Geochemistry of cadmium, indium, tin, tellurium and sulfur in mantle derived rocks.

Abstract

Volatile loss and metal segregation fractionate the volatile chalcophile elements, which offers an opportunity to evaluate the nature of the chondritic late veneer and core formation. However, many volatile chalcophile elements are poorly understood geochemically speaking because of a dearth of high quality concentration data. In this dissertation precise isotope dilution techniques are established for measuring Cd, In, Sn and Te at the parts per billion levels in geological materials with multiple collector inductively coupled plasma mass spectrometry. Cadmium, In, and Sn are slightly to moderately incompatible like middle to heavy rare earth elements during partial melting of the upper mantle. Tellurium becomes compatible during segregation of an immiscible Cu-bearing sulfide liquid, although it behaves incompatibly during partial melting. The concentrations of Cd and In in submarine oceanic basalts are remarkably uniform irrespective of tectonic setting, but are more variable in ultramafic rocks. Correlations between Cd, In and Sn display continuities from basalts to ultramafic rocks, indicating that these rocks are related to each other by a common melting process. However, Sn may be enriched in ultramafic rocks that are affected by silicate melt metasomatism. The platinum group element Pd appears to be closely related with Te. Large fractionations between Cd and In are found in hydrothermally altered ocean floor basalts. This heterogeneity must be eliminated after slabs of oceanic crust became subducted into the mantle. Tellurium concentrations in submarine basaltic glasses from the Loihi seamount are high, probably reflecting accumulation and/or assimilation of Cu-bearing sulfide. Cadmium and Te appear to have both been strongly partitioned into the core; Sn only moderately so. Indium behaved as a lithophile element. The highly volatile elements C, S, Se, and Te are in chondritic relative proportions similar to the more refractory platinum group elements, consistent with the addition of a late chondritic veneer after core formation.