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In the Lehenberg (Lehberg or Limberg North) quarry in the NW part of the Megablock Zone of the Nördlinger Ries impact crater, granite and micaschist lithoclasts occur in a polymict suevite impact breccia. The lithoclasts display the petrographic characteristics of the shock metamorphism scale, as cavities filled with diaplectic glass, decorated planar elements in quartz grains, and severely kinked mica. In petrographic thin sections, monazite grains were detected by scanning electron microscope based automated mineralogy methods of spectral mapping. In backscattered electron imaging (BSE), monazite revealed the typical crystal shapes, and internal Th zoning and distribution pattern as known from igneous and metamorphic crystallisation. Intragrain signs of shock metamorphism in a minority of monazite grains are strictly straight and parallel crack pattern resembling lamellae structures. Monazite mineral chemistry and bulk chemical Th-U-Pb ages were investigated by electron probe microanalyser (EPMA). The igneous and metamorphic monazites display contrasting and typical mineral-chemical properties. Metamorphic monazites follow strictly the cheralite substitution trend in Th + U vs Ca coordinates. Igneous monazite in alkali feldspar granite has the highest Y2O3 contents (~2 wt%) among all studied samples. In ThO2* vs PbO coordinates the monazite data define isochrones. Micaschist lithoclasts yielded 328 ±3 Ma, 326 ±6 Ma and 324 ±5 Ma, interpreted to represent the thermal peak and post-peak age of metamorphic monazite crystallisation. The 328 ±5 Ma age of igneous monazite in the alkali feldspar granite in contact to micaschist is interpreted to date the crystallisation of a synmetamorphic anatectic melt. This contrasts the 313 ±3 Ma monazite crystallisation age in a post-tectonic monzogranite. No indications of bulk Pb loss in monazite by shock metamorphism have been observed. The EPMA Th-U-Pb monazite ages from the lithoclasts match data from granites and meta-psammopelites in the outcropping pre-Mesozoic basement in the Western Bohemian Massif and the Black Forest. They confirm that the bottom of the Nördlinger Ries impact crater is situated in crystalline basement rocks belonging to the Moldanubian Zone. [ABSTRACT FROM AUTHOR]

Austroalpine Saualpe basement in Carinthia (Austria, Eastern Alps) display a polymetamorphic microstructural and mineral-chemical evolution. SEM automated mineralogy methods and analysis by EPMA were applied for garnet mineralchemical characterisation and monazite dating. Two garnet generations with monophase and polyphase porphyroblasts and two monazite age populations have been revealed in low-Ca and high-Al-metapelites. Garnet 1 in both Kliening and Preims complexes has decreasing Mn, low Ca and significantly increasing Mg from cores to rims. Geothermobarometry of garnet 1 assemblages signals a crystallisation along a M1 prograde metamorphic P-T path culminating at 600-650 °C/7 kbar, followed by decompression. In the Preims Complex a subsequent crystallisation of a ~265 Ma monazite 1 population with high-Y and high-Gd indicates a Permian minimum age for the M1 metamorphic event. Monazite 1 crystallisation coincides with the intrusion of Permian and Early Triassic pegmatites. In the Kliening Complex where pegmatites are lacking, no Permian monazite is observed. Resorption of garnet 1 rims and corona structures of apatite and allanite around Permian monazite in the Preims Complex signal a retrogressive stage. An M2 metamorphic event with garnet 2 postdates the monazite corona structures. Garnet 2 displays always low Mn at high Ca and Mg. The XCa is increasing and then decreasing, while XMg is decreasing and then increasing toward the rims. The garnet 2 assemblages record a prograde P-T path from 530 °C/8 kbar to 700 °C/10-13 kbar in the Kliening Complex, and from 620 °C/10-12 kbar to 700 °C/14-15 kbar in the Preims Complex. Monazite 2 populations with ages between 95 and 81 Ma and with lower Y and Gd contents crystallised at decreasing pressure subsequent to garnet 2 and indicate a Cretaceous (Eo-Alpine) age for the metamorphic event M2. In the histogram view, the monazite age pattern in the Preims Complex and the overlying Saualpe Eclogite Complex are quite similar with Permian and Cretaceous age maxima. These patterns differ from other Austroalpine basement areas with unimodal Carboniferous or bimodal Carboniferous and Permian monazite age populations. [ABSTRACT FROM AUTHOR]