P–T Evolution of a Variscan Lower-Crustal Segment: a Study of Granulites from the Schwarzwald, Germany
P–T Evolution of a Variscan Lower-Crustal Segment: a Study of Granulites from the Schwarzwald, Germany
复制标题
DOI：
10.1093/petrology/44.2.227
复制
发表时间：
2003-02
影响因子：
3.9
通讯作者：
H. Marschall;A. Kalt;M. Hanel
中科院分区：
文献类型：
--
作者：
H. Marschall;A. Kalt;M. Hanel
Pressure–temperature–time (P–T–t) paths of orogenic granulites INTRODUCTION provide important information on the thermal and chemical structure General background of the lower continental crust through time, and constraints on tectonic Granulites are typical rocks of the Earth’s middle to processes. We present the first detailed petrological investigation of lower crust under high-temperature conditions. They are granulites from the Variscan Schwarzwald. Pelitic granulites from the found as xenoliths in basaltic volcanic rocks, mainly Central Schwarzwald Gneiss Complex (CSGC) are characterized by within continental rifts, but most granulites occur as the peak assemblage garnet + rutile + kyanite + antiperthite complexes or terranes in orogenic settings. Orogenic ± quartz. Felsic to intermediate granulites from the Southern granulites display a wide compositional range (Harley, Schwarzwald Gneiss Complex (SSGC) exhibit different peak as1989, 1998) and are known from a variety of collisional semblages with clinopyroxene, orthopyroxene, ternary feldspar, garnet, belts that formed during different episodes since the quartz and sillimanite, and manifold retrograde reaction textures. Archaean (e.g. Harley, 1998; Clarke et al., 2000; Moller Peak P–T conditions were calculated by two-feldspar thermometry, et al., 2000). Determination of bulk-rock and mineral garnet–orthopyroxene thermometry and various geobarometers. Minicompositions, calculation of peak equilibration conmum estimates for peak conditions are 950–1010°C and 1·4–1·8 ditions, and dating of orogenic granulites thus provide us GPa for the granulites of the CSGC, which followed a clockwise with important constraints on the thermal and chemical P–T path. The retrograde path is characterized by initial isothermal structure of the Earth’s continental crust at different decompression, associated with partial melting, followed by isobaric geological times. cooling. Peak conditions for the SSGC are 1015°C and 1·5 GPa Harley (1989) showed that equilibration conditions (minimum temperature, maximum pressure). No prograde relics are deduced from natural orogenic granulites cover a wide preserved, and isothermal decompression was less pronounced than range. In particular, pressures are highly variable, and in the CSGC. Other Variscan HP–HT granulites from Central the granulite field may be divided into a low-pressure Europe show similar lithologies, equilibration temperatures and (LP), a medium-pressure (MP) and a high-pressure (HP) ages (340–335 Ma). The heat for widespread high-temperature facies according to Green & Ringwood (1967). Peak metamorphism in the Variscan lower crust could have been supplied temperatures of many granulite terranes scatter around by repeated intrusion of subduction-related basic magmas. Rapid, 800°C (Bohlen, 1987), but an increasing number of near-isothermal decompression of the granulites may have been ultra-high-temperature (UHT) granulite complexes facilitated by considerable volumes of partial melt and by orogenic extension. (900–1100°C and 0·7–1·3 GPa; Harley, 1998) are being recognized (e.g. Harley & Hensen, 1990; Dasgupta et al., 1995; Klemd & Brocker, 1999; Hokada, 2001). Regarding retrograde P–T paths, Harley (1989) distinguished two
