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The Jurassic Bokan Mountain complex (BMC), composed of arfvedsonite and/or aegirine-bearing peralkaline A-type granitic rocks, is a circular body about 3 km in diameter located in southeastern Alaska. Like many other highly fractionated granitic bodies, the BMC granites were affected by late magmatic or post-magmatic processes, which, however, did not modify the contents of major elements. The granitic rocks are distinctly enriched in high-field-strength elements (HFSEs), rare earth elements (REEs), Y, Th, and U but depleted in Ba, Sr, and Eu and have high positive ɛNd(T) values. Unlike the variations in the major elements, Sr and Ba, which can be accounted by fractional crystallization, the abundance of REE, Y, HFSE, U, and Th (the elements which are hosted in accessory phases) were modified by F-rich hydrothermal fluids. The BMC hosts significant rare metal mineralization related to the late-stage crystallization history of the complex involving late magmatic and/or post-magmatic fluids. The min...

The basement of most peri-Gondwanan terranes in Mexico, the Appalachians, the Caledonides, and the Variscides is buried beneath younger Ediacaran arc, Palaeozoic passive margin, and/or Mesozoic–Cenozoic platformal carbonates. However, it is exposed in the Oaxaquia terrane of Mexico (Oaxacan, Novillo, Huiznopala, and Guichicovi complexes), where it is characterized by ca. 1.0–1.3 billion year protolith ages and igneous rocks with depleted mantle model ages (T DM) of 1.35–1.77 billion years. The T DM ages represent a bulk average composition of the source and can be used as a tracer; these T DM ages overlap with those in ca. 546 Ma arc clasts from the 65.5 Ma Chicxulub bolide breccia, suggesting that the northern Maya block is also underlain by Oaxaquia-type basement. Similar T DM ages occur in Ediacaran arc rocks in Suwannee (Florida), NW Avalonia, Ganderia, Iberia, Armorica, and Bohemia, and in lower Palaeozoic plutons cutting adjacent Palaeozoic passive margin rocks (Acatlan Complex, Gander Group), sugge...

The basement of the Maya block of eastern Mexico is generally covered by Mesozoic and Cenozoic platformal carbonate rocks. However, the 65.5 Ma Chicxulub meteorite impact in the northern Yucatan Peninsula excavated deep into the crust and brought crystalline basement fragments into the impact breccias. Common Pb isotopic data from impact melt and a granitic clast from drill core (Y6) are highly radiogenic, consistent with the Archaean derivation. A granodiorite clast in this breccia from drill core (Yaxcopoil-1) yielded a continuous range of concordant 206Pb/238U laser ablation inductively coupled plasma mass spectrometry zircon ages between 546 ± 5 Ma and 465 Ma, with three discordant zircons having 206Pb/238U ages between 130 Ma and 345 Ma. The ca. 546 Ma age is interpreted as the age of granodiorite intrusion, with younger ages representing variable Pb loss during melting associated with the meteorite impact. This is consistent with previous U–Pb zircon data that gave an upper intercept age of 550 ± 15...

The chemical composition and origin of the isotopically identified end-member mantle components have been difficult to describe because their melted samples—oceanic basalts—are affected by many processes such as variable degrees of partial melting. Exploratory data analysis [multidimensional scaling (MDS)] applied to ∼200 basalts from French Polynesia reveals over 100 ratios of similarly incompatible elements (SIER) that are minimally affected by these processes. Ratios from elements with dissimilar incompatibility are identified as affected by melting percentages. When basalt samples are compared simultaneously using ∼100 SIER and MDS, they organise in the same way that they would with isotopes, according to mantle component type. Applying discriminant analysis to the most extreme French Polynesia samples representing each mantle component yields preliminary discrimination diagrams that improve the description of chemical variation in the mantle. As a test of their utility and reliability, they are used ...

Migmatized amphibolite-facies gneisses and amphibolites of the Francisco Gneiss exposed in the northern part of the Guerrero composite arc terrane have been interpreted as either Precambrian basement, a Triassic metamorphic complex, or a distinct terrane. Field observations suggest exposure in a metamorphic core complex of a protolith composed of interleaved bimodal igneous and sedimentary rocks. Geochemical data indicate that the amphibolites are within-plate, continental tholeiites. Recalculated TDM ages for the rhyolites are consistent with partial melting of the Grenvillian basement of North America projected beneath the area. U-Pb isotopic analyses of zircon from two felsic rocks yielded concordant ages between 216 and 197 Ma due to a combination of inheritance and Pb-loss: the best estimate of protolith age is ∼206 Ma—i.e., Norian, Late Triassic. Concordant U-Pb titanite ages range from 112 to 98 Ma, whereas nearly concordant U-Pb xenotime ranges from 91 to 51 Ma. These are inferred to result from p...

Paleozoic rocks exposed in northeast Hidalgo State, Mexico, have traditionally been assigned to the Guacamaya Formation, a orogenic flysch assemblage associated with the collision of South and North America during the formation of Pangea. However, major differences exist in the stratigraphy of these rocks and those of the Guacamaya Formation at its type section. The rocks of Hidalgo are here redefined as the Tuzancoa Formation, and comprise interbedded submarine andesitic-basaltic lava flows, siliciclastic turbidites, volcaniclastic turbidites, calcareous debris-flows, and lenses of conglomerate. The Tuzancoa Formation contains abundant Permian (Wolfcampian-Leonardian) fossils. The lavas and volcaniclastics are andesitic to basaltic in composition, and are related to subduction. Their REE patterns are similar to those of recent island arc magmas, with slight enrichment in LREE, flat HREE, and no Eu anomaly. The eNd(280) of +4.38 in a representative sample is also similar to island arcs and suggests little...

The Buck Creek volcanic complex of the Intermontane Superterrane of the Canadian Cordillera records a long history of volcanic activity from the Cretaceous through to the Eocene, when magmatic activity peaked, to the Miocene. Its basement includes primitive continental arc volcanic rocks of the Jurassic Hazelton Group (∼200 Ma; mainly basalt and andesites) emplaced prior to the accretion of Stikinia during the Mesozoic. In contrast, in the post-accretionary volcanic complex, the major pulse of volcanism started with the extrusion of continental margin calc-alkaline rocks (basaltic andesites to rhyolites) of the Cretaceous Tip Top Hill Formation (∼85 Ma). Their Nd-Sr isotopic compositions resemble those of the pre-accretionary Hazelton Group. However, this post-accretionary Cretaceous arc was more evolved and its crust was significantly thicker than the Hazelton. Mafic rocks of both the Hazelton and Tip Top Hill suites were generated from a spinel-bearing mantle source. The Eocene volcanics (∼50 Ma) evolve...

Intrusive calcareous bodies, marbles and calc-silicate rocks, are a distinctive feature of the highgrade metamorphic suites of the ~1 Ga northern Oaxacan Complex. They typically form dike-like intrusions up to 4 m thick which cut across the surrounding high-grade granulite- and upperamphibolite facies metamorphic rocks. Various protoliths are possible for these carbonate bodies: (1) sediments including evaporites; (2) metasomatic skarns; and (3) carbonatites. An evaporitic protolith is supported by the predominance of scapolite, low abundances of incompatible trace elements (including Nb and rare-earth elements) relative to carbonatites, and the presence of a sharp contact with host rocks without a significant contact metamorphic aureole or fenitization. It is inferred that limestones and related rocks were remobilized under granulite-facies conditions and intruded into the host rocks. The widespread distribution of such evaporites in the Oaxacan Complex is consistent with deposition after the worldwide ~...