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        Detrital zircon geochronology and sandstone provenance of basement Waipapa Terrane (Triassic–Cretaceous) and Cretaceous cover rocks (Northland Allochthon and Houhora Complex) in northern North Island, New Zealand
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        Detrital zircon geochronology and sandstone provenance of basement Waipapa Terrane (Triassic–Cretaceous) and Cretaceous cover rocks (Northland Allochthon and Houhora Complex) in northern North Island, New Zealand
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        Detrital zircon geochronology and sandstone provenance of basement Waipapa Terrane (Triassic–Cretaceous) and Cretaceous cover rocks (Northland Allochthon and Houhora Complex) in northern North Island, New Zealand
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Abstract

Detrital zircon U–Pb ages are reported for 14 sandstones of mainly Cretaceous age from the Northland Allochthon, Houhora Complex and Waipapa Terrane of northern North Island, New Zealand. Results from the Waipapa Terrane samples, selected from sequences in the Bay of Plenty, Coromandel Peninsula and Great Barrier Island, show that deposition continued into late Early Cretaceous time and, as in the Torlesse Composite Terrane, finally waned at c. 110–114 Ma. Upper Lower Cretaceous and Upper Cretaceous sedimentary successions in the Houhora Complex and Northland Allochthon have dominant sediment sources derived from local, contemporary volcanism, with a minor older contribution from the Murihiku Terrane to the west. As in eastern North Island, upper Upper Cretaceous sandstones lack major Albian magmatic components and their sources are solely in the Murihiku Terrane, and possibly the Western Province. We propose a Cretaceous palaeogeographic model that invokes a recently extinct orogen and a partially submerged continental borderland, dissected by rivers supplying submarine fans.

1. Introduction

The mid-Cretaceous interval (110 to 85 Ma), approximately spanning the Albian to Santonian stages, witnessed a radical change in the tectonic situation of New Zealand. Oblique, plate-margin convergence had continued along the Zealandia sector of Eastern Gondwanaland from Middle Permian to Early Cretaceous time, developing accretionary complexes and fore-arc basins with varying inputs of terrigenous and redeposited volcaniclastic sediments. Then, during mid-Cretaceous time, the convergent active-margin regime was replaced by an extensional passive margin setting in which shallower-water and rift-related Upper Cretaceous cover successions developed. Various Permian–Early Cretaceous accretionary and fore-arc depositional basement terranes (e.g. Torlesse, Waipapa, Caples, Maitai and Murihiku) were amalgamated during Cretaceous time, to be finally consolidated as New Zealand's Eastern Province by Albian time.

Detailed provenance studies suggest that the Permian and Triassic sandstones in the Eastern Province were derived from sources in northeastern Australia, while the Cretaceous sandstones were derived from local New Zealand sources (Pickard, Adams & Barley, 2000; Adams, Campbell & Griffin, 2007). Thus, by interpolation, it is possible that the Jurassic sandstones originated on parts of the intervening Lord Howe Rise (Tasman Sea). The characteristic age patterns of detrital zircons inherited from the Eastern Province are widespread in sandstones of the Upper Cretaceous cover successions that rest upon Torlesse basement in eastern New Zealand (Adams et al. in press). In contrast, in the Waipapa Terrane of the North Island, limited areas of Cretaceous sedimentary rocks occurring in Northland are only allochthonous (Northland Allochthon) or possibly allochthonous (Houhora Complex). The former is in tectonic contact with the Waipapa Terrane but the latter has no observed contact with basement.

We report here new dating studies of detrital zircons from 14 sandstones from the youngest (Late Jurassic–Early Cretaceous) parts of the Waipapa Terrane and the late Early–Late Cretaceous parts of the now spatially adjacent Northland Allochthon and Houhora Complex to (1) constrain the depositional ages of formations that are otherwise sparsely fossiliferous or unfossiliferous, (2) compare the provenances of Waipapa basement and nearby younger sandstones and investigate their possible relationships, and (3) develop a Cretaceous palaeogeographic model relating the Waipapa Terrane, Northland Allochthon and Houhora Complex rocks to the contemporary Zealandia margin, including the Reinga Ridge, Norfolk Ridge (Tasman Sea) and New Caledonia.

2. Geological outline

Cretaceous sedimentary rocks have been extensively studied throughout New Zealand, and local series and stages specific to New Zealand, closely linked to International Stages, are well established (Cooper, 2004). In view of their considerable coal and hydrocarbon potential, they have formed part of several studies of Cretaceous–Cenozoic basins and regional compilations of stratigraphy, sedimentology and hydrocarbon prospectivity, of which those in Northland and East Coast regions are relevant to the present work (Isaac et al. 1994; Field et al. 1997).

Extensive revision of the Cretaceous of New Zealand has also informed a large part of the new New Zealand 1:250000 (QMAP) geological map series. Those dealing with the Kaitaia (Isaac, 1996), Whangarei (Edbrooke & Brook, 2009), Auckland (Edbrooke, 2001), Raukumara (Mazengarb & Speden, 2000), Rotorua (Leonard, Begg & Wilson, 2011) and Wairarapa (Lee & Begg, 2002) map sheets relate directly or indirectly to the present study. Comprehensive descriptions of Cretaceous histories and evaluation of previous field studies are found in these works and their standardized stratigraphic nomenclature is followed here. The descriptions below summarize only a few points particularly relevant to the geochronological results and their interpretation.

2.a. Waipapa Terrane

The Waipapa Terrane was originally defined in central and northern North Island (Spörli, 1978; Adams & Maas, 2004) but extends southwards to Kapiti Island, Wellington (Adams et al. 2009) (Fig. 1) and in the South Island to northernmost Marlborough (Mortimer, 1993, 1994; Adams et al. 2009; Adams, Campbell & Griffin, 2009) and, more speculatively, further south to the Otago region of the southern South Island (Adams & Graham, 1997; Adams, Campbell & Griffin, 2007). Waipapa Terrane successions are similar to those in the Torlesse Terrane: extensive tracts of sandstone-dominated redeposited (mainly turbiditic) sedimentary rocks that accumulated in a structurally complex accretionary environment, and have been metamorphosed to zeolite to pumpellyite-actinolite facies (Kear, 1971; Spörli, 1978; Korsch & Wellman, 1988; Black, 1994). The sediments have a more volcaniclastic (acid-intermediate) petrographic composition than the Torlesse rocks, but the probable volcanic sources for these are unknown.

