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 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 (∼11–8 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; Grunder 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.

We report ion-microprobe U-Pb zircon ages from charnockites of a large Proterozoic composite batholith, Mawson Coast, Australian Antarctic Territory. The charnockites crystallized from orogenic magmas of intermediate composition (mainly 54–68% SiO2) intruded into a granulite-facies metasedimentary gneiss sequence between the second and third recognized deformations. A sample of low-Ti charnockite provides an age of 954 ± 12 Ma and a high-Ti charnockite is dated at 985 ± 29 Ma (all ages quoted at 95% confidence). The age difference is not significant at the 95% confidence level. Both these ages were obtained from zircons with igneous zoning and/or morphology and thus are thought to date igneous crystallization. Zircons from a felsic gneiss xenolith within the charnockite have cores of various ages, many from 1.7 to 2.0 Ga, but with other grains between 1.0 and 1.5 Ga and a single 2.5 Ga zircon. These zircon cores are direct evidence for an early to middle Proterozoic age for the supracrustal basement sequence in this mobile belt. Many of these zircon cores are concordant but abundant discordant grains suggest a complex history of multiple Pb-loss events. Zircon rims grew at 921 ± 19 Ma, probably during the post-charnockite deformation (D3). Previously obtained Rb-Sr dates for charnockite of 886 ± 48 Ma and 910 ± 18 Ma were probably also rest during D3. A Rb-Sr isochron date of 1061 ± 36 Ma previously reported for high-Ti charnockite from Mawson Rock is thought to be erroneous, and a new date of 959 ± 58 Ma (consistent with both the igneous and reset dates above) is interpreted from those data.

The Miocene Baltoro granite forms a massive plutonic unit within the Karakoram batholith, and is composed of comagmatic monzogranites and leucogranites with a mineralogy consisting of quartz-K-feldspar-plagioclase-biotite ± muscovite ± garnet, with accessory sphene, zircon, monazite and opaques. Geochemically the Baltoro granites are mildly peraluminous, and show a calc-alkaline trend on trace-element normalised diagrams with high LIL/HFS element ratios and negative Nb, P and Ti anomalies. REE are strongly fractionated with little or no Eu anomaly. Leucogranites are depleted in most elements compared to monzogranites with notable exceptions being Rb, K and the HREEs. Initial 87Sr/86Sr ratios are 0·7072-0·7128, considerably lower than High Himalayan leucogranites (0·74-0·79), and are indicative of a lower continental crust source. The probable petrogenesis of the Baltoro granite involves dehydration melting of a biotite-rich pelite to produce a voluminous, hot, water-undersaturated magma which could then separate from its source and intrude through an already thickened and still hot crust. Fractional crystallisation of the monzogranites produced the leucogranites and a pegmatite dyke swarm. A suite of lamprophyre dykes including amphibolerich vogesites and biotite-rich minettes intrude the country rock, dominantly to the north, around the Baltoro granite. These calc-alkaline shoshonitic lamprophyres are volatile-rich mantle-derived melts intruded around the same time as the granite, indicating simultaneous melting of the mantle and lower crust beneath the Karakoram during the Miocene, approximately 30 Ma after the India-Asia collision which initially caused the crustal thickening. Intrusion of mantle melts provided heat to promote crustal melting and may have selectively contaminated the granite magma.

The Baltoro granite intrudes sillimanite gneisses with melt pods along the southern margin indicating temperatures above 700°C at the time of intrusion. Locally, internal fabrics and numerous aligned xenoliths along the southern margin in the Biafo glacier region indicate steep, southward-directed thrusting during emplacement. Along the northern contact, the Baltoro granite intrudes anchimetamorphic to greenschist facies metasedimentary rocks with an andalusite-bearing contact aureole. Northward-directed culmination collapse normal faulting during Miocene emplacement is inferred, in order to explain the P-T differences either side of the pluton. This also provided an extensional stress regime in the upper crust to accommodate the rising magma.

