Titanomagnetites and ilmenites from the Early Cenozoic basalts and limburgites of the Northern Tien Shan |
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| Authors: | A F Grachev D M Pechersky V A Tsel’movich |
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| Institution: | 1.Schmidt Institute of Physics of the Earth,Russian Academy of Sciences,Moscow,Russia;2.Borok Geophysical Observatory, Schmidt Institute of Physics of the Earth,Russian Academy of Sciences,Borok, Yaroslavl Region,Russia |
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| Abstract: | Based on X-ray spectrometry and thermomagnetic analysis, the chemical composition is studied and the Curie points are determined
for the Early Cenozoic basalts and limburgites of the Northern Tien Shan. The microprobe analysis used in combination with
the thermomagnetic analysis unambiguously identified a series of homogeneous primarily magmatic titanomagnetites in the studied
samples against the broad variety of grains of titanomagnetite that underwent single-phase heterophase oxidation, which are
often undetectable by a microprobe alone. The titanium content or TiO2/FeO ratio in titanomagnetites and, correspondingly, the Curie points reflect the depth of the most recent equilibrium state
of the magma, i.e., the depth of the magma sources. According to the dependence of the content of primarily magmatic titanomagnetite
on the source depth, the latest equilibrium state of the magmatic melt of the Northern Tien Shan occurred at a depth of 40
± 5 km. The obtained results agree with the reduction in the seismic velocities by a few percent below the Moho revealed by
seismic tomography. |
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