Heavy minerals and the provenance history of Waitemata Basin sediments (early Miocene, Northland, New Zealand)

Abstract

Census data from 100 heavy mineral samples from the early Miocene Waitemata Basin (81 samples) and its potential source rocks (19 samples) from Auckland and southern Northland, New Zealand, were analysed by cluster analysis, multidimensional scaling, and factor analysis. These analyses give rise to seven groups, each characterised by a distinctive mineralogy (factor): (1) dominated by clinopyroxene plus magnetite, from a Miocene andesitic provenance; (2) dominated by ilmenite plus zircon and apatite, from a Mesozoic greywacke (Waipapa) and Paleogene sedimentary (Motatau, Mangakahia) provenance; (3) dominated by hornblende, from a Miocene volcanic or Cretaceous igneous (Tangihua) provenance; (4) co-dominated by hornblende, magnetite and ilmenite, from a Tangihua provenance; (5) dominated by semi-opaque debris plus ilmenite, from a Waipapa provenance; (6) co-dominated by biotite and ilmenite, from a mixed Miocene rhyolitic, Tangihua and Motatau provenance; and (7) dominated by orthopyroxene plus clinopyroxene, from a two-pyroxene andesite provenance.Using these provenance interpretations for the heavy mineral groups, in conjunction with their stratigraphic and geographic distributions, we deduced a model for the paleogeographic and provenance history of the Waitemata Basin, and refined traditional models for the basin.

Thermal history of the early Miocene Waitemata Basin and adjacent Waipapa Group, North Island, New Zealand

“…The Waipapa Group rocks may therefore have been a source of sediment. This result is compatible with earlier findings (Ballance 1974;Hayward & Smale 1992) that suggest Waipapa Group rocks have been one of the sources that supplied sediments to the basin, either directly or indirectly.…”

“…Over 85% of the single-grain ages belong to the 85 Ma population, confirming the earlier observation that most of the sediments for the basal part of the Waitemata Group were derived from Waipapa Group rocks (Ballance 1974;Ricketts et al 1989). The younger population, although minor, is important as the 28 ± 6 Ma age is concordant with the oldest K-Ar ages (Smith et al 1989;Hayward & Smale 1992) from the volcanics. Although this age has a low precision, it helps constrain the initiation of subductionrelated volcanism.…”

“…A previous detailed study of heavy mineral suites from the sandstone beds of the basin elucidated considerable information about their provenance (Hayward & Smale 1992). AFT analysis is potentially useful because it can provide: (1) independent evidence about the potential source areas for the basin; (2) independent evidence for early Miocene volcanic activity; (3) chronological evidence for the variation in source area across the basin; and (4) new constraints on the thermal history of the Waipapa Group (one of the source terranes).…”

Foraminifera‐based estimates of paleobathymetry using Modern Analogue Technique, and the subsidence history of the early Miocene Waitemata Basin

“…Throughout the central and northern parts of the region, substantial terrigenous sedimentation did not recommence until the basin had subsided to sufficient depths to create a submarine slope down which turbidity currents could flow from their source area 50-100 km to the northwest (Ballance 1974;Hayward & Smale 1992;Hayward 1993). In the north, paleodepth estimates for foraminiferal association 8 faunas in the starvation interval mudstone (samples 3, 6, 7) imply that the basin had subsided to at least lower bathyal and probably greater depths (>1700 m) before the arrival of the first turbidite sand.…”

“…Rock fragments and heavy minerals indicate derivation exclusively from the local underlying Waipapa Terrane greywacke or Te Kuiti Group (Hayward & Smale 1992).…”