The Jandaq lamprophyres occur as eight mostly parallel dykes, which cross-cut Eocene volcanic and sedimentary rocks of the Pis-Kuh Formation in dominant north to south direction. These lamprophyres are mainly composed of kaersutite, clinopyroxene, olivine, feldspar, ilmenite, and spinel as primary minerals. The rocks studied here are enriched in alkalis, TiO 2 , large ion lithophile elements, and light rare-earth elements (LREE), with SiO 2 content between 41.7 and 46.2 wt%, and are classified as camptonite and alkaline lamprophyre according to the mineralogical and chemical characteristics. These rocks exhibit positive Eu anomalies (Eu/Eu* = 1.08-1.39) and are characterized by strong enrichment in LREE relative to heavy REEs, and also by varied Zr/Hf ratios. The geochemical features of the rocks suggest that the lamprophyre magmas were derived from low-degree melting of an amphibole garnet lherzolite that experienced strong metasomatism by carbonate-rich fluids in response to dehydration melting from the subducted slab. The Jandaq lamprophyric magmatism has been attributed to the former subduction of the Central-East Iranian microcontinent confining oceanic crust from the Triassic to Eocene, and decompression melting induced by the extensional basin of the Jandaq area in the early Oligocene.
Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO
2 (67.8–71.0 wt%), Al
2
O
3 (14.9–17.1 wt%) and Na
2
O (5.3–8.6 wt%), low K
2
O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area.
Lamprophyric stocks and pillow lavas are situated in Pal-e-Havand area (South-East of Anarak, North-East of Isfahan Province, Iran) along the Turkmeni-Ordib fault. The predominant minerals of these rocks are amphibole (kaersutite), plagioclase (albite), Kfeldspar (sanidine), Cr-Ti spinel, ilmenite, and apatite, with minor amounts of magnetite, chlorite, pumpellyite, epidote, sphene, leucoxene and calcite. Textures are porphyritic, microlitic and variolitic, with calcite amygdals. Combined petrological and geochemical studies classify these rocks as alkaline lamprophyre, in general, and camptonites in particular. The rocks studied are enriched in alkalis, TiO 2 and LREE, with SiO 2 content between 40 to 52 weight percent (wt.%). Similar geochemical characteristics of pillow lavas and stocks and parallel chondrite REE patterns of all samples reveal that they were all derived from a similar mantle source region and underwent similar melt extraction. These rocks are intracontinental alkaline lamprophyres, produced by low degree of partial melting of upper mantle garnet lherzolites. The Paleo-Tethys subduction from Lower Paleozoic is the cause of mantle enrichment in volatiles and lamprophyric magmatism in Upper Paleozoic along the Turkmeni-Ordib fault.
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