PROTOLITH NATURE AND TECTONOMAGMATIC FEATURES OF AMPHIBOLITES FROM THE QUSHCHI AREA, WEST AZERBAIJAN, NW IRAN

Year 2014, Volume: 149 Issue: 149, 139 - 152, 01.12.2014

Mohssen Moazzen

https://doi.org/10.19111/bmre.89886

Cited By: 1

Abstract

Amphibolites
from the Qushchi area in west Azerbaijan province, NW Iran are metabasites containing
hornblende, plagioclase, epidote, garnet, relict igneous clinopyroxene and titanite,
apatite and opaque minerals as accessory phases. They are spatially associated
with an ophiolitic melange but their relationship is not clear. Based on whole
rock geochemistry of the amphibolites, they are formed from sub-alkaline
andesite-basalt with a tholeiitic affinity. TiO2
content of the analyzed amphibolite samples is
mainly less than 1%, indicating an EMORB original character for the magma.
Major and trace element geochemistry of the studied rocks indicate a volcanic
arc setting for the rocks. Chemistry of relict igneous clinopyroxene shows that
they are diopside in composition with Mg# of 86.75-88.78 and indicating
tholeiitic magma type derived from volcanic arc setting, which is in agreement
with the results from the whole rock chemistry. Low Ti content of the clinopyroxene
points to a depleted mantle source for the magma of the protoliths of Qushchi
amphibolites. There is no isotopic age constrains on the studied amphibolites, therefore
their relation to the ophiolitic melange of the area is uncertain especially
that the melange is allochthonous. Three possibilities can be proposed for the
formation of the studied amphibolites. If these rocks are Late Cretaceous-
Paleocene in age, they might have been formed as parts of a volcanic arc in the
Neotethyan oceanic crust. In this case, the ophiolitic complex and the volcanic
arc rocks all are metamorphosed at amphibolite facies following the Neotethys
ocean closure and the continental collision. Based on field relations and
comparing the studied amphibolites with similar amphibolites from the adjacent
Khoy area, alternatively the amphibolite formation can be consider to predate
the formation of Neotethys-related ophiolite melange. Since the serpentinite in
the ophiolitic melange is not metamorphosed, the second explanations can be
valid for the formation of the amphibolites. The third possibility is that the
protolith of the amphibolites was contemporaneous with ophiolite formation, but
this protolith is metamorphosed within the accretionary prism but the obducted
ophiolitic rocks (including serpentinite) not subjected to metamorphism.

Keywords

Amphibolite, subalkaline magma, relict clinopyroxene, volcanic arc, W Azerbaijan, NW Iran

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