The Lar Igneous Complex represents an Eocene-Oligocene igneous event located in the South Eastern Iran, along the Sistan Suture Zone. Such a suture belongs to the Alpine-Himalayan orogenic belt that started to form during the Cretaceous, due to the closure of a branch of the Neo-Tethys and the subsequent collision of the Lut and the Helmand (Afghan) block. The Lar complex is made of intrusive and hypabyssal igneous rocks characterised by shoshonitic to ultrapotassic petrological affinities, variable degrees of silica saturation, and with a clear orogenic geochemical fingerprint. Alkaline silica-undersaturated igneous rocks include lamprophyres, nepheline-syenite and phonolitic dykes, on one side, and silica-saturated and -oversaturated rocks represented by syenitic to trachytic dykes and monzonitic bodies, on the other one. Lamprophyres and nepheline-syenites show symplectitic domains involving nepheline and K-feldspar, and minor kalsilite, recalling pseudoleucite textures, a peculiar petrographic feature typical of intrusive conditions. Lamprophyres are characterized by cumulus olivine (Fo content up to 91) and clinopyroxene (Mg# up to 0.83). The latter are characterised, in most of the samples, by abundant phlogopite inclusions. Primordia Mantle-normalised incompatible trace element patterns show LILE enrichments and HFSE depletions, typical of subduction-related magmas, with the alkaline potassic and silica-undersaturated rocks characterised by higher LREE/HREE (LaN/YbN from 12 to 22) than silica-saturated and -oversaturated rocks (LaN/YbN from 10 to 12). The Sr-Nd-Pb isotopic composition of the less differentiated samples from the Lar suite displays an almost homogeneous signature, suggesting a common mantle source. The occurrence of continental crustal contamination processes coupled to crystal fractionation affects only the most differentiated products. An isotopic-based geochemical modelling highlights a mantle source metasomatized by partial melts from carbonate-rich (over subordinate carbonate-poor) recycled sediments within the upper mantle.
Petrology and geochemistry of the Eocene-Oligocene subduction-related Lar igneous complex (SE Iran) / Ghiotto M., Natali C., Bragagni A., Braschi E., Avanzinelli R., Casalini M., Ghafaribjar S., Alvin M., Conticelli S.. - STAMPA. - (2023), pp. 335-335. (Intervento presentato al convegno The Geoscience paradigm: Resources, Risks and future perspectives tenutosi a Potenza nel 19-21 Settembre 2023) [10.3301/ABSGI.2023.02].
Petrology and geochemistry of the Eocene-Oligocene subduction-related Lar igneous complex (SE Iran)
Ghiotto M.;Natali C.;Bragagni A.;Braschi E.;Avanzinelli R.;Casalini M.;Conticelli S.
2023
Abstract
The Lar Igneous Complex represents an Eocene-Oligocene igneous event located in the South Eastern Iran, along the Sistan Suture Zone. Such a suture belongs to the Alpine-Himalayan orogenic belt that started to form during the Cretaceous, due to the closure of a branch of the Neo-Tethys and the subsequent collision of the Lut and the Helmand (Afghan) block. The Lar complex is made of intrusive and hypabyssal igneous rocks characterised by shoshonitic to ultrapotassic petrological affinities, variable degrees of silica saturation, and with a clear orogenic geochemical fingerprint. Alkaline silica-undersaturated igneous rocks include lamprophyres, nepheline-syenite and phonolitic dykes, on one side, and silica-saturated and -oversaturated rocks represented by syenitic to trachytic dykes and monzonitic bodies, on the other one. Lamprophyres and nepheline-syenites show symplectitic domains involving nepheline and K-feldspar, and minor kalsilite, recalling pseudoleucite textures, a peculiar petrographic feature typical of intrusive conditions. Lamprophyres are characterized by cumulus olivine (Fo content up to 91) and clinopyroxene (Mg# up to 0.83). The latter are characterised, in most of the samples, by abundant phlogopite inclusions. Primordia Mantle-normalised incompatible trace element patterns show LILE enrichments and HFSE depletions, typical of subduction-related magmas, with the alkaline potassic and silica-undersaturated rocks characterised by higher LREE/HREE (LaN/YbN from 12 to 22) than silica-saturated and -oversaturated rocks (LaN/YbN from 10 to 12). The Sr-Nd-Pb isotopic composition of the less differentiated samples from the Lar suite displays an almost homogeneous signature, suggesting a common mantle source. The occurrence of continental crustal contamination processes coupled to crystal fractionation affects only the most differentiated products. An isotopic-based geochemical modelling highlights a mantle source metasomatized by partial melts from carbonate-rich (over subordinate carbonate-poor) recycled sediments within the upper mantle.
I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
