Ferrar Province Research Articles

Sr, Nd, Pb, and Os Isotope Systematics and Derivation of Mesozoic Plume-Related Basalts of Antarctica: Karoo-Maud and Kerguelen Plume Realm

The study of Re–Os isotopic systematics of the Mesozoic magmas in East Antarctica and its comparison with Sr–Nd–Pb–Os published data allowed us to reveal the main features of Antarctic magmatism associated with the activity of the Karoo–Maud (Dronning Maud Land (DML), Karoo and Ferrar provinces) and the Kerguelen (Lambert rift area) plumes. It is shown that a melt source of the 180-Ma Karoo–Maud plume could be enriched lithospheric mantle. Variations of the 187Os/188Os ratio in the range of 0.1242–0.1426 characterize almost all types of melts in the Karoo and DML provinces, including both high- and low-Ti magmas as well as high-Mg ferropicrites produced by melting of mantle pyroxenite. This observation is consistent with previous assumption that magmas derived from pyroxenite mantle at the initial stage of plume impact represented melts of deep lithospheric fragments of ancient Gondwana paleocontinent that were entrapped by plume. Thereby, mantle heterogeneity recorded in the Nd–Pb–Sr isotopic compositions of the basalts is not expressed in the systematic variations of Re–Os isotope system. The magmatic source of the basalts of the Ferrar province differs from the source of Mesozoic magmatism in the Karoo and DML provinces by great variations in the 187Os/188Os ratio: from 0.1 to 0.31, and by the lower osmium contents, with limited variations of other isotopic systems, indicating an admixture of enriched EM-II source. This is consistent with inferred subduction reworking of the mantle of the western Antarctic margin (Sushchevskaya et al., 2022). Ultramafic picritic magmas from the Lambert Glacier area are characterized by a radiogenic osmium isotopic composition: 187Os/188Os 0.1582–0.2388. Source of these magmas could be ancient depleted mantle, which later experienced mantle metasomatism due to the multiple interactions with fluid-saturated melts. Picritic melts of the paleorift zone of the Lambert Glacier are close to a magma source of the Karoo and DML provinces in terms of Sr-Nd isotopic composition, but differ in more radiogenic lead.

Do spores herald the Toarcian Oceanic Anoxic Event?

The environmental perturbations of the Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) were associated with the widespread deposition of black shales, such as the Posidonia Shale Formation in southwest Germany. We recently published a detailed palynological analysis of the deposits of the Posidonia Shale Formation at Dormettingen, investigating pollen, spores, and marine plankton. In addition to the comprehensive palynological analysis, we point out the occurrence of possible teratological features (i.e. unseparated spore tetrads and dark-coloured sporomorphs) before the T-OAE. These features have been tentatively linked to environmental changes, such as increased UV-B irradiation or heavy metal pollution associated with the large-scale volcanism of the Karoo Ferrar province (Galasso et al., 2022). Our interpretation has drawn criticism (Riding et al., 2022). Here we present a more substantiated discussion of why spore tetrads and darkened spores might not be sedimentological artefacts but indicators of aggravating environmental conditions prior to the T-OAE. The combined occurrence of several teratomorphic features (i.e. spore tetrads, dark sporomorph walls, and even polyploidy) during the earliest Toarcian (Tenuicostatum Zone) is interpreted as a signal of environmental stress in land plants, although for each individual morphological variation a much easier explanation exists.

The age and palaeomagnetism of Jurassic dykes, western Dronning Maud Land: implications for Gondwana breakup

Abstract New 40 Ar/ 39 Ar data from dykes intruded into Sverdrupfjella and Ahlmanryggen, Dronning Maud Land, Antarctica, indicate that dyke emplacement commenced at c. 207 Ma and lasted until c. 178 Ma. Whereas the ages ascribed to the Karoo-age magmatism contributing to Gondwana breakup are typically inferred as being c. 182 Ma, the data indicate that ages older than c. 192 Ma in the broader Karoo Province are restricted to western Dronning Maud Land, Antarctica, indicating the locality where breakup was initiated. Limited palaeomagnetic data from c. 178–185 Ma dykes combined with published palaeomagnetic data from similar-aged dykes in Vestfjella and the Ferrar Province, suggest that Antarctica had already drifted/rifted significantly away from southern Africa from c. 207 to c. 180 Ma, earlier than previously thought. The data, if correct, require a re-evaluation of the ages ascribed to ocean-floor anomalies used to constrain reconstructions of Gondwana and may provide insight into the history of microcontinental blocks including the Falkland Islands, Haag nunataks, Ellsworth–Whitmore block and Maurice Ewing Bank. Supplementary material: Petrography, Ar isotope data from all samples and summary of ages are available at https://doi.org/10.6084/m9.figshare.c.5612838