Granites of the Batholith of Central Patagonia were emplaced into late Precambrian metamorphic basement rocks and Palaeozoic orthogneisses (here dated by Rb–Sr whole-rock errorchrons at 346 ±35 Ma and 267 ±27 Ma), and are in fault-contact with younger volcanic rocks, mostly andesites. Two main suites of granites are recognised: both are much younger than their previously-supposed Late Palaeozoic age. The Gastre Suite is composed predominantly of hornblende-biotite granodiorite and monzogranite, often slightly foliated, and has yielded a Rb-Sr whole-rock isochron age of 220 ±3 Ma. The Lipetrén Suite includes biotite monzogranite and leucogranite, grading into quartz-feldspar porphyries and felsites, and has been dated at 208 ±1 Ma. A minor granodioritic unit yields an apparently Middle Jurassic age of 172 ±15 Ma. Textural evidence and hornblende geobarometry confirm that these are high-level sub-volcanic intrusions. Metaluminous compositions are common in the Gastre Suite, but are subordinate to highly siliceous (>70% SiO2) and peraluminous varieties in the Lipetrén Suite. Despite this compositional bias, the granites are almost entirely calcalkaline and I-type, and have volcanic-arc rather than intraplate or collisional trace element characteristics. Initial 87Sr/86Sr ratios of 0·706 and –2·5 are also relatively primitive and are thought to indicate a juvenile crustal contribution (Nd “depleted mantle” model ages are less than 1,000 Ma).

The Triassic “Gondwana” magmatic episode is thus not an expression of Permo-Triassic collision of an allochthonous Patagonian terrane with the rest of southern S America, but may be related to the initial stages of supercontinent rifting.

The Tibetan–Tethys zone of the Zanskar Himalaya shows a complete Mesozoic shelf carbonate sequence overlying metamorphic basement of the Central crystalline complex and Palaeozoic sedimentary rocks. Continental rifting in the Permian produced the alkaline and basaltic Panjal volcanic rocks and by Triassic time a small ocean basin was developed in the Indus-Tsangpo zone. Stable sedimentation continued until the Middle-Late Cretaceous when a thick sequence of tholeiitic to andesitic island arc lavas (Dras arc) were erupted in the basin above a N-dipping subduction zone. The Spontang ophiolite was emplaced southwards onto the Zanskar shelf edge during latest Cretaceous or earliest Tertiary times.

Following emplacement of the Spontang ophiolite, deep-sea sedimentation ended abruptly with initial collision between the Indian plate and the Dras island arc. Emplacement of the massive Ladakh (Trans-Himalayan) batholith along the southern margin of Tibet in late Cretaceous-Eocene time occurred by crustal melting as a result of northward subduction of Mesozoic oceanic crust along the Indus subduction zone. Southward-directed thrusting in both Zanskar and Indus zones accompanied ocean closure during the late Cretaceous–Eocene. Late Tertiary compression caused intense folding, overturning and a phase of northward-directed thrusting along the Indus suture zone and the northern margin of the Tibetan–Tethys zone, resulting in a large amount of crustal shortening.

Fourteen granitoid plutons studied in the Baie d'Espoir area of southern Newfoundland are divisible into a northern group of eight and a southern group of six. The former tend to be undeformed, have thermal aureoles, and intrude greenschist facies Ordovician and Silurian rocks of the Dunnage zone following a period of folding and thrusting towards the SE. Four Rb-Sr whole-rock isochrons yield similar ages around 430 Ma for these plutons, fixing the deformation within early Silurian times. The latter plutons syntectonically intruded without aureole effects, and are all foliated and elongate parallel to the regional fabric of amphibolite facies gneisses and migmatites of the Gander zone. Whole-rock Rb-Sr isochrons around 350 Ma for both syntectonic and post-tectonic plutons indicate a rapid metamorphism, deformation, intrusion and uplift of the Gander zone in this area. There appear to be no systematic relationships between petrological and geochemical characteristics of the plutons and their tectono-stratigraphic setting. This study conclusively invalidates earlier hypotheses that deformed granitoid rocks of the Gander zone are older than the undeformed granitoids of the Dunnage zone; indeed, just the reverse is true.