A preliminary geochemical study of zircons and monazites from Deccan felsic dikes, Rajula, Gujarat, India: Implications for crustal melting

Journal of Earth system science

Somdev Bhattacharji2¹  Nilanjan Chatterjee1² 

[1] Department of Geology, Brooklyn College and Graduate Center of the City University of New York, Brooklyn, New York 11210, U.S.A.$$;Department of Earth, Atmospheric and Planetary Sciences, Room 54-1216, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, U.S.A.$$

关键词: Deccan Trap;    zircon;    monazite;    felsic dikes;    geochemistry;    crustal melting.;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

Zircons of 10–100 𝜇 m size and monazites of up to 10 𝜇 m size are present in rhyolite and trachyte dikes associated with Deccan basalts around Rajula in the southern Saurashtra Peninsula of Gujarat. On the basis of structural conformity of the felsic and basaltic dikes, K-Ar ages and trace element considerations, a previous study concluded that the felsic rocks are coeval with the Deccan Volcanics and originated by crustal anatexis. The felsic rocks contain two populations of zircons and monazites, one that crystallized from the felsic melt and the other that contains inherited crustal material. Trace element variations in the rhyolites and trachytes indicate that zircons and monazites crystallized from the felsic melts, but compositional analysis of a zircon indicates the presence of a small core possibly inherited from the crust. Hf compositional zoning profile of this zircon indicates that it grew from the host rhyolitic melt while the melt differentiated, and Y and LREE contents suggest that this zircon crystallized from the host melt. Pb contents of some monazites also suggest the presence of inherited crustal cores. Hence, any age determination by the U-Th-Pb isotopic method should be interpreted with due consideration to crustal inheritance. Temperatures estimated from zircon and monazite saturation thermometry indicate that the crust around Rajula may have been heated to a maximum of approximately 900°C by the intruding Deccan magma. Crustal melting models of other workers indicate that a 1-2 million year emplacement time for the Deccan Traps may be appropriate for crustal melting characteristics observed in the Rajula area through the felsic dikes.

【 授权许可】

Unknown