The Ferrar Large Igneous Province: field and geochemical constraints on supra-crustal (high-level) emplacement of the magmatic system

Abstract The Ferrar Large Igneous Province forms a linear outcrop belt for 3250 km across Antarctica, which then diverges into SE Australia and New Zealand. The province comprises numerous sills, a layered mafic intrusion, remnants of extensive lava fields and minor pyroclastic deposits. High-precision zircon geochronology demonstrates a restricted emplacement duration (<0.4 myr) at c. 182.7 Ma, and geochemistry demonstrates marked coherence for most of the Ferrar province. Dyke swarms forming magma feeders have not been recognized, but locally have been inferred geophysically. The emplacement order of the various components of the magmatic system at supra-crustal levels has been inferred to be from the top-down lavas first, followed by progressively deeper emplacement of sills. This order was primarily controlled by magma density, and the emptying of large differentiated magma bodies from depth. An alternative proposal is that the magma transport paths were through sills, with magmas moving upwards to eventually reach the surface to be erupted as extrusive rocks. These two hypotheses are evaluated in terms of field relationships and geochemistry in the five regional areas where both lavas and sills crop out. Either scenario is possible in one or more instances, but neither hypothesis applies on a province-wide basis.

High-resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian–Toarcian ammonites (Cephalopoda)

Abstract: The Pliensbachian–Toarcian interval was marked by major environmental disturbances and by a second-order mass extinction. Here, we reappraise the taxonomic, spatiotemporal and selective dynamics of extinctions over the whole interval, by analysing a high-resolution dataset of 772 ammonite species from NW Tethyan and Arctic domains. On average, 40–65% of ammonite species disappeared during each subchronozone, but higher extinction pulses (reaching 70–90%) prevailed from the Margaritatus to the Dispansum Chronozone. The main extinctions, corresponding to the Gibbosus, Pliensbachian–Toarcian boundary, Semicelatum, Bifrons–Variabilis, and Dispansum events, differed in their dynamics, suggesting episodes of ecological stress related to climate change, regression, disturbance in the carbon cycle or anoxia. The multi-pulsed volcanic activity in the Karoo–Ferrar province could well have triggered these ecological changes. In addition, ammonites experienced a morphological bottleneck during the Gibbosus event, 1 Ma before the Early Toarcian diversity collapse. Typically, drops in richness were related both to high extinctions and to declines in origination rates. This feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances. After the Early Toarcian crisis, the recovery of ammonites was rapid (2 Ma) and probably influenced by a coeval marine transgression. Supplementary material: Figures showing a comparison of extinction and origination patterns based on different datasets, and variations of the morphospace occupation are available at http://www.geolsoc.org.uk/SUP18381 .

Coal-fragment rank and contact relationships of debris avalanche and primary pyroclastic deposits in the Mawson Formation, Ferrar LIP, Allan Hills, Antarctica

Mafic volcaniclastic deposits are known from many large igneous provinces, and are generally ascribed to explosive phreatomagmatic activity that modifies the climatic effects of flood-basalt volcanism. The volcaniclastic deposits occur both as vent-complex infills and as more widely dispersed deposits that may be strongly localized in pre-LIP topography. At Allan Hills, in the Ferrar Province of Antarctica, mafic volcaniclastic deposits are separated from country rock of the Beacon Supergroup by country rock-derived sandstone breccias. These are coarse, monomict and matrix-poor near the contact, grade upward to polymict breccias derived from several country rock units, and are overlain by mafic volcaniclastic deposits. Fragments of Beacon coal show progressively higher rank away from the country rock contact, interpreted to indicate heating by basaltic fragments in the volcaniclastic deposits. The sequence overall is inferred to represent volcaniclastic deposits overlying a debris–avalanche deposit, with damaged in situ country rock at the base of the avalanche. Rocks in this area lie along one margin of volcaniclastic deposits extending over tens of kms 2. Relationships among them are a reminder that analysis of contact zones is critical to establishing the origin and context of LIP volcaniclastic deposits.

