Granulite

About: Granulite is a research topic. Over the lifetime, 6763 publications have been published within this topic receiving 268925 citations.

Ultrahigh-temperature Metamorphism (1150°C, 12 kbar) and Multistage Evolution of Mg-, Al-rich Granulites from the Central Highland Complex, Sri Lanka

Abstract: Mgand Al-rich granulites of the central Highland Complex, Sri Lanka preserve a range of reaction textures indicative of a multistage P–T history following an ultrahigh-temperature metamorphic peak. The granulites contain a near-peak assemblage of sapphirine–garnet–orthopyroxene–sillimanite–quartz–K-feldspar, which was later overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel. Biotite-rims, kornerupine and orthopyroxene-rims on biotite are considered to be late assemblages. Thermobarometric calculations yield an estimated P–T of at least 1100 C and 12 kbar for the near-peak metamorphism. Isopleths of Al2O3 in orthopyroxene are consistent with a peak temperature above 1150 C. The P–T path consists of four segments. Initial isobaric cooling after peak metamorphism (Segment A), which produced the garnet–sapphirine–quartz assemblage, was followed by near-isothermal decompression at ultrahigh temperature (Segment B), which produced the multiphase symplectites. Further isobaric cooling (Segment C) resulted in the formation of biotite and kornerupine, and late isothermal decompression (Segment D) formed orthopyroxene rims on biotite. This evolution can be correlated with similar P–T paths elsewhere, but there are not yet sufficient geochronological and structural data available from the Highland Complex to allow the tectonic implications to be fully assessed.

A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

Abstract: We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400- km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0 6 0.2 km/s, 6.5 6 0.1 km/s, and 6.8 6 0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0 6 0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24 6 0.02 in the upper crust to 0.27 6 0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (,5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.