Cretaceous oblique detachment tectonics in the Fosdick Mountains, Marie Byrd Land, Antarctica

McFadden, Rory R.; Siddoway, C. S.; Teyssier, Christian; Fanning, C. Mark; Kruckenberg, Seth C.

doi:10.3133/ofr20071047srp046

Cited by 2 publications

(13 citation statements)

References 21 publications

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“…6a), broadly similar to U–Pb zircon ages from granites and gneisses (Fig. 6b) determined by SHRIMP (McFadden et al. , 2007, 2010b; Siddoway, 2008; Siddoway & Fanning, 2009) and LA–ICP–MS (Korhonen et al.…”

Section: Monazite Chemistrysupporting

confidence: 77%

“…The spread of spot ages broadly correlate with zircon crystallization ages of Cretaceous leucosomes and granites in the complex (Fig. 6b; McFadden et al. , 2007, 2010b; Siddoway, 2008; Korhonen et al.…”

Section: U–pb Monazite Geochronologymentioning

confidence: 67%

“…Renewed activity in the Cretaceous is indicated by zircon and monazite ages in granites and gneisses between c. 117 and 93 Ma (Fig. 9; also McFadden et al. , 2007, 2010a,b; Siddoway, 2008; Korhonen et al.…”

Section: Discussionmentioning

confidence: 99%

“…U–Pb monazite ages from foliated to apparently isotropic granites (Richard et al. , 1994) and U–Pb zircon and titanite ages from granites that intruded the South Fosdick detachment (McFadden et al. , 2007, 2010b) constrain the timing of granite emplacement and motion on the detachment zone to c .…”

Section: Geological Backgroundmentioning

confidence: 99%

“… Histogram comparing the frequency of single spot preliminary monazite (U–Th)–Pb dates analysed by electron probe microanalyser (unpublished data) and single spot zircon U–Pb dates. Zircon data determined by SHRIMP (from McFadden et al. , 2007, 2010b; Siddoway, 2008; Siddoway & Fanning, 2009) and LA–ICP–MS (from Korhonen et al.…”

Section: Monazite Chemistrymentioning

confidence: 99%

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Separating metamorphic events in the Fosdick migmatite–granite complex, West Antarctica

Korhonen

Brown

Grove

et al. 2011

Journal Metamorphic Geology

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The Fosdick migmatite-granite complex in West Antarctica records evidence for two high-temperature metamorphic events, the first during the Devonian-Carboniferous and the second during the Cretaceous. The conditions of each high-temperature metamorphic event, both of which involved melting and multiple melt-loss events, are investigated using phase equilibria modelling during successive melt-loss events, microstructural observations and mineral chemistry. In situ SHRIMP monazite and TIMS Sm-Nd garnet ages are integrated with these results to constrain the timing of the two events. In areas that preferentially preserve the Devonian-Carboniferous (M 1 ) event, monazite grains in leucosomes and core domains of monazite inclusions in Cretaceous cordierite yield an age of c. 346 Ma, which is interpreted to record the timing of monazite growth during peak M 1 metamorphism (820-870°C, 7.5-11.5 kbar) and the formation of garnet-sillimanite-biotite-melt-bearing assemblages. Slightly younger monazite spot ages between c. 331 and 314 Ma are identified from grains located in fractured garnet porphyroblasts, and from inclusions in plagioclase that surround relict garnet and in matrix biotite. These ages record the growth of monazite during garnet breakdown associated with cooling from peak M 1 conditions. The Cretaceous (M 2 ) overprint is recorded in compositionally homogeneous monazite grains and rim domains in zoned monazite grains. This monazite yields a protracted range of spot ages with a dominant population between c. 111 and 96 Ma. Rim domains of monazite inclusions in cordierite surrounding garnet and in coarse-grained poikiloblasts of cordierite yield a weighted mean age of c. 102 Ma, interpreted to constrain the age of cordierite growth. TIMS Sm-Nd ages for garnet are similar at 102-99 Ma. Mineral equilibria modelling of the residual protolith composition after Carboniferous melt loss and removal of inert M 1 garnet constrains M 2 conditions to 830-870°C and 6-7.5 kbar. The modelling results suggest that there was growth and resorption of garnet during the M 2 event, which would facilitate overprinting of M 1 compositions during the M 2 prograde metamorphism. Measured garnet compositions and Sm-Nd diffusion modelling of garnet in the migmatitic gneisses suggest resetting of major elements and the Sm-Nd system during the Cretaceous M 1 overprint. The c. 102-99 Ma garnet Sm-Nd ÔclosureÕ ages correspond to cooling below 700°C during the rapid exhumation of the Fosdick migmatite-granite complex.

