SHRIMP U‐Pb geochronology of Cretaceous magmatism in northwest Nelson‐Westland, South Island, New Zealand

The New Zealand local Clarence Series spans the Lower/Upper Cretaceous boundary and includes three stages, in ascending order, the Urutawan, Motuan, and Ngaterian. All three were defined originally from a type section at Motu Falls, Raukumara Peninsula. To address problems with their original definitions and to improve correlations between the New Zealand time-scale and Global Chronostratigraphic Scale, four key sections have been restudied: the Motu Falls and adjacent Te Waka sections, and the Coverham and Seymour sections in the Clarence valley, Marlborough. The sections contain locally abundant macrofossils and have been sampled at a reconnaissance level for dinoflagellates. In addition, a middle Motuan tuff bed in the Motu Falls section has yielded a zircon U-Pb age of 101.6 ± 0.2 Ma, and an upper Ngaterian basalt flow in the Seymour section has yielded a plagioclase Ar/Ar age of 96.1 ± 0.6 Ma. The older of these dates allows, for the first time, direct age correlation of Clarence Series stages that are based on marine strata in eastern New Zealand, with non-marine rocks in the west. Thus, the Stitts Tuff, at the base of the Pororari Group in the western South Island, is shown to be middle Motuan. the Motuan is defined using the lowest occurrence of the bivalve Aucellina euglypha in the same section. The base of the Ngaterian is defined using the lowest occurrence of the inoceramid "I." tawhanus in the Te Waka section. In all three cases, the placements of the lowest occurrence datums are subject to uncertainties that can only be resolved by further biostratigraphic and/or taxonomic study. Based on biostratigraphic data and the new radiometric dates, the following international correlations are proposed: Urutawan Stage = lower-middle Albian (108-103 Ma); Motuan Stage = middle-upper Albian (103-100 Ma); Ngaterian Stage = upper Albian to middle Cenomanian (100-95 Ma).

“…1). Muir et al (1997) reported 206 Pb/ 238U ion probe ages of 101 + 2 and 102 ± 3 Ma for two samples of the Stitts Tuff from the lower Buller Gorge, western South Island (Fig. 1).…”

Section: Correlations Between Marine and Non-marine Motuan Stratamentioning

confidence: 99%

Definition, age, and correlation of the Clarence series stages in New Zealand (late early to early late Cretaceous)

Crampton¹,

Tulloch

Wilson

et al. 2004

“…Muir et al (1997) reported SHRIMP (sensitive high resolution ion microprobe) U-Pb zircon ages of 101 ± 2 Ma and 102 ± 3 Ma from two samples of the Stitts Tuff at the base of the Pororari Group in the lower Buller Gorge. These ages are thought to reflect the onset of Cretaceous extension following prolonged Permian-Cretaceous subduction on the Pacific margin of the Gondwana supercontinent (Laird 1993(Laird , 1994.…”

Section: Discussionmentioning

confidence: 99%

“…Whereas the Stitts Tuff Member in the Buller Gorge (Muir et al 1997), tuffs and lavas in the Greymouth Coalfield (Gage 1952), volcanogenic material in the Pike River Coalfield (Newman 1985), and lavas drilled by the exploration well at Arahua-1 and located at Mt Camelback (Sewell et al 1988) establish the link between lithospheric extension and volcanism in North Westland, the Buttress Point Member, Arnott Basalt, and Tokakoriri Formation record thermal events related to lithospheric extension during the Cretaceous-Paleocene of South Westland.…”

Section: Discussionmentioning

confidence: 99%

Geochronological constraints on Cretaceous‐Paleocene volcanism in South Westland, New Zealand

Phillips

Cooper

Palzin

et al. 2005

Cretaceous and Paleocene sedimentation in South Westland, New Zealand, is recorded in the Otumotu Formation, Tauperikaka Coal Measures, Whakapohai Sandstone, Arnott Basalt, Buttress Conglomerate, and Tokakoriri Formation, originally named and mapped by Nathan in 1977. Within this stratigraphic sequence, the name Buttress Conglomerate was used to describe volcanic conglomerates at Porphyry and Buttress Points that contained rounded clasts of plagioclasephyric intermediate volcanic rocks. Stratigraphically, the volcanic conglomerate at Porphyry Point forms sharp contacts with the underlying Arnott Basalt (Haumurian) and overlying Tokakoriri Formation (Teurian). The volcanic conglomerate at Buttress Point, however, is entirely fault-bounded. Clasts from each unit were collected and U-Pb zircon dated using the TIMS and ELA-ICP-MS methods. A trachyandesite clast collected at Buttress Point gives an age of 96.9 ±1.6 Ma, whereas a rhyolite clast collected at Porphyry Point gives an age of 61.4 ± 0.8 Ma. Petrological, geochemical, and stratigraphic data suggest that erosion of the clasts closely followed volcanism, and that these ages accurately reflect the depositional ages of the conglomerates. Conglomerates at Porphyry and Buttress Points have been formally renamed the Porphyry Point Member of the Tokakoriri Formation and the Buttress Point Conglomerate, respectively.

“…The granitoids and the core complex fabrics in the Western Province have been dated using U-Pb zircon and 40 Ar/ 39 Ar methods (Kimbrough & Tulloch 1989;Tulloch & Kimbrough 1989;Muir et al 1997;Spell et al 2000;Sagar & Palin 2011), and the occurrences of Cenozoic mafic magmatism in the Western Province and elsewhere in New Zealand have recently been reviewed by Timm et al (2010). The timing of Late Cretaceous-Early Cenozoic lamprophyric and other mafic magmatism in the Western Province, coeval with extension and rifting, is much less precisely known.…”

Section: Introductionmentioning

confidence: 99%

Magmatism during Gondwana break-up: new geochronological data from Westland, New Zealand

Meer

Scott

Waight

et al. 2013

Newly determined Late Cretaceous 40 Ar/ 39 Ar ages on megacrystic kaersutite from four lamprophyre dikes, and a U-Pb zircon age on a trachyte, from central and north Westland (New Zealand) are presented. These ages suggest that the intrusion of mafic dikes (88-86 and 69 Ma) was not necessarily restricted to the previously established narrow age range of 80-92 Ma. The younger lamprophyre and trachyte dikes (c. 68-70 Ma) imply that tensional stresses in the Western Province were either renewed at this time, or that extension and related magmatism continued during opening of the Tasman Sea. Extension-related magmatism in the region not only preceded Tasman seafloor spreading initiation (starting at c. 83 Ma, lasting to c. 53 Ma), but may have sporadically continued for up to 15 Ma after continental break-up.