Showing 3 results for Continental Margin
Volume 8, Issue 3 (2-2009)
Abstract
Malayer granitoid rocks, as a part of Sanandaj-Sirjan plutonism, are located at latitude 34°00´-34°18´ and longitude 48°30´-48°52´. Tectono-magmatic investigation on the history of Sanandaj-Sirjan Zone attributed the formation of these plutonic rocks to convergence of Iranian and Arabian plates in conjunction with subduction of Neo-Tethys in the western part of Sanandaj-Sirjan Zone. Geochemical studies of Major and Trace elements on Malayer granitic rocks reveal that these granitic plutons are formed in a compressive environment, such as active continental margin in the convergent zone of oceanic crust and continental plate at the magmatic arc of continental margin. High ratio of LILEs/HFSEs and negative anomaly of Sr, Nb, Ba and Ta confirm the relation of these granitoids to subduction zone. These, also point out the role of shallow continental crust in formation and evolution of granitoidic magma. Broad range of mineral composition in petrographical observations and large variations in field studies, high-K calc-alkaline affinity and assessment of trends observed in AFM, K2O-SiO2, FeO-MgO diagrams versus those of plutons of known tectonic setting accentuate the similarities between Malayer granitic rocks and Andian type Magmatic Arc of Active Continental Margins and as a result highlights the role of upper mantle mafic magmas and tectonic movement in formation of their parental magma.
Volume 8, Issue 3 (2-2009)
Abstract
The area under study is located in central Iran and 235 kilometers of south west of Tehran is a part of Qom quadrangle. Volcanic sequences, which constitute the most major parts of the outcrops in the region mainly, have seen in north eastern and east of Ashian. These volcanic rocks are included of andesite basalt, andesite, trachy andesite, dacite, rhyodacite and rhyolite that are emplaced during Eocene (middle Lutetian to late Lutetian) along the Oromieh-Dokhtar volcanic belt that divided to six members from E1 to E6 in Tafresh and Ashtian area. Plutonic rocks related to Oligo-Miocene. There are not any rocks older than Triassic in area under study. Volcanic rocks both pyroclastics and laves have covered the most of area and could be seen in the continental and marine so we can see ignimbrite and tuffs. Acid eruptions are more than basic in this area. Mineralogically, these rocks have plagioclase, alkali feldespar, quartz, clinopyroxene, amphibole, biotite and a lesser amount olivine. Plagioclases have zoning structure and amphibole crystals have opacite rimmed. This phenomenon shows that magma responsible for rocks had a high temperature. Geochemically, petrographically and petrologically studies based on major and trace elements and differentiation index versus SiO2 indicate that changes in the volcanic processes at the area are the result of magmatic crystallization and differentiation magmatic rocks magma of area under study is calc-alkaline and they belong to subduction. Using of petrological and tectonic setting diagrams indicate that these Eocene magmatic rocks are compared to calc-alkaline series of subduction orogenic andesitic belts. The rare and trace element patterns of thes rocks have investigated and the examples of anomalies are related to Sr and Nb. Also the study of trend show that the calc-alkaline magma has formed in the upper mantle. Similarities between volcanic and plutonic rocks in Ashtian area show that these rocks may be having the same origin.
, , Mohammad Mohajjel,
Volume 12, Issue 2 (11-2012)
Abstract
The Alut granitoid complex is located in the northwestern part of the Sanandaj–Sirjan zone. This complex comprises three main units i.e. monzogranite to granodiorite bodies (SiO2 = 65–77 wt %) which is widespread throughout the area, a quartz-diorite to tonalite unit (SiO2 = 52–63 wt %) exposed as two stocks and mylonitic granitoid scattered as separate outcrops through the area. NE-SW trending microquartz-diorite and NW-SE trending aplite dykes are also present in this complex. The quartz-diorite to tonalite unit has relatively high CaO,FeO, MgO, Al2O3 and low Rb/Sr, Sr/Y, and (La/Yb)N, which preclude an origin of variably fractionated mantle melts and favour a mafic lower crustal source. Dehydration melting of biotite-bearing metasedimentary sources at relatively low pressures is proposed for the origin of monzogranite to granodiorite unit. Geochemically this complex is metaluminous to slightly peraluminous, typical of I-type granites. It belongs to low K (and high K for some monzogranite samples) calc-alkaline series and displays the geochemical characteristics typical of volcanic arc plutons related to an active continental margin area (e.g. significant Nb, Ti, P and Sr depletion). Based on collected geochemical data, the Alut granitoids originated by partial melting of crustal protoliths having different compositions in a deformed active margin.
