Breakup Of Gondwana Research Articles

Animal survival strategies in Neoproterozoic ice worlds.

The timing of the first appearance of animals is of crucial importance for understanding the evolution of life on Earth. Although the fossil record places the earliest metazoans at 572-602 Ma, molecular clock studies suggest a far earlier origination, as far back as ~850 Ma. The difference in these dates would place the rise of animal life into a time period punctuated by multiple colossal, potentially global, glacial events. Although the two schools of thought debate the limitations of each other's methods, little time has been dedicated to how animal life might have survived if it did arise before or during these global glacial periods. The history of recent polar biota shows that organisms have found ways of persisting on and around the ice of the Antarctic continent throughout the Last Glacial Maximum (33-14 Ka), with some endemic species present before the breakup of Gondwana (180-23 Ma). Here we discuss the survival strategies and habitats of modern polar marine organisms in environments analogous to those that could have existed during Neoproterozoic glaciations. We discuss how, despite the apparent harshness of many ice covered, sub-zero, Antarctic marine habitats, animal life thrives on, in and under the ice. Ice dominated systems and processes make some local environments more habitable through water circulation, oxygenation, terrigenous nutrient input and novel habitats. We consider how the physical conditions of Neoproterozoic glaciations would likely have dramatically impacted conditions for potential life in the shallows and erased any possible fossil evidence from the continental shelves. The recent glacial cycle has driven the evolution of Antarctica's unique fauna by acting as a "diversity pump," and the same could be true for the late Proterozoic and the evolution of animal life on Earth, and the existence of life elsewhere in the universe on icy worlds or moons.

Aptian ostracods from the Santana Group, Araripe Basin, Brazil

The Class Ostracoda provides a well preserved and diverse microfossil succession throughout the Aptian Santana Group, Araripe Basin, Brazil. The Santana Group, consisting of the Barbalha, Crato, Ipubi and Romualdo formations, records the post-rift sequence (Alagoas local stage) of the Gondwana break-up. The Alagoas Stage is characterised by ostracods grouped as Cytheridea? spp. 201–218 of which several have been identified as belonging to Pattersoncypris Bate and Damonella Anderson. From 2 well cores and 10 outcrops of the Santana Group, 25 taxa were identified, 5 of which are here newly described. Throughout the Santana Group, Pattersoncypris micropapillosa Bate and Damonella grandiensis Tomé, Lima Filho and Neumann were recovered. Restricted to the Barbalha Formation, Candonopsis? alagoensis Tomé, Lima Filho and Neumann and Pattersoncypris cucurves nov. sp are abundant. The Crato Formation shows higher ostracod diversity with Damonella grandiensis being the most abundant and associated with Cypridea araripensis Silva, Brasacypris subovatum Do Carmo, Coimbra, Whatley, Antonietto and Citon, Damonella pumila nov. sp., Pattersoncypris alta (Antonietto, Gobbo, Do Carmo, Assine, Fernandes and Silva), Zonocypris berthoui Piovesan, Melo, Cabral and Guzmán, Zonocypris dorsoconvexa Piovesan, Melo, Cabral and Guzmán, Ilyocypris coimbrai nov. sp., Neuquenocypris berthoui Colin and Dépêche, Neuquenocypris sp., Rhinocypris spinata nov. sp., Theriosynoecum silvai (Silva), Theriosynoecum sp., Timiriasevia? sp. and Alicenula martinsi (Silva). The Ipubi and Romualdo formations record abundant Pattersoncypris crepata (Do Carmo, Coimbra, Whatley, Antonietto and Citon) in association with P. alta, Pattersoncypris kroemmelbeini nov. sp., P. symmetrica (Krömmelbein and Weber) and Alicenula martinsi (Silva). Theriosynoecum colini Do Carmo, Coimbra, Whatley, Antonietto and Citon, Ilyocypris coimbrai nov. sp. and Rhinocypris spinata nov. sp. also occur in the Ipubi Formation.

