Last stage of Variscan granitoid magmatism in the Strzelin Massif (SW Poland): petrology and age of the biotite-muscovite granites

Abstract

Oberc-Dziedzic, T., Kryza, R., Pin, Ch., 2015. Last stage of Variscan granitoid magmatism in the Strzelin Mas sif (SW Poland): pe trol ogy and age of the bi o tite-mus co vite gran ites. Geo log i cal Quar terly, 59 (4): 718-737, doi: 10.7306/gq.1248 New petrographic and geo chem i cal data show some dif fer ences be tween Variscan Bt-Ms gran ites oc cur ring ei ther as small plutons or dykes in the Strzelin Mas sif (SW Po land). The gran ites of the Gromnik and Górka Sobocka plutons are rich in micas and crys tal lised from "wet" mag mas; the gran ites of the dykes and the Gêbczyce Pluton are mica-poorer and cor di erite-bear ing rocks de rived from "dryer" mag mas. The lower ini tial eNd = -5.4 to -5.9 val ues in the Bt-Ms gran ites of the dykes, com pared with those in the plutons (eNd = -4.5 to -4.9), re flect a more "crustal" sig na ture of the for mer, pos si bly due to lo cal crustal as sim i la tion, via AFC, shortly be fore em place ment. Much more ra dio genic ini tial 87 Sr/ 86 Sr ra tios in the dykes, up to 0.726, fur ther sug gest the in volve ment of ex tra ne ous, hy drous crustal flu ids en riched in 87 Sr dur ing the evo lu tion of late-stage magma de riv a tives. The new U-Pb SHRIMP zir con age of 296 ± 6 Ma for the Gêbczyce Bt-Ms gran ite shows that this body be longs to the third stage of magmatism in the Strzelin Mas sif. The U-Pb SHRIMP zir con data for the Bt-Ms gran ite dykes pro vide ages sim i lar to those of their host rocks: c. 295 Ma for the Gêsiniec tonalite and the en closed Bt-Ms gran ite, and c. 285 Ma for the Strzelin bi o tite gran ite and its Bt-Ms gran ite dykes. These new data from peraluminous rock-types comple ment our pre vi ous stud ies fo cused on the tonalites, granodiorites and bi o tite gran ites, and shed light on the late-stage igne ous evo lu tion of the Strzelin Mas sif.

Two-mica andalusite-bearing granite with no primary muscovite: constraints on the origin of post-magmatic muscovite in two-mica granites

“…The An content in the rims is 2-3 % ( Table 2, analyses 13 and, 14). Small, rounded grains associated with micas are albitic (10-2% An; Table 2, analyses [15][16][17]. The anorthite content measured in this study is similar to that presented in Oberc-Dziedzic et al (2015).…”