Geochemistry and petrology of rift-related maﬁc sills and
arc-related Gabbro–Diorite bodies, Northern Bafq District,
S. M. Niktabar
N. Rashidnejad Omran
Received: 20 September 2016 / Revised: 30 May 2017 / Accepted: 16 June 2017 / Published online: 4 July 2017
Ó Science Press, Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany 2017
Abstract Two types of maﬁc intrusions have been recog-
nized in the north of the Bafq district, Central Iran. A number
of olivine-gabbroic to gabbroic sills intruded the Rizu For-
mation, comprised of alternating carbonate and volcanic
rocks. Mineralogical data show that olivine ? pyroxene ?
brown amphibole (kaersutite) ? calcic plagioclase ?
opaque comprise the olivine-gabbroic rocks, and interme-
diate (or sodic) plagioclase ? altered pyroxene and altered
amphibole to biotite ? opaque minerals the gabbroic rocks.
Both rock types have shown within-plate and alkaline
characters and have been presumed to be related to rift for-
mation. The maﬁc-alkaline magma source of the sills is
proposed to have been derived from enriched mantle.
Regionally, two Gabbro–Diorite intrusions have been iden-
tiﬁed in the metamorphic complexes. Mineralogical data
suggest that the pyroxene ? amphibole (hornblende) ?
plagioclase ? biotite ? opaque minerals formed the gabbro
to diorite intrusions. These rocks have shown characteristics
of calc-alkaline and volcanic arc magmatism.
Keywords Sills Á Rizu formation Á Rift Á Volcanic arc
The Central Iranian Terrane is an approximately 2300 km
region of moderate relief surrounded by fold-and-thrust
belts, within the Alpine–Himalayan orogenic system
(Ramezani and Tucker 2003). The concept of a distinct and
fault-bounded Central-East Iranian Micro-continent
(CEIM), which was once encircled by Red Sea—type
oceanic tracts now represented by strips of ophiolitic rocks,
was ﬁrst introduced by Takin (1972). From Paleozoic to
Triassic time, CEIM appears to have approached and col-
lided with the Turan Plate (Schmidt and Soffel 1983).
The Precambrian (formerly Infracambrian) volcanic
rocks in Central Iran are related to deep crustal cracks that
formed during the Katangian orogeny. Alkaline volcanic
rocks suggest a within-plate rift in the Iranian cratonic
crust. A commonly proposed model for the Late Neopro-
terozoic–Early Cambrian magmatism and sedimentation in
Iran is crustal extension associated with continental rifting
(Berberian and King 1981; Samani 1988).
The Rizu intrusions (sills) seem to have intruded parallel
to the Precambrian Rizu Formation (in the vicinity of
Zarigan village) in the north of the Bafq district, which is
consistent with the hypothesis of carbonate-alkaline vol-
canic rock alternation. In this paper, the gabbroic sills in
the Rizu Formation are discussed for the ﬁrst time. The
sills contain important clues about the tectonic-magmatic
evolution. They have previously been compared with
Gabbro–Diorite intrusions in the region.
Gabbro–Diorite intrusion bodies are situated in Pre-
cambrian metamorphic complexes in the vicinity of the
Rizu Formation. The study area has been affected by
several stages of plutonism, from Precambrian to Tertiary
(Haghipour 1974), but there is no general agreement on age
Generally, most of the hypotheses presented for the
geodynamic of Central Iran have been divided into two
groups (Ramezani and Tucker 2003). In the old model, the
geologic structure of the area was based on horsts of high-
grade metamorphic rocks of the Chapedony Formation, and
grabens covered by thick Phanerozoic sediments (Stocklin
& N. Rashidnejad Omran
Department of Geology, Tarbiat Modares University, Tehran,
Acta Geochim (2018) 37(2):180–192