Molecular Evolutionary Relationships of Side-Necked Turtle Hemoglobin:cDNA-Derived Primary Structures and Computer-Assisted Tertiary Structuresof α<sup>A</sup>, α<sup>D</sup>, and β Globin Chains

Extant side-necked turtles consist of three families: Chelidae, Pelomedusidae, and Podocnemididae. The lasttwo families (the subject of this study) include five genera, three of which are endemic to Africa (Pelomedusa andPelusios) and Madagascar (Erymnochelys), while the other two (Podocnemis and Peltocephalus) are restrictedto South America. This study was undertaken to determine the molecular relationships of side-necked turtlesbased on the primary and tertiary structures of α^A, α^D, and β globin chains as deduced by cDNA sequencing and amachine-learning algorithm for protein structure prediction, AlphaFold2. Analyses of the globin primary structures of four species from different genera provide three major insights. (1) The genera Pelomedusa and Pelusiosmight be endemic taxa that diversified in Africa after the Gondwana separation. (2) Although the extant species ofErymnochelys and Podocnemis are restricted to Africa and South America, respectively, they are closely related toeach other, and thus, these genera apparently diversified during the breakup of Gondwana. Thus, the colonizationof the ancestral population of Podocnemis unifilis in South America might have coincided with continental drift.(3) The divergence times of the four species based on globin genealogy were estimated to have begun 120–11million years ago (mya), which generally coincides with the break-up of Gondwana 135–65 mya. In addition,tertiary structures predicted by AlphaFold2 were compared using a PyMOL overlaying technique. An in-depth examination of the four α^A globin chains revealed considerable consistency among species, and a similar pattern wasobserved for α^D and β globin chains. Additionally, species-specific differences were recognized among the primarystructures, and their higher-order structures (i.e., tertiary structures) were consistent, offering new information onthe molecular phylogeny of side-necked turtles.

Magmatic records of Gondwana assembly and break-up in the eastern Himalayan syntaxis, northeast India

The Indian sub-continent was an integral part of the Gondwana supercontinent with multiple magmatic episodes during the Gondwana assembly and break-up events. However, most of these vital records to understand the past magmatism were obliterated during the Himalayan orogeny due to the subduction of the Indian plate. In this contribution, we attempt to tackle this issue by investigating the Abor magmatic rocks from the eastern Himalayan syntaxis, which are likely to represent the leftover fragments of the eastern Gondwana continental margin. This study uses zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopic ratios data of the mafic intrusive and felsic volcanic rocks of the Abor magmatism. The mafic intrusive rocks have zircon ages of 500–473 Ma, while the felsic rocks yield ages of 145–132 Ma, indicating two temporally separated episodes of magmatism. The mafic intrusives are sub-alkaline/tholeiitic (Nb/Y < 0.65), with high TiO2 (1.63–3.42 wt%) and ocean island basalt to enriched-mid oceanic ridge basalt affinities. A relatively narrow range of initial 87Sr/86Sr (0.703887–0.705513), 143Nd/144Nd (0.511978–0.512118), and εNd(t) (-0.323–+2.43) of the mafic intrusives suggest fractional crystallization with negligible crustal contamination, generated by low degree (∼3–13 %) partial melting of a primitive mantle (garnet and spinel lherzolite). The felsic rocks display low MgO (0.38–1.17 wt%), CaO (1.06–5.31 wt%), LREE and LILE (Rb, K, Pb) enrichment, depletion in HREE, Sr, Nb, Ti, with strong negative Eu-anomaly (0.48–0.73), high initial 87Sr/86Sr (0.707878–0.717650), and negative εNd(t) (-14.35 to −9.21), suggesting A-type felsic magmatism. The older mafic intrusions were thus attributed to the events of the Gondwana assembly and were inferred to form in an extensional passive margin during the early Paleozoic. However, the younger felsic rocks were likely to have been generated by the interaction of the upwelling Kerguelen mantle plume and the pre-existing crust during the initiation of the eastern Gondwana break-up during the early Cretaceous. Our new findings reveal that two episodic magmatic events related to the eastern Gondwana assembly and the subsequent Gondwana break-up are responsible for the magmatism in the Siang window of eastern Himalayan syntaxis, northeast India.

