21 research outputs found
Comments on "Garnet-bearing ultramafic rocks from the Dominican Republic:Fossil mantle plume fragments in an ultra high pressure oceanic complex?" by Gazel et al. [Lithos 125 (2011) 393-404]
Recent advances in the analysis of volatiles and fluid-mobile elements in melt inclusions by Secondary Ion Mass Spectrometry (SIMS)
Metamorphic olivine records external fluid infiltration during serpentinite dehydration
International audienc
Trace-element geochemistry of diamond-hosted olivine inclusions from the Akwatia Mine, West African Craton: implications for diamond paragenesis and geothermobarometry
Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry
Multi-stage subduction-related metasomatism recorded in whiteschists from the Dora-Maira Massif, Western Alps
Halogen (F, Cl, Br, I) behaviour in subducting slabs: a study of lawsonite blueschists in western Turkey
Constraints on crustal recycling from boron isotopes in Italian melt inclusions
Boron represents an important tracer of crustal recycling processes in subduction zones, because it is readily mobilised from the subducted lithosphere and different components in the slab are isotopically distinct. Profiles of boron content and isotope ratio across magmatic arcs generally show that B concentrations decrease with increasing slab depth, which implies decreasing amount of slab-derived fluids. To date, however, data on continental-collision zones and post-collisional subduction settings are scarce. This study examines Plio-Quaternary Italian magmatism to quantify crustal recycling in a complex subduction setting. Magmatic products vary from (ultra)potassic along the Tyrrhenian side in the north, to calcalkaline and Na-alkaline in the south. Combined major and trace element and [B] content and δ11B values are reported in 99 Melt Inclusions (MIs), analyses from a wide range of Italian lavas. [B] vary from 4 to 298 µg/g and δ11B from -29.2 to -3.9‰. The B isotopic values are considerably lower than previously reported in arcs and other post-collisional setting magmatism. We infer a role for phengite in the source of all studied Italian magmas (with the exception of Mt. Etna lavas). This white mica is stable to high pressures in subducted sediments of altered oceanic crust and records dehydration and 11B depletion due to dehydration processes. MIs hosted in highly fosteritic olivines (Fo >74; median of 89) from across Italy reveal that primary melts tap heterogeneous mantle including subducted oceanic and continental components that were introduced during the Alpine, and Adriatic and Ionian subduction phases. The combined geochemical data record the involvement of sediments that variably metasomatized the mantle wedge. We propose that slab detachment and consequent heat input from the inflow of hot asthenosphere was responsible for phengite breakdown in subducted sediments and locally produced metasomatism of the mantle wedge, imposing a characteristic B isotope signature to the overlying mantle. Continued heating due to asthenosphere inflow led to melting of the metasomatized mantle wedge and generation of the Italian magmatism. Mt. Etna represents an exception being dominated by asthenosphere upwelling through a slab window with minimal influence from active subduction.</p