Cretaceous Of Gondwana Research Articles

Phylogenetic nomenclature of Notosuchia (Crocodylomorpha; Crocodyliformes)

Notosuchia is a large and diverse clade of Mesozoic crocodyliforms that thrived in continental environments especially during the Cretaceous of Gondwana. This clade has been the focus of several phylogenetic studies that led to the consensus of two main topological arrangements, mostly differing in the position of the clade Sebecidae: the sebecosuchian and sebecian hypotheses. In this manuscript we review the main phylogenetic definitions of several clades of notosuchians in the context of these hypotheses. As a result, besides the clade names previously established under the ICPN/Phylocode (including registration in RegNum) by Ruiz et al. (2021) (Notosuchia, Xenodontosuchia, Sphagesauria, Sphagesauridae) and Darlim et al. (2021a) (Baurusuchia, Baurusuchidae, Baurusuchinae, Pissarrachampsinae), eleven clade names have been registered and are defined in this contribution. Ten of these represent converted clade names (Uruguaysuchidae, Mahajangasuchidae, Peirosauridae, Itasuchidae, Ziphosuchia, Sphagesaurinae, Caipirasuchinae, Sebecia, Sebecosuchia, and Sebecia), while one represents a new clade name (Peirosauria). Furthermore, the definition of Xenodontosuchia is emended (unrestricted emendation) so that the name can be used in the context of a wider array of topologies.

The Norfolk Ridge: A Proximal Record of the Tonga‐Kermadec Subduction Initiation

AbstractNorfolk Ridge bounds the northeastern edge of the continent of Zealandia and is proximal to where Cenozoic Tonga‐Kermadec subduction initiation occurred. We present and analyze new seismic reflection, bathymetric and rock data from Norfolk Ridge that show it is composed of a thick sedimentary succession and that it was formed and acquired its present‐day ridge physiography and architecture during Eocene to Oligocene uplift, emergence and erosion. Contemporaneous subsidence of the adjacent New Caledonia Trough shaped the western slope of Norfolk Ridge and was accompanied by volcanism. Neogene extension along the eastern slope of Norfolk Ridge led to the opening of the Norfolk Basin. Our observations reveal little or no contractional deformation, in contrast to observations elsewhere in Zealandia, and are hence significant for understanding the mechanics of subduction initiation. We suggest that subduction nucleated north of Norfolk Ridge and propagated rapidly along the ridge during the period 40‐35 Ma, giving it a linear and narrow shape. Slab roll‐back following subduction initiation may have preserved the ridge and created its eastern flank. Our observations suggest that pre‐existing structures, which were likely inherited from Cretaceous Gondwana subduction, were well‐oriented to propagate rupture and create self‐sustaining subduction.

Alienopterix santonicus sp. n., a metallic cockroach from the Late Cretaceous ajkaite amber (Bakony Mts, western Hungary) documents Alienopteridae within the Mesozoic Laurasia

Cockroaches (Blattaria s. str.) were documented from numerous amber localities around the world, representing both extinct and extant families. Alienopteridae is an extinct cockroach family known only from the Cretaceous of Gondwana (Brazil, Botswana, Myanmar amber) and the Cenozoic of North America. Alienopterix santonicus sp. n. from the Late Cretaceous amber of the Ajka Coal Formation (Bakony Mts, western Hungary) extends the rich geographical distribution of the family into Laurasia during the Mesozoic. As a member of the presumably pollinator cohort Alienopteridae, this species could have played an important role in the Ajka Coal ecosystem during the Santonian. The microrectangular structures of the forewing suggest that the new species likely possessed a metallic colouration already known from the group. Combined with the disruptive body pattern this could have served as an advanced camouflage. The microrectangular structures of the forewing were compared to integument microstructures of extant insects with metallic colouration. Various arthropod taxa are already known from ajkaite, and the new discovery further emphasizes the importance of this amber.