Correlations among large igneous provinces related to the West Gondwana breakup: A geochemical database reappraisal of Early Cretaceous plumbing systems

The opening and spreading of the Atlantic Ocean between Africa and South America evolved during the Early Cretaceous and were preceded by dramatic tholeiitic (mafic) magmatism and minor silicic and alkaline volcanism. These features are presently recognized from the equatorial regions of Brazil and Africa to the Falklands and South Africa. In southeastern South America, continental flood basalts and related plumbing systems constitute the Paraná Magmatic Province (PMP), whose African counterpart is the Etendeka Magmatic Province (EMP). In northeastern Brazil, dike swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). As a common feature, these provinces are chemically represented by two prevalent magma types: (1) tholeiitic basalts and basaltic andesites with low Ti (TiO2 < ∼2 wt.%), also including transitional Ti tholeiites with TiO2 ∼ 2.7–1.7 wt.%, and low incompatible element contents. This type is predominantly found in the southern PMP and EMP, with minor occurrences in the EQUAMP. (2) Tholeiitic basalts and basaltic andesites with high Ti (TiO2 > ∼2 wt.%) and incompatible element contents. High Ti tholeiites are relevant in the northern PMP and EMP, and dominant in EQUAMP. Evolved rocks (SiO2 = 57–65 wt.%) interpreted as byproducts of assimilation and/or fractional crystallization (AFC) processes from high Ti tholeiitic magmas, are scarce (but present) in all three provinces. An accurate analysis of multivariable databases collected from the literature for dikes and sills, including major and trace element and radiogenic isotope data, reveals close similarities in their geochemical signatures. In a paleogeographic reconstruction of West Gondwana, the intrusive remnants of the PMP, EMP and EQUAMP are spread over an area of nearly 10 × 106 km2, forming perhaps the most extensive set of plumbing systems on Earth, with a relatively consistent chronology based on a vast collection of K–Ar and 40Ar/39Ar data available in the literature. This work provides the first comprehensive data comparison to support the existence of what may have been a single intercontinental-scale magmatic province of West Gondwana.

Seismic investigations around an aseismic Comorin ridge, Indian Ocean

Aseismic ridges and oceanic plateaux, typically buried under thick post-rift sediments, are isolated entities of enigmatic crustal character. Limited availability of deep seismic soundings hinders their precise characterization. Here, we present new crustal images from the Comorin ridge and adjoining basins in the Central Indian Ocean. Further, we seismically characterize the oldest oceanic crust south of Sri Lanka. We observe that the NW–SE-trending Comorin ridge, having distinct topography, is bounded by crustal blocks of contrasting ages and characters. Using seismic interpretation and potential field modelling, we propose its genesis as a transverse ridge with an anomalously thick ( c. 14 km) oceanic crust including considerable magmatic underplating. Additional constraints from plate reconstruction modelling suggest that a linear oceanic transform developed between India and Madagascar during their separation while the Marion hotspot remained in their close proximity. Based on several lines of evidence, we infer that shearing motion along the transform and coeval hotspot interactions are the likely emplacement mechanism for the ridge. The high-resolution seismic images demonstrate widespread crustal deformation in the form of high-angle faulting and long-wavelength folding. New findings have important implications for an improved understanding of the early Gondwana break-up, seafloor creation and subsequent compressional tectonics in the Indian Ocean. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6073139

Modeling Lithospheric Thickness Along the Conjugate South Atlantic Passive Margins Implies Asymmetric Rift Initiation

AbstractThe lithospheric architecture of passive margins is crucial for understanding the tectonic processes that caused the breakup of Gondwana. We highlight the evolution of the South Atlantic passive margins by a simple thermal lithosphere‐asthenosphere boundary (LAB) model based on onset and cessation of rifting, crustal thickness, and stretching factors. We simulate lithospheric thinning and select the LAB as the T = 1,330°C isotherm, which is calculated by 1D advection and diffusion. Stretching factors and margin geometry are adjusted to state‐of‐the‐art data sets, giving a thermal LAB model that is especially designed for the continental margins of the South Atlantic. Our LAB model shows distinct variations along the passive margins that are not imaged by global LAB models, indicating different rifting mechanisms. For example, we model up to 200 km deep lithosphere in the South American Santos Basin and shallow lithosphere less than 60 km in the Namibe Basin offshore Africa. These two conjugate basins reflect a strong asymmetry in LAB depth that resembles variations in margin width. In a Gondwana reconstruction, we discuss these patterns together with seismic velocity perturbations for the Central and Austral Segments of the margins. The shallow lithosphere in the Namibe Basin correlates with signatures of the Angola Dome, attributed to epeirogenic uplift in the Neogene, suggesting an additional component of post‐breakup lithospheric thinning.

