Systematics of internal zircon morphology in major Variscan granitoid types

Hf contents and Zr/Hf ratios in granitic zircons

“…One is colorless, with high transparency and birefringence, small and variable typological indices (I pr , I py and I el ), nearly homogeneous internal structure and low U and Th contents; this type commonly is included within the early-forming minerals such as biotite and phenocrysts of plagioclase. The second type is characterized by brownish color, poor transparency and low birefringence due to metamictization, large and similar typological indices (I pr , I py and I el ), oscillatory zoning and high U and Th contents; this type commonly is included within the late forming-minerals such as K-feldspar and quartz (Speer, 1982;Broska et al, 1990;Vavra, 1994;Poitrasson et al, 1998;Pupin, 2000;Rubatto, 2002;Wang et al, 2007). Both types commonly occur together in granitic rocks in the form of single grains (Krasnobayev, 1980;Wang et al, 2007) or core-rim overgrowths (Krasnobayev, 1980;Speer, 1982;Hansmann et al, 1983;Broska et al, 1990;Paterson et al, 1992;Halden et al, 1993;Benisek and Finger, 1993;Vavra, 1994;Poitrasson et al, 1998;Nasdala et al, 1999;Charlier and Zellmer, 2000;Wang et al, 2007).…”

“…The second type of zircon is suggested to have crystallized at the site of emplacement, involving undercooling of the magma (Speer, 1982;Wang et al, 2007). Consequently, the two types of zircon could be regarded as the early zircon and the late zircon, respectively (Krasnobayev, 1980;Scharer et al, 1994;Vavra, 1994;Pupin, 2000;Wang et al, 2007).…”

SHRIMP U-Pb zircon dating of Pedras Grandes Suite, southern Santa Catarina State, Brazil

“…Euhedral zoning is more prominent towards the grain rims. More rarely, some zircons show internal cores with faint oscillatory zoning which resembles the zoning derived from magmatic growth (Vavra 1994 Twenty-one SHRIMP spots were analyzed in fifteen zircon grains for this sample (Table II) and the U-Pb isotopic data plotted in a concordia diagram (Fig. 3).…”

An insight into a gneiss core of the Orlica-Śnieżnik Dome, NE Bohemian Massif: new structural and U–Pb zircon data

“…The pres ence of nu mer ous long pris matic crys tals (# 3, 8, 10, 12 and 16), mainly with poor planar or sec tor zon ing, dif fers this pop u la tion from other two zircon sam ples re trieved from rocks of the Giera³tów For ma tion. Most grains have the {110} prism faces that may im ply crystallisation from rel a tively cold, H 2 O-and alu mina-rich magmas and emplaced close to the place of ex trac tion (Vavra, 1994). These would be in line with leucocratic neosome or i gin of their host vein.…”

“…3C), the fol low ing in fer ences can be made: (1) dis cor dant vein is youn ger than the de formed host gneiss; (2) zir con is inher ited from the protolith with sig nif i cant ~600-540 Ma com ponent; (3) some old grains have no out growth or merely very thin CL black rims, which sug gests that they have never been in an ef fec tive con tact with the mag matic melt; (4) crystallisation from melt pro duced new, dom i nantly slen der, pris matic grains and out growths on older grains at 500 Ma; leucocratic melt de veloped via par tial melt ing of the host gneiss es or rocks sim i lar to them and rep re sented larger por tions of the mo bi lized migmatitic neosome; (5) zir con crys tals dom i nated by the {110} prisms typ i cal of gran ites crys tal lised from H 2 O-rich, "cold" magmas (Vavra, 1994); (6) such con di tions likely char ac ter ized the neosome for ma tion in the course of migmatisation ob served in sam ple MD46, and pre sum ably in the Giera³tów gneiss es in gen eral. In cip i ent migmatisation was ac com plished un der struc tural con trol, as ev i denced by the fold-hinge lo cated porphyroblasts, leucocratic ag gre gates and leucosome segregations or in jec tions; (7) lack of signs of strain in the cross-cut ting vein rock does not sup port the pos si bil ity that the 726 Aleksandra Redliñska-Marczyñska, Andrzej ¯elaŸniewicz and C. Mark Fanning…”