Arc magmas and the continental crust share many chemical features, but a major question remains as to whether these features are created by subduction or are recycled from subducting sediment. This question is explored here using Th/La, which is low in oceanic basalts (<0 2), elevated in the continents (>0 25) and varies in arc basalts and marine sediments (0 09–0 34). Volcanic arcs form linear...

Acanthomorphic acritarch fossils, including some interpreted to be the fossils of the earliest animal embryos, first appear in the lower Doushantuo Formation of the Yangtze Gorges area (YGA). Further, the complete paleontological and geochemical record for the YGA has played a central role in defining the global biological and geochemical backdrop that presaged and witnessed the dawn of diverse...

[1] Dust fluxes are of wide interest because of the effects of dust on climate, oceanic primary productivity, terrestrial biogeochemical cycles, and regolith composition. Estimating long‐ term dust deposition rates, however, can be difficult, especially in steep, eroding terrain. Here we present a geochemical mass balance method for estimating long‐term average rates of dust incorporation into ...

JULY 2005, GSA TODAY ABSTRACT The subduction factory processes raw materials such as oceanic sediments and oceanic crust and manufactures magmas and continental crust as products. Aqueous fluids, which are extracted from oceanic raw materials via dehydration reactions during subduction, dissolve particular elements and overprint such elements onto the mantle wedge to generate chemically distinc...

Following accretion of southern Siberian microcontinents to the compositions reveal up to one order of magnitude variation of some trace elements and ratios between suites, and show a progressive Siberian craton in the Early Paleozoic, five cycles of K-rich silicic magmatism, progressively decaying in volume, occurred on batholithic change in trace element concentration with decreasing age. Pla...

A sequence of sixteen photomicrographs of thin sections of unaltered quartz diorite through a zone of deformation to myrmekite-bearing granite near Temecula, California, shows the textural and mineralogical changes that occurred in a quartz diorite as (1) K-metasomatism altered the primary plagioclase crystals to form microcline, myrmekite, quartz-bleb clusters, and recrystallized sodic plagioc...

IN a previous account (Brown, ~967) of the granitic sheets and veins in the Loch Coire migmatite complex, a metasomatic origin was postulated. This has now been confirmed by new analyses. Read (I93I) described the Loch Coire complex as made of three zones; one of unmigmatized meta-sediments, one of granitic veins and one of 'injection' or migmatite. The sheets and veins of granite (sensu lato),...

At low temperatures (<750 °C at moderate to high crustal pressures), the production of suffi cient melt to reach the melt connectivity transition (~7 vol%), enabling melt drainage, requires an infl ux of aqueous fl uid along structurally controlled pathways or recycling of fl uid via migration of melt and exsolution during crystallization. At higher temperatures, melting occurs by fl uid-absent...

Palaeoproterozoic sedimentary basins of north-eastern and central-eastern Australia are host to large amounts of variably deformed and metamorphosed Fe-rich tholeiitic rocks. Emplacement and/or extrusion of the mafic rocks occurred during one or more episodes of crustal thinning relating to a period of regional extension and sedimentation across Palaeoproterozoic northeastern Australia (ca. 173...