The South Range Breccia Belt of the Sudbury Impact Structure: A possible terrace collapse feature

Details The South Range Breccia Belt of the Sudbury Impact Structure: A possible terrace collapse feature The South Range Breccia Belt of the Sudbury Impact Structure: A possible terrace collapse feature

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35..505s&link_type=abstract

Meteoritics & Planetary Science, vol. 35, no. 3, pp. 505-520 (2000).

Computer Science

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Scientific paper

The South Range Breccia Belt (SRBB) is an arcuate, 45 km long zone of Sudbury Breccia in the South Range of the 1.85 Ga Sudbury Impact Structure. The belt varies in thickness between tens of meters to hundreds of meters, and is composed of a polymict assemblage of Huronian Supergroup (2.49-2.20 Ga), Nipissing Diabase (2.2 Ga) and Proterozoic granitoid breccia fragments ranging in size from a few millimeters to tens of meters. The SRBB matrix is composed of a fine-grained (~100 μm) assemblage of biotite, quartz and ilmenite, with trace amounts of plagioclase, zircon, titanite, epidote, pyrite, chalcopyrite, pyrrhotite and occasionally chlorite. The SRBB hosts the Frood-Stobie, Vermilion and Kirkwood quartz diorite Offset Dykes, the former being associated with one of the largest Ni-Cu-PGE sulphide deposits in the world. Optical petrography and whole rock geochemistry concur with previous studies that have suggested that the matrix of the SRBB is derived from comminution and at least partial frictional melting of the wall rock Huronian Supergroup lithologies. REE data from all sampled lithologies associated with the SRBB exhibit crustal signatures when normalized to C1 chondrite values. Additionally, REE data from the quartz diorites, disseminated sulphides in Sudbury Breccia and a sample of an aphanitic biotite-hornblende tonalite dyke exhibit flat slopes when compared to the mafic and felsic norites, quartz gabbro and granophyre units of the Sudbury Igneous Complex (SIC), suggesting that these lithologies are representative of bulk SIC melt. We suggest that the SRBB was formed by high strain-rate (> 1 m/s), gravity driven seismogenic slip of the inner ring of the Sudbury Impact Structure during post-impact crustal re-adjustment (crater modification stage). Failure of the hanging wall may have facilitated the injection of bulk SIC melt into the SRBB, along with the Ni-Cu-PGE sulfides of the Frood-Stobie deposit. Post-impact Penokean (1.9-1.7 Ga) tectonism, particularly north-west directed shearing along the South Range Shear Zone (SRSZ) and associated thrust faulting could account for the present sub-vertical orientation of the SRBB, and the apparent lack of a connection at depth with the SIC.

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