Contrasting thermal evolution of the West African Equatorial and Central Atlantic continental margins

The landscape of the West African continental margins is the product of tectonic, thermal and surface processes acting in concert during and following the breakup of Gondwana. Central Atlantic opening was marked by the emplacement of the Central Atlantic Magmatic Province (CAMP) and continental breakup proceeded through Late Jurassic and Early Cretaceous divergent tectonics while opening of the Equatorial Atlantic was dominated by early and mid-Cretaceous transform movement. The onshore erosional response to these events is poorly constrained yet is a crucial component of our understanding of topographic evolution and sediment transfer across continental margins. We present new apatite fission-track (AFT) data for 24 samples from Guinea and 11 samples from Ivory Coast, and thermal histories from inverse modelling. Our data and thermal histories show the following: the thermal effect of the CAMP across Guinea and Ivory Coast; rapid cooling along the coast during the early to mid-Cretaceous related to erosion of short-wavelength rift-shoulders; moderate cooling across longer wavelengths reflecting a pattern of erosion across flexural margin upwarps; and low cooling rates from the start of the Cenozoic to present day, consistent with low magnitudes of erosion inferred by onshore geomorphological data. We present our results alongside the published regional AFT dataset and draw inferences on the thermal and tectonic evolution of the onshore margin.

Reconstructing a dismembered Neogene basin along the active Hikurangi subduction margin, New Zealand

AbstractThe East Coast Basin (ECB), New Zealand, preserves the most complete onshore stratigraphic record of the Cretaceous–Neogene development of Zealandia from Gondwana breakup, through rift-drift, to evolution of the modern Hikurangi subduction margin and Pacific-Australia plate boundary. As such, it provides important constraints for southwest Pacific plate tectonic reconstructions. The basin is, however, deformed and variably dismembered, and in previous tectonic models it has been treated as a zone of poorly constrained deformation. Here, multiple geological and geophysical data sets are integrated with a tectonic reconstruction to provide a synthesis of regional and intrabasin-scale structural evolution of the ECB during the Neogene, producing a new geologically constrained approach toward qualitative and quantitative assessment of deformation across the New Zealand plate boundary zone. We produce the first palinspastic reconstructions for the entire basin during key times in plate boundary development, within a well-constrained plate-tectonic framework, supported by independent deformation estimates. These reconstructions account for contraction, strike-slip, and vertical-axis rotation of crustal blocks. In the context of the reconstruction model, the ECB has dominantly experienced upper-plate shortening and vertical-axis rotations; strike-slip processes are considered comparatively minor. Comparison of the reconstruction model with independent data highlight several pronounced deformation intervals (26–23 Ma, 20–15 Ma, 11 Ma, and 7–4 Ma) in the structural and sedimentary evolution of the ECB, Hikurangi subduction margin, and New Zealand plate boundary zone, demonstrating that it is possible to integrate a wide range of geological data sets to develop meaningful reconstructions in highly tectonised regions.

Late Permian rift-related volcanic rocks from the Zhongba Terrane, Southern Tibet: implications for the opening of the Neotethys

