TY - JOUR

T1 - Genesis of peraluminous granites II. mineralogy and chemistry of the tourem complex (North Portugal). sequential melting vs. restite unmixing

AU - Holtz, Francois

AU - Barbey, Pierre

N1 - Funding Information: ACKNOWLEDGEMENTS This work was supported by a European Community grant (ST2*0257) and PROCOPE. Technical assistance was provided by D. Mangin and F. Schulze. Discussions on an early draft with P. Le Fort and J. M. Montel were particularly helpful. Reviews by N. Le Breton and S. A. Morse are gratefully acknowledged. Thanks are also due to P. Nabelek for critical comments and improving the English. Copyright: Copyright 2010 Elsevier B.V., All rights reserved.

PY - 1991/10/1

Y1 - 1991/10/1

N2 - The Tourem granitic complex (North Portugal) consists of quartz- and alkali-feldspar-rich felsic granites, biotite- and plagioclase-rich heterogeneous granites, and cordierite-biotite granites, containing numerous enclaves of orthogneisses and metapelitic schists. Mineralogical, chemical, and experimental data suggest that all the granites and the orthogneiss enclaves are genetically related.The felsic granites are characterized by normally zoned plagioclase, absence of cordierite, high SiO2 and K2O (72-74 wt.% and 5·4-6·4 wt.%, respectively), moderate P2O5 and REE (0·22-0·24% and 85·0-95·7 ppm), and low Fe2O3* and Zr contents (1·3-1·5% and 80-90 ppm). These features are consistent with those of restite-free melts formed by low extents of melting. Melting experiments show that these felsic granites are likely to be derived by melting of a source material similar to the orthogneiss enclaves under low water activities (∼0·5), at relatively high temperature (∼ 800°C) and <30% melting.The heterogeneous and cordierite-biotite granites display high cordierite contents (up to 30%) in addition to biotite (5-25%), complexly zoned plagioclase, and high Fe2O3 (2·72-6·99%), CaO (0·56-1·95%), Zr (101-213 ppm), and Ce (39·8-98·1 ppm) contents, suggesting that the melts contained significant proportions of residual biotite, cordierite, plagioclase, and accessories. Experimental data indicate that the melts were generated under water-undersaturated conditions but by higher extents of melting (30-60% melting) with probably a larger amount of available water compared with the felsic granites.The major and trace element chemical trends of the granites, which do not define single arrays on two-element variation diagrams, and experimental data show that the generation of the Tourem anatectic complex cannot be explained by the restite unmixing model but could have resulted from sequential low extents of melting with efficient melt segregation followed by higher extents of melting with restite retention.

AB - The Tourem granitic complex (North Portugal) consists of quartz- and alkali-feldspar-rich felsic granites, biotite- and plagioclase-rich heterogeneous granites, and cordierite-biotite granites, containing numerous enclaves of orthogneisses and metapelitic schists. Mineralogical, chemical, and experimental data suggest that all the granites and the orthogneiss enclaves are genetically related.The felsic granites are characterized by normally zoned plagioclase, absence of cordierite, high SiO2 and K2O (72-74 wt.% and 5·4-6·4 wt.%, respectively), moderate P2O5 and REE (0·22-0·24% and 85·0-95·7 ppm), and low Fe2O3* and Zr contents (1·3-1·5% and 80-90 ppm). These features are consistent with those of restite-free melts formed by low extents of melting. Melting experiments show that these felsic granites are likely to be derived by melting of a source material similar to the orthogneiss enclaves under low water activities (∼0·5), at relatively high temperature (∼ 800°C) and <30% melting.The heterogeneous and cordierite-biotite granites display high cordierite contents (up to 30%) in addition to biotite (5-25%), complexly zoned plagioclase, and high Fe2O3 (2·72-6·99%), CaO (0·56-1·95%), Zr (101-213 ppm), and Ce (39·8-98·1 ppm) contents, suggesting that the melts contained significant proportions of residual biotite, cordierite, plagioclase, and accessories. Experimental data indicate that the melts were generated under water-undersaturated conditions but by higher extents of melting (30-60% melting) with probably a larger amount of available water compared with the felsic granites.The major and trace element chemical trends of the granites, which do not define single arrays on two-element variation diagrams, and experimental data show that the generation of the Tourem anatectic complex cannot be explained by the restite unmixing model but could have resulted from sequential low extents of melting with efficient melt segregation followed by higher extents of melting with restite retention.

UR - http://www.scopus.com/inward/record.url?scp=0026286468&partnerID=8YFLogxK

U2 - 10.1093/petrology/32.5.959

DO - 10.1093/petrology/32.5.959

M3 - Article

AN - SCOPUS:0026286468

VL - 32

SP - 959

EP - 978

JO - Journal of Petrology

JF - Journal of Petrology

SN - 0022-3530

IS - 5

ER -