Description of the first Cretaceous (Santonian) articulated skeletal lungfish remains from South America, Argentina

The fossil record of dipnoans is mostly represented by tooth plates and jaw bones, whereas nearly complete or complete skulls are rare. Here, we describe a new dipnoan from the Santonian (Upper Cretaceous) of Patagonia (Argentina) using three-dimensional renderings generated by CT scans. It consists of a near-complete skull and postcranial material. Rinconodus salvadori n. gen., n. sp. is diagnosed by a combination of features, such as medial series composed of two unpaired bones, mediolateral series composed of two paired bones, lateral series with at least one bone, medial edge of tooth plates longer than the lingual edge and equally curved, upper tooth plates contiguous or close to one another with five denticulations, lower tooth plates widely separated with four denticulations, first denticulation of upper tooth plates longer and thinner than the remaining denticulations, and posteriorly curved, first denticulation of lower tooth plates relatively straight and longer than the remaining ones, among other characters. The new species is based on the first two nearly complete Santonian dipnoan skulls from South America. Moreover, the materials presented here are the geologically youngest dipnoan remains consisting of a near-complete skull and postcranium from the Cretaceous of Gondwana.

Biomechanical performance of the cranio-mandibular complex of the small notosuchian Araripesuchus gomesii (Notosuchia, Uruguaysuchidae).

Notosuchia is a clade of crocodyliforms that was highly successful and diverse in the Cretaceous of Gondwana. Araripesuchus gomesii is a small notosuchian from the Early Cretaceous of Brazil that belongs to Uruguaysuchidae, one of the subgroups of notosuchians that first radiated, during the Aptian-Albian. Here we present a finite element analysis of A. gomesii based on a model reconstructed from CT scans and performed using published bone properties for crocodiles. The adductor musculature and their respective attachment areas were reconstructed based on Extant Phylogenetic Bracket. Different functional scenarios were tested applying an estimated 158 N bite force: unilateral bite, bilateral bite, pullback, head-shake, and head-twist. The results obtained were compared with those of Alligator mississippiensis, one of its closest living relatives. In the different simulations, the skull and lower jaws of Araripesuchus suffers more stress in the head-shake movement, followed by the unilateral and pullback bites with stress focalized in the premaxillary region. In contrast, the head-twist is the one with smaller stress values. Araripesuchus possess an oreinirostral skull that may provide greater overall resistance in the different scenarios on average, unlike Alligator that has a platyrostral skull with less resistance to dorsoventral mechanical loads. Previous hypotheses that considered A. gomesii as omnivorous coupled with our results, its small size, and likely limited bite force, suggest this taxon probably fed on small prey and other trophic items that could catch and handle entirely with its mouth, such as insects and small vertebrates.

Morphological variation in the dentition of Uruguaysuchidae (Crocodyliformes: Notosuchia).

Uruguaysuchidae was a diverse group of crocodyliforms with widespread Gondwanan distribution. Recent phylogenies recover a clade comprising six species of Araripesuchus and one Uruguaysuchus. We reviewed the morphological variation in the dentition of uruguaysuchid specimens, including unpublished fossils from the Crato (SMNK PAL 6404) and Romualdo (MN 7061-V) formations of the Araripe Basin. Dental patterns are clearly distinct between species, with important taxonomic and possible ecological implications. Neither Araripesuchus nor Uruguaysuchus have characters suggesting exclusive herbivory, even for species in which tooth-tooth occlusion is observed. New data on A. gomesii shows differences in teeth number between the new specimen MN 7061-V and the holotype, probably due to preservation. The specimen SMNK PAL 6404 has a unique combination of dental characters, which reinforces the hypothesis that it might belong to a new Araripesuchus species. The alveoli pattern of A. rattoides is very distinctive in comparison to other araripesuchids, what also suggests different taxonomic affinities. One interpretation for the morphological variation in the dentition of Uruguaysuchidae is foraging specializations for different life habits. Niche partitioning and ecological specialization could have been an important process in explaining the high taxonomic diversity and widespread spatial distribution of these animals in the Cretaceous of Gondwana.