ABSTRACT The questions of how and when the Neotethys Ocean opened are crucial for understanding the evolution of the Tethys Realm and the break-up of Gondwana. However, the evolution of the Neotethys remains controversial. Herein, we report the zircon U–Pb ages, whole-rock major as well as trace elements, and Sr–Nd isotopic data for the basaltic volcanic rocks from the Zhongba Terrane in the western Yalung–Zangbo Suture Zone. The results demonstrate that the Saga basalts were extruded during the Late Permian (257–258 Ma). All samples are characterized based on the low SiO2 content (44.03–50.33 wt%) and belong to the high-K calc-alkaline series. Furthermore, they exhibit light rare earth element enrichment ((La/Yb)N = 12.7–26.7); slightly positive Eu anomaly(Eu/Eu* = 1.01–1.14); prominent Nb and Ta positive anomalies; slightly negative Zr, Hf, and Ti anomalies and exhibit high ratios of Ta/Hf (0.93–1.21), Zr/Y (8.68–10.63), and Nb/Zr (0.39–0.45). The (87Sr/86Sr)i ratio varied from 0.7050 to 0.7063, with relatively constant and depleted εNd(t) values ranging from 0.52 to 1.08. The rocks were probably sourced from a low-degree partial melting of the asthenospheric mantle in a rift environment and had undergone the process of fractional crystallization. These characteristics indicate that the Saga basalts differ from the rift-related magmatic rocks produced by the Panjal Traps. Consequently, combined with the recently reported detailed fieldwork, the Zhongba Terrane disintegrated from the northern margin of Gondwana during the Late Permian, promoting the opening of the Neotethys Ocean, which is most likely caused by the northward subduction of the Paleotethys Ocean.

Unlocking the Hydrocarbon Potential of the Mannar Basin (Sri Lanka) Based on New Data and New Ideas

The Mannar Basin is a failed rift basin located between Sri Lanka and India. Massive flood basalts have been deposited during latest Cretaceous/earliest Paleocene magmatic activity that is also represented by numerous igneous sill intrusions. The two discoveries are associated with this magmatism: Barracuda and Dorado, both discovered in 2011, have been drilled in the northern part. One of the key challenges for hydrocarbon exploration in volcanic provinces is sub-basalt imaging due to the velocity contrast between basalts and siliciclastics. To unlock hidden play types and identify geological features within Mesozoic intervals we utilized both infill 2D seismic data acquired in 2018 and vintage 2D seismic data reprocessed in 2021. These provide new insights for hydrocarbon exploration and the tectono-stratigraphic evolution of Sri Lanka’s offshore basins. We integrated these new study results into a regional 2D petroleum system modelling study. Modelling results indicate hydrocarbon potential for several play types: Cretaceous reef, turbidite and fan plays. Since the tectonic evolution of the Mannar Basin is still a matter of debate, especially related to timing and duration of extension and Sri Lanka’s position during Gondwana breakup, we created different heat flow scenarios to validate the impact on the hydrocarbon prospectivity.

Endemicity and radiation in waterfalls of the Western Ghats: The genus Cremnoconchus (Gastropoda: Littorinidae)

Snails of the genus Cremnoconchus – the only freshwater members of the gastropod family Littorinidae – are endemic to the spray zones of numerous waterfalls in the Western Ghats of India. Cremnoconchus consists of nine described and possibly numerous undescribed species as many of these appear to be restricted to specific waterfalls. This is the first attempt at resolving the relationships between the various species in this genus and establishing its monophyly in the family. Further, we also undertake species delimitation analysis to characterize cryptic diversity in this group. Phylogenetic analyses based on nuclear and mitochondrial genes support the monophyly of Cremnoconchus within the family. A fossil-calibrated Bayesian time tree suggests that this freshwater lineage diverged from its marine counterparts around 90.40 million years ago. The separation of Cremnoconchus from its marine ancestors might have been facilitated by the break-up of Gondwana or fluctuating sea levels during this period. Species delimitation analysis retrieved 12 potentially undescribed species in this group. These species formed two distinct clades in the phylogeny, one largely confined to the northern Western Ghats and the other to the central Western Ghats. Species belonging to the northern and central Western Ghats seem to have separated around 56.11 mya, i.e. after the northern Western Ghats were formed. Additionally, spatial isolation due to the patchiness of suitable habitats (waterfalls) and low mobility might have facilitated their diversification.