Geological evolution of the Coombs–Allan Hills area, Ferrar large igneous province, Antarctica: Debris avalanches, mafic pyroclastic density currents, phreatocauldrons

The Jurassic Ferrar large igneous province of Antarctica comprises igneous intrusions, flood lavas, and mafic volcaniclastic deposits (now lithified). The latter rocks are particularly diverse and well-exposed in the Coombs–Allan Hills area of South Victoria Land, where they are assigned to the Mawson Formation. In this paper we use these rocks in conjunction with the pre-Ferrar sedimentary rocks (Beacon Supergroup) and the lavas themselves (Kirkpatrick Basalt) to reconstruct the geomorphological and geological evolution of the landscape. In the Early Jurassic, the surface of the region was an alluvial plain, with perhaps 1 km of mostly continental siliciclastic sediments underlying it. After the fall of silicic ash from an unknown but probably distal source, mafic magmatism of the Ferrar province began. The oldest record of this event at Allan Hills is a ≤ 180 m-thick debris-avalanche deposit (member m 1 of the Mawson Formation) which contains globular domains of mafic igneous rock. These domains are inferred to represent dismembered Ferrar intrusions emplaced in the source area of the debris avalanche; shallow emplacement of Ferrar magmas caused a slope failure that mobilized the uppermost Beacon Supergroup, and the silicic ash deposits, into a pre-existing valley or basin. The period which followed (‘Mawson time’) was the main stage for explosive eruptions in the Ferrar province, and several cubic kilometres of both new magma and sedimentary rock were fragmented over many years. Phreatomagmatic explosions were the dominant fragmentation mechanism, with magma–water interaction taking place in both sedimentary aquifers and existing vents filled by volcaniclastic debris. At Coombs Hills, a vent complex or ‘phreatocauldron’ was formed by coalescence of diatreme-like structures; at Allan Hills, member m 2 of the Mawson Formation consists mostly of thick, coarse-grained, poorly sorted layers inferred to represent the lithified deposits of pyroclastic density currents. Meanwhile at Carapace Nunatak, mafic clasts were mixed with detrital material to form the Carapace Sandstone in alluvial and eventually lacustrine environments. Eruptions then became largely effusive, producing hundreds of metres of flood lavas that covered the landscape (‘Kirkpatrick time’). In places, lava flowed into ephemeral lakes to form pillow-palagonite breccias (base of sequence, Carapace Nunatak) or pillow lavas (top of sequence, Coombs Hills). Several generations of Ferrar intrusions were emplaced during the course of these events; at least three can be distinguished based on field relations. New geochemical data indicates that for the Ferrar province, magma involved in the explosive eruptions had the same major element composition as that which produced shallow intrusions and lavas. We also note the possibility that flood lavas were fed by plugs cross-cutting the Mawson Formation at Coombs Hills, rather than by major dikes extending to the surface. Finally, we infer that eruption plumes were limited to the troposphere and that direct environmental impacts were thus likely restricted to the southern hemisphere.

Physical volcanology and geological relationships of the Jurassic Ferrar Large Igneous Province, Antarctica

The Ferrar Large Igneous Province forms a linear belt for 3500 km along the Transantarctic Mountains, and as a geochemical province extends into southeastern Australasia. The principal components of the Ferrar are: intrusive — Ferrar Dolerite sills and dikes, and Dufek intrusion; pyroclastic — the Prebble, Mawson and Exposure Hill Formations; effusive — the Kirkpatrick Basalt. In terms of the three dimensional architecture of the Ferrar, a range of “facies” can be recognized in each of the principal components. The Ferrar province was initiated with a major episode of phreatomagmatism leading to formation of tephra cones and associated deposits, and near-surface vent structures. Activity switched to predominantly quiet effusion of alternating thick flood basalt flows and thin pahoehoe lobes and flows. Intrusive bodies were emplaced early, given the occurrence of dolerite clasts in tuff–breccias, but most sills were probably intruded after accumulation of extrusive rocks. Pre-existing rift structures played a major role in controlling the transport and distribution of the Ferrar magmas and the apparent centers of extrusive activity. The associated paleohydrology controlled the eruption styles.

