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The oxidized I-type Eagle Lake Granite stock in southwestern New Brunswick, Canada, is texturally divided into porphyritic and equigranular phases. The porphyritic granite consists of phenocrysts (i.e., plagioclase, K-feldspar, quartz, and biotite) and microcrystalline groundmass with minor magnetite–ilmenite, titanite, apatite, and zircon. The equigranular phase has a similar primary mineral assemblage to the porphyritic phase. Their common magnetite-ilmenite-titanite assemblage reflects co-crystallization (magnetite series) from a magma imparting some redox control. However, these granite phases show minor potassic to propylitic alteration mineral assemblages with very minor sulfides, suggesting localized fluid–rock reaction. The composition of plagioclase varies between albite and oligoclase, and K-feldspar is orthoclase commonly displaying considerable turbidity. The An% versus Al/(Ca+Na+K) data indicate that these feldspars are slightly aluminous, reflecting cryptic alteration. Biotite is rich in Fe, plotting near the boundary of primary and re-equilibrated biotite; these biotites formed at temperatures ranging from 670 to 725 °C, based on Ti-in-biotite thermometry. Secondary biotite grains are also locally evident, formed from magmatic-hydrothermal fluids. Secondary fine-grained biotite associated with fine-grained magnetite-pyrite indicates potassic alteration and related Cu±Mo±Au mineralization. Some of these various biotites are partially altered to chlorite at ∼301–361 °C. Like biotite, apatite occurs as both igneous and hydrothermal phases. Based on the concentration of F (4.21–2.90 wt.%), all these apatites are fluorapatites with content of light rare earth elements about 7000 ppm and Eu/Eu* = 0.16.

This study investigates for the first time melt inclusions (MI) that are found within fundamental minerals of subvolcanic rocks in Torud-Ahmad Abad magmatic belt. The Torud-Ahmad Abad magmatic belt is situated in south-southeast of Shahrood and belongs to the northern part of central Iran structural zone. Melt inclusions represent liquids that were trapped along growth zones (primary) or healed fractures of mineral phases, which crystallized from the silicate liquid as it cooled. Based on SEM analysis of these melt inclusions, their compositions are dacite, andesite and basaltic andesite. Thus, with the use of melt inclusions in the volcanic rocks of Torud-Ahmad Abad magmatic belt, we attempt to show the compositional evolution and origin of magma. The effective factors on magma evolution are magma mixing, fractional crystallization and crustal contamination. Περίληψη Σε αυτή την εργασία, εξετάζονται για πρώτη φορά, τα εγκλείσματα τήγματος (melt inclusions -MI) που φιλοξενούνται μέσα στα ορυκτά συστατικά των υποηφαιστειακών πετρωμάτων της μαγματικής ζώνης Torud-Ahmad Abad, νότια-νοτιοανατολικά του Shahrood (στο βόρειο τμήμα της τεκτονικής ενότητας του κεντρικού Ιράν). Τα Volume 55 εγκλείσματα τήγματος αντιπροσωπεύουν ρευστά που εγκλωβίστηκαν κατά τη διάρκεια της ανάπτυξης των ζωνών (πρωτογενής) ή κατά την επούλωση ρωγμών των ορυκτών φάσεων, οι οποίες κρυσταλλώθηκαν από ένα πυριτικό τήγμα κατά τη διάρκεια της ψύξης. Αυτά τα εγκλείσματα τήγματος, με βάση τις αναλύσεις SEM, αντιστοιχούν σε σύσταση δακίτη, ανδεσίτη και βασαλτικού ανδεσίτη. Έτσι, με την χρήση των εγκλεισμάτων τήγματος των ηφαιστειακών πετρωμάτων της μαγματικής ζώνης Torud-Ahmad Abad, φαίνεται η εξέλιξη και η προέλευση του μάγματος. Οι παράγοντες που συνέβαλαν στην εξέλιξη αυτών των μαγμάτων είναι η μίξη μαγμάτων, η κλασματική κρυστάλλωση και η μόλυνση από τον φλοιό. Λέξεις κλειδιά: εγκλείσματα τήγματος, υποηφαιστειακά πετρώματα, εξέλιξη μάγματος, μαγματική ζώνη Torud-Ahmad Abad.

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in the northern part of the Central Iran zone, are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood. These igneous rocks include hypabyssal dacite, trachyte, andesite, trachy-andesite, and basaltic andesite; they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with minor biotite and titanomagnetite; they form domal structures (plugs and stocks), dikes, and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences. Based on isotopic analysis of these intermediate to acidic rocks, initial ratios of 143 Nd/ 144 Nd range from 0.512 775 to 0.512 893 and initial ratios of 87 Sr/ 86 Sr range from 0.703 746 to 0.705 314, with quite positive ɛ Nd(i) values of +3.69 to +6.00. They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements, the SiO 2 content is (52-62) wt.%, and Na 2 O content >3 wt.%, Al 2 O 3 content >16 wt.%, Yb <1.8 ppm, and Y <18 ppm. These geological, geochemical, and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab (Sabzevar branch) and lithospheric suprasubduction zone mantle. The mantle signatures typifying the rapidly emplaced adakitic rocks (slab (high-silica adakite) and suprasubduction zone (low-silica adakite) melts) together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting; and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin arc environment to rifting (basalts to adakites) towards submarine conditions in the Neogene. KEY WORDS: isotope geochemistry, adakite rocks, Central Iran zone, Shahrood, Iran.

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