The tectonic evolution of a N eo‐ T ethyan ( E ocene– O ligocene) island‐arc ( W alash and N aopurdan groups) in the K urdistan region of the N ortheast I raqi Z agros S uture Z one

Abstract

The W alash and N aopurdan groups are incorporated into the lower allochthonous thrust sheet in the I raqi Z agros S uture Z one ( IZSZ ). 40 A r– 39 A r dates on magmatic feldspar separates from both W alash and N aopurdan volcanic rocks indicate an E ocene– O ligocene age (43.01 ± 0.15 to 24.31 ± 0.60 M a). The W alash and N aopurdan groups form a thrust sheet that is structurally overlain by an upper allochthon of C retaceous arc‐related rocks (106–92 M a) now known as the H asanbag igneous complex (formerly known as the G emo– Q andil G roup). The W alash and N aopurdan lower allochthon is thrust over the foreland basin R ed B eds series. Volcanic and subvolcanic units in the W alash and N aopurdan groups were studied from the M awat, G alalah– C homan, L eren, and Q alander– S heikhan provinces. Most of these rocks are basaltic to andesitic for both the N aopurdan and W alash suites. The petrographic study shows that these rocks are affected by metamorphic alteration under greenschist facies conditions, but preserve primary porphyritic textures with some relict igneous plagioclase, pyroxene, and hornblende. The enrichments in LREE / HREE and high T h/ N b and N b/ Z r show that the W alash and N aopurdan rocks have distinct subduction‐related signatures: specifically island‐arc tholeiite for the N aopurdan and calc‐alkaline to alkaline for the W alash suites. Hence the W alash and N aopurdan suites are back‐arc and arc systems, respectively, that developed 43–24 M a. Accordingly, the IZSZ contains a full record of N eo‐ T ethys pre‐collision‐related volcanism in dual subduction settings, from the E arly C retaceous ( H asanbag igneous complex) to the E ocene– O ligocene ( W alash– N aopurdan suites). Final continent–continent collision started when the last of the N eo‐ T ethys O cean was subducted beneath the I ranian continent, resulting in its collision with the A rabian P late, probably during the M iddle M iocene. This reinforces a continuity of events along the entire edge of the A rabian P late from T urkey, through I raq and I ran, and into O man.

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