Time-dependent variation of lead isotopes of lead white in 17th century Dutch paintings

This study investigates how lead isotopes in lead white pigment can be used as an additional diagnostic tool to constrain the production time of 17th century Dutch paintings. Analysis of 77 well-dated paintings from 27 different Dutch artists reveal significant change in the source of lead used in lead white at the start, middle, and end of the 17th century. Isotopic shifts are related to major historical and socioeconomical events such as the English Civil War and Anglo-Dutch-French conflicts. These observations offer the prospect that lead isotope analysis of lead white could aid attribution and authentication of Dutch 17th century paintings and provide insights into artists’ international travels as well as lead production and trading.

A post-collision slab-breakoff model for the orgin of the Middle Eocene magmatic rocks of the Armutlu–Almacık belt, NW Turkey and its regional implications

Middle Eocene magmatic rocks (MEMR) (49.3±2 to 38.1±1.9 Ma) formed an east–west trending belt after continental collision and rest unconformably on pre-Middle Eocene units as a common cover. The origin and tectonic setting of MEMR are controversial as both arc and post-collisional settings are proposed. We present new geological and petrological data from the western part of the belt, between the Armutlu Peninsula and the Almacık Mountains. The MEMR are represented by basic to intermediate volcanic rocks, dykes and coeval granites. The lavas exhibit a continuous trend from basalt to dacite. The MEMR as a whole display low- to medium-K subalkaline (to rarely mildly alkaline) affinities and a calc-alkaline trend. On N-type Mid Ocean Ridge Basalt-normalized spidergrams these rocks display relative enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, but depletion in Ta and Nb. Geochemical data and Sr, Nd, Pb and δ18O isotope compositions, coupled with εNd(T) values, reveal that the MEMR magma was of hybrid type, with both depleted sub-continental lithospheric mantle and crustal components. We conclude that the MEMR was produced in a post-collisional setting, and we favour a slab-breakoff mechanism to explain this as it is consistent with the known Middle Eocene tectonic evolution of northwestern Turkey.

Timing and tectonic controls in the evolving orogen of SE Asia and the western Pacific and some implications for ore generation

SE Asia lies at the convergence of the Eurasian, Pacific and Australian plates. The region is made up of many active arcs, extensional basins, and the remnants of similar tectonic environments developed throughout the Cenozoic. There are many important hydrothermal mineral deposits and prospects in SE Asia but their formation is often poorly understood due to the complicated tectonic history of this region and the knowledge of relationships between mineralization and tectonics. Plate reconstruction offers a framework to integrate geological and geochemical data that can be used to unravel the large-scale tectonic processes that affected mineralized provinces. We present examples of the information that can be derived from this approach and discuss the implications for understanding the origin of some hydrothermal mineral deposits in SE Asia.

U-Th Isotopes in Arc Magmas: Implications for Element Transfer from the Subducted Crust

Uranium-thorium isotope results from island arc volcanic rocks were used to investigate the rates of transfer of fluids and sediments from the downgoing slab. Uranium, but not thorium, is readily mobilized in the fluid. A negative array between thorium/cerium and neodymium-143/neodymium-144 indicates that significant amounts of the thorium in arc rocks are derived from subducted sediments, although perhaps only about 30 percent of the thorium in subducted sediments is returned to the crust in this way. The transfer times for fluid through the mantle wedge are about 30,000 to 120,000 years, whereas those for sediment melts may be several million years. The low average uranium/thorium ratios of bulk crust primarily reflect different crustal generation processes in the Archaean.