Relationships between volcanism and plate tectonics: A case-study from the Canterbury Basin, New Zealand

Buried volcanoes and igneous intrusions of Cretaceous to Pleistocene age are widespread in the Canterbury Basin, New Zealand. Interpretation of 2D and 3D seismic reflection lines correlated to petroleum exploration wells reveal over 185 buried volcanic systems formed in association with tectonic activity since the separation of Zealandia from Eastern Gondwana. We characterise these volcanoes according to their size, age and spatial distribution. Small-volume scattered monogenetic (<10 km3) and polygenetic vents (>10 km3) erupted during ~105–85, ~65–13 and ~ 5–1 Ma time intervals. In contrast, large polygenetic volcanic complexes (>100 km3 of erupted magma) formed from ~85–66 and ~ 13–5 Ma. Magmatic intrusions are widespread in the basin, where they are commonly emplaced into Cretaceous to Eocene sedimentary strata. The eruption rates within the offshore Canterbury Basin varied through time, reaching maximum values of ~58–127 km3/Myr immediately after the onset of Late Cretaceous Gondwana break-up (~85–66 Ma) and in the Mid-Late Miocene (~15–5 Ma). Late Cretaceous volcanism may reflect the far-field (>600 km) manifestation of volcanism along the Antarctica-Zealandia spreading centre. Vents and intrusions are located near Cretaceous rift faults which, in some cases act as conduits for magma to ascend to the surface.

A Cretaceous Gondwana origin of the wax palm subfamily (Ceroxyloideae: Arecaceae) and its paleobiogeographic context

Here we study a well-preserved petrified palm stem from the latest Maastrichtian (Late Cretaceous) to earliest Danian (early Paleocene) sediments (c. 66–65 Ma old) of the Deccan Intertrappean Beds of Madhya Pradesh, Central India. We infer its systematic relationships and relevance to palm evolution. The significant anatomical attributes of the fossil include the presence of fibrovascular bundles (fvbs) with reniform dorsal fibrous sclerenchyma (dcap), 2 to >4 metaxylem vessel elements in each fvb, lacunar ground parenchyma tissue, and centrifugal differentiation of the fibrous dcap parts of the fvbs. These features reveal a close resemblance to extant taxa of the wax palm subfamily Ceroxyloideae, now with a disjunct distribution in America, Australia, Madagascar and the Comoros. The Cretaceous stem is described here as Palmoxylon ceroxyloides Khan, Hazra et Bera, sp. nov. This is the oldest reliable occurrence of Ceroxyloideae in the fossil record. Present fossil evidence indicates that the sub-family was already present in India in the Late Cretaceous (Maastrichtian), about 10–15 million years before the collision of India with Eurasia. Post-collision the subfamily may have been dispersed to East Asia and then to North America via the Bering land bridge (BLB), finally reaching South America via the Isthmus of Panama link during the Miocene. However, the present-day distribution of Ceroxyloideae in Australia, Madagascar and Comoros may be explained by a historical long-distance dispersal (LDD) hypothesis.

New species of Myrmicium Westwood (Psedosiricidae = Myrmiciidae: Hymenoptera, Insecta) from the Early Cretaceous (Aptian) of the Araripe Basin, Brazil.

This paper records the first occurrence of the genus Myrmicium Westwood, 1854 in the Cretaceous of Gondwana and describes it as a new species Myrmicium araripterum sp. nov, based on the most complete specimen of this genus yet known, which represents the largest specimen of the grade "Symphyta" ever found in the Crato Formation.

Biomarker signatures of Cretaceous Gondwana amber from Ipubi Formation (Araripe Basin, Brazil) and their palaeobotanical significance

An amber (UFRPE 5037), from the black shales of the Ipubi Formation, Araripe Basin (Brazil), has been analyzed to understand its organic geochemical characteristics and possible botanical source using gas chromatography–mass spectrometry (GC–MS). The analyses carried out detected monoterpenes, hydrocarbonic sesquiterpenes, and aliphatic diterpanes like abietanes and norabietanes, as well as aromatic diterpanes such as simonellite, norsimonellite, retene, hinokiol, ferruginol and dehydroabietic acid. Such a combination of components is mainly known to have originated from gymnosperms. The individual identification of diterpenoids allowed the suggestion of Cheirolepidiaceae or Podocarpaceae families as possible amber producers, pointing to a flora similar to the underlying Crato Formation. Therefore, UFRPE 5037 consists on the first amber record in the Ipubi Formation, allowing the acquisition of important information regarding the botanical sources associated to new Brazilian amber occurrence described here.

