Prograde infiltration of Cl-rich fluid into the granulitic continental crust from a collision zone in East Antarctica (Perlebandet, Sør Rondane Mountains)

Abstract

Utilizing microstructures of Cl-bearing biotite in pelitic and felsic metamorphic rocks, the timing of Cl-rich fluid infiltration is correlated with the pressure-temperature-time (P-T-t) path of upper amphibolite-to granulite-facies metamorphic rocks from Perlebandet, Sør Rondane Mountains (SRM), East Antarctica. Microstructural observation indicates that the stable Al2SiO5 polymorph changed from sillimanite to kyanite + andalusite + sillimanite, and P-T estimates from geothermobarometry point to a counterclockwise P-T path characteristic of the SW terrane of the SRM. In situ laser ablation inductively coupled plasma mass spectrometry for U-Pb dating of zircon inclusions in garnet yielded ca. 580 Ma, likely representing the age of garnet-forming metamorphism at Perlebandet. Inclusion-host relationships among garnet, sillimanite, and Cl-rich biotite (Cl > 0.4 wt%) reveal that formation of Cl-rich biotite took place during prograde metamorphism in the sillimanite stability field. This process probably predated partial melting consuming biotite (Cl = 0.1-0.3 wt%). This was followed by retrograde, moderately Cl-bearing biotite (Cl = 0.1-0.3 wt%) replacing garnet. Similar timings of Cl-rich biotite formation in different samples, and similar f(H2O)/f(HCl) values of coexisting fluid estimated for each stage can be best explained by prograde Cl-rich fluid infiltration. Fluid-present partial melting at the onset of prograde metamorphism probably contributed to elevate the Cl concentration (and possibly salinity) of the fluid, and consumption of the fluid resulted in the progress of dehydration melting. The retrograde fluid was released from crystallizing Cl-bearing partial melts or derived externally. The prograde Cl-rich fluid infiltration in Perlebandet presumably took place at the uppermost part of the footwall of the collision boundary. Localized distribution of Cl-rich biotite and hornblende along large-scale shear zones and detachments in the SRM supports external input of Cl-rich fluids through tectonic boundaries during continental collision.

Pressure–temperature–time path of a metapelite from Mefjell, Sør Rondane Mountains, East Antarctica

“…In contrast, metamorphic rocks from the central SRM such as Brattnipene and Menipa reached peak conditions (900°C, 6-7 kbar and 800°C, 6 kbar) after compression, and were followed by nearly isobaric cooling, indicating anti-clockwise P-T paths (Owada et al, 2008;Adachi et al, 2013;Baba et al, 2013). An anti-clockwise P-T path has been reported from the western SRM recently (Perlebandet; Kawakami et al, 2017). However, the prograde metamorphic path of Mefjell is unclear.…”

“…Location of MTB is after Osanai et al (2013). Key minerals used in understanding the metamorphic evolution are indicated (Asami et al, 2007;Osanai et al, 2013;Kawakami et al, 2017). The studied sample was collected from Mefjell indicated by the white star.…”

Ultrahigh–temperature metamorphism and melt inclusions from the Sør Rondane Mountains, East Antarctica

“…Grantham et al (2013) proposes a top-to-the-southwest mega-nappe complex involving collision between Northern and Southern Gondwana during the Kuunga Orogeny in eastern SRM. Although Osanai et al (2013) proposed the tectonic model in which the SRM is divided into the NE-and the SW-terranes by the Main Tectonic Boundary, various P-T paths and geochronological data recently reported from the entire SRM suggest that the tectonic model in the SRM needs to be re-evaluated (e.g., Kawakami et al, 2017;Tsubokawa et al, 2017;Ruppel et al, 2021).…”

PetroChron Antarctica: A Geological Database for Interdisciplinary Use

“…A “metamorphic age” map (Figure 4b) based on U‐Pb and Sm‐Nd isotopic data from zircon, monazite, garnet and whole‐rock samples, show the predominance of late Neoproterozoic‒Cambrian (∼630‒500 Ma) ages in the Transantarctic Mountains, Dronning Maud Land, MacRobertson Land, and Princess Elizabeth Land (e.g., Baba et al., 2015; Bisnath et al., 2006; Board et al., 2005; De Vries Van Leeuwen et al., 2019; Goodge & Fanning, 2016; Halpin et al., 2007; Jacobs et al., 2003; Kawakami et al., 2017; Liu et al., 2018; Mikhalsky et al., 2013; Morrissey et al., 2016; Wang et al., 2016). These tectonothermal events record prolonged ocean closure, terrane accretion and collision‐related processes related to Gondwana amalgamation and active margin tectonics (e.g., Boger, 2011; Fitzsimons, 2003; Goodge, 2020; Harley et al., 2013; Jacobs et al., 2015; Jordan et al., 2020; Mulder et al., 2019).…”