Figure 1. Outcrop map of Triassic–Jurassic (dark grey) and Cretaceous (mid-grey) basement terranes of the Eastern Province of North Island, New Zealand (see also inset map of terranes). Surface extent of Cretaceous–Cenozoic Northland Allochthon and other correlative allochthons in the East Cape and Wairarapa districts are shown as dotted envelopes (with pale grey outcrop). Detrital zircon dating localities of this study (closed dots) and previously published (open dots) are shown with locality number in italics. A probable boundary between the Torlesse Composite Terrane and Waipapa Terrane is indicated by a dashed line.

Two facies are recognized: (1) the Hunua Facies dominated by fine-grained, thin-bedded volcaniclastic successions of sandstone and siltstone with abundant melange and occasional chert horizons (Edbrooke, 2001; Edbrooke & Brook, 2009); (2) the Morrinsville Facies (including the Manaia Hill Group; Skinner, 1972) of more massive, coarser successions of sandstone–fine conglomerate in which melange and chert are absent (Kear, 1971; A. Saeed, unpub. Ph.D. thesis, Univ. Auckland, 2000; Fig. 1). The Hunua Facies, of Permian to Jurassic age, occurs mainly in the north in Northland and North Auckland, while the Jurassic–Cretaceous Morrinsville Facies crops out predominantly to the south, in South Auckland and Waikato (Figs 1, 2).

Figure 2. Stratigraphic columns illustrating the approximate ranges of the Hunua Facies and Morrinsville Facies of the Waipapa Terrane in North Island, New Zealand and their relationship to Cretaceous cover successions of the Northland Allochthon and Houhora Complex in Northland. Some small areas of sedimentary rocks of oceanic association, either stratigraphically beneath, or tectonically intercalated within, the main Waipapa Terrane terrigenous clastic rocks are designated as triangles with ‘O’. The estimated stratigraphic positions of sandstone samples discussed in the text are shown by closed dots. The New Zealand and International timescales are from Cooper (2004).

The relationship between the two facies is nowhere clearly seen, but Edbrooke (2001) and Edbrooke & Brook (2009) grouped them both within a Waipapa Composite Terrane. This definition of a composite terrane differs from that of the Torlesse Composite Terrane, which includes the Rakaia, Kaweka and Pahau terrane subunits, each having some observable mutual tectonic boundaries. In the absence of any tectonic boundaries between Hunua and Morrinsville facies, and to avoid differing usages of the term ‘composite terrane’, we prefer in this work to retain the term Waipapa Terrane, thus leaving open the possibility that these two facies could have lithostratigraphic or possibly chronostratigraphic significance, or more regionally, could be real tectonic (terrane) subunits.

Fossil occurrences are rare throughout the Waipapa Terrane (Speden, 1976). In the Hunua Facies only two in situ macrofossil localities are known within the extensive terrigenous clastic successions: Late Jurassic at Tawharanui Peninsula, North Auckland (Spörli & Grant-Mackie, 1976) and Late Triassic at Stephenson Island, Northland (H. J. Campbell, unpub. record). There are more frequent microfossils (radiolaria, conodonts) of Permian, Triassic and Jurassic age in local (100 m scale) successions of oceanic association: melanges with spilite, pelagic argillite, chert and rare limestone and tuff, which underlie the terrigenous clastic sediments or are tectonically intercalated within them (Spörli, 1978; Aiti & Spörli, 1992, 1994; Spörli, Takemura & Hori, 2007). In the Morrinsville Facies, fossils in the dominant terrigenous clastic sediments are equally rare and mostly Late Jurassic in age (Speden, 1976) but at Motumaoho, near Morrinsville, Late Triassic bivalves (reworked) occur in sandstone clasts within conglomerate.

Age patterns of detrital zircons in sandstones of the Upper Jurassic Morrinsville Facies in the Bay of Plenty and South Auckland districts, reported by Cawood et al. (1999), display significant Late Jurassic and Permian–Triassic groups, with minor components of Late Devonian–Carboniferous and early Palaeozoic age. These authors recognized that such zircons could originate in many parts of the Eastern Gondwanaland margin, from West Antarctica to northeastern Australia, but preferred sources in the Ross–Delamerian and Lachlan fold belts of Antarctica and southeastern Australia. Subsequent age studies on detrital zircons of sandstones from both the Morrinsville and the Hunua facies (Pickard, Adams & Barley, 2000; Adams, Campbell & Griffin, 2007, 2009; Adams et al. 2009), ranging from Late Triassic to Early Cretaceous age, showed similar prominent Late Permian and Late Jurassic age groups and variable (up to 15%) proportions of Precambrian–early Palaeozoic zircons, but few or no Late Devonian to Carboniferous zircons. To explain the paucity of Late Devonian–Carboniferous zircons and the dominance of Permian–Triassic zircons, these authors preferred a more northerly provenance within the New England Orogen in NE New South Wales. In a comparison of sandstones from the Waipapa Terrane and Torlesse Composite Terrane, Adams et al. (2009) unexpectedly obtained Cretaceous ages, c. 133 Ma, from Waipapa rocks on Great Barrier Island. These rocks were previously regarded as Jurassic on the basis of sparse shelly macrofossil occurrences (Moore & Kenny, 1985). Reinterpretation of these fossils, coupled with several new fossil collections, has established no diagnostic Jurassic age at this locality. An Early Cretaceous age is therefore permissible, compatible with the detrital zircon ages. This indicates that the accretionary environment within the Waipapa Terrane continued well into Cretaceous times, in parallel with a similar situation in the Pahau Terrane (Torlesse Composite Terrane) to the south, and also far to the north in New Caledonia (Cluzel et al. 2010a).

