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L ate P ermian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust
Author(s) -
TORABI GHODRAT
Publication year - 2012
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2012.00817.x
Subject(s) - geology , geochemistry , zircon , protolith , continental crust , partial melting , ophiolite , mafic , amphibole , oceanic crust , subduction , petrology , epidote , crust , quartz , chlorite , seismology , paleontology , tectonics
L ate P ermian trondhjemites in the A narak area occur as stocks and dykes, which cross cut the A narak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern A narak 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 A narak 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.