The North-East Greenland Caledonides record a complex history of crustal thickening and extension during the Paleozoic collision of Baltica with Laurentia. We divide the southern portion of the orogen (70°N–76°N) into three plates separated by low-angle fault systems that are interpreted as extensional detachments superimposed on, and perhaps coeval with, the thrust geometry of the orogen. From structurally lowest to highest, the plates include amphibolite-facies Archean to Paleoproterozoic orthogneiss and lesser paragneiss that retain relics of Devonian high-pressure metamorphism, migmatitic Mesoproterozoic metasedimentary rocks with Silurian leucogranites and lesser orthogneiss at amphibolite-facies conditions, and low-grade Neoproterozoic to Ordovician sedimentary rocks. Individual detachments are characterized by superposition of cataclastic features on mylonitic fabrics, and they record progressive deformation that accommodated exhumation. The extensional faults define two detachment systems that evolved at different crustal levels during two episodes of movement. The upper detachment system, which separates the upper and middle plates, exhumed the midcrustal rocks after ca. 420 Ma. Extension was contemporaneous with crustal thickening and closely followed leucogranite emplacement. The structure may be analogous to the South Tibetan detachment system in the present-day Himalayas. Continental Old Red Sandstone deposition began in the Eifelian, closely following high-pressure metamorphism in the lower plate at ca. 405 Ma. The lower detachment was probably active at some depth below the evolving Devonian basins. The lower detachment system brought lower-plate metamorphic rocks to shallower crustal levels after 400 Ma, excising the overlying extensional system. This second period of extension was similar in timing and style to extension in the Scandinavian Caledonides. Displacement on the younger detachments, which exhumed lower-plate rocks, was broadly syncollisional, as indicated by the overlap in age with ultrahigh-pressure metamorphism in the north at 365–350 Ma, and it may have been synchronous with young thrusts that emplaced high-pressure lower-plate rocks over the foreland and with strike-slip faults in the hinterland. Conversion to extension, accommodated by high-angle brittle faulting in the Carboniferous (after 345 Ma), may mark the final transition to plate divergence that ultimately led to continental rifting.

The Caltepec shear zone is a dextral transpressional tectonic boundary between the Oaxacan and Acatlán Complexes, which are crystalline basements of the Zapo-teco and Mixteco terranes in southern México, respectively. The terrane boundary (2–6 km wide) reveals protracted and polyphase tectonic activity from at least Early Permian to the present. The major tectonothermal event in the Caltepec fault zone was related to the oblique collision of the metamorphic complexes during the amalgamation of Pangea. An anatectic leucosome and the resulting syntectonic granite (Cozahuico Granite) in the fault zone yielded U-Pb zircon ages of 275.6 ± 1.0 Ma and 270.4 ± 2.6 Ma, respectively. The initial 87Sr/86Sr ratios (0.70435–0.70686) and Sm-Nd model ages (TDM) (1.0–1.6 Ga) for the Cozahuico Granite and leucosome indicate a magmatic mixture that originated from melted Proterozoic crust and a component of depleted mantle. The Leonardian age of the cover (Matzitzi Formation) and a 40Ar/39Ar cooling age (muscovite) of 268.59 ± 1.27 Ma for mylonitic mica schist at the base of the thrust imply high cooling rates (∼180 °C/Ma) and uplift during the Permian. The adjacent sedimentological record indicates intense tectonic reactivation during Early Cretaceous, Paleogene, and Neogene along the long-lived Caltepec fault zone, alternating with periods of relative tectonic quiescence during Triassic, Jurassic, and Mid-Cretaceous times. The trend of the Caltepec fault zone parallel to the Oaxaca fault, 50 km to the east, is interpreted as part of a synchronous and dynamically coupled tectonic system that has been releasing tectonic stresses associated with the rupture of Pangea and the evolution of the Pacific margin of southern México from Jurassic to Holocene times.