2.b. Upper Cretaceous rocks in northern New Zealand

Cretaceous sedimentary cover successions, both marine and fluvial, are widespread across the South Island of southern Zealandia and marine successions are particularly well developed in the Marlborough, Wairarapa and Raukumara districts (Mazengarb & Speden, 2000; Lee & Begg, 2002; Rattenbury, Townsend & Johnston, 2006). In striking contrast, none are known to rest on the Waipapa Terrane basement. While Cretaceous strata might be present in offshore basins east and west of Northland and Auckland (Isaac et al. 1994; Uruski, 2010), the only Upper Cretaceous sedimentary rocks onshore occur within the Houhora Complex (itself a possible suspect terrane) and the Northland Allochthon (Figs 1, 2). A tiny (kilometre scale) area of Cretaceous sandstone in the Tupou Complex on the Northland coast may be a detached portion of the Northland Allochthon or Houhora Complex. The Upper Cretaceous rocks of the Northland Allochthon are in low-angle thrust contact with Waipapa Terrane basement (the allochthon was emplaced during Early Miocene time) and the contact between the Houhora Complex and older units is nowhere exposed (Black, 1994; Isaac, 1996; Edbrooke & Brook, 2009). The probable relative age relationship of Upper Cretaceous rocks to Waipapa Terrane basement is shown schematically in Figure 2.

The Houhora Complex comprises sedimentary rocks of the Tokerau Facies intercalated with contemporaneous basalt–andesite–rhyolite sills and lavas (Rangiawhia Volcanics). Fossils in the former and zircon ages from the latter indicate a mid-Cretaceous, probable Albian age (Isaac, 1996; Tulloch et al. 2009; Fig. 2). In the far north, on Three Kings Islands, there are similar outcrops of presumed Cretaceous sandstones intercalated with volcanic successions (Hayward & Moore, 1987; Nicholson, Black & Spörli, 2008). On the basis of clear geological differences with neighbouring geological units, the Houhora Complex has been termed the Mt Camel Terrane by Isaac (1996). Our detrital zircon work has some bearing on its possible terrane status but in the absence of demonstrable fault boundaries, we will refer to these rocks as the Houhora Complex.

Within the Northland Allochthon, the oldest sedimentary rocks are fossiliferous (Late Cretaceous), thin-bedded sandstone and mudstone of the Motukaraka and Punakitere Sandstone formations of the Mangakahia Complex (Late Cretaceous–Palaeogene; Figs 1, 2). Although Cretaceous rocks apparently are extensive, exposure is poor, and there is substantial tectonic disruption within the allochthon beneath major volcanic/plutonic massifs of the Cretaceous–Palaeogene Tangihua Volcanics (Isaac, 1996; Edbrooke & Brook, 2009). The allochthon can be traced in seismic lines offshore west of Northland (up to 85 km) and was emplaced on the Waipapa, Caples and Murihiku terranes during Late Oligocene–Early Miocene time (Isaac et al. 1994) with possibly up to 200 km transport from northeast to southwest (Rait, 2000).

3. Technical details and presentation of results

Samples for U–Pb detrital zircon dating were collected from small outcrop areas (1–10 m sections) of sandstone horizons in the Waipapa Terrane, Houhora Complex and the Northland Allochthon. Locations of new samples and those reported in previous studies are shown in Figure 1, with further details listed in Table 1. Where cited in the text, locality numbers are bracketed in italics, e.g. (11), and those from previous work have an alphabetic upper case suffix, e.g. (11C).

Table 1. Cretaceous cover and basement terrane sandstones, northern New Zealand: sample localities

* Facies attribution uncertain.

Locality No.: bold type are samples from this work; others are from previously published work (numbered references 1– Cawood et al. (1999); 2 – Pickard, Adams & Barley (2000); 3 – Adams, Campbell & Griffin (2007); 4 – Adams et al. (2009); 5 – Adams, Campbell & Griffin (2009); 6 – this work.

Stratigraphic Age (New Zealand Series and Stages): M – Mata Series (late Late Cretaceous): Mh – Haumurian (65–84 Ma); C – Clarence Series (mid-Cretaceous): Cm – Motuan (100–103 Ma); Cu – Urutawan 103–108 Ma).

Grid Reference: Map Series NZMS260 (1: 50000), with alphanumeric sheet number and then six-figure reference (e.g. A12/123456).

Procedures for zircon separation, age determination, technical calibration, common-Pb correction and data interpretation are identical to those used and described in a parallel study of Cretaceous rocks in eastern New Zealand (Adams et al. in press).

U–Pb isotopic ratios for new analyses are tabulated in the online Supplementary Material at http://journals.cambridge.org/geo together with age calculations and probability density diagrams as described below. Accepted age datasets of concordant 207Pb–235U and 206Pb–238U analyses were then used to create combined probability density/histogram diagrams of 206Pb–238U ages using the ISOPLOT 3.0 software (Ludwig, 2003); figures are plotted using a common format with a 0–500 Ma timescale.

Datasets from previously published studies were treated in a similar way. Where the probability density plots show clear components, their ages were computed using a weighted average. Where some overlap of age components is apparent then the ISOPLOT ‘Unmix Ages’ algorithms were used. These zircon component ages, their errors at 95% confidence levels and the percentage of each component (subset n) in relation to the total set (N), are listed in Table 2.

Table 2. Cretaceous cover successions and basement terranes, northern New Zealand: detrital zircon age components

Sample Information: GNS geochronology sample archive R number given in brackets.

Data in bold this work; other data from previously published work (see Table 1).

e – errors are 95% confidence limits; n – number of grains in age group; N – total population.

Decay constants used in this work are those recommended by Steiger & Jäger (1977), and all ages are referred to the New Zealand Geological Timescale of Cooper (2004), to preserve consistency with previously published Jurassic–Cretaceous basement age data cited throughout the text.

The detrital zircon age data are illustrated in two ways (Figs 3–7). Firstly, they are subdivided in terms of the proportions (as percentages of a total set) of zircon ages falling within selected geological periods (see inset boxes in the online Supplementary Material tables at http://journals.cambridge.org/geo; Fig. 3). These data from the present and previously published studies are organized into basement terrane/cover groups and within each they are stacked in order of maximum stratigraphic age as indicated from fossil evidence where available, or the youngest zircon age components where not. This form of presentation assigns equal weight to individual zircon analyses and provides a simple graphic display of similarities and trends within the large database.