Perspectives on Cretaceous Gondwana break-up from detrital zircon provenance of southern Zealandia sandstones

AbstractDetrital zircon U–Pb ages in 37 sandstones from late Early – Late Cretaceous marine and non-marine successions across southern Zealandia indicate a provenance from local basement within present-day Zealandia. Samples from Taranaki Basin were derived from Median and Karamea batholith granitoids with transport directions from west to east. Samples from West Coast, Western Southland and Great South basins contain components derived more locally and more variably from Median Batholith and Rahu Suite granitoids and/or the Palaeozoic Buller Terrane. West Coast Basin samples have more plutonic contributions and Great South Basin localities have more Albian-aged (c. 110–100 Ma) zircons. Samples from Canterbury Basin were sourced from Torlesse Composite Terrane basement. The provenance variations are present in both marine and non-marine sandstones and suggest localized watersheds. This fits an interpretation of Late Cretaceous deposition in rift-controlled basins across southern Zealandia during pre-Gondwana break-up regional extension. More speculatively, some additional source areas may have been created at the rifted margins of Zealandia during this break-up.

Seismic stratigraphy and paleogeographic evolution of Fairway Basin, Northern Zealandia, Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

AbstractWe present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.

Temporal links between pluton emplacement, garnet granulite metamorphism, partial melting and extensional collapse in the lower crust of a Cretaceous magmatic arc, Fiordland, New Zealand

AbstractGarnet granulite facies mid‐to lower crust in Fiordland, New Zealand, provides evidence for pulsed intrusion and deformation occurring in the mid‐to lower crust of magmatic arcs. 238U‐206Pb zircon ages constrain emplacement of the ∼595 km2 Malaspina Pluton to 116–114 Ma. Nine Sm‐Nd garnet ages (multi‐point garnet‐rock isochrons) ranging from 115.6 ± 2.6 to 110.6 ± 2.0 Ma indicate that garnet granulite facies metamorphism was synchronous or near synchronous throughout the pluton. Hence, partial melting and garnet granulite facies metamorphism lasted &lt;5 Ma and began within 5 Ma of pluton emplacement. Garnet granulite facies L‐S tectonites in the eastern part of the Malaspina Pluton record the onset of extensional strain and arc collapse. An Sm‐Nd garnet age and thermobarometric results for these rocks directly below the amphibolite facies Doubtful Sound shear zone provide the oldest known age for extension in Fiordland at ≥112.8 ± 2.2 Ma at ∼920 °C and 14–15 kbar. Narrow high Ca rims in garnet from some of these suprasolidus rocks could reflect a ≤ 1.5 kbar pressure increase, but may be largely a result of temperature decrease based on the Ca content of garnet predicted from pseudosections. At peak metamorphic conditions &gt;900 °C, garnet contained ∼4000 ppm Ti; subsequently, rutile inclusions grew during declining temperature with limited pressure change. Garnet granulite metamorphism of the Malaspina Pluton is c. 10 Ma younger than similar metamorphism of the Pembroke Granulite in northern Fiordland; therefore, high‐P metamorphism and partial melting must have been diachronous for this &gt;3000 km² area of mid‐to‐lower crust. Thus, two or more pulses of intrusion shortly followed by garnet granulite metamorphism and extensional strain occurred from north to south along the axis of the lower crustal root of the Cretaceous Gondwana arc.

The Influence of Inherited Structures on Dike Emplacement during Gondwana Breakup in Southwestern Africa

