Loch Burn Formation, Fiordland, New Zealand: SHRIMP U‐Pb ages, geochemistry and provenance

Abstract

New SHRIMP U-Pb ages and geochemical data have been obtained for the volcano-sedimentary Loch Burn Formation (LBF). A rhyolitic clast from the tops of the Stuart Mountains gave a SHRIMP age of 150.3 ± 1.9 Ma, and a very fine sandstone from the same area was dominated by 147.9 ±2.1 Ma zircons. These ages imply a <148 Ma depositional age for the LBF in this area, in contrast to a previous 195 -1 +3

Early Cretaceous dextral transpressional deformation within the Median Batholith, Stewart Island, New Zealand

“…The presence of a similar narrow belt of loch Burn Formation and largs Group volcanic rocks in eastern Fiordland, and at Port craig on the south coast of the South Island ( Fig. 1) (King 1984;Turnbull & uruski 1995;ewing et al 2007;Scott et al 2008), implies that these Jurassic basins may have formed a semi-continuous belt up to several hundreds of kilometres in length (Fig. 1).…”

Petrology and geochronology of the volcaniclastic and volcanogenic Mesozoic Loch Burn Formation in eastern Fiordland, New Zealand

“…However, subsequent u-Pb zircon geochronology identified Late Jurassic (c. 150-148 Ma) volcanic clasts and volcaniclastic sediments in the central Stuart Mountains (Ewing et al 2007). Based on these age differences, Ewing et al (2007) subdivided the formation in the Stuart Mountains into an older (c. 195 Ma) and a younger (c. 150-148 Ma) informal geochronological member. No contact has yet been recognised between members, and wholerock geochemistry has been unsuccessful in differentiating volcanic clasts or lavas from either member (Ewing et al 2007).…”

“…The Median Tectonic Zone (or Median Batholith, Tutoko Complex) in southern New Zealand is composed of Carboniferous-Cretaceous intrusive rocks with subordinate metasedimentary units (Williams 1978;King 1984;Bradshaw 1993;Smith 1993;Kimbrough et al 1994;Muir et al 1998;Mortimer et al 1999a,b;Wandres & Bradshaw 2005;Ewing et al 2007). The most extensive metasediments belong to the Largs Group in northern Fiordland (Largs Terrane of Williams 1978; renamed by Mortimer etal.…”

“…However, further work is needed to confirm our tentative correlation of some, if not all, of these metasediments with Loch Burn Formation. Integration of data from all localities described in this paper, coupled with the geochronological framework of Ewing et al (2007), provides insights into the petrology and tectonic evolution of eastern Fiordland. These new data also enable an in-depth comparison of the Loch Burn Formation with the Largs and Paterson groups.…”

“…An Early Jurassic depositional age was established based on a u-Pb zircon age of 195 (+3-1) Ma for a meta-rhyolitic ignimbrite or tuff intercalated with sediments from North Fiord (Kimbrough et al 1994). However, subsequent u-Pb zircon geochronology identified Late Jurassic (c. 150-148 Ma) volcanic clasts and volcaniclastic sediments in the central Stuart Mountains (Ewing et al 2007). Based on these age differences, Ewing et al (2007) subdivided the formation in the Stuart Mountains into an older (c. 195 Ma) and a younger (c. 150-148 Ma) informal geochronological member.…”