Early stages of Gondwana breakup: The 40Ar/39Ar geochronology of Jurassic basaltic rocks from western Dronning Maud Land, Antarctica, and implications for the timing of magmatic and hydrothermal events

The timing of magmatic events forming Jurassic basaltic rocks in Dronning Maud Land (DML), Antarctica, and hydrothermal activity that affected them is addressed with detailed 40Ar/39Ar incremental heating dating of feldspars. Plagioclase from an Utpostane gabbro and from a Kirwanveggen dolerite dike yield indistinguishable plateau ages at 177 ± 1.8 Ma. Because of geologic controls, this establishes the age of tholeiites in Vestfjella. These plateau ages demonstrate synchroneity of tholeiitic magmatism of both DML and the well‐documented Ferrar Province of Antarctica, which together with the closely temporal Karoo constitute the Gondwana breakup magmatism. Vug‐filling microclines from Vestfjella yield plateau ages of 150 and 139 Ma which are interpreted to give the ages of secondary mineralization events. These results suggest a lengthy period of extension, possibly accompanied by pervasive low‐temperature hydrothermal activity, between flood basalt magmatism and inception of seafloor spreading (circa 160–165 Ma), with younger moderate temperature events recorded by K‐feldspars and related to early stages of spreading and/or changes in plate motions. The majority of plagioclase samples yield discordant age spectra that reflect primarily overprinting by younger events and incorporation of excess Ar, and they illustrate the complexities that can be produced.

Ultramafic lamprophyres of the Ferrar large igneous province: evidence for a HIMU mantle component

Ultramafic lamprophyre (UML) dykes from the Ferrar Province (Pensacola Mountains) of Antarctica preserve trace element and isotope signatures similar to Bouvet volcanic rocks, which are considered to reflect the palaeo composition of the Bouvet mantle plume. We report Sr, Nd, Pb, and Os isotope compositions for three ultramafic lamprophyre dykes emplaced at 183.2±2.2 Ma, coincident with the main Karoo–Ferrar magmatic event. The ultramafic lamprophyre dykes are characterized by high Ti, Cr, Ni, Nb/La, La N/Yb N, and Mg# values, and are the most primitive rocks of the Ferrar Province. The dykes have initial (183 Ma) 87Sr/ 86Sr ratios of 0.7044–0.7055, εNd of 4.6–4.8, 208Pb/ 204Pb of 39.6–40.3, and 187Os/ 188Os of 0.120–0.146 and contrast markedly with even the most primitive rocks of the Ferrar and Karoo provinces. The trace element and isotope characteristics have affinities to ocean island basalt (OIB) and the highly radiogenic character of 208Pb/ 204Pb and 206Pb/ 204Pb bear closest resemblance to Bouvet, which has previously been postulated as the plume responsible for the Ferrar Province. The ultramafic lamprophyres are believed to be the result of melting enriched Bouvet mantle plume material and represent one of the mantle end members in the Karoo–Ferrar province.

On the origin of Tasmanian dolerites

The Tasmanian dolerites, part of the Ferrar Province of Australia and Antarctica, have some trace‐element and isotopic compositions that suggest continental contamination of mantle‐derived magmas. The debate has centred on whether the contamination occurred during intrusion into the crust, or if the mantle source itself was contaminated. The behaviour of Sr and O isotopes suggests that the mantle source had a δ18O composition of +6‰ and an initial 87Sr/86Sr ratio of 0.709, which supports the latter contention. Recently published Re–Os data likewise dismiss upper crustal contamination: Re–Os isotopic compositions of magnetite‐rich mineral separates from seven Tasmanian dolerites yield an isochron that gives the same age, within uncertainties, as other dating techniques, namely 175 ± 5 Ma. Moreover, Re–Os data from a study of Antarctic Ferrar Province samples lie on the same isochron and the data together give an age of 177.3 ± 3.5 Ma. The initial 187Os/188Os of 0.125 ± 0.033 is the calculated mantle composition at the time. These results support previous models that attribute chemical features of the Ferrar magmas to re‐enrichment of a depleted mantle source region rather than processes involving assimilation of crust by basaltic magma.