A kinematic analysis of Cretaceous and pre-Cretaceous structures was carried out along the west coast of southern Africa extending from the Cape Town area into Namibia with the aim of investigating whether inherited structural discontinuities controlled Gondwana breakup and the associated opening of the South Atlantic in the Cretaceous. This was augmented by map and satellite image analyses of mainly Cretaceous mafic dikes exposed from SW Angola to the southern tip of Africa. The combined results provide consistent evidence of E-W- to NE-SW-directed extension during the Cretaceous. E-W extension dominated from southern Angola to the Namibian–South African border, and NE-SW-directed extension occurred in an area extending from west-central Namibia to the southwestern coast of South Africa. These two extension directions overlap from west-central Namibia to southernmost Namibia. The kinematic analysis of Pan-African structures provides evidence of ENE-WSW-directed shortening in the western Saldania Belt in SW South Africa and ENE-WSW- to ESE-WNW-oriented constriction in the Gariep Belt near the border between South Africa and Namibia. Thus, the Pan-African shortening directions that led to the Late Neoproterozoic/Early Cambrian amalgamation of SW Gondwana are parallel to the main extension directions during Early Cretaceous Gondwana breakup and the initiation of South Atlantic rifting in southwestern Africa. This implies that opening of the modern South Atlantic was controlled by Pan-African (or older) structural discontinuities that were reutilized during the Early Cretaceous. The inherited structural basement anisotropies, which are generally parallel to major lineaments and/or crustal-scale shear zones, apparently controlled dike emplacement in the Early Cretaceous and the location of rifting at that time.

On the Permian permineralized woods of the "Fossil Flora of the Coal Measures of Brazil" (D. White, 1908): taxonomic re-evaluation

White published, in 1908, the “Report on the Fossil Flora of the Coal Measures of Brazil”, an important work that became a reference for the study of fossil plants collected mainly from Early Permian sediments of the Paraná Basin. In this work, the author described for the first time a large number of plant fossils collected in the states of Santa Catarina and Rio Grande do Sul, including a few pieces of permineralized wood. This paper presents the first taxonomic reevaluation of the permineralized woods described by D. White, using the samples on which he based his descriptions. Sigillaria (?) muralis White is transferred to the genus Scalaroxylon, due to presence of scalariform pitting on the radial walls of the tracheids, thus forming a new combination Scalaroxylon muralis (White); Araucarioxylon nummularium (White) Maheshwari is transferred to the genus Brachyoxylon, because of the araucarioid character of its radial- wall pits and cross- fields, thus forming a new combination Brachyoxylon nummularium (White); Araucarioxylon meridionale (White) Maheshwari is considered as an dubios taxon due to non- preservation of its cross- field pits. The re-evaluation of the fossils described by White enabled a better understanding of the botanical affinities of the Glossopteris flora from southern Brazil. For the first time, the genus Scaraloxylon is recorded in the Permian; until now it had only been found in the Triassic and Cretaceous of Gondwana.

The Hybodontiformes (Chondrichthyes: Elasmobranchii) from the Missão Velha Formation (?Lower Cretaceous) of the Araripe Basin, North-East Brazil

The ?Early Cretaceous (pre-Aptian) Missão Velha Formation of the Araripe Basin of North-East Brazil yields remains referred to two hybodontiform shark taxa: the hybodontid Planohybodus and the lonchidiid Parvodus. Paleoenvironmental analysis of this formation suggests freshwater or perhaps brackish deposition. The specimens described here were collected from a new locality and are found in association with actinopterygian and sarcopterygian fishes and rarer turtles, crocodylomorphs and theropod dinosaurs. The chondrichthyan assemblage is represented by isolated teeth, cephalic spines, and dorsal fin spines. This is the first record of Planohybodus in the Araripe Basin and the first record of Parvodus in the Cretaceous of Gondwana.

The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana

Fossil crocodyliforms discovered in recent years have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144-65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown-crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.

The first crocodyliform from the Chubut Group (Chubut Province, Argentina) and its phylogenetic position within basal Mesoeucrocodylia

A new crocodyliform specimen is presented here found in the Cerro Castaño Member of the Cerro Barcino Formation (Chubut Group). The material consists of cranial and postcranial remains that represent a new taxon that has strong affinities with Peirosauridae, but also shares derived features present in Araripesuchus. The phylogenetic relationships of this new taxon were tested through a cladistic analysis depicting it as a member of the Peirosauridae. The inclusion of Barcinosuchus within this clade of basal mesoeucrocodylians is supported by the presence of hypapophyses up to the third or fourth dorsal vertebrae, anterolateral facing edge on postorbital, quadrate dorsal surface divided in two planes by a ridge; mandibular symphysis tapering anterirorly in ventral view, lateral surface of dentary convex anterior to mandibular fenestra, distal body of quadrate well developed, anteroposteriorly thin and lateromedially broad. The new specimen broadens the temporal and geographical distribution of Peirosauridae during the Cretaceous of Gondwana, representing the southern-most and the most ancient record of the group in Patagonia. The new material also provides insights on the postcranial anatomy of peirosaurids, a group that has been so far studied almost exclusively from cranial material.