The Granjeno Schist of northeastern México is the oldest component of the Sierra Madre terrane and comprises polydeformed, pelitic metasedimentary and metavolcaniclastic rocks that enclose lenses of serpentinite-metagabbro. This low-grade Paleozoic assemblage is exposed in the core of a NNW-trending frontal anticline of the Laramide fold-thrust belt where it is tectonically juxtaposed against ca. 1 Ga granulites of the Novillo Gneiss. Silurian strata that unconformably overlie the Novillo Gneiss are unmetamorphosed and contain fauna of Gondwanan affinity. LA-ICPMS (laser ablation inductively coupled plasma mass spectroscopy)U-Pb ages for detrital zircons from a Granjeno phyllite yield age populations that cluster in the ranges ca. 1375–880 Ma, ca. 650–525 Ma, and ca. 460–435 Ma and slightly discordant grains with individual ages of ca. 1435 Ma, ca. 1640 Ma, ca. 2105 Ma, and ca. 2730 Ma. The youngest detrital zircon indicates a maximum depositional age for the Granjeno Schist of ca. 435 Ma (Lower Silurian). Detrital zircons of Neoproterozoic–Cambrian age suggest a provenance in the Maya terrane beneath the Yucatan Peninsula or the Brasiliano orogens of South America, and a source for the detrital zircons of Ordovician–Silurian age is present in the Acatlán Complex of southern México. Provenance of the Mesoproterozoic detrital zircons is likely to have been the adjacent Novillo Gneiss, which has yielded ages of ca. 990–980 Ma, ca. 1035–1010 Ma, and ca. 1235–1115 Ma. These detrital ages closely match those recorded from the Cosoltepec Formation of the Acatlán Complex and support correlation of the two units, which are both interpreted to be vestiges of the southern margin of the Rheic Ocean.

High-strain zones are common in basement terranes, and understanding their tectonic significance requires quantitative knowledge of deformation kinematics. We report on strained rocks from different tectonic settings that record pure shear dominated (Wm =≤0.4) deformations. Mylonitic rocks derived from Mesoproterozoic basement granitoids are exposed in the Lawhorne Mill high-strain zone in the Virginia Blue Ridge. Chemical and mineralogical differences between the leucogranitoid protolith and mylonite are consistent with ∼50% volume loss during deformation. Minimum finite strains in XZ sections range from 4:1 to 7:1, and three-dimensional strains plot in the field of apparent flattening; however, with volume loss these rocks likely experienced bulk plane strain. The Rs/Θ and quartz c-axis vorticity gauges yield Wm values of 0.0–0.6. Fabric asymmetries normal to both foliation and lineation are consistent with modest triclinic deformation symmetry. Mylonitic rocks from the Lawhorne Mill high-strain zone record a pure shear dominated deformation that produced ∼70% contraction across the zone with only minimal displacement parallel to the zone (<0.5 km). Pure shear dominated high-strain zones occur in a variety of mid-crustal settings. Ultramylonites from metamorphic core complexes in Arizona record very low vorticity values (Wm < 0.4). Well-foliated, steeply dipping, upper amphibolite facies rocks from the Coast shear zone in British Columbia are characterized by orthorhombic fabrics formed during pure shear dominated deformation that accommodated crustal contraction. These zones differ from simple and general shear zones because displacement across these zones is minimal relative to the overall finite strain. However, zone-normal shortening and zone-parallel stretching are significant in pure shear dominated zones. Steeply dipping zones formed in contractional settings serve to effectively shorten and thicken the crust across basement massifs, whereas gently dipping zones formed in extensional settings thin the crust.

Fluid dynamic modelling of crystallising calc-alkalic magma bodies has predicted that differentiated liquids will ascend as boundary layers and that accumulation of these buoyant liquids near chamber roofs will result in compositionally stratified magma chambers. This paper reports physical features in La Gloria Pluton that can be interpreted as trapped ascending differentiated liquids. Leucogranitic layers decimetres thick, which are locally stratified, are trapped beneath overhanging wall contacts. The same felsic magmas were also preserved where they were injected into the wall rocks as dykes and as large sill complexes. These rocks do not represent differentiated magmas produced by crystallisation along the exposed walls because the felsic layers occur at the wall rock contact, not inboard of it. Rather, we speculate that evolved felsic liquids are generated by crystallisation all across the deep levels of chambers and that initial melt segregation occurs by flowage of melt into tension fractures. Melt bodies so formed may be large enough to have significant ascent velocities as diapirs and/or dykes. The other way in which the leucogranite occurrence is at variance with the convective fractionation model is that the ascending liquids did not feed a highly differentiated cap to the chamber, as the composition at the roof, although the most felsic in this vertically and concentrically zoned pluton, is considerably more mafic than the trapped leucogranitic liquids. This suggests that these evolved liquids were usually mixed back into the main body of the chamber. Backmixing may be general in continental-margin calc-alkalic magmatic systems, which, in contrast to those in intracontinental settings, rarely produce volcanic rocks more silicic than rhyodacite. That the highly differentiated liquids are preserved at all at La Gloria is a result of the unusual stepped nature of the contact and the entirely passive mode of emplacement of the pluton, which, in contrast to ballooning in place, does not result in wall zones being “scoured”.