Mesozoic dolerite dykes of the Falkland Islands: petrology, petrogenesis and implications for geochemical provinciality in Gondwanaland low-Ti basaltic rocks

The dolerite dykes of central West Falkland provided the first palaeomagnetic evidence of the near-180° rotation of the islands during the break-up of Gondwanaland. Here we present the results of a petrological and geochemical study of those dolerites. Most of the dykes sampled can be assigned to one of two suites named north-south and east-west respectively in recognition of their dominant strike. E–W dykes have compositional affinities with magmas such as the Rooi Rand dolerites of SE Africa whose geochemical characteristics (e.g. 87 Sr/ 86 Sr<0.704) are suggestive of predominantly asthenospheric mantle derivation. N–S dykes, which are the most numerous, resemble the Ferrar magma type of Antarctica and the rare Hangnest and Kraai River magma types of the Karoo. The N–S dykes evolved by assimilation and fractional crystallization (AFC), most likely at crustal levels, leading to initial 87 Sr/ 86 Sr=0.708–0.712, but there is no compelling evidence for initial 87 Sr/ 86 Sr<0.708, perhaps suggesting an enriched lithospheric mantle source. Dykes from Lively Island and Mount Alice appear to be correlatives of other Karoo magma types. All the Falklands dykes are low-Ti in character. However, within this one small area a variety of Karoo low-Ti magma types coexist with the Ferrar magma type of Antarctica. This overlap in space of different low-Ti magma types resembles the situation in Coats Land, Antarctica and enables us to propose an extension of the boundary of the Ferrar province parallel to the subducting margin of Gondwanaland.

An active mantle mechanism for Gondwana breakup : Storey B.C. & Kyle P.R., South African Journal of Geology, 1997, 100/4 (283–290)

Despite over thirty years of plate tectonic theory, the reasons why supercontinents like Gondwana disintegrate into smaller continents and disperse remain enigmatic. Current ideas mostly involve changes in plate-boundary driving forces (passive mantle hypothesis) in preference to an active plume mechanism, even though mantle plumes were present at most stages of Gondwana breakup. The role of these plumes in the breakup process is uncertain, and ideas vary from the chance unroofing of a pre-existing plume, which only contributed in the production of extensive flood basalts, to plumes that controlled the position of breakup. The magmatic and tectonic record along the proto-Pacific margin of Gondwana indicates that there were important changes in subduction zone forces during the initial stages of Gondwana breakup. However, the absence of subduction along the Neotethyan margin at the time of breakup, together with the fact that the initial rift formed almost at right angles to the active subducting margin, suggest a potential active role for a mantle plume in the initial separation. An active mantle mechanism, involving a very large thermal disturbance or megaplume, may, in contrast to a passive mantle hypothesis, more readily explain the formation and rotation of microplates in the South Atlantic region. It accounts also for the production of unusually large igneous provinces (Chon Aike province in Patagonia, Karoo province in southern Africa, and Ferrar province in Antarctica) just prior to breakup.

The timing and duration of the Karoo igneous event, southern Gondwana

A volcanic event of immense scale occurred within a relatively short period in early Jurassic time over large regions of the contiguous Gondwana supercontinent. In southern Africa, associated remnants of thick volcanic successions of lava flows and extensive dike and sill complexes of similar composition have been grouped together as the Karoo Igneous Province. Correlative volcanic and plutonic rocks occur in Antarctica and Australia as the Ferrar Province. Thirty‐two new 40Ar‐39Ar incremental heating experiments on feldspars and whole rocks from Namibia, South Africa and East Antarctica produce highly resolved ages with a vast majority at 183±1 Ma and a total range of 184 to 179 Ma. These are indistinguishable from recent, high‐resolution 40Ar‐39Ar and U‐Pb age determinations reported from the Antarctic portion of the province. Initial Karoo volcanism (Lesotho‐type compositions) occurred across the entire South African craton. The ubiquitous distribution of a plexus of generally nonoriented feeder dikes and sills intruding Precambrian crystalline rocks and Phanerozoic sediments indicates that these magmas penetrated the craton over a broad region. Lithosphere thinning of the continent followed the main pulse of igneous activity, with volcanism focused in the Lebombo‐Nuanetsi region, near the eventual split between Africa and Antarctica. Seafloor spreading and dispersion of east and west Gondwana followed some 10–20 m.y. afterward. The volume of the combined Karoo‐Ferrar province (∼2.5×106 km3) makes it one of the largest continental flood basalt events. The timing of this event correlates with a moderate mass extinction (Toarcian‐Aalenian), affecting largely marine invertebrates. This extinction event was not as severe as those recorded at the Permian‐Triassic or Cretaceous‐Tertiary boundaries associated with the Siberian and Deccan flood basalts events, respectively. The difference may be due to the high southerly latitude and somewhat lower eruption rates of the Karoo event.

Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology

Research Article| February 01, 1995 Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology N. Mortimer; N. Mortimer 1Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand Search for other works by this author on: GSW Google Scholar D. Parkinson; D. Parkinson 2Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand, and Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar J. I. Raine; J. I. Raine 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar C. J. Adams; C. J. Adams 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar I. J. Graham; I. J. Graham 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar P. J. Oliver; P. J. Oliver 4Peter Oliver & Associates, P.O. Box 40–482, Upper Hutt, New Zealand Search for other works by this author on: GSW Google Scholar K. Palmer K. Palmer 5Analytical Facility, Victoria University, P.O. Box 600, Wellington, New Zealand Search for other works by this author on: GSW Google Scholar Author and Article Information N. Mortimer 1Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand D. Parkinson 2Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand, and Department of Geological Sciences, University of California, Santa Barbara, California 93106 J. I. Raine 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand C. J. Adams 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand I. J. Graham 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand P. J. Oliver 4Peter Oliver & Associates, P.O. Box 40–482, Upper Hutt, New Zealand K. Palmer 5Analytical Facility, Victoria University, P.O. Box 600, Wellington, New Zealand Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1995) 23 (2): 185–188. https://doi.org/10.1130/0091-7613(1995)023<0185:FMPRDI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation N. Mortimer, D. Parkinson, J. I. Raine, C. J. Adams, I. J. Graham, P. J. Oliver, K. Palmer; Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology. Geology 1995;; 23 (2): 185–188. doi: https://doi.org/10.1130/0091-7613(1995)023<0185:FMPRDI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract On the basis of similar ages, major and trace element concentrations, and Sr, Nd, and Pb isotopic ratios, we correlate the Kirwans Dolerite of western New Zealand with Jurassic low-Ti tholeiites of the well-known Ferrar magmatic province of Gondwana. Field relations and preliminary paleomagnetic data also support this correlation. Although the 1 km2 Kirwans Dolerite is the first, and so far only, Ferrar correlative to be reported from New Zealand, it considerably increases the known shape and areal extent of the Ferrar province to close to the paleo-Gondwana margin. The presence of Ferrar rocks in New Zealand can be used to test several models of Ferrar magma genesis and Gondwana regional tectonics. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A short interval of Jurassic continental flood basalt volcanism in Antarctica as demonstrated by [formula omitted] geochronology

A continental flood basalt province, the Ferrar Group (Kirkpatrick Basalt and Ferrar Dolerite), crops out along 3000 km of the Transantarctic Mountains in Antarctica and is temporally related to the break-up of Gondwanaland. Although a wide range of dates, between 90 and 193 Ma, have been published for the Kirkpatrick Basalt, it is now recognized that the young dates reflect non-ideal behavior of Ar in the matrix. In order to refine the geochronology, feldspar separates have been analyzed by the 40 Ar 39 Ar incremental heating method. The main objectives are to constrain the duration of extrusive activity and the timing of volcanism along the outcrop belt. Basalt samples have been studied from the three principal outcrop areas, yielding the following apparent ages: central Transantarctic Mountains 176.8 ± 0.5 Ma; south Victoria Land 176.4 ± 0.4 Ma; north Victoria Land 176.6 ± 0.7 Ma. Ages from different stratigraphic levels within each area and from the three different areas are not analytically distinct. The data imply that the eruptive activity which produced the Kirkpatrick Basalt occurred within a short interval of less than about 1 m.y. at 176.6 ± 1.8 Ma, over an area which included more than 1200 km of the Transantarctic Mountains. The Jurassic volcanism in Antarctica represents a short episode of magmatism, comparable in duration with other well dated continental flood basalt provinces. The linearly extensive outcrop of the Ferrar Province and the rapid eruption of the lavas suggests that lithospheric stretching exerted a major control on magmatism. The poorly constrained age of the Bajocian-Bathonian boundary makes the previously suggested connection between Ferrar volcanism and an extinction event at that boundary uncertain.