roofs and walls and by focused channel flow by ductile strain along walls are common processes during the rise of Cordilleran plutons, and is one process that contributes to crustal thickening and the growth of crustal roots.

The arid climate of the Altiplano has preserved a volcanic history of ∼11 million years at the Aucanquilcha Volcanic Cluster (AVC), northern Chile, which is built on thick continental crust. The AVC has a systematic temporal, spatial, compositional and mineralogical development shared by other long-lived volcanic complexes, indicating a common pattern in continental magmatism with implications for the development of underlying plutonic complexes, that in turn create batholiths.

The AVC is a ∼700-km2, Tertiary to Recent cluster of at least 19 volcanoes that have erupted andesite and dacite lavas (∼55 to 68 wt.% SiO2) and a small ash-flow tuff, totalling 327 ± 20 km3. Forty 40Ar/39Ar ages for the AVC range from 10.97 ± 0.35 to 0.24 ± 0.05 Ma and define three major 1-5 to 3 million-year pulses of volcanism followed by the present pulse expressed as Volcán Aucanquilcha. The first stage of activity (∼ll-8 Ma, Alconcha Group) produced seven volcanoes and the 2-km3 Ujina ignimbrite and is a crudely bimodal suite of pyroxene andesite and dacite. After a possible two million year hiatus, the second stage of volcanism (∼ 6-4 Ma, Gordo Group) produced at least five volcanoes ranging from pyroxene andesite to dacite. The third stage (∼4-2 Ma, Polan Group) represents a voluminous pulse of activity, with eruption of at least another five volcanoes, broadly distributed in the centre of the AVC, and composed dominantly of biotite amphibole dacite; andesites at this stage occur as magmatic inclusions. The most recent activity ( 1 Ma to recent) is in the centre of the AVC at Volcán Aucanquilcha, a potentially active composite volcano made of biotite-amphibole dacite with andesite and dacite magmatic inclusions.

These successive eruptive groups describe (1) a spatial pattern of volcanism from peripheral to central, (2) a corresponding change from compositionally diverse andesite-dacite volcanism to compositionally increasingly restricted and increasingly silicic dacite, (3) a change from early anhydrous mafic silicate assemblages (pyroxene dominant) to later biotite amphibole dacite, (4) an abrupt increase in eruption rate; and (5) the onset of pervasive hydrothermal alteration.

The evolutionary succession of the 327-km3 AVC is similar to other long-lived intermediate volcanic complexes of very different volumes, e.g., eastern Nevada (thousands of km3, Gans et al. 1989; Grander 1995), Yanacocha, Perú (tens of km3, Longo 2005), and the San Juan Volcanic System (tens of thousands of km3, Lipman 2007) and finds an analogue in the 10-m.y. history and incremental growth of the Cretaceous Tuolumne Intrusive Suite (Coleman et al. 2004; Glazner et al. 2004). The present authors interpret the AVC to reflect episodic sampling of the protracted and fitful development of an integrated and silicic middle to upper crustal magma reservoir over a period of at least 11 million years.

The Late Caledonian granites of Donegal are all intruded into metasediments of the Dalradian Supergroup of Neoproterozoic age, which were metamorphosed and deformed during the Grampian Phase of the Caledonian orogeny at c. 470-460 m.y. They were intruded in a singular pulse well after the main tectonic event, apparently peaking at 407-402 m.y.; importantly after the strong collision of Laurentia with Baltica on closure of the Iapetus Ocean. The plutons are mainly made up of granodiorite and granite, and are all ‘I’ type, but different to Cordilleran ‘I’ types of the eastern Pacific margin. Major element chemistry indicates they are high-K calc-alkaline rocks with a large range in SiO2 content. However three of the plutons (Fanad, Thorr, Ardara), have very high Ba and Sr contents, even higher than Mainland Scotland counterparts; they are high Ba-Sr plutons. Three plutons (Barnesmore, Rosses, Trawenagh Bay) are evolved and are low-Ba-Sr types, while one (Main Donegal) has atypical, intermediate characteristics. The origin of the magmas is still much debated; here we suggest slab breakoff on Iapetus Ocean closure accounts for the special compositions of these magmas and the other major features of Late Caledonian granitic magmatism, including the singular intrusion peak and the associated appinite-lamprophyre suite.

The Trawenagh Bay Granite (TBG) is shown to be a tabular pluton with gently inclined contacts that, from anisotropy of magnetic susceptibility (AMS) studies, was emplaced as a series of flow lobes whose geometries indicate that it flowed horizontally towards the W out of late stage adjacent steeply inclined monzogranite sheets of the Main Donegal Granite (MDG). We thus confirm in detail the central broad idea of the Pitcher & Read (1959) model that the Main Donegal Granite fed the Trawenagh Bay Granite. Early TBG flow lobes cut and are cut by deformation associated with the sinistral shear zone in which the MDG lies, thus demonstrating synchronicity of shearing and magmatism. The TBG magma leaked out of the shear zone and emplaced into undeformed country rocks and was probably guided by shear zone splays that die out along its northern and southern margins. At a late stage in the development of MDG, the splays developed from the NNE-trending SW boundary of the shear zone and caused a gap in this structure through which TBG magma was channelled out of the MDG. A review is presented of the last twenty-five years of published and unpublished work on the batholith, showing that the MDG shear zone was a long-lived structure almost certainly in existence before the emplacement of that body, and that four of the contiguous granitiods (Thorr, Ardara, and Rosses, as well as Trawenagh Bay) were all sourced within the shear zone. A new model is presented for the development of the batholith. The pre-existing crustal structure was a deep-seated N12°E fault in the basement to the Dalradian wall rocks of the granites, that was coupled to up to six other more minor WNW-ESE basement faults in the W. A NE-SW-trending sinistral shear zone was initiated at the end of the Caledonian orogeny, as calc-alkaline and deep-seated appinites were generated in the area. This shearing activated the pre-existing structures at the current crustal level, and the N12°E structure acted as a continental transform fault which allowed the dilation needed to facilitate the wedging space requirements of the MDG and the other units in the shear zone, as well as transferring regional sinistral shear through the system. The Thorr and Ardara plutons were emplaced first into the shear zone and then those magmas leaked out into the adjacent wall rocks: one to form a large laccolith, the other to form a balloon. Steep early MDG complex sheets (granodiorites and tonalities) were emplaced in the shear zone between the Thorr and Ardara emplacement sites. Dilation continued until late stage extensive monzogranite sheets were intruded in the NW and SE of the pluton. One of these probably leaked material westward to form the Rosses laccolith and southwestwards to form the TBG in the final stages of shear zone movement.

Mauna Kea in Hawaii is the world’s tallest mountain — about 1000 m taller than Mount Everest (Science, volume 313, 22 September 2006, p. 1732). Near the summit, at an altitude of 4092 m, is the James Clerk Maxwell Telescope (JCMT) — the largest astronomical telescope designed to operate in the sub-millimetre wavelength region of the spectrum. In 1987 the JCMT was dedicated by HRH Prince Philip, Duke of Edinburgh, and named for the physicist James Clerk Maxwell (1831-1879). Sir John Dutton Clerk of Penicuik Bt, CBE, VRD, DL FRSE (1917-2002) represented the family.