The Layos Granite forms elongated massifs within the Toledo Complex of central Spain. It is late-tectonic with respect to the F2 regional phase and simultaneous with the metamorphic peak of the region, which reached a maximum temperature of 800–850°C and pressures of 400–600 MPa. Field studies indicate that this intrusion belongs to the “regional migmatite terrane granite” type. This granite is typically interlayered with sill-like veins and elongated bodies of cordierite/garnet-bearing leucogranites. Enclaves are widespread and comprise restitic types (quartz lumps, biotite, cordierite and sillimanite-rich enclaves) and refractory metamorphic country-rocks including orthogneisses, amphibolites, quartzites, conglomerates and calc-silicate rocks. These granites vary from quartz-rich tonalites to melamonzogranites and define a S-type trend on a QAP plot. Cordierite and biotite are the mafic phases of the rocks. The particularly high percentage of cordierite (10%–30%) varies inversely with the silica content. Sillimanite is a common accessory mineral, always included in cordierite, suggesting a restitic origin. The mineral chemistry of the Layos Granite is similar to that of the leucogranites and country-rock peraluminous granulites (kinzigites), indicating a close approach to equilibrium. The uniform composition of plagioclase (An25), the high albitic content of the K-feldspar, the continuous variation in the Fe/Mg ratios of the mafic minerals, and the high Ti content of the biotites (2.5–6.5%) suggest a genetic relationship. Geochemically, the Layos Granite is strongly peraluminous. Normative corundum lies between 4% and 10% and varies inversely with increase in SiO2. The CaO content is typically low (<1.25%) and shows little variation; similarly the LILE show a limited range. On many variation diagrams, linear trends from peraluminous granulites to the Layos Granite and associated leucogranite can be observed. The chemical characteristics argue against an igneous fractionation or fusion mechanism for the diversification of the Layos Granite. A restite unmixing model between a granulitic pole (represented by the granulites of the Toledo Complex) and a minimum melt (leucogranites) could explain the main chemical variation of the Layos Granite. Melting of a pelitic protolith under anhydrous conditions (biotite dehydration melting) could lead to minimum-temperature melt compositions and a strongly peraluminous residuum. For the most mafic granites (61–63% SiO2), it is estimated that the trapped restite component must have been around 65%. This high proportion of restite is close to the estimated rheological critical melt fraction, but field evidence suggests that this critical value has been exceeded. This high restite component implies high viscosity of the melt which, together with the anhydrous assemblage of the Layos Granite and the associated leucogranites, indicates H2O-undersaturated melting conditions. Under such conditions, the high viscosity magma (crystal-liquid mush) had a restricted movement capacity, leading to the development of parautochthonous plutonic bodies.

Two north-south–trending Triassic-Jurassic plutonic belts are recognized in the Andes of central Chile (30 to 33°S). Both belts contain plutons of similar age and spatially temporally related mafic (in part lamprophyric) and felsic dikes. The High Andes Belt (HAB) comprises Triassic to Lower Jurassic hornblende-biotite leucogranite, two-mica leucogranite, leucogranodiorite, and granodiorite. The Coast Belt (CB) located 100 km west of the HAB, is composed of Upper Triassic to Lower Jurassic biotite-hornblende leucogranite, related gabbro, and Middle to Upper Jurassic granitoids that range from gabbro to granite, with a dominance of hornblende-biotite tonalités, granodiorites, and diorites. The HAB leucogranites are metaluminous to slightly peralkaline and similar to A-type granites. The HAB two-mica plutons are distinctly peraluminous, similar to S-type granites, and have highly fractionated rare-earth element (REE) patterns. The CB leucogranites exhibit alumina saturation indexes, Na2O/K2O and Rb/Sr ratios, and moderately fractionated REE patterns with large negative Eu anomalies similar to those of the HAB leucogranites, but they are less alkaline. The HAB and CB leucogranites could result from partial melting of a quartzo-feldspathic source, probably upper Paleozoic plutonic rocks. The two-mica HAB leuco-granitoids could be derived from a garnet-bearing metasedimentary source, and the mafic dikes could be derived from subcrustal sources under conditions of high PH2O. The compositional differences in the two belts suggest different tectonic regimes, with a major change in the conditions of magma generation during the Early Jurassic. Whereas the Triassic to Lower Jurassic leucogranites and mafic dikes developed in a tensional environment that promoted fusion and emplacement of crustal- and mantle-derived magmas, the Middle to Upper Jurassic granitoids represent subduction-related magmatism.

