Stable isotopic evidence for fluid infiltration during contact metamorphism in a multiply‐metamorphosed terrane: the Reynolds Range, Arunta Block, central Australia

Abstract

The Lander Rock Beds form the local basement of the Reynolds Range in the Arunta Inlier of central Australia. These dominantly quartzose and pelitic lithologies underwent low-grade (c. 400°C) regional metamorphism prior to contact metamorphism (c. 2.5 kbar) around S-type megacrystic granitoids at 1820-1800 Ma. The Lander Rock Beds are overlain by metasediments of the Reynolds Range Group, which were subsequently intruded by granitoids at c. 1780 Ma. Regional metamorphism at 1590-1580 Ma produced grades varying from greenschist (400°C at 4-5 kbar) to granulite (750-800°C at 4-5 kbar) from north-west to south-east along the length of the Reynolds Range. Oxygen isotope ratios of the Lander Rock Beds were reset from 13.4±0.8‰ to as low as 6.7‰ adjacent to the contacts of the larger plutons, and to 10.3±1.1‰ around the smaller plutons. Biotite in all the major rock types found in the aureoles has dD values between −52 and −69‰, probably reflecting resetting by a cooling igneous+metamorphic fluid near the plutons. Sapphirine-bearing and other Mg-and Al-rich rock types have low d18O values (4.0±0.7‰). The precursors to these rocks were probably low-temperature (c. 200°C) diagenetic-hydrothermal deposits of Mg-rich chlorite, analogous to those in Proterozoic stratiform precious metal and uranium deposits that form by the infiltration of basin brines or seawater. As in the overlying Reynolds Range Group, regional metamorphism involved little fluid-rock interaction and isotopic resetting.

LA-MC-ICPMS Pb–Pb dating of rutile from slowly cooled granulites: Confirmation of the high closure temperature for Pb diffusion in rutile

“…1584 Ma, during the final (ca. 1594-1555 Ma) high grade metamorphic episode (Williams et al, 1996;Vry and Cartwright, 1998;Rubatto et al, 2001). Because the rocks in the pods crystallized from unusual new precursor materials that formed after the early regional and contact metamorphic history had already taken place, the rutile-bearing samples studied here record an isolated part of the complex overall metamorphic history.…”

Fluid-rock interaction in the Reynolds Range, central Australia: superimposed, episodic, and channelled fluid flow systems

“…Quartzites, psammites, and pelites of the Lander Rock Beds underwent low-grade contact metamorphism at 250 MPa and <500°C around the older granites at 1.8-1.82 Ga (Vry & Cartwright 1998). Oxygen isotope ratios of the Lander Rock Beds range from 13.4 4-0.8%o to as low as 6.7%0 near the contacts of the larger plutons, and to 10.3 + 1.1%o around the smaller plutons (Fig.…”

“…The early granites were emplaced at 1.82-1.80 Ga (Collins & Williams 1995;Vry et al 1996). Inclusion trails of quartz and muscovite in contact metamorphic andalusite porphyroblasts around these early granites indicate some deformation and low-grade metamorphism of the Lander Rock beds occurred prior to 1.82-1.80 Ga (Vry & Cartwright 1998 (Dirks et al 1991;Vry & Cartwright 1994;Buick et al 1998). SHRIMP U-Pb zircon ages suggest that the peak of regional metamorphism was at c. 1.6Ga Williams et al 1996), contemporaneous with the Chewings Orogeny that affected rocks within the southern Arunta Inlier (Collins & Shaw 1995).…”

“…In this study the geochronological framework of Vry et al (1996), Williams et al (1996, Vry & Cartwright (1998 is used (Table 1). SHRIMP ages from detrital zircons from the Lander Rock Beds indicate that it was deposited after 1840 Ma .…”

“…In the northwest of the terrain, Lander Rock Bed psammites comprise mainly quartz with beards of white mica and locally-abundant detrital zircon and tourmaline (Vry & Cartwright 1998). Pelitic rocks are fine-grained slates with less quartz, and biotite that may be partially detrital.…”