Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth, Planets and Space 66 (2014): 81, doi:10.1186/1880-5981-66-81.

Description: Investigation of olivine-hosted melt inclusions provides information about the abundance of volatile elements that are often lost during subaerial eruptions of lavas. We have measured the abundances of H2O, CO2, F, Cl, and S as well as Pb isotopes in 29 melt inclusions in the scoria of the 1686 eruption of the Iwate volcano, a frontal-arc volcano in the northeast Japan arc. Pb Isotope compositions identify that Iwate magma is derived from a mixture of depleted mantle, subducted basalt, and sediment. Systematics of F in comparison to MORB and other arc magma indicates that (1) the slab surface temperature must be among the lowest on Earth and (2) hydrous minerals, such as amphibole, humites, and/or mica, must be present as residual phases during the dehydration of the slab.

Description: The authors acknowledge financial support from the French Agence Nationale de la Recherche (projects: SlabFlux grant no. ANR 2009 Blanc 0338 and DegazMag, grant no. ANR 2011 Blanc SIMI 5-6 003). This research was financed by the French Government Laboratory of Excellence initiative no. ANR-10-LABX-0006, the Région Auvergne, and the European Regional Development Fund.

Description: The integrated approach of field work, microscopy, whole-rock and mineral-scale geochemistry, and in situ U-Th-Pb zircon geochronology has proven to be useful for recognizing the type, timing, and sequence of complex Na and K fluid alteration related to the development of Kiruna-type magnetite-apatite deposits and the tectonic evolution of the granites that host these deposits. The Lyon Mountain Granite in the northeastern Adirondack Mountains of New York State has undergone multiple episodes of hydrothermal fluid alteration and Fe mineralization. Perthite granite containing ubiquitous 1060-1050 Ma zircon grains was overprinted by potassic alteration, which in turn was overprinted by pervasive Na alteration. During the Na alteration, preexisting orebodies, consisting of magnetite, clinopyroxene, and apatite, were overprinted and remobilized to form new deposits that contain magnetite, apatite, quartz, and zircon. The U-Th-Pb zircon geochronology data suggest that the Lyon Mountain Granite intruded the Adirondack Highlands during the Ottawan orogeny between ca. 1060 and 1050 Ma. However, subsequent alteration obscured much of the prehistory of the LMG. Amphibolite layers within the Lyon Mountain Granite and granitic dikes and pegmatites that crosscut the foliation in the Lyon Mountain Granite have been dated between 1045 and 1016 Ma. These ages coincide with previous published zircon age data from second-generation orebodies associated with Na alteration.

Description: New zircon U-Pb age data and geochemistry for the Sa'al metamorphic complex (SMC) in Sinai (Egypt) provide the first robust evidence of latest Mesoproterozoic island arc rocks at the northernmost Arabian-Nubian Shield, possibly indicating that formation of the shield commenced prior to 870 Ma. An older series of calc-alkaline volcanic and intrusive rocks yielded ages of ca. 1.03–1.02 Ga. Zircon xenocrysts within these rocks attest to arc magmatism predating the SMC by ∼80 m.y., as well as the minor contribution of Paleoproterozoic crust. Detrital zircons of the SMC pelites exhibit textural and U-Pb age patterns supporting their derivation from the volcanic rocks as arc detritus. A ca. 820 Ma gneissic pluton intruding the SMC indicates that by Cryogenian time, the SMC was already incorporated within the evolving Arabian-Nubian Shield. The 1.0–1.1 Ga SMC rocks provide a possible connection between latest Mesoproterozoic ocean closure during the assembly of Rodinia and the later buildup of Gondwana. There is growing indication, including the findings of this study, that 1.0–1.1 Ga crust composed a more significant component in northernmost Gondwana than hitherto recognized.

Description: Field observations from the Trinity Peninsula Group at View Point on the Antarctic Peninsula indicate that thick, southward-younging and overturned clastic sedimentary rocks, comprising unusually coarse conglomeratic lenses within a succession of fine-grained sandstone–mudstone couplets, are the deposits of debris and turbidity flows on or at the foot of a submarine slope. Three detrital zircons from the sandstone–mudstone couplets date deposition at 302 ± 3 Ma, at or shortly after the Carboniferous–Permian boundary. Conglomerates predominantly consist of quartzite and granite and contain boulders exceeding 500 mm in diameter. Zircons from granitoid clasts and a silicic volcanic clast yield U–Pb ages of 466 ± 3 Ma, 373 ± 5 Ma and 487 ± 4 Ma, respectively and have corresponding average εHft values between +0.3 and +7.6. A quartzite clast, conglomerate matrix and sandstone interbedded with the conglomerate units have broadly similar detrital zircon age distributions and Hf isotope compositions. The clast and detrital zircon ages match well with sources within Patagonia; however, the age of one granite clast and the εHf characteristics of some detrital zircons point to a lesser South Africa or Ellsworth Mountain-like contribution, and the quartzite and granite-dominated composition of the conglomerates is similar to upper Palaeozoic diamictites in the Ellsworth Mountains. Unlike detrital zircons, large conglomerate clasts limit possible transport distance, and suggest sedimentation took place on or near the edge of continental crust. Comparison with other upper Palaeozoic to Mesozoic sediments in the Antarctic Peninsula and Patagonia, including detrital zircon composition and the style of deformation, suggests deposition of the Trinity Peninsula Group in an upper plate basin on an active margin, rather than a subduction-related accretionary setting, with slow extension and rifting punctuated by short periods of compression.