In the Chanaral–El Salvador area of northern Chile, Permian-Triassic plutonic complexes, emplaced into upper Paleozoic metasedimentary basement, occur in two parallel belts in the Coastal Range and Altiplano. Geochronological data show that these two belts of magmatic activity are coeval. In the Coastal Range, rock types present vary from tonalite, through granodiorite and granite, to leucogranite; in the Altiplano, leucogranite is not represented and granite is less common. To investigate whether the two magmatic belts could have been part of the same arc system and to discriminate their tectonic setting, 72 samples from the Coastal Range complexes and 55 samples from the Altiplano complexes have been analyzed for a range of major, minor, and trace elements, and a subset of 31 samples has been analyzed for the REE, Hf, Ta, Th, and U. The geochemistry of the Permian-Triassic complexes from both belts is similar. Both are calcic and metaluminous to mildly peraluminous with TiO2 and Ni decreasing with increasing SiO2. Rb increases, Sr decreases, and Ba first increases and then decreases with increasing SiO2. K/Rb is variable around 200, and Ba/La may be constant or decrease with increasing SiO2. In general, the Altiplano complexes have similar total REE contents, degree of fractionation, and variably negative Eu anomalies to those from the Coastal Range, but without the flat REE patterns with extreme negative Eu anomalies characteristic of the leucogranites of the Coastal Range. The phases required in any fractional crystallization model to explain the REE concentrations and patterns are consistent with petrographic observations and petrogenetic modeling of other trace element distributions, such as Rb, Sr, and Ba. A model of mantle-derived magma that underwent modification by interaction with the crust followed by fractional crystallization is preferred, but the leucogranites could represent either extreme fractionation at high-silica contents or crustal melts. Trace element discrimination diagrams for tectonic interpretation of granitic rocks suggest a volcanic arc origin for both magmatic belts. It is concluded that the Permian-Triassic plutonic complexes of the Coastal Range and Altiplano could have been part of the same magmatic arc system located on the western edge of South America. This arc was split by late Triassic to early Cretaceous behind-arc extension and basin development while South America was essentially static in mantle reference frame.

The Achala batholith is a post-orogenic intrusion of probable Silurian age exposed in the Sierra de Cordoba in the eastern Sierras Pampeanas of central Argentina (31°6′S to 32°2′S; 64°29′W to 65°7′W). The batholith was emplaced into late Precambrian amphibolite- and granulite-facies metamorphic rocks. Five comagmatic granitoid facies, all monzogranite in composition, have been recognized. Geochemical data suggest these granitoids formed by a magmatic differentiation process that began with porphyritic and fine-grained facies B, C, and D, and ended with leucogranite facies A. Biotite-apatite enclaves that are interpreted as cumulates and tonalitic nodules occur in facies B. Less abundant rock types are quartz-muscovite greisens, feldspathic episyenites, pegmatites, and aplites. The granitoids have S-type chemical affinities and are consistent with a within-plate granite tectonic setting.

Two pulses of granitoid magmatism occurred in the Cordillera Real in the eastern Andes of Bolivia (La Paz department), one in the Middle to Upper Triassic and the other in the late Oligocene to Miocene. This magmatism occurred along the southward extension of the rift-controlled inner magmatic arc of the southeastern Andes of Peru. The peraluminous chemistry, the high but restricted silica range, and the low CaO and MgO contents of these “S-like” plutonic rocks suggest that they formed by fractional crystallization followed by variable assimilation of supracrustal rocks. The Pb isotopic data of Tilton and others (1981) supports a mantle component in the Cordillera Real melts. The Cordillera Real granites are characterized by high tin contents. Geochemical indicators such as TiO2 content and Rb/Sr, Rb/Ba, and Mg/Li ratios suggest that the tin was introduced by assimilation during the late and post-magmatic stages of the plutons.