New age and lake chemistry constraints on the Aptian pre-salt carbonates of the central South Atlantic

AbstractThe Cretaceous lacustrine carbonates of the offshore Brazilian and West African presalt basins represent some of the most extensive non-marine carbonates discovered in the geologic record. Despite being intensively studied over the past decade, the age of these carbonates and the overlying regional salt sequences is highly controversial. Similarly, the conditions under which these carbonates were deposited remains poorly understood. Here, we provide the first integrated geochronology-thermometry study of these carbonates to develop an improved understanding of when and under what conditions they formed. We utilize carbonate clumped isotope and 87Sr/86Sr geochemistry alongside traditional petrographic techniques to identify samples minimally altered from burial diagenesis that may yield reliable age and lake chemistry constraints. Carbonate clumped isotope apparent temperatures for the studied carbonates range from 36 °C to 91 °C, which we infer to represent a range in sample preservation from minimally altered depositional temperatures through to those that have been overprinted by burial diagenesis. 87Sr/86Sr values of our samples are consistent with those of previous studies for Cretaceous pre-salt carbonates that have not experienced significant alteration from hydrothermal fluids. Through this approach, we measured the first high resolution isotope dilution U-Pb age constraint of 115.83 ± 1.56 Ma (2σ) on a well preserved carbonate. Combined with overlapping lower resolution laser ablation U-Pb ages for time-equivalent stratigraphy on two separate carbonate platforms of 114.46 ± 4.72 Ma and 109.73 ± 9.26 Ma, these ages provide the first robust direct age calibration for pre-salt carbonates deposited on either side of the South Atlantic during the final stages of the break-up of Gondwana in the Early Cretaceous. These ages also provide the first calibration for a combined 87Sr/86Sr-facieslog based relative age framework within the Santos Basin, offshore Brazil. We further utilize δ18O constraints on samples that yield depositional clumped isotope apparent temperatures to constrain the δ18O of the water in these ancient lakes to between 1.9 and 4.9‰Vienna standard mean ocean water. Such heavy values reveal a picture of a hot and arid environment. This is consistent with prior biostratigraphic studies of the carbonates that show a decrease in faunal diversity in these lakes prior to marine ingress and the development of open marine conditions in the South Atlantic Ocean.

A quantitative depositional model of a large distributive fluvial system (Megafan) with terminal aeolian interaction: The Upper Jurassic Guará DFS in southwestern Gondwana

ABSTRACT Recent studies have shown that distributive fluvial systems are the dominant fluvial forms in modern continental sedimentary basins, thus composing a large part of the stratigraphic record. This study provides a basin-scale architectural analysis of the Guará Formation, from the Upper Jurassic record of southwestern Gondwana, and attempts to compare the formation's depositional model to those developed for distributive fluvial system (DFS) successions. This time interval is significant because it was a period of intense tectonic activity related to the Paraná–Etendeka plume and the Gondwana breakup. Quantitative analyses were performed on stratigraphic sections at 17 locations (exposing a total of 720 m of stratigraphy) located in southern Brazil and northern Uruguay, from a larger dataset of 64 locations (comprising a total of 1070 m of stratigraphy). Four facies associations were identified: perennial fluvial channel fills, ephemeral fluvial channel fills, floodplain deposits, and aeolian deposits, indicating a dryland climate. Spatial trends were analyzed along a downstream-oriented transect (NNE–SSW) across the system. Grain size, channel-body thickness, number of stories, and bar thickness decrease downstream, indicating a reduction in channel depth, flow capacity, and channelization of the fluvial system, interpreted to be associated with downstream-increasing bifurcation, infiltration, and evapotranspiration. Based on spatial trends and distribution of facies associations, the deposits are interpreted to have been accumulated from a large DFS which can be divided into four zones, from proximal to distal: Zone 1, dominated by perennial fluvial channels; Zone 2, a mixture of perennial and ephemeral channels; Zones 3 and 4, deposits situated externally of the fluvial channel belts dominated by aeolian and floodplain deposits prevailing in each zone, respectively. The Guará Formation likely records the stratigraphic signature of the largest distributive fluvial systems reconstructed from both modern and ancient datasets, and one of the first where fluvio–aeolian interaction is quantified. The Guará Formation DFS model presented herein is key to understanding paleoenvironmental, paleoclimatic, and geotectonic changes related to Gondwanan fragmentation.

