№ 1,
2017
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Petrogenetic role of iron-titanium oxide minerals in formation process of the late cretaceous volcanic complexes of the Lesser Caucasus
Institute of Geology and Geophysics of Azerbaijan National Academy of Sciences, AZ1143, Baku, H.Javid av., 119
Summary
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On the base of conducted integrated petrological, mineralogical and petromagnetic research it was defined that melts corresponding to various differentiates of the Late Cretaceous magmatic complexes of the Lesser Caucasus by composition were crystallized in different depth intermittent vents.
In this case earlier differentiates of basalt – andesibasalt complex of Gazakh trough consisting of picrobasalts and picrodolerite were crystallized in higher thermobaric conditions (t=1000-12000C, P=8,50-9,2 kbar) according to olivine-chrome spinel balance. Basalt and dolerites of Gazakh, Agjakend and Agdere troughs were formed in deeper seats (16-21 km).
However, during Late Santonian-Early Campanian changes of geological conditions in abovementioned troughs led to reduction of permeability of magma supply faults. Therefore within Gazakh trough surface intermittent vents formed. It can be supported by availability of isolated volcanic centres which dispersed throughout the trough area. Volcanic centers consist of andesibasalt, andesite, dacite, rhyolite, perlite, obsidian and others. Cation-deficient moderate titanium maghemites, hematites and others are found in composition of these rocks as impregnations.
Depth of intermittent vents of dacite-rhyolite complex according to value of tested and estimated Curie point varies from 4 km to 8 km. Mainly hematite and rarely maghemite are typical for the rocks of this complex.
In Khojavend trough rocks of trachybasalt-trachydolerite complex characterize the early sub-stage of Santonian volcanism and contain moderate titanium magnetites and maghemites. At the second sub-stage of volcano-plutonism rocks formation of tephrite-teschenite complex was accompanied by oxidation of fluids and high aluminous titanium-magmatite crystallized earlier chromdiopside and salite. However, in teschenite composition ulvospinel titanium magnetite closely associates with barkevikite and kaersutite and crystallize by relatively higher temperature.
Chromous titanomagnetite and sometimes chromite along with moderate titanium magnetite are found in composition of Senonian volcanites of Azykh trough. The same mineralogical diversity is typical for Gochass trough as well.
Therefore, differences obtained from iron-titanium oxidizing minerals can be petrogenetic indicator in definition of physical-chemical conditions of magmatic rocks crystallization in evolution process of Late Cretaceous magmatic melts within Lok-Garabagh structural and formational zone of the Lesser Caucasus.