Spreading Episode Research Articles

Along-Strike Morphologic Variations of the Kyushu-Palau Ridge at 13°–17° N and Their Tectonic Implications

The paper provides a detailed description of the topographical distribution characteristics, along-strike morphologic variations, and tectonic implications of the Kyushu-Palau Ridge (KPR) in the 13°–17° N regions. The description is based on multibeam bathymetric data that was recently collected in the mid-southern segment of KPR and its surrounding areas. The findings indicate that the KPR in the studied region comprises several discontinuous seamounts and seamount chains. Along the ridge running from east to west, there is significant variation in the topography of the seafloor. Visible on this ridge are numerous deep-sea depressions and apparent topographical discontinuities. Geological tectonic processes such as plate subduction and seafloor spreading largely determine the topography of the seafloor. During the beginning of the Parece Vela Basin (PVB) spreading, the pre-existing volcanic arcs fractured under east-west extensional stress, resulting in the development of prominent seamounts, sharp ridges, relief alternations, and rift basins in the KPR. The east-west stress was subsequently transmitted to the weak and inactive mid-ocean ridge in the West Philippine Basin (WPB), which was reactivated and resulted in an episode of magma-poor spreading during 30–26 Ma. This episode caused the KPR to move eastward, stretched, and destroyed its pre-existing structure.

The integration of millet into the diet of Central Asian populations in the third millennium BC

Stable isotope analyses demonstrate that C4plants played an important dietary role in Eurasian prehistory. Uncertainty remains, however, about when and how crops were integrated into the diet of Central Asian populations. Here, the authors present δ13C and δ15N stable isotope analysis of human and animal bone collagen from Kyrgyzstan, revealing C4plant—likely broomcorn millet—consumption in the third millennium BC. Combining this evidence with AMS radiocarbon dating and animal collagen peptide fingerprinting demonstrates that broomcorn millet was consumed by humans and animals during the earliest episodes of the westward spread of this crop plant. The results contribute to debates about the timing and means by which domesticated millets were dispersed across Eurasia.

Containment strategies for COVID-19 in India: lessons from the second wave

ABSTRACT Introduction The COVID-19 pandemic in India has resulted in mass destruction in the form of second wave.Indian citizens and government were badly affected and were left constrained with basic medical facilities in treating the heavy load of patients. The possibility of reemergence of virulent strains of SARS-CoV-2 still exists. Area covered In this article, we tend to discuss why India is at high risk to be to be affected by the other waves and what strategies could be implemented to contain the viral spread. It provides these insights with reference to the gaps and the lessons learnt from the second wave along with the possible solutions to tackle these problems that were not effectively handled during the previous episodes of viral spread. We propose strategies for implementing effective vaccination programs, focus on speeding up different ways of diagnosis, management of essential hospital aids, prevention from vaccine escape mutant strains and implementation of COVID-appropriate behavior in rural areas of India. Expert opinion This article has significance to the researchers and government officials in understanding the gaps that led to COVID-19 second wave in India and provides an opportunity to improve on certain areas for handling the future waves with more vigilance. Abbreviations: COVID-19 – Coronavirus disease 2019; SARS-COV-2 – severe acute respiratory syndrome – Coronavirus 2; δ – Delta variant; δ+ – Delta plus variant; WHO – World Health Organization; RT –PCR – Reverse transcription PCR; IFN-1 – Interferon 1; VOCs – Variants of concern; HCWs – healthcare workers

Modelling the chronology and dynamics of the spread of Asian rice from ca. 8000 BCE to 1000 CE

This paper presents a quantitative chronology for the spread of rice, based on the global Rice Chronology Database that builds upon direct datings of archaeological rice remains. Bayesian and spatio-temporal modelling suggest eastern China (lower Yangzi, middle Yangzi, southern Huai River, and Shandong) and northeastern South Asia as two key origins of rice cultivation, dating to ca. 7430 and 6460 BCE, respectively. At least two episodes of spread of rice are identified. The first, dating to the 4th and 3rd millennia BCE, accounts for the appearance of rice in the middle Yellow River and Wei River regions, southeastern China, southwestern China, and Southeast Asia. An examination of population dynamics in China shows that this episode of spread might be associated with farmers whose subsistence was based largely on millets. During a second episode of spread, dating between the 1st millennium BCE and 1st millennium CE, rice spread to the Liao River region, Central Asia, and Africa.

Morphotectonic signatures and revised timing of opening of the Andaman Backarc Basin, Northeast Indian Ocean

The Andaman Backarc Basin is believed to have been formed by the present episode of seafloor spreading in the Andaman Sea, separating the Alcock Rise in the north (Burmese Plate) and the Sewell Rise in the south (Sunda Plate). The geophysical investigations carried out so far in this basin provided detailed information on the morphotectonic signatures of its central sector, however, such understanding of the eastern sector is still awaited. Those studies also inferred continual seafloor spreading in the Andaman Backarc Basin starting from 4.0 Ma, however, some of the subsequent studies, based on deep water sedimentation, postulated an episodic seafloor spreading responsible for the formation of the Andaman Backarc Basin. To address these problems, we revisited the morphotectonic signatures and evolution of the Andaman Backarc Basin using a new set of multibeam bathymetry and magnetic data from the central and eastern sectors of the Andaman Backarc Basin, complemented by the existing geophysical data from the central sector. Our updated bathymetry map of the newly surveyed northernmost segment (referred as Segment D), is characterized by the presence of a well-defined rift valley, with an along-axis gentle dip from the east to the west. The segment D is also characterized by the absence of significant magnetic anomalies, as in the case of segment C, corroborating the concept of replacement of layer 2A by a sill-sediment-metasedimentary layer, in a sedimented spreading centre. Further, our revisit to the magnetic anomaly identifications suggests that the magnetic anomalies over the segment B of the Andaman Backarc Basin can reasonably be explained in terms of continual seafloor spreading from chron C3An.1ny (5.894 Ma) till the present (0.0 Ma). Based on these identifications of magnetic anomalies and the plate tectonic reconstructions, we revise the age of opening of the Andaman Backarc Basin from 4.0 Ma to ~5.9 Ma.