Figure 3. Percentage proportions of detrital zircon 238U–206Pb ages (as % of total) occurring within selected geological periods in Cretaceous cover rocks and Waipapa Terrane basement. In each group, datasets are stacked from top to bottom in ascending maximum stratigraphic age, or where this is unknown, their youngest significant zircon age component. Data values in bold type are from the present work, other datasets are taken from previously published work. The percentage proportions are categorized, and shown on a colour scale. References: 1 – Cawood et al. (1999); 2 – Pickard, Adams & Barley (2000); 3 – Adams, Campbell & Griffin (2007); 4 – Adams et al. (2009); 5 – Adams, Campbell & Griffin (2009); 6 – this work.

Figure 4. Representative examples of combined probability density/histograms of detrital zircon 238U–206Pb ages for Waipapa Terrane sandstones of Jurassic Morrinsville Facies (TWHX1), Jurassic Hunua Facies (TWX1), probable Triassic Hunua Facies (RWH1) and Caples Terrane (PKTX2), northern North Island, New Zealand. Ages > 500 Ma are stacked at the right margin.

Figure 5. Representative examples of combined probability density/histograms of detrital zircon 238U–206Pb ages in sandstones from (left column) mid-Cretaceous horizons in the Northland Allochthon (HOK1) and Houhora Complex (TOKX1) and (right column) late Late Cretaceous horizons in the Northland Allochthon (HOU1) and Waioeka Terrane, Raukumara (ECAP5) North Island, New Zealand. Ages > 500 Ma are stacked at right margin.

Figure 6. Detrital zircon 238U–206Pb age patterns in sandstones of Waipapa and Caples terrane basement and Cretaceous horizons within the Northland Allochthon and Houhora Complex of northern North Island, New Zealand. Diagrams in left column are all-data probability density/histogram compilations using a common 0–500 Ma format, with ages > 500 Ma stacked at right margin. Diagrams in the right column are compilations of significant age components as listed in Table 2, with individual datasets stacked in order of maximum stratigraphic age (as determined from fossil evidence where available, and the youngest significant detrital zircon ages where not). Locality dataset numbers are shown at right margin. The width of the individual data boxes corresponds to the error of the component age (at 95% confidence limits) and the height reflects the proportion of that component to the set total (as %, a scale bar is shown at right margin).

Figure 7. Detrital zircon 238U–206Pb all-data age compilations from Cretaceous sandstones (left column) within the Houhora Complex and Northland Allochthon of northern North Island compared with correlative rocks from the East Coast/Wairarapa allochthons and probable autochthonous counterparts in the Waioeka Terrane of eastern North Island. Some possible zircon contributions to Cretaceous sandstones from the Triassic–Cretaceous basement terranes of the North Island are illustrated (right column) by similar compilations for the Murihiku, Waipapa and Caples terranes. The diagrams all use a common 0–500 Ma format, with ages > 500 Ma stacked at right margins.

Secondly, in Figures 4–7, the age data are organized in the same basement/cover groups and shown as combined probability density/histograms. Figure 4 shows four representative datasets from the basement rocks of the Waipapa Terrane (Hunua and Morrinsville facies) and the Caples Terrane. Figure 5 shows two representative datasets from the Cretaceous cover successions in the Northland Allochthon and Houhora Complex. Also included for comparison is a dataset (ECAP5) from an analogous upper Upper Cretaceous succession in the Waioeka Terrane, Raukumara (Adams et al. in press). The complete set of such diagrams may be found in the online Supplementary Material at http://journals.cambridge.org/geo. In Figure 6, ‘all-data’ age sets of the basement/cover groups are displayed in the left column, while those age data only forming significant components (as listed in Table 2) are displayed in the right column. Following Adams, Campbell & Griffin (2007), the choice of the latter is restricted by relatively conservative acceptance criteria, namely that any age group must (1) contain at least three, preferably four, zircon grains (dependent on dataset size) and (2) comprise at least 4% of the total dataset, and (3) have 206Pb–238U and 207Pb–235U ages that coincide at 95% confidence limits. The first criterion is sometimes n = 3 where some previously published datasets are rather small (n < 40) yet have age groups > 4% of total. However, more normally the zircon age components comprise larger groups, n = 6 to n = 35. The datasets are then organized in maximum stratigraphic age order as described above. The width of individual data boxes indicates the component age error and the height represents the proportion of that component (n/N, as a percentage of the total). This presentation has the advantage of displaying only age data that form significant clusters. Finally, in Figure 7, all-data histograms for the Upper Cretaceous sandstones in the Northland Allochthon and Houhora Complex are compared with similar data published for analogues in the Waioeka Terrane and East Coast Allochthon (Adams et al. in press).

4. Results

4.a. Waipapa Terrane

The data from the Morrinsville Facies and Hunua Facies in Figure 3 show some similarities and age trends.

Firstly, all samples, irrespective of their broad spread of Late Triassic to Early Cretaceous stratigraphic ages, have large groups of Permian–Triassic zircons: 15–95% but usually 30–50% (although the Steens Quarry locality (12C) is an important exception). This is a feature of nearly all zircon age patterns in all the Eastern Province terranes (Cawood et al. 1999; Pickard et al. 2000; Adams, 2003; Adams, Campbell & Griffin, 2007, 2009; Adams et al. 2009).

Secondly, the youngest zircon ages invariably form a large group, and where sample depositional age is known, they coincide with this, for example (8A, 9x), Late Triassic and (9), Late Jurassic. This suggests that a significant proportion of the sediments originate from contemporaneous volcanic sources, a feature that is reflected in their petrography (Mortimer, 1994) and geochemistry (Roser & Korsch, 1986). If one assumes that this behaviour is general and that it applies equally to localities without biostratigraphic control, then the high proportion of Triassic zircons (> 75%) at localities (8, 8B, 8C) could indicate Triassic depositional ages. Thus large areas of the Hunua Facies might be Late Triassic (mostly Norian) rather than Jurassic in age as previously assumed.

Finally, there is a trend from essentially unimodal patterns in the Late Triassic (8, 8B, 9x), to polymodal patterns in the Cretaceous (11, 11B). The contributions of Precambrian and early Palaeozoic zircons (up to 28%) increase at the expense of (mainly) Permian zircons. This trend is emphasized even more when analogous Caples Terrane data from the North Island (13A–D) are considered (Fig. 3).

