GRANITIC-ROCKS AS A SOURCE OF GRANITE - THE GOSTA AND SUNDSTA GRANITES, SOUTH-WEST SWEDEN

Granites, among them three generations of microline-rich granites, int ruded repeatedly between 1600 and 900 Ma in the South-western Swedish Gneiss Complex. The deformed and metamorphosed Gosta and Sundsta grani tes are medium-grained, pale greyish red rocks belonging to the oldest generation of microcline-rich granites. Biotite dominates over hornbl ende. Allanite, titanite, apatite and zircon are important accessory m inerals. The granites are metaluminous and syeno- to monzogranitic in composition. SiO2 varies between 70.4 and 78.7% and K2O/Na2O between 0 .86 and 2.32. Na and K are poorly correlated with the other major elem ents. The rocks are low in MgO (< 0.9%) and FeO (< 3.6%). They are cha racterized by high Rb/Sr, Ba/Sr and Ba/Rb ratios. The ratio Nb/Ta is a lmost constant (approximate to 12) and the ratio Al/Ga decreases sligh tly with increasing SiO2 content. The Gosta granite has small, negativ e Eu anomalies, differentiated light and almost flat heavy rare earth element patterns. It intruded into continental crust approximately 156 0 Ma ago. It is argued that the granites formed from continental rocks by pseudoeutectic partial melting at a fairly shallow depth. The sour ce is older than the dominant country rock.