The Strait of Sicily Rift Zone (SSRZ) is a northwest-southeast trending transtensional rift situated in the Mediterranean Sea between Sicily and north Africa. The SSRZ consists of three basins: the Pantelleria Trough, the Linosa Basin, and the Malta Trough. Volcanoes are situated in or adjacent to all except the Malta Trough, and include two islands (Pantelleria and Linosa) and several seamounts. The thickness of the crust throughout the region is 25-35 km, but thins to 16-18 km in the basins of the SSRZ. The Pantelleria Trough is characterized by high average heat flow values and a strong positive Bourger anomaly, which suggest assthenospheric upwelling to ~60 km and the presence of abundant basaltic material at depth.Mafic lavas ranging in composition from alkaline and transitional basalt to hawaiite (~45-50 wt% SiO2) comprise the dominant volume of eruptive products in the SSRZ; evolved rocks (trachyte and pantellerite) and common only on Pantelleria, where they crop out over ~94% of the island’s surface. Mafic lavas on Pantelleria are also the most evolved with Mg# ≤ 58, Ni ≤ 98 ppm, and Cr ≤ 183 ppm; more primitive mafic lavas can be found forming the seamounts (Mg# ≤ 67, Ni ≤ 280 ppm, and Cr ≤ 391 ppm) and cropping out on the island of Linosa (Mg# ≤ 71, Ni ≤ 409 ppm, and Cr ≤ 674 ppm) . There are two distinct mafic series on Pantelleria: a generally older (>50 ka) High Ti-P series (“Paleo-Pantelleria”), characterized by TiO2 > 3.0, P2O5 > 0.9, and high REE ratios; and a generally younger (<50 ka) Low Ti-P series (“Neo-Pantelleria”), characterized by TiO2 < 3.0, P2O5 < 0.75, and low REE ratios. Linosa mafic lavas are more similar to the Neo-Pantelleria series, whereas Seamounts may be more similar to either series.To constrain the melting conditions in the SSRZ we have attempted to estimate the ancestral magma compositions for the most primitive basalts following Hertzberg and O’Hara (2002) and Leeman et al. (2005, 2009) by which equilibrium olivine is incrementally added to basalt until the calculated ancestral basalt has a Mg# shown experimentally to have been in equilibrium with mantle peridotite. From this composition, the temperature of magmatic segregation may be calculated following Sugawara (2000), and the pressure of segretation may be calculated following Alberede (1992). For the purposes of our investigation, we assumed FeO/FeO* = 0.85, with KD for MgO-FeO between olivine and melt calculated following Hertzberg and O’Hara (2002). From our pressure estimates, we inferred depths of segregation assuming a 17 km thick crust with an average crustal density of 2.69 g/cm3 and an average mantle density of 3.20 g/cm3. Results are presented in Figure 1. High Ti-P magmas are the result of partial melting at greater depths (69-75 km), near the spinel-garnet transition zone, whereas Low Ti-P magams are the result of partial melting at shallower depths (52-62 km).
|Numero di pagine||3|
|Stato di pubblicazione||Published - 2013|