Overall, the data patterns from the Morrinsville Facies conform to the general trends observed above. In contrast, in the Hunua Facies, only the Jurassic localities (9, 9A, 9B) conform to the pattern seen in the Morrinsville Facies, while the remainder, a ‘Triassic-dominated’ group (8, 8A–C, 9x), form a pattern (in particular a tendency to unimodality) that more resembles the data from the Caples Terrane. This difference is well illustrated (Fig. 4) by a comparison of significant age components in the two patterns: all samples from the Morrinsville Facies and Jurassic localities of the Hunua Facies have clusters of components in the Late Permian–Middle Triassic (particularly at 260, 235 and 230 Ma), in the Jurassic–earliest Cretaceous (particularly at 180 Ma) and close to their known depositional ages (150–140 Ma). In the remainder of the Hunua Facies and North Island Caples Terrane localities, there are no Jurassic components and the predominant Triassic age components are different from those above, namely at 240 and 220 Ma. In both Hunua Facies and Morrinsville Facies there are few significant pre-Triassic zircon age components, unlike the patterns from the Torlesse Composite Terrane, in which Cambrian–Ordovician and Late Carboniferous–Permian age components are a minor but common feature (Pickard, Adams & Barley, 2000; Adams, Campbell & Griffin, 2007).

4.b. Houhora Complex and Northland Allochthon

Cretaceous sandstones in the Houhora Complex and Northland Allochthon appear to have inherited only some of the features seen in the Waipapa and Caples terrane basement (Fig. 3). In all samples, except that from a late Late Cretaceous locality (4) at Parengarenga, the Permian–Triassic zircons that dominate the basement age patterns are much fewer but still present. This is a consequence of the overwhelming contribution of Cretaceous zircons in all the mid-Cretaceous localities (1–3, 5–7), but which are absent in the youngest Cretaceous locality (4). At many localities (1, 3, 5, 6) the sandstones contain high proportions of pre-Permian zircons (up to 30%), in particular of Devonian–Carboniferous age. The sandstone from Three Kings Islands (1) contains the oldest known terrestrial mineral grain thus far dated in New Zealand, 3465 ± 16 Ma.

In Figure 5 and 6, the significant zircon age components in the Houhora Complex and Northland Allochthon are seen to be quite similar. Within the prominent Cretaceous zircon group, there is a very sharp cut-off at 100 Ma and both have major late Early Cretaceous components at 130, 118 and 108 Ma, probably all comprising recycled zircons. In general however, these patterns are devoid of the numerous significant Jurassic and Triassic components that dominate the Waipapa and Caples autochthonous basement age patterns, respectively.

There are very few differences in the zircon patterns for the Houhora Complex and Northland Allochthon samples, as seen in all-data histograms in Figure 6. The Cretaceous and Permian–Triassic peaks are the same but Jurassic and early Early Cretaceous zircons are more abundant in the samples from the Northland Allochthon.

5. Discussion

5.a. Depositional history in the Waipapa Terrane

In the Waipapa Terrane, there remains at present no evidence for deposition of Early–Middle Jurassic terrigenous clastic rocks similar to those in the Kaweka Terrane of the Torlesse Composite Terrane (Adams et al. 2011). However, good fossil evidence in the Morrinsville Facies (and partly Hunua Facies) indicates deposition through Late Jurassic to earliest Cretaceous time, 160–140 Ma. The detrital zircon ages now extend this through the Early Cretaceous to the Aptian, c. 112 Ma (11B). In reviewing offshore exploration data, Uruski (2010) tentatively indicated sedimentary basins of this age east of Northland but there has been no confirmation of this from offshore drilling. The depositional history of the Morrinsville Facies thus appears to bridge the apparent depositional time gap between youngest Kaweka Terrane (latest Jurassic, Tithonian) and oldest Pahau Terrane (late Early Cretaceous, Barremian; Adams, Campbell & Griffin, 2009; Adams et al. 2011). As in both the Kaweka and the Pahau terranes, contemporary volcaniclastic zircon inputs in the Waipapa Terrane appear to decrease slightly through this period and to a large extent are replaced by those from Late Permian– Middle Triassic (and older) sources. As in the rocks from the Pahau Terrane, the Cretaceous zircons have no known source within the Waipapa Terrane itself and they most likely originate from within the Median Batholith, a major part of which is now seen as voluminous granitoid plutons of Early Cretaceous (major) and Late Jurassic (minor) age (Muir et al. 1995; Mortimer, Tulloch & Ireland, 1997; Mortimer et al. 1999b). It is probable that the batholith would have been subjacent to contemporary volcanic centres (now largely eroded away) that could have supplied the late Early Cretaceous zircons (c. 110–130 Ma) to the Waipapa accretionary wedge.

Although there is only limited fossil evidence, the zircon data from the sandstones of the Hunua Facies suggest that some terrigenous clastic rocks are as old as Late Triassic (Norian). The predominantly unimodal Triassic zircon age patterns at localities (8, 8A–C) suggest a depositional basin isolated from continent-derived sediment. In this respect it is a close companion to the Triassic Caples Terrane, which is extensive throughout New Zealand, from Otago to Northland (Adams et al. 2009). Permian and Triassic sediment sources for Waipapa sandstones of appropriate age, extent and composition, are absent in New Zealand. Consequently, a more distant provenance is suggested, which requires either river/marine transport over long distances or depositional basins forming close to the continental margin and then tectonically transported along it as suspect terranes, to their present position. The predominantly coarse lithologies (sandstone–conglomerate) of the Morrinsville Facies would better fit the latter scenario.

The present zircon data support the original conclusions of Pickard, Adams & Barley (2000) and Adams, Campbell & Griffin (2007), and add further detail.

(1) Sources for Triassic sandstones of the Waipapa Terrane were within the southern sector of the New England Orogen of eastern Australia. These supplied dominantly Triassic (and Late Permian) zircons from widespread granitoids dated at c. 235, 250 and 260–270 Ma (see compilations in Veevers, 2000). A minor zircon contribution would have come from Late Devonian–Carboniferous volcanic sequences of the Tamworth Fold Belt. However, unlike Triassic sandstones in the Torlesse Composite Terrane, the depositional basin was isolated from a Precambrian and early Palaeozoic hinterland.