The Devonian batholiths of western Tasmania represent a diverse assemblage of highly fractionated intrusions (70 to 77 percent SiO2) that are the products of different source materials. The Housetop batholith exhibits compositional affinities to a fluorine-rich I-type magma. The Meredith batholith also has characteristics indicative of I-type source materials. The Heemskirk batholith is composite, and consists of a volatile (F, B, H2O)–rich S-type granite underlying an I-type granite. The Three Hummock Island, Interview River, Sandy Cape, and Conical Rocks plutons probably have an S-type source and are grouped together as the Sandy Cape Suite. Rapakivi texture is common in the Housetop, Meredith, and Heemkirk batholiths. Quartz-tourmaline nodules are found in the Conical Rocks pluton and the S-type portion of the Heemskirk batholith. The Conical Rocks and Interview River plutons yield high initial Sr isotopic ratios of 0.74242 and 0.76009, respectively. The Housetop and Meredith batholiths yield the lowest initial Sr isotopic ratios of 0.71041 and 0.71445, respectively. The S-type portion of the Heemskirk batholith has an initial Sr isotopic ratio of 0.76387. The 40Ar/39Ar release spectrum and Rb/Sr mineral isochron analyses corroborate previously reported Devonian to Carboniferous age estimates for these batholiths. A relatively low-temperature thermal event (<200°C) caused argon loss from the K-feldspars at about 105 Ma. This heating event is probably related to the continental breakup of Australia from Antarctica. Major-element compositions of the western Tasmanian granites are very similar. The highly fractionated Sandy Cape Suite leucogranites exhibit high Ga/Al ratios typical of A-type granites, but not their extreme Zr, Y, or Ce enrichments. A distinctive feature of the Sandy Cape Suite is the increase in P2O5 concentration with fractionation. The increase in P2O5 with fractionation is apparently due to extremely low Ca activity, which precludes the formation of apatite, thus allowing P2O5 to behave incompatibly in the melt. All of the granitoids have LREE–enriched chondrite-normalized rare earth element patterns. REE fractionation within the individual granitoids can be summarized by two trends: those with LREE >> HREE depletion (Housetop, Meredith, and Heemskirk batholiths), and those with LREE = HREE depletion (Sandy Cape Suite). The first trend is caused by the initial undersaturation of accessory mineral assemblage that resulted from high concentrations of volatiles and/or alkali complexes. The second trend is caused by early saturation of accessory phases and/or refractory accessory phases.

Two distinct granite plutons occur above the Main Central Thrust north of Uttarkashi in the upper valley of the Bhagirathi River and its source, the Gangotri Glacier, in Garhwal, India. The structurally lower pluton is a biotite granite with mineralogic and major and trace element characteristics similar to late Precambrian to early Paleozoic plutons of the Northern and Lesser Himalayan belts of Indian shield granites. The structurally higher pluton, intruded into the Martoli Formation and Vaikrita Group of the Tethyan sedimentary rocks, is an aluminous S-type muscovite-tourmaline leucogranite similar to other Cenozoic High Himalayan leucogranites with respect to its mineralogy and major element chemistry, as well as its high concentrations of Rb, Cs, and U, combined with low concentrations of Sr, Zr, Th, and rare-earth elements. Whole-rock Rb-Sr data for five samples from the main leucogranite define two clusters on an isochron of 64 ± 11 Ma. This isochron may reflect (1) a significant age, (2) variations of initial 87Sr/86Sr in the magma at the time of crystallization, or (3) multiple pulses of magma with different isotopic compositions. An Rb-Sr mineral isochron for one of the leucogranite samples yields an age of 21.1 ± 0.9 Ma, whereas a K-Ar age on a muscovite separate from the same rock yields an age of 18.9 ± 1.3 Ma. Whatever the actual age of the leucogranite magma within the range of these different determinations, it clearly had a high initial 87Sr/86Sr, greater than 0.746. The initial 143Nd/144Nd is correspondingly low, less than 0.51190. These data suggest that the granitic magma developed by anatectic melting of older continental crust. Although the timing of anatectic melting is equivocal, constraints on the conditions required to produce the melts imply that postcollisional, intracontinental subduction along the Main Central Thrust (MCT) could not produce the leucogranites without some preheating of the Indian continental crust. This heating may have occurred when delaminated Indian subcontinental lithosphere was replaced by hot asthenosphere in the initial stages of the continental collision. Crustal anatexis to produce the leucogranites might have already occurred at this early stage of collision. Alternatively, once the crust was so heated, crustal anatexis may have occurred within the hot crystalline Higher Himalayan slab due to influx of volatiles from the Lesser Himalayan slab as the former was emplaced over the latter by intracontinental subduction. Continued continental convergence led to uplift of the Higher Himalaya due to displacement along a major crustal footwall ramp of the Main Central Thrust. The mineral ages are interpreted as dating cooling related to this uplift, which may have coincided with termination of active motion of the MCT and the initiation of motion along the Main Boundary Thrust.