Abstract
The Tabas Black Land volcanic field (14 Ma) is on the major right lateral Nayband fault, on the Lut Block, Iran. It has a central area of eroded ventd, surrounded by lavas. Lavas are tilted and folded on the east by the Nayband fault. To the west lavas are undeformed and are in inverted relief. We study the evolution of the volcanic field and assess its relationship to the regional tectonics. The Tabas Black Land products are basaltic trachyandesite – basaltic andesite, with intraplate sodic alkaline affinity and represent post-collisional magmatism. Geochemical and isotopic data show that magmas formed from 5% partial melting of garnet peridotite mantle. Modest K2O values, ~1.25 wt%, indicate hydrous phases (e.g., phlogopite) in the source. The average of P2O5/K2O ratios (0.31) indicate very low crustal contamination caused a sub-alkaline tendency in few differentiated samples. Comparing with other studies, we conclude that partial melting in Tabas is higher than at other Lut Block volcanoes, but have the least crustal contamination. Tabas magma storage and differentiation happened in the middle crust (400-500 MPa = 15-19 km), for temperatures of 1150 - 1200 oC. The Nayband has caused several destructive earthquakes during the 20th century. Volcanism has localised along the fault since 14 million years, with a similar source, but decreasing degrees partial melting and a shift towards the south from Tabas Black Lands. Thus, Nayaband magmatism appears to be dwindling, even if the fault itself remains active.
Highlights
The Tabas Black Land volcanic field (‘Tabas’ for short) lies between 57°04’ and 57°34’ E, and 32°40’ to 33°05’ N, 180 km southwest of Birjand city and 120 km south of Tabas city. It lies on the edge of the Nayband Fault, which forms the western margin of the Lut Block in central eastern Iran (Figure 1)
Based on observations for the Sr–Nd–Pb isotope data, and after eliminating the role of extensive crustal contamination, we suggest that all volcanism in the Lut Block has the same source composition consisting of a mantle enriched by a EM-1 component (Figure 10)
The Tabas Black Land monogenetic volcanic field has a sodic alkaline affinity. These mafic rocks are an example of within-plate magmatism within an active continental collision zone without involvement of a mantle plume or subduction components in their petrogenesis
Summary
The Tabas Black Land volcanic field (‘Tabas’ for short) lies between 57°04’ and 57°34’ E, and 32°40’ to 33°05’ N, 180 km southwest of Birjand city and 120 km south of Tabas city. It lies on the edge of the Nayband Fault, which forms the western margin of the Lut Block in central eastern Iran (Figure 1). We carried out field and remote sensing mapping, and analysed field samples for whole rock chemistry, and Nd, Sr and Pb isotopes We compare these results with data from the other volcanoes along the Nayband Fault to chart the degrees of partial melting, crustal contamination, and fractional crystallization. We compare in particular with the Gandom Beryan volcanic field, which is located in the southern part of Nayband Fault where compositions [Yousefi et al 2017] and ages are best known [2.2–2.6 Ma; Walker et al 2009]
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