|
چکیده
|
The Late Eocene Kuh-e Dom composite intrusion forms a segment of the Urumieh-Dokhtar magmatic arc, which recorded syn- to post-collisional magmatism during the Alpine–Himalayan orogeny in central Iran. Numerous acid and intermediate–basic dikes intrude the composite intrusive complex of the arc segment and its host-rock assemblage. The silicic dikes of porphyric microgranite, porphyric microgranodiorite and aplite consist of quartz, K-feldspar, plagioclase (albite), biotite and rare amphibole. The dikes are of subaluminous composition with shoshonitic affinity. Trace-element patterns exhibit pronounced negative anomalies of Nb, Ta, Ti, P and Sr together with positive anomalies of Cs, Th, U and La suggesting partial melting of a quartzo-feldspathic crustal source. The intermediate–basic dikes with phonolite, basanite and trachyandesite chemical compositions typically contain pyroxene (diopside–augite) and plagioclase phenocrysts (An30–60 and An98), calcic amphiboles (magnesiohornblende– magnesiohastingsite), magnesian biotites and alkali-feldspars (Or95). The rocks show shoshonitic geochemical affinities. Low Ba/Rb ratios and high Rb/Sr ratios suggest that the primary dike melt originated by partial melting of a phlogopite- -bearing lithospheric mantle, whereas LILE and LREE enrichment along with low Nb/Zr and Hf/Sm ratios and high Ba/ Nb and Rb/Nb ratios imply that these rocks formed at a convergent continental margin. The acidic dikes were emplaced in a transitional syn-collisional subduction setting whereas the intermediate–basic dikes have developed from remnant melt batches after cessation of active subduction, mostly in the post-collisional setting
|