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Volume 25 Issue 7 (July 2015)

GSA Today

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Article, pp. 4-8 | Full Text | PDF (2.3MB)

Lithospheric thinning associated with formation of a metamorphic core complex and subsequent formation of the Iranian plateau

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Fariba Kargaranbafghi1, Franz Neubauer2

1 Dept. Geography and Geology, University of Salzburg, Salzburg, Austria, and Dept. of Geology, University of Yazd, Yazd, Iran
2 Dept. Geography and Geology, University of Salzburg, Salzburg, Austria


The formation of metamorphic core complexes is not well understood, which is why these large geological structures are still interesting subjects. They seem to have been formed by erosion of upper crustal rocks and exhumation of mid-crustal rocks. However, it is not clear how the lower crust and underlying mantle have responded. Many core complexes in the western United States are underlain by a flat Moho discontinuity, and some others possess a crustal root. Here, we present evidence of the Chapedony metamorphic core complex in the Central Iranian plateau. We show that the overall lithosphere and continental crust were thinned beneath regions of surface extension. The core complex is located within a continental rift and was exhumed at a rate of ~0.75–1.3 km/m.y. during the main phase of oceanic subduction of the Arabian plate beneath the Central Iranian block between ca. 49 and 30 Ma. The thinning of the underlying lithosphere appears to have been compensated by hot asthenosphere, as indicated by low seismic velocities in the Central Iranian block. We conclude that the development of the core complex involved lithospheric removal associated with extension and upwelling of hot asthenosphere, although we are aware of the fact that the structure could have been substantially modified by subsequent processes like slab break-off and associated uplift of the Central Iranian plateau.

DOI: 10.1130/GSATG229A.1

Manuscript received 25 Aug. 2014; accepted 6 Jan. 2015.