S-type granites: Their origin and distribution through time as determined from detrital zircons

Abstract

A global compilation of 6911 detrital zircon U-Pb ages and trace element data from 52 major rivers shows secular variations in the relative contributions of I-type and S-type granites through time. The average abundance of S-type granites has been quantified using two methods: (i) comparing the cumulative distribution of P concentrations for selected time intervals, and (ii) using plots of molar P against rare earth elements (REE) plus Y. The former is based on the average P content in S-type granite zircons being greater than in I-types, resulting from the high solubility of apatite in strongly peraluminous S-type granitic magmas. The latter is based on the substitution of (REE3+ + Y3+) for Zr in zircon from S-type granites being charge-balanced by P5+, leading to a near 1:1 correlation between (REE + Y) and P. The results from both methods show a similar pattern: the most important period of S-type zircon production coincides with the assembly of Gondwana and the least important with the formation of Superia (Archean). Both methods also show that Rodinia was a period of relatively low S-type zircon production, compared with the adjacent periods of supercontinent formation: Gondwana and Nuna.Turbidites are an essential component of the S-type granite source region: greywackes provide quartz and feldspar and the interbedded shales water and K. Together these form the essential components for granite minimum melting. We attribute the high production rate of S-type granites during the amalgamation of Pangea, Gondwana and Nuna to the formation of extensive turbidite fans, produced by rapid erosion of the super high mountains that formed during continent-continent collisions. The low production of S-type granites during the assembly of Rodinia is attributed to the dominance of Andean type margins during that period: Andean type margins do not form the giant fans that are essential for the formation of voluminous S-type granite suites.