(2) Sources for Jurassic sandstones are more difficult to locate. The required extensive Jurassic volcaniclastic detritus, with contemporary zircons, has no known sources, and the above authors speculated that Jurassic volcanic arcs, possibly northern continuations of the Median Batholith magmatic arc, might lie buried under Cenozoic cover on the Lord Howe Rise or Challenger Plateau. Upper Jurassic volcanic and volcaniclastic sedimentary rocks are found locally within the Fiordland complex of New Zealand and Upper Jurassic plutonic rocks compose a minor proportion of the Median Batholith (Mortimer et al. 1999a; Ewing et al. 2007; Turnbull, Allibone & Jongens, 2010) but their specific occurrence west of the North Island is unproven. The present areal extent of these rocks (< 100 km2) is far less than the probable area of the Waipapa sedimentary basins (> 10000 km2, extending up to 750 km N–S and 150 km E–W). Rocks similar to Palaeozoic granites on the Challenger Plateau (Tulloch, Kimbrough & Wood, 1991) might be the source of the moderate proportions of pre-Permian zircons in the younger Waipapa rocks.

(3) The Cretaceous sandstones probably have sources closer to North Island, with dominant Early Cretaceous zircons coming from the Median Batholith and Permian–Triassic zircons reworked from older Waipapa rocks or a combination of sources from the adjacent Caples and Murihiku terranes to the west (and possibly the Torlesse Composite Terrane to the south). The early Precambrian–Palaeozoic zircons could have sources in the Western Province of New Zealand, but this scenario assumes that the terranes of the Eastern and Western Provinces were juxtaposed by late Early Cretaceous time.

In summary, the Waipapa Terrane includes imbricated remnants of Late Triassic, Late Jurassic and (new from this study) Early Cretaceous depositional basins, all formed as an accretionary wedge that contains older rocks of oceanic association. Arguably, the original Waipapa depositional basins developed at progressively more southerly positions along the Eastern Gondwanaland margin, but all north of present-day New Zealand.

5.b. Comparison with the Pahau and Waioeka terranes of eastern New Zealand

The Cretaceous depositional histories of the Waipapa and Torlesse terranes demonstrate, with some overlap, the last stages of a long-lived Mesozoic accretionary wedge. The depositional environment, structural style, petrographic constitution and detrital zircon record all form a coherent picture of an active convergent margin, in which products of contemporary volcanism are present but are more usually overwhelmed by recycled debris from a Permian–Triassic orogen. To this may be added an interesting mid-Cretaceous (c. 95–105 Ma) sector that is probably recorded in the Waioeka Terrane (Mazengarb & Harris, 1994). Although it records the final stage of the accretionary front, all these sedimentary rocks of Albian age have a radically different provenance: they are principally derived from a Cretaceous magmatic arc and to a lesser extent the Western Province (Adams et al. in press).

The Torlesse Composite Terrane records major sedimentary pulses in the Permian–Triassic (Rakaia Terrane), Jurassic (Kaweka Terrane) and Early Cretaceous (Pahau Terrane). After an initial overwhelming flood of juvenile magmatic debris, each accretionary pulse wanes to a final stage where a ‘background’ of Precambrian–early Palaeozoic, continent-derived sediment becomes dominant in Late Triassic, Late Jurassic and late Early Cretaceous time, respectively.

In the Waipapa Terrane, this sequence is slightly displaced, with a first pulse (linked with that in the Caples Terrane) starting in Late Triassic time. Unlike contemporary Torlesse sediments, Waipapa sediments were derived overwhelmingly from contemporary magmatic sources. There is then an apparent gap in the Early–Middle Jurassic record, but a second phase in Late Jurassic–Early Cretaceous time records the increasing influence of old continent-derived sediments. The termination of the accretionary activity, and hence active-margin convergence, is uncertain but such activity certainly continued until late Aptian time (c. 112 Ma). Within the Waipapa Terrane itself there is no known equivalent of the youngest (< 112 Ma) rocks of the Omaio Facies of the Waioeka Terrane of eastern New Zealand and in fact the latter are more probably represented in the Houhora Complex (Mortimer, 1994).

5.c. Origin of Cretaceous sandstones in the Houhora Complex and Northland Allochthon

In Figure 7, zircon age datasets for Cretaceous sandstones in the Houhora Complex and Northland Allochthon are compared with age equivalents in the East Coast/Wairarapa allochthons and the corresponding Waioeka Terrane autochthon (Adams et al. in press). Also shown here (right column) are all-data histograms for adjacent Triassic–Cretaceous basement rocks of the Murihiku, Caples and Waipapa terranes. These demonstrate clear similarities with histograms for the Cretaceous sandstones in the East Coast and the Wairarapa allochthons and Waioeka Terrane of eastern New Zealand, but they contrast strongly with datasets from their adjacent basement terranes in Northland and Auckland. The contribution of Permian–Triassic zircons is very much reduced at the expense of overwhelming proportions of Cretaceous zircons, and to a lesser extent of Devonian–Carboniferous zircons. Since none of the analysed Cretaceous sandstones are likely to be older than mid-Albian, then the great majority (> 70%) of the Cretaceous zircons i.e. those > 105 Ma, must be recycled.