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Section: Monazite Chemistrysupporting

confidence: 77%

Section: U–pb Monazite Geochronologymentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Section: Geological Backgroundmentioning

confidence: 99%

Section: Monazite Chemistrymentioning

confidence: 99%

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Separating metamorphic events in the Fosdick migmatite–granite complex, West Antarctica

Korhonen

Brown

Grove

et al. 2011

Journal Metamorphic Geology

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Thermochronology of extensional orogenic collapse in the deep crust of Zealandia

et al. 2016

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The exhumed Fiordland sector of Zealandia offers a deep-crustal view into the life cycle of a Cordilleran-type orogen from final magmatic construction to extensional orogenic collapse. We integrate U-Pb thermochronologic data from metamorphic zircon and titanite with structural observations from >2000 km 2 of central Fiordland to document the tempo and thermal evolution of the lower crust during the tectonic transition from arc construction and crustal thickening to crustal thinning and extensional collapse. Data reveal that garnet granulite facies metamorphism and partial melting in the lower crust partially overlapped with crustal thickening and batholith construction during emplacement of the Western Fiordland Orthogneiss (WFO) from 118 to 115 Ma. Metamorphic zircons in metasedimentary rocks yield 206 Pb/ 238 U (sensitive high-resolution ion microprobe-reverse geometry) dates of 116.3-112.0 Ma. Titanite laser ablation split stream inductively coupled plasma-mass spectrometry chronology from the same rocks yielded complex results, with relict Paleozoic 206 Pb/ 238 U dates preserved at the margins of the WFO. Within extensional shear zones that developed in the thermal aureole of the WFO, titanite dates range from 116.2 to 107.6 Ma and have zirconium-in-titanite temperatures of ~900-750 °C. A minor population of metamorphic zircon rims and titanites in the Doubtful Sound region yield younger dates of 105.6-102.3 Ma with corresponding temperatures of 740-730 °C. Many samples record Cretaceous overdispersed dates with 5-10 m.y. ranges. Core-rim traverses and grain maps show complex chemical and temporal variations that cannot easily be attributed to thermally activated volume diffusion or simple core-rim crystallization. We interpret these Cretaceous titanites not as cooling ages, but rather as recording protracted growth and/or crystallization or recrystallization in response to fluid flow, deformation, and/or metamorphic reactions during the transition from garnet granulite to upper amphibolite facies metamorphism. We propose a thermotectonic model that integrates our results with structural observations. Our data reveal a clear tectonic break at 108-106 Ma that marks a change in processes deep within the arc. Prior to this break, arc construction processes dominated and involved (1) emplacement of mafic to intermediate magmas of the Malaspina and Misty plutons from 118 to 115 Ma, (2) contractional deformation at the roof of the Misty pluton in the Caswell Sound fold-thrust belt from 117 to 113 Ma, and (3) eclogite to garnet granulite facies metamorphism and partial melting over >8 m.y. from 116 to 108 Ma. These processes were accompanied by complex patterns of lower crustal flow involving both horizontal and vertical displacements. After this interval, extensional orogenic collapse initiated along upper amphibolite facies shear zones in the Doubtful Sound shear zone at 108-106 Ma. Zircon and titanite growth and/or crystallization or recrystallization at this time clearly link upper amphibo lite facies metamorph...

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Cretaceous oblique detachment tectonics in the Fosdick Mountains, Marie Byrd Land, Antarctica

Cited by 2 publications

References 21 publications

Separating metamorphic events in the Fosdick migmatite–granite complex, West Antarctica

Separating metamorphic events in the Fosdick migmatite–granite complex, West Antarctica

Thermochronology of extensional orogenic collapse in the deep crust of Zealandia

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