Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Across-arc variations of isotope and trace element compositions from Quaternary basaltic volcanic rocks in northeastern Japan: Implications for interaction between subducted oceanic slab and mantle wedge

Abstract: Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for Quaternary island arc basaltic rocks from northeastern Japan. Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front toward the back arc. The isotopic compositions nearest the back arc side are nearly identical to those of mid-ocean ridge basalt (MORB). The high field strength elements and heavy rare earth elements show homogeneous and MORB-like characteristics. These observations indicate that the mantle wedge beneath northeastern Japan originally had a MORB-type mantle composition that was homogeneous across the arc. Pb isotope compositions show a mixing relationship between mantle wedge and oceanic sediments reflecting the introduction of subduction component into the mantle wedge, Across-arc isotopic variations were caused by interaction between MORB-type mantle wedge and the subducting slab, and the amount of subduction component correlates with the depth to the slab. The isotopic compositions of subduction component are expressed by bulk mixing of 15 wt % of oceanic sediment and 85 wt % of altered MORB. Inversion analyses of isotopic compositions using two-component mixing relationships show that the Sr/Nd and Pb/Nd ratios in subduction component decrease with increasing depth to the slab, while the Sr/Pb ratio is nearly constant. These changes can be explained only by a preferential discharge of the elements into the wedge mantle associated with continuous dehydration of the subducting slab. The present study further demonstrates that a very wide range of isotopic and elemental compositions in island arc magmas is a consequence of the interaction between subducting slab and mantle wedge without the involvement of an oceanic island basalts component, and the slab can carry water and supply a subduction component as a fluid to the overlying mantle wedge to depths exceeding 150 km.

Across-arc geochemical trends in the Izu-Bonin arc: Contributions from the subducting slab, revisited

Abstract: New Sr, Nd, Hf, and Pb isotope and trace element data are presented for basalts erupted in the Izu back arc. We propose that across-arc differences in the geochemistry of Izu-Bonin arc basalts are controlled by the addition of aqueous slab fluids to the volcanic front and hydrous partial melt of the slab to the back arc. The volcanic front has the lowest concentrations of incompatible elements, the strongest relative enrichments of fluid-mobile elements, and the most radiogenic Sr, Nd, Hf, and Pb, suggesting the volcanic front is the result of high degrees of partial melting of a previously depleted mantle source caused by an aqueous fluid flux from the slab. Relative to the volcanic front, the back arc has higher concentrations of incompatible elements and elevated La/Yb and Nb/Zr, suggesting lower degrees of partial melting of a less depleted or even enriched mantle source. Positive linear correlations between fluid-immobile element concentrations and the estimated degree of mantle melting suggest the slab contribution added to the mantle wedge in the Izu back arc is a supercritical melt. Pb, Nd, and Hf isotopes and Th/La systematics of back-arc basalts are consistent with a slab melt composed of >90% altered oceanic crust and <10% sediment; that is, altered oceanic crust, not subducted sediment, dominates the slab contribution. High field strength element systematics require supercritical melts to be in equilibrium with residual rutile and zircon.

Geochemical confirmation of the Kula-Farallon slab window beneath the Pacific Northwest in Eocene time

Abstract: Plate tectonic models indicate subduction of the Kula-Farallon spreading ridge, and thus imply formation of the Kula-Farallon slab window, beneath western North America from Late Cretaceous to middle Eocene time. Seafloor magnetic anomalies, however, pro- vide few constraints on the configuration of the subducted ridge and the location of the slab window. We use geochemical data from Eocene igneous rocks to provide an estimate of the slab window's position at 50 Ma. Contouring of the trace element ratios K 2O/SiO2, Rb/Zr, and Ta/Ce for lavas of the Eocene Challis-Kamloops volcanic belt demonstrates a southward trend toward enriched geochemical character. This trend is consistent with a Pacific Northwest position for the slab window; this is supported by the presence of adak- ites (slab melts) near the Canada-United States border, and by ca. 51 Ma forearc intru- sions and volcanic rocks on Vancouver Island that are regarded as products of ridge subduction. A new reconstruction of the slab window's geometry over time indicates that its chemically defined position is kinematically viable.

Comparison of Fly Ash, Pva Fiber, Mgo and Shrinkage-Reducing Admixture on the Frost Resistance of Face Slab Concrete via Pore Structural and Fractal Analysis

Abstract: Face slab concrete suffers from serious frost damage in the cold regions in China. How to improve the frost resistance of face slab concrete in cold regions is one of the important issues in concre...