In the Houhora Complex, the Tokerau Facies sandstones (1–3) have the youngest (and dominant) Albian zircon components at 102, 103 and 108 Ma. These are in good agreement with a zircon age of 101.6 ± 0.1 Ma for an ignimbrite within the associated Rangiawhia Volcanics (Tulloch et al. 2009; zircons in this study were abraded to remove outer rims and thus may not record the youngest crystallization age). Although these felsic volcanic rocks are only extremely local (a few square kilometres in area), they must formerly have been more extensive to contribute an important contemporary sediment component into the Houhora Complex, which is thought to extend at least from Mt Camel to Three Kings Islands. The remainder of the Cretaceous zircons (> 108 Ma) have age components at c. 110, 118 and 130 Ma, similar to those found in the youngest sandstones of the Waipapa, Pahau and Waioeka terranes and, like them, may be derived from the Median Batholith. Such a provenance would then allow some small additional contributions from adjacent Devonian–Carboniferous granitoids in the Western Province and older zircons from their hinterland. The small proportion of Permian–Triassic zircons is more difficult to source. A provenance in the Caples Terrane (Fig. 7) is possible but by itself would not contribute any Precambrian–early Palaeozoic zircons. Waipapa Terrane sources are also possible but they would bring with them Jurassic and Precambrian–early Palaeozoic zircons that are not well represented in the patterns. This leaves the Murihiku Terrane as a likely source (Fig. 7); its depositional basins are overwhelmingly comprised of volcaniclastic successions that include felsic compositions, especially in the Late Triassic–earliest Jurassic and Late Jurassic intervals. If this is the case, then the Houhora Complex Cretaceous depositional basin received (1) local Albian felsic volcanic and volcaniclastic inputs, and then from a westerly direction (2) sediment from the Median Batholith and its immediate Western Province hinterland (Cretaceous and Palaeozoic, respectively) and (3) minor inputs from the Murihiku Terrane (and possibly Triassic Caples Terrane). This Northland scenario differs slightly from that proposed (Adams et al. in press) for contemporary mid-Cretaceous rocks of the Waioeka Terrane and East Coast/Wairarapa allochthons to the south in eastern New Zealand. While the Median Batholith still dominates there as a source of zircons, the proportion of Carboniferous–Devonian zircons is slightly larger and that of Permian–Jurassic zircons is slightly smaller. Adams et al. (in press) reconciled this pattern with a major privileged and short-lived (Albian) W-to-E sediment corridor between northern and southern Zealandia.

5.d. Origin of Cretaceous sandstones in the Northland Allochthon

Unlike the Houhora Complex, there is no record in the Northland Allochthon of contemporary Albian silicic, i.e. zircon-bearing, volcanism equivalent to the Rangiawhia Volcanics. The sparse fossil evidence from the Punakitere Sandstone suggests a rather younger and longer depositional history, probably spanning early Late Cretaceous (Cenomanian–Santonian) time (100–83 Ma) (Isaac, 1996, and pers comm.). Sandstones from this formation have Cretaceous zircon age components predominantly at c. 110, 118 and 130 Ma, similar to those from the Houhora Complex but significantly, the Northland Allochthon patterns also includes a single youngest component at 96 ± 4 Ma (5). The great majority of the Cretaceous zircons are thus clearly recycled and not derived from contemporary volcanism. Their origin therefore follows that proposed for the Houhora Complex (Section 5.c above) with the small exception that the Northland Allochthon has a larger proportion of early Early Cretaceous zircons (145–130 Ma). This feature is similar to the Omaio Facies (Barremian–Aptian) of the Waioeka Terrane (Adams et al. in press) and probably reflects exhumation of Cretaceous parts of the Median Batholith, older than those exhumed for the Houhora Complex.

In the far north of the Northland Allochthon, at Paua Road, Parengarenga Harbour (4), an upper Upper Cretaceous (Campanian, < 83 Ma) sandstone shows a zircon age pattern (Fig. 5) that is dramatically different from those in the Punakitere Sandstone (above) but better matches contemporary Coniacian–Campanian sandstones in the cover successions of eastern New Zealand in Marlborough and Raukumara (Adams et al. in press). It contains no Cretaceous zircons at all (Figs 3, 5) and the resultant pattern, comprising 100% reworked zircons, offers a rare glimpse of the pre-Cretaceous basement hinterland. The zircon ages spread across the Permian–Jurassic range in a manner seen only in datasets from the Murihiku Terrane (Fig. 7), and additionally demonstrates a possible Western Province source for the small group of Carboniferous–Late Devonian zircons with age peaks at 306, 343, 348 and 363 Ma. Most importantly, this sample dataset implies that the earlier dominant Median Batholith sources were completely closed off at that time and place. While residual uplands of the Murihiku Terrane seem to have persisted into late Late Cretaceous time, it is likely that initial opening of the Tasman Sea at 83 Ma was accompanied by internal rifting close to the western Zealandia margin, which was sufficient to disrupt previously established access to Median Batholith sediment sources.

5.e. Cretaceous palaeogeography of northern New Zealand

The Cretaceous was a time of changing tectonic regime in New Zealand. On the East Coast of North Island, Adams et al. (in press) have shown similarities in detrital zircon age patterns between the youngest Torlesse Composite Terrane (Omaio Facies of Waioeka Terrane) and Cretaceous sandstones of the East Coast Allochthon. The latter, like the Northland Allochthon, is a Cretaceous–Oligocene mafic volcanic and sedimentary assemblage that formed in a marginal basin off Zealandia and was emplaced onto Zealandia in the earliest Miocene. Adams et al. (in press) particularly drew attention to the dominance of Cretaceous zircons over Permian–Triassic and Precambrian–early Palaeozoic groups and the distinctive presence of a group of Devonian–Carboniferous ages. These features suggest a more westerly source than previously anticipated, mostly in the Median Batholith and its immediate hinterland. In this regard, similarities can also be drawn between the detrital zircon age patterns seen in the Cretaceous rocks of the Houhora Complex, Northland Allochthon and the aforementioned East Coast North Island units, and similar sources seem likely.

A further inference is that the Kaweka, Rakaia and Waipapa terranes, the central Permian–Jurassic ‘core’ of the Eastern Province in the North Island, do not seem to have contributed zircons to the Cretaceous rocks in the allochthons, which are instead dominated by Cretaceous zircons. Our new data and results are thus in agreement with earlier work (e.g. Cluzel et al. 2010a,b) that has pointed out many similarities in the lithological and petrological content of the East Coast and Northland allochthons, and with Mortimer (1994) who proposed sources like the Houhora Complex for conglomerate clasts in the Omaio Facies of the Waioeka Terrane and the East Coast Allochthon. Our new detrital zircon age data do not provide a test of a subduction (Nicholson, Black & Spörli, 2008) versus an intra-plate (Tulloch et al. 2009) origin for the Houhora Complex, nor of how allochthonous the Houhora Complex (in the absence of contact relations) really is (Toy & Spörli, 2008). Some detrital linkage of the Houhora Complex with Zealandia is required because there are small proportions of Jurassic, Triassic–Permian, Carboniferous–Devonian and a few Precambrian zircons (Fig. 6). However, the proportions of these minor components suggest a source different from that supplying the contemporary Eastern Province accretionary wedge (Caples, Waipapa and Torlesse terranes).