Deformation along the Deseado Massif (Patagonia, Argentina) during the Jurassic Period and its relationship with the Gondwana breakup: paleomagnetic and geochronological constraints

This work presents the analysis of paleomagnetic results obtained from four sampling areas of the Jurassic Bahía Laura Complex in the Deseado Massif and their implications on the regional deformation history during the breakup of Gondwana. Paleomagnetic data show cessation of tectonic block rotations about vertical axes around 160 Ma and a change from a transtensional to a mainly extensional tectonic regime. Two biotite samples yielded 40Ar–39Ar radiometric ages: one from the eastern outcrops of the Chon Aike Formation (plateau age of 184.66 ± 0.55 Ma) and the other from the La Matilde Formation (plateau age of 157.40 ± 0.65 Ma), located at the central part of the Deseado Massif. Finally, an apparent polar wander path (APWP) was calculated for the Jurassic of South America (200 to 140 Ma). This APWP indicates that South America experienced a northward drift between 200 Ma and 170 Ma, a clockwise rotation (~10°) between 170 Ma and 160 Ma, and a westward drift between 160 Ma and 140 Ma. The 170–160 Ma rotation could has been triggered by the combined effects of the uncoupling of the Antarctic Peninsula, the high rates of subduction of the Phoenix plate beneath Patagonia, the opening of the Rocas Verdes basin and the Weddell Sea, and the cessation of the Tethys slab-pull. Furthermore, the calculated APWP for South America does not support a Jurassic massive true polar wander event.

Molecular Phylogeny Reveals the Past Transoceanic Voyages of Drywood Termites (Isoptera, Kalotermitidae).

Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Ma (75–93 Ma 95% highest posterior density), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at <50 Ma, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae.

Gone with Gondwana: Amphipod diversification in freshwaters followed the breakup of the supercontinent

The evolutionary origins of modern taxa are best understood as arising from the interplay of vicariance and dispersal. Vicariant events have long been considered responsible for Gondwanan distributions; such species are relics of the eponymic supercontinent on which they were thought to have originated. One such set of taxa are the freshwater members of the amphipod superfamily Hyaloidea, which due to their marine relatives and current distributions serve as an excellent model for testing vicariance and dispersal hypotheses. We investigated the evolutionary and biogeographic histories of the Hyaloidea using a molecular phylogenetic approach. Maximum likelihood analyses and Bayesian inference, using two nuclear genes and one mitochondrial gene, reveal the freshwater amphipods within the superfamily (Hyalellidae/Chiltoniidae) as a monophyletic group diverging from their extant marine ancestors during the Mesozoic. This is suggestive of the group entering freshwater relatively early, instead of geologically recent marine invasions as have been previously hypothesized. Despite the group’s apparent monophyly, it is likely that marine hyaloids exploited shallow water marine/brackish habitats created following the breakup of Gondwana to invade continental freshwaters. Given the divergence times recorded and shallow cladogenetic events observed, it is possible that this occurred through multiple invasions by closely related taxa. Mesozoic invasions by the Hyaloidea suggest that freshwater members represent a much older lineage than previously considered, occupying continental freshwaters prior to the gammarids in the Cenozoic and contemporaneouslywith the crangonyctids in the Mesozoic. Our results highlight the Gondwanan origin of taxa with enigmatic distributions and the utility of amphipods for testing biogeographic hypotheses that infer the origin of freshwater taxa.

Episodic continental extension in eastern Gondwana during the mid-late mesozoic: insights from geochronology and geochemistry of mafic rocks in the Tethyan Himalaya

