Title: Variscan granitoid plutonism in the Strzelin Massif (SW Poland): petrology and age of the composite Strzelin granite intrusion
Abstract: Pet ro log i cal data and re cently pub lished U/Pb zir con SHRIMP ages re veal a pro tracted Variscan mag matic evo lu tion in the Strzelin Mas sif (SW Po land), with three main stages of granitoid plutonism: 1 -tonalitic I, 2 -granodioritic and 3 -tonalitic II/gra nitic.The granitoids of the sec ond and third stages form the Strzelin in tru sion that is com posed of three va ri et ies: medium-grained bi o tite gran ite, fine-grained bi o tite gran ite and fine-grained bi o tite-mus co vite gran ite.New SHRIMP data show that the me dium-grained and fine-grained bi o tite gran ites com prise dif fer ent zir con pop u la tions that re flect com plex and prolonged plutonic pro cesses.Two dis tinct mag matic events seem to be rep re sented by well-de fined zir con pop u la tions with ap par ent 206 Pb/ 238 U ages of 303 ± 2 Ma in the me dium-grained bi o tite gran ite, and 283 ± 8 Ma in the fine-grained bi o tite granite.These dates, how ever, do not nec es sar ily re flect the true mag matic ages, pos si bly be ing "re ju ve nated" by ra dio genic lead loss in zir cons (im pos si ble to re solve based on rou tine SHRIMP data).Based on field ev i dence, the third va ri ety, the bi otite-mus co vite gran ite, post dates both types of bi o tite gran ites.The petrographic and geo chem i cal fea tures, in clud ing Nd isotope sig na ture, along with var i ous zir con in her i tance pat terns and ages, sug gest that the pa ren tal mag mas of the three gran ites orig i nated from dif fer ent crustal sources and were emplaced dur ing three suc ces sive mag matic pulses.