The Niassa Gold Belt, northern Mozambique – A segment of a continental-scale Pan-African gold-bearing structure?

The Niassa Gold Belt, in northernmost Mozambique, is hosted in the Txitonga Group, a Neoproterozoic rift sequence overlying Paleoproterozoic crust of the Congo–Tanzania Craton and deformed during the Pan-African Orogeny. The Txitonga Group is made up of greenschist-facies greywacke and schist and is characterized by bimodal, mainly mafic, magmatism. A zircon U–Pb age for a felsic volcanite dates deposition of the sequence at 714 ± 17 Ma. Gold is mined artisanally from alluvial deposits and primary chalcopyrite-pyrite-bearing quartz veins containing up to 19 ppm Au have been analyzed. In the Cagurué and M’Papa gold fields, dominantly N–S trending quartz veins, hosted in metagabbro and schist, are regarded as tension gashes related to regional strike-slip NE–SW-trending Pan-African shear zones. These gold deposits have been classified as mesozonal and metamorphic in origin. Re–Os isotopic data on sulfides suggest two periods of gold deposition for the Cagurué Gold Field. A coarse-crystalline pyrite–chalcopyrite assemblage yields an imprecise Pan-African age of 483 ± 72 Ma, dating deposition of the quartz veins. Remobilization of early-formed sulfides, particularly chalcopyrite, took place at 112 ± 14 Ma, during Lower Cretaceous Gondwana dispersal. The ∼483 Ma assemblage yields a chondritic initial 187Os/ 188Os ratio of 0.123 ± 0.058. This implies a juvenile source for the ore fluids, possibly involving the hosting Neoproterozoic metagabbro. The Niassa Gold Belt is situated at the eastern end of a SW–NE trending continental-scale lineament defined by the Mwembeshi Shear Zone and the southern end of a NW–SE trending lineament defined by the Rukwa Shear Zone. We offer a review of gold deposits in Zambia and Tanzania associated with these polyphase lineaments and speculate on their interrelation.

Hikurangi Plateau: Crustal structure, rifted formation, and Gondwana subduction history

Seismic reflection profiles across the Hikurangi Plateau Large Igneous Province and adjacent margins reveal the faulted volcanic basement and overlying Mesozoic‐Cenozoic sedimentary units as well as the structure of the paleoconvergent Gondwana margin at the southern plateau limit. The Hikurangi Plateau crust can be traced 50–100 km southward beneath the Chatham Rise where subduction cessation timing and geometry are interpreted to be variable along the margin. A model fit of the Hikurangi Plateau back against the Manihiki Plateau aligns the Manihiki Scarp with the eastern margin of the Rekohu Embayment. Extensional and rotated block faults which formed during the breakup of the combined Manihiki‐Hikurangi plateau are interpreted in seismic sections of the Hikurangi Plateau basement. Guyots and ridge‐like seamounts which are widely scattered across the Hikurangi Plateau are interpreted to have formed at 99–89 Ma immediately following Hikurangi Plateau jamming of the Gondwana convergent margin at ∼100 Ma. Volcanism from this period cannot be separately resolved in the seismic reflection data from basement volcanism; hence seamount formation during Manihiki‐Hikurangi Plateau emplacement and breakup (125–120 Ma) cannot be ruled out. Seismic reflection data and gravity modeling suggest the 20‐Ma‐old Hikurangi Plateau choked the Cretaceous Gondwana convergent margin within 5 Ma of entry. Subsequent uplift of the Chatham Rise and slab detachment has led to the deposition of a Mesozoic sedimentary unit that thins from ∼1 km thickness northward across the plateau. The contrast with the present Hikurangi Plateau subduction beneath North Island, New Zealand, suggests a possible buoyancy cutoff range for LIP subduction consistent with earlier modeling.