Staurolite as the U-Pb isotope geochronometer

Levskii L. К., LobikovA. F.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 2. P. 1-13

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Language: Russian


The new approach is suggested for measuring the real U-Pb and Pb-Pb ages of the rock-forming metamorphic staurolite. Previously, there were used two approaches: in the first case the isotopic composition of lead, uranium and lead contents are measured in leached substance, after dissolution of initial mineral, and the age is calculated by plotting the Pb-Pb «leaching isochrone». In the second case isotopic data and contents are measured in the mineral material without leaching. by stepwise dissolution minerals, and these were used. In both cases, it is a priori assumed that inclusions, overgrowths and secondary phases, and the host mineral are co-genetic. This assumption can lead to mistaken values of the measured age. Techniques of the present research included the use of various acids and reagents to purify staurolite from abovementioned secondary phases, with obtaining of the staurolite «pure culture», its subsequent leaching, input of the mixture tracer, segregation of lead and uranium compounds, and, finally, revealing of the real staurolite age. Its value was calculated by using several samples for plotting the monomineral Pb-Pb isochrone, or presentation of measured Pb/U ratios on the plot with concordia. Obtained data may be used then to reconstruct the P-T-t evolution of metamorfism.

Key words: staurolite, U-Pb method, leaching isochrone.