Figure 8 shows a speculative palaeogeographic model in which the 102 Ma Houhora Complex extends along the Zealandia continental margin in present-day northern New Zealand. A marginal basin is situated offshore of this and extends along the present-day eastern part of the North Island. Receiving sediment reworked from the Houhora Complex and Median Batholith, this basin becomes the site of deposition of sedimentary rocks of the Northland and (possibly) East Coast allochthons (sub-basin A in Fig. 8). An important aspect here is that by 105 Ma, the long-lived major Zealandia magmatic source of igneous zircons (the Median Batholith) has become extinct. The narrowing arc-trench gap in the left of Figure 8, compared with that shown on the right, implies the absence of most of the strike width of the Eastern Province terranes in Northland. This may explain the lack of Waipapa- and Torlesse-derived zircons in the younger Cretaceous sandstones of the allochthons. This latter feature led Adams et al. (in press) to conclude that zircon origins in the Median Batholith and Western Province that were implied for mid-Cretaceous sediments in the Wairarapa/East Coast allochthons could only be supplied along a privileged corridor between northern and southern Zealandia to sub-basin B in Figure 8.

Figure 8. A palaeogeographic reconstruction of Zealandia in relation to the Eastern Gondwanaland margin during late Albian to early Campanian time, c. 99–83 Ma. During this period, the Houhora Complex (solid triangle denotes 102 Ma volcanism) and associated volcaniclastic sedimentary rocks (light grey) were eroding and providing input into a sedimentary basin (sub-basin A) that is now only represented within the Northland Allochthon. Other significant basement terranes exposed and providing sediment at this time were the Murihiku Terrane (Eastern Province), an extinct and diminishing Median Batholith and possibly parts of the Western Province (see solid sediment transport arrows). Contemporaneous sedimentary basins in the Waioeka Terrane of Raukumara and the East Coast Allochthon and Wairarapa Allochthon (sub-basin B) have diminished inputs from the Murihiku Terrane, and Adams et al. (in press) suggested alternative sediment origins for these in the Median Batholith and Western Province along a short-lived restricted transport corridor between north and south Zealandia.

6. Conclusions

New detrital zircon age determinations are presented here for 14 sandstones of mainly Cretaceous age from northern North Island New Zealand. The results provide confirmation of previous interpretations. Most significantly, they also establish a previously unrecognized record of Cretaceous sedimentation within the Waipapa Terrane.

On the basis of fossil and detrital zircon ages, clastic terrigenous sand deposition in the Waipapa Terrane appears to span c. 115 Ma of Mesozoic time, from the Late Triassic (early Norian) to Early Cretaceous (late Aptian; 227–112 Ma). However, as yet there is no evidence for deposition during Early–Middle Jurassic time. The Late Jurassic–Early Cretaceous component of Waipapa Terrane deposition fills an apparent time gap between the youngest Kaweka Terrane (Tithonian) and the oldest Pahau Terrane (Barremian).

Analysis of the detrital zircon age data provides constraints on the Mesozoic palaeogeographic history of the Waipapa Terrane and the northern North Island Zealandia segment of the Eastern Gondwanaland margin. The following key conclusions are drawn:

Triassic sandstones in the Waipapa Terrane are derived largely from sources in the southern New England Orogen of eastern Australia. Detrital zircon age components, and hence granitoid parent rocks, are notable at c. 235, 250 and 260–270 Ma.

Jurassic sandstones in the Waipapa Terrane may be derived from Median Batholith sources that are now buried beneath younger deposits on the Challenger Plateau and Lord Howe Rise.

Cretaceous sandstones in the Waipapa Terrane are derived from multiple sources within Eastern Province terranes (including older Waipapa Terrane), the Median Batholith and the Western Province.

Both facies recognized within the Waipapa Terrane demonstrate similar Jurassic provenance and age trends. Previously unsuspected large areas of (unfossiliferous) Hunua Facies are probably Late Triassic in age.

Cretaceous sandstones in the Northland Allochthon accumulated during Cenomanian to Santonian time (100–83 Ma); dominant Cretaceous detrital zircon age peaks at 110, 118 and 130 Ma reflect significant reworking and, for the most part, a common provenance with the Houhora Complex. Zircon age patterns reflect several probable sources for the Northland Allochthon: local contemporary Albian volcanism, the Median Batholith and Western Province, and to a lesser extent the Murihiku Terrane (and possibly Caples Terrane). Jurassic and early Early Cretaceous (145–130 Ma) zircons are more abundant in the Northland Allochthon than in the Houhora Complex, a feature similar to the Barremian–Aptian Omaio Facies of the Waioeka Terrane.

Cretaceous sandstones in the Houhora Complex (Tokerau Facies) are younger than mid-Albian (105 Ma) yet the great majority (> 70%) of Cretaceous zircons are older than 105 Ma and must thus be recycled. Zircon age patterns reflect multiple sources: local contemporary Albian volcanism, the Murihiku Terrane (and possibly Caples Terrane), the Median Batholith and the Western Province.

There are important similarities in detrital zircon age patterns for the allochthons considered herein: Northland, East Coast and Wairarapa, which all indicate similar Cretaceous sediment sources principally in the Median Batholith and the adjacent Western Province. The Houhora Complex also exhibits much in common with these allochthons and this suggests that it is also probably allochthonous.

Acknowledgements

This is contribution 28 from the ARC Centre of Excellence for Core to Crust Fluid Systems (www.CCFS.mq.edu.au) and contribution 763 from the GEMOC Key Centre (Geochemical Evolution and Metallogeny of Continents) (www.gemoc.mq.edu.au) at Macquarie University, Sydney. The analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS, industry partners and Macquarie University. Drs Norman Pearson and William Powell are thanked for their technical assistance at the GEMOC. The analytical data were obtained using instrumentation funded by the DEST Systemic Infrastructure Grants, ARC, LIEF, NCIRS, industry partners and Macquarie University. The authors also wish to acknowledge their QMAP colleagues’ enthusiastic and wise advice, particularly Mark Rattenbury, John Begg, Steve Edbrooke, Mike Isaac, Julie Lee and Andy Tulloch. Philippa Black is also thanked for the donation of samples from Three Kings Islands. This paper benefitted from external referees including Peter Kamp and an anonymous reviewer. This research was funded by the New Zealand Foundation for Research Science and Technology.

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