The address is a wide-ranging commentary on the physical aspects of granitic magma and deals especially with the mode of emplacement. Recommendations on the nomenclature of plutons and batholiths involve both a description of the actual shape and their modeling by experimental and salt-diapir analogues. The nature of granitic crystal-mushes, wet or dry, is discussed in the light of the special properties of pseudoplastics, particularly the influence of the physical state on the sinking of crystals and xenoliths, on magma mobility in zoned plutons, and on the final rock structure. The longevity of plutonic events and their episodic character are commented on in relation to the subduction process. The generation of granitic magmas, their upwelling and the structural control of their intrusion, whether forceful or permissive, are discussed. The structural form of batholiths in depth is described in terms of a batholith denudation series particularly in the circum-Pacific context. Finally, two main orogenic environments of granites are contrasted in terms of the Hercynotype and Andinotype, and composition and structure are interrelated in a proposed general model for the emplacement of batholiths.

The nature, ascent and emplacement of granitic magmas

Fission track, K–Ar, and Rb–Sr mineral dates for the Ecstall and Quottoon plutons were determined to resolve the different cooling histories indicated by Rb–Sr whole-rock and mineral isochrons and ...

Geochronology and thermal history of the Coast Plutonic Complex, near Prince Rupert, British Columbia

Previously published and new U-Pb geochronologic analyses provide 313 zircon and 59 titanite ages that constrain the igneous and cooling history of the Coast Mountains batholith in north-coastal British Columbia. First-order findings are as follows:
 (1) This segment of the batholith consists of three portions: a western magmatic belt (emplaced into the outboard Alexander and Wrangellia terranes) that was active 177–162 Ma, 157–142 Ma, and 118–100 Ma; an eastern belt (emplaced into the inboard Stikine and Yukon-Tanana terranes) that was active ca. 180–110 Ma; and a 100–50 Ma belt that was emplaced across much of the orogen during and following mid-Cretaceous juxtaposition of outboard and inboard terranes. (2) Magmatism migrated eastward from 120 to 80 (or 60) Ma at a rate of 2.0–2.7 km/Ma, a rate similar to that recorded by the Sierra Nevada batholith. (3) Magmatic flux was quite variable through time, with high (>35–50 km 3 /Ma per km strike length) flux at 160–140 Ma, 120–78 Ma, and 55–48 Ma, and magmatic lulls at 140–120 Ma and 78–55 Ma. (4) High U/Th values record widespread growth (and/or recrystallization) of metamorphic zircon at 88–76 Ma and 62–52 Ma. (5) U-Pb ages of titanite record rapid cooling of axial portions of the batholith at ca. 55–48 Ma in response to east-side-down motion on regional extensional structures. (6) The magmatic history of this portion of the Coast Mountains batholith is consistent with a tectonic model involving formation of a Late Jurassic–earliest Cretaceous magmatic arc along the northern Cordilleran margin; duplication of this arc system in Early Cretaceous time by >800 km (perhaps 1000–1200 km) of sinistral motion (bringing the northern portion outboard of the southern portion); high-flux magmatism prior to and during orthogonal mid-Cretaceous terrane accretion; low-flux magmatism during Late Cretaceous–Paleocene dextral transpressional motion; and high-flux Eocene magmatism during rapid exhumation in a regime of regional crustal extension.

U-Th-Pb geochronology of the Coast Mountains batholith in north-coastal British Columbia: Constraints on age and tectonic evolution

Two Neoarchean supercontinents? Evidence from the Paleoproterozoic

Provenance and U-Pb geochronology of the Mesoproterozoic Belt Supergroup (northwestern United States): implications for age of deposition and pre-Panthalassa plate reconstructions

New U–Pb and Rb–Sr isotopic and major and trace element geochemical data are reported for Late Triassic to Eocene granite bodies that intrude the Cache Creek and Stikine terranes in the Atlin–Benne...

Age of emplacement and basement character of the Cache Creek terrane as constrained by new isotopic and geochemical data

The minimum age of the Ecstall pluton is 78–79 Ma, based on Rb–Sr mineral isochrons for two pegmatites. At that time the entire body of the pluton, zoned concentrically from quartz monzonite to diorite, was Sr rich – Rb poor, relatively homogeneous in Rb/Sr ratio (0.024–0.061), and somewhat variable in initial Sr isotopic composition (87Sr/86Sr = 0.7044 to 0.7048). Late-stage leucocratic dikes contain radiogenic Sr that is probably derived from old and Rb-rich country rocks. Pegmatite dikes from two different localities are similar to one another in Rb/Sr and 87Sr/86Sr and either have high initial ratios (0.7055 and 0.7058), like the leucocratic dikes (0.7051 and 0.7059), or the pluton and its pegmatite dikes are very much older (~190 Ma) than the 78–79 Ma pegmatite mineral isochrons. Sr isotopic data do not resolve this ambiguity. The Kitkiata pluton has an initial 87Sr/86Sr ratio of 0.7042–0.7043, depending on its age. One radiogenic Sr-rich sample gives a model date of 165 ± 11 Ma, but the possibility ...

Rb–Sr geochronometry of the Ecstall, Kitkiata, and Quottoon plutons and their country rocks, Prince Rupert region, Coast Plutonic Complex, British Columbia

New U–Pb, K–Ar, and Rb–Sr dates from the Eagle Plutonic Complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the Intermontane Belt. U–Pb zircon minimum dates for Eagle tonalite and gneiss (148 ± 6, 156 ± 4, and 157 ± 4 Ma) document previously unrecognized Middle to Late Jurassic magmatism and syn-intrusive deformation along the eastern margin of the Eagle Plutonic Complex and the southwestern margin of the Intermontane terrane. Widespread mid-Cretaceous (Albian–Cenomanian) resetting of K–Ar and Rb–Sr isotopic systematics in Jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the Fallslake Plutonic Suite (110.5 ± 2 Ma, U–Pb) which crosscut Jurassic plutons and structures but were themselves ductilely deformed along the Pasayten fault during sinistral, east-side-up, reverse displacement. K–Ar and Rb–Sr cooling dates for the Fallslake Suite of ca. 100 Ma, including dates from mylonites along the Pasayten fau...

Geochronometry of the Eagle Plutonic Complex and the Coquihalla area, southwestern British Columbia

New K-Ar and U-Pb dates for the Cambria Icefield area, northwestern British Columbia

The protolith age of high-grade metamorphic rocks exposed in structurally deep parts of the Omineca Crystalline Belt has been the subject of investigation and controversy for decades. We have applied multiple isotopic dating techniques to rocks of three structural culminations: the Monashee complex (which includes the Frenchman Cap and Thor–Odin gneiss domes), the Grand Forks horst, and the Vaseaux Formation, which lies in the footwall of the Okanagan Valley fault.Frenchman Cap core gneisses contain highly radiogenic Sr that scatters about a 2206 ± 117 Ma (1σ) Rb–Sr isochron with 87Sr/86Sr initial ratio of 0.700 ± 0.002. Monazite and zircon dates for the same rocks are 1851 ± 7 to 2103 ± 16 Ma (only U–Pb dates are given with 2σ errors), with lower intercepts from about 100 to 300 Ma. Sm–Nd whole-rock and crustal-residence (TDM) dates are 2.3 ± 0.2 Ga. Mafic–felsic layering in the core gneiss is also of Early Proterozoic age. There is no geochronometric evidence for Late Proterozoic or Mesozoic migmatizati...

Early Proterozoic basement exposures in the southern Canadian Cordillera: core gneiss of Frenchman Cap, Unit I of the Grand Forks Gneiss, and the Vaseaux Formation

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