عنوان

پترولوژی و پتروژنز سنگ های ماگمائی پلیو-کواترنری آذربایجان ( شمال غرب ایران)

Number

‭۳۹۸۸پ‬

.Language of Text, Soundtrack etc

per

Title Proper

پترولوژی و پتروژنز سنگ های ماگمائی پلیو-کواترنری آذربایجان ( شمال غرب ایران)

First Statement of Responsibility

/نصیر عامل

Name of Publisher, Distributor, etc.

: دانشکده علوم طبیعی

Date of Publication, Distribution, etc.

، ‮‭۱۳۸۶‬

Text of Note

چاپی

Text of Note

فاقد اطلاعات کامل

Dissertation or thesis details and type of degree

دکتری

Discipline of degree

زمین شناسی ـپترولوژی

Date of degree

‮‭۱۳۸۶/۱۲/۲۵‬

Body granting the degree

دانشگاه تبریز

Text of Note

‮‭The Plio-Quaternary volcanic units are situated in the different parts of Azerbaijan in NW Iran. In the study areas volcanic rocks consist of wide range of pyroclastics and lavas, which can be seen in different forms such as flow lavas, domes, stratovolcano units, and prismatic structures. These rocks have erupted with distinct pattern, in a way that pyroclastic rocks have considerable thickness and explosive facies are formed at the onset of eruptions and are mainly covered by young basaltic rocks in studied volcanic units. Pyroclastic volcanic units cut the upper red formation sediments with upper Miocene age or cover them with angular discontinuity in most of the studied areas . Field observations indicate emplacement of volcanic matearils in association with linear tectonic structures such as fractures and major faults and axes of young folds, which shows the important role of tectonic structures in Plio-Quaternary eruptions in Azerbaigan. The study areas are situated at western Alborz-Azerbaijan zone and are important part of collisional zone between Arabian and Eurasia plates. Following the closure of Neo-Tethys and collision of the plates in the late Cretaceous, convergence continued and became more intence in Pliocene. This process caused considerable shortening, thickening and uplifting in NW Iran and East of Turkey. Meanwhile wide spread Plio-Quaternary volcanic activities occurred. Volcanic rocks successions facies in the study areas show that first eruptions of volcanoes had been explosive and accompanied with calm phases of volcanism. Continuation of young tectonic activities in Quaternary caused volcanic eruptions forming basaltic rocks. These rocks are situated on top of Quaternary alluviums in some of regions and have made prismatic basalts Volcanic successions in the study areas belong to different magmatic series and members of rocks in this series have not genetic relation. Pyroclastic rocks in the study areas include basalt, basaltic andesite, trachy andesite, trachyte, dacite and rhyodacite, and rhyolite which belong to the calk-alkaline and high- K calk-alkaline magmatic series. Young basaltic lavas consist of basalt, olivine basalts, tephrite, lueicite basalt, hornblend basalt, which all belong to alkaline magmatic series. Regarding composition and verities of rocks and existence of two series of magmas it seems that Plio-Quaternary eruptions have bimodal properties and have made reverse sequences of rocks in the study areas. Lack of geochemical relation between major and trace elements of rocks in members of two series could be due to different origin and evolution for magma series, which have made the rocks. The resorbed rims of some of the minerals, poikilitic and sieve textures, two generations of minerals, and magma mixing evidence, dark mafic magma mixed with light acidic magma in thin sections, existence of mafic xenoliths in the intermediate rocks, and similarity between chemical composition of studied andesite and average of chemical composition of crust all display that magma mixing process was effected in genesis and evolution of the intermediate rocks. Basic magma with mantle origin mixed with acidic magma with crustal origin and formed hybrid magma. Hybrid magma evolved with fractionation and assimilation processes and made intermediate-acidic rocks in magma chamber and during ascending and emplacement in the upper levels. The studied samples are enriched in K, Ba, Rb, Th, U, Cs. This reflects the role of continental crust in evolvution of the intermediate magma. The study of chemical behavior of Cr, Ni, Co, Ti, V and MgO versus SiO۲ on diagrams for basaltic rocks show wide compositional ranges and have scatter pattern. This feature is related to contamination process and evolving of original basic magma after generation. Variation of rare earth elements for basaltic samples on diagrams show enrichment in LREE and depletion in HREE. This feature displays that basaltic magma was originated from asthenospheric mantle with garnet in source and low degree of partial melting. Also positive anomalies for Cs, U, Ba, Rb and K and low negative anomalies for Ta, Nb and Eu in the basaltic samples can be interpreted by crustal contamination. Study of AFC influences in evolving of magma for whole samples on the Ta/Yb versus Th/Yb diagram display that contamination process had important role.. Intermediate-acidic volcanic units in some areas are cut by lamprophyre dykes.. Composition of the dykes is calk-alkaline to shoshonitic and they belong to minett group. Studied lamprophyres have phenocrysts of biotite and hornblende. Probably lamprophyric magma has generated from interaction of basic magma with residue of acidic melts with crustal origin in magma chamber. Tectonic setting of samples on discriminate diagrams is post collision volcanic arc Different tectonomagmatic models are suggested for Plio-Quaternary magmatism in east of Turkey, which have similar geological specifications with NW Iran volcanism. The important mechanism suggested for magmatism in Anatolian-Iranian collision zone is continuing convergence of Arabian and Eurasia plates after collision in Late Cretaceous and intensification of it in Pliocene. Active convergence caused wide deformation including shortening, thickening and uplifting of crust which is occurred in east Turkey, NW Iran and Azerbaijan. New period of magmatic activities started and made volcanic appearances at the same time Different factors are suggested for generation of original basic alkaline magma in this model. For example thermal perturbation in crust and mantle layers, abrupt drop of pressure in mantle because of generatation of fractures and deep faults, which all caused partial melting started in asthenospheric mantle and made original alkaline basic magma. Hot basic magma evolved with contamination and fractionation processes during ascending and accumulating in upper levels of magma chamber in the crust. This caused partial melting of the crust and generation of acidic magma. In the first eruptions of volcanoes, viscose acidic magma with explosion had made variety of pyroclastic rocks such as agglomerate, brecciated lava, bombs, tuff, pounce, volcanic ash and intrusion of domes with ignimbrite, dacite and rhyodacite composition in the studied areas. Then mixing of basic and acidic magma in magma chamber generated hybride magma, which formed intermediate rocks. As a result of continuing convergence and young tectonic activities because of uplifiting and dominance of extensional forces along the crashed regions of the collision zone and movement along the faults specially strike slip faults and pull-apart basins and intersections region of the faults and the axes of young folds, fissure eruptions occurred and made basaltic lavas in studied area with prismatic structures‬

Magmatism

Plio-Quaternary

Azerbaijan

Volcanoes

Bimodal magmatism

Calkalkaline

Alkaline

Magma Mixing

Hybrid magma

عامل، نصیر

مؤید،محسن، استاد راهنما

عامری، علی، استاد راهنما

وثوقی عابدینی، منصور، استاد مشاور

مؤذن،محسن، استاد مشاور

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