ABSTRACT Mesozoic extension and rifting processes of the Gondwana continent are critical for understanding the opening and formation of the Indian Ocean. Here, we report petrological, geochemical, zircon U–Pb age, and Lu–Hf isotopic data of mafic dikes in the central Tethyan Himalaya to reveal the timing and mechanism of the eastern Gondwana rifting. These mafic rocks exhibit two groups in terms of TiO2 and MgO contents (Group I with TiO2 < 2.0 wt.%, whereas Group II with TiO2 > 2.0 wt.%), but (1) they have similar trace elements patterns and exhibit enriched Light Rare Earth Element (LREE) patterns without Eu anomalies and (2) they have a wide range of zircon εHf(t) values. Both the above geochemical characteristics are similar to those of the Oceanic Island Basalt (OIB). However, they also show typical features of continental crust input. Compared to Group II, Group I has higher MgO, Cr, and Ni abundances (more primitive) and more depleted Nb-Ta contents, which are similar to those of lower TiO2 Dala mafic rocks, suggesting that the continental crust signature was mainly inherited from the Greater India subcontinental lithospheric mantle (GI-SCLM). Therefore, the mafic rocks here were mainly derived from a hybrid source from both OIB-like enriched mantle and GI-SCLM. Furthermore, two groups of zircon U–Pb ages have been identified: the first group with a weight mean age of 139.9 ± 0.2 Ma, whereas the second group with a weight mean age of 163.2 ± 0.9 Ma. The Middle Jurassic zircons show similar characteristics to those of intermediate to acidic igneous rocks in the continental setting, and thus they might record a stage of magmatism associated with a tectonic extension event in the Indian passive continental margin. The Early Cretaceous ages represent the crystallization timing of the mafic dikes, which are coeval with most mafic rocks in the Tethyan Himalaya. Based on these observations and the literature data in the Tethyan Himalaya, we proposed that the Kerguelen plume was incubating underneath the Tethyan Himalaya at ca. 140 Ma, but it was not located in the triple junction among the Antarctic, Australian and Indian plates. Therefore, the Kerguelen plume might play a synergistic role in the break-up of eastern Gondwana, which had experienced at least two stages of tectonic extension during the Mid-Late Mesozoic.

Petrogenesis of Lava from Christmas Island, Northeast Indian Ocean: Implications for the Nature of Recycled Components in Non-Plume Intraplate Settings

Lava samples from the Christmas Island Seamount Province (CHRISP) record an extreme range in enriched mantle (EM) type Sr-Nd-Pb-Hf isotope signatures. Here we report osmium isotope data obtained on four samples from the youngest, Pliocene petit-spot phase (Upper Volcanic Series, UVS; ~4.4 Ma), and four samples from the earlier, Eocene (Lower Volcanic Series, LVS; ~40 Ma) shield building phase of Christmas Island. Osmium concentrations are low (5–82 ppt) with initial Os isotopic values (187Os/188Osi) ranging from (0.1230–0.1679). Along with additional new geochemical data (major and trace elements, Sr-Nd-Pb isotopes, olivine δ18O values), we demonstrate the following: (1) The UVS is consistent with melting of shallow Indian mid-ocean ridge basalt (MORB) mantle enriched with both lower continental crust (LCC) and subcontinental lithospheric mantle (SCLM) components; and (2) The LVS is consistent with recycling of SCLM components related to Gondwana break-up. The SCLM component has FOZO or HIMU like characteristics. One of the LVS samples has less radiogenic Os (γOs –3.4) and provides evidence for the presence of ancient SCLM in the source. The geochemistry of the Christmas Island lava series supports the idea that continental breakup causes shallow recycling of lithospheric and lower crustal components into the ambient MORB mantle.

Rifting of the Indian passive continental margin: Insights from the Langjiexue basalts in the central Tethyan Himalaya, southern Tibet

Abstract The Triassic tectonic setting of the Tethyan Himalaya in southern Tibet remains controversial and is key to revealing the mechanism of Neo-Tethys Ocean opening and the breakup history of Gondwana. This paper reports 227–225 Ma mafic volcanic rocks interbedded within the Tethyan Himalaya sequence in southern Tibet, which were formed in a typical passive continental margin setting. The basalts are tholeiitic with high TiO2 (3.20–3.38 wt%) and moderate MgO (4.05–5.40 wt%) contents and exhibit enrichment in light rare earth elements and weak negative Nb, Ta, Eu, and Ti anomalies. These geochemical compositions, combined with uniform whole-rock εNd(t) (+1.50 to +2.70) values, indicate that the magmas were derived by low-degree melting of a deep-seated garnet source that was heterogeneously modified by an oceanic island basalt-type of component. Given the other geological evidence, we propose that the magmatic evolution of the Tethyan Himalaya during the late Paleozoic–Mesozoic was generally a lithospheric thinning process, that is, it evolved from a fully developed continental rift system during the Late Permian to wane during the Triassic. This interpretation further supports the hypothesis that the Neo-Tethys Ocean opened in a passive pattern and that the breakup of Gondwana in the late Paleozoic was initiated by lithospheric thinning. Therefore, the subsequent magmatism was related to the passive upwelling of normal asthenospheric materials.