COVID-19: Chittagong Port and aftermath

After first unveiled in China, by March 2020, the wide spreading episode of coronavirus diseases 2019 (COVID-19) spread over Europe and the rest of the world. Besides the public health crisis, not only the Chinese economy but also the global economy as well as the supply chain faced a significant slowdown. Port is not apart from this. Chittagong Port is considered the economic nerve of Bangladesh. A significant segment of export-import moved through Chittagong Port. Like the entire globe, the outbreak of coronavirus affects the country’s prime seaport adversely. This study examines the issues concerning port operation. This study has a qualitative approach that depended on data collected from both primary and secondary sources. Primary data were collected from field surveys using semi-structured questionnaires and in-depth interviews with government agencies, policymakers, researchers, businessmen, port users and entrepreneurs. Secondary data were sourced from different policy documents, scholarly articles, reports and the internet. This study provides an overview of COVID-19 impacts on the port and shipping activities in Chittagong Port, which include impacts on port of call, warehouse and distribution activities, hinterland connections and port employees. Therefore, this study discussed those issues to date, identify impacts and authority response to address the impacts. Finally, this study put forward strategies for their mitigation.

A mathematical model for the spread of COVID-19 and control mechanisms in Saudi Arabia

In this work, we develop and analyze a nonautonomous mathematical model for the spread of the new corona-virus disease (COVID-19) in Saudi Arabia. The model includes eight time-dependent compartments: the dynamics of low-risk S_{L} and high-risk S_{M} susceptible individuals; the compartment of exposed individuals E; the compartment of infected individuals (divided into two compartments, namely those of infected undiagnosed individuals I_{U} and the one consisting of infected diagnosed individuals I_{D}); the compartment of recovered undiagnosed individuals R_{U}, that of recovered diagnosed R_{D} individuals, and the compartment of extinct Ex individuals. We investigate the persistence and the local stability including the reproduction number of the model, taking into account the control measures imposed by the authorities. We perform a parameter estimation over a short period of the total duration of the pandemic based on the COVID-19 epidemiological data, including the number of infected, recovered, and extinct individuals, in different time episodes of the COVID-19 spread.

Features of the work of a dentist and maxillofacial surgeon in a pandemic of a new coronavirus infection (COVID-19). World experience and own practice

Relevance. SARS-CoV-2 caused the pandemic of the new coronavirus infection (COVID-19) in the world. The virus belongs to the family of RNA-containing coronaviruses and is a representative of the Beta-CoV B line. Epidemiological analysis shows that the disease is transmitted by airborne droplets, airborne dust and contact routes. During dental treatment, patients are face-to-face with the doctor. Coughing, sneezing, salivation and blood may occur when using an ultrasonic or high-speed handpiece. If the patient is infected, then standard protective measures in everyday clinical work are not effective enough to prevent the spread of COVID-19, even if the patients are in an asymptomatic incubation period. Purpose. A generalization of colleagues ’knowledge and their own practical experience is necessary for the proper organization of the provision of dental care to patients and minimization of the risk of infection in a pandemic of a new coronavirus infection. Materials and methods . We analyzed the data of colleagues of dentists from different countries, and also presented our own understanding of the issues of dental care during a pandemic of a new coronavirus infection. Results. In conclusion: the main important steps in the implementation of dental practice are during a pandemic: the doctor's compliance with the recommendations of the Ministry of Health of the Russian Federation on the prevention, diagnosis and treatment of new coronavirus infection (COVID-19); strict observance by the dentist and maxillofacial surgeon of the rules of their own safety; obtaining additional information from the history of possible risk factors for the patient; the correct use of the diagnostic algorithm depending on the pathology of the patient; the use of mainly disposable materials; flawless sterilization and disinfection of materials that are reused; competent aseptic processing of hands and mandatory work with gloves; prudent and proper use of personal protective equipment; disinfection measures; Class B medical waste disposal. Conclusion. Knowledge of the clinical manifestations of the new coronavirus infection and methods for preventing infection of patients and medical personnel is necessary for each dentist and maxillofacial surgeon to prevent new episodes of spread and provide quality medical care.

First documentation of seismic stratigraphy and depositional signatures of Zhongsha atoll (Macclesfield Bank), South China Sea

Carbonate platforms form informative archives for paleoclimates and their internal structures can also hold crucial information about the tectonic history and carbonate evolution of the ocean basins. The Zhongsha atoll (Macclesfield Bank) forms the largest atoll system in the South China Sea with a surface area of 23500 km 2 . However, the internal structure and evolution of this atoll system is completely unknown. 2D multichannel seismic reflection data were acquired in 2017 over the Zhongsha atoll in the South China Sea to unravel the stratigraphy, geomorphology, depositional processes, and seismic facies of one of the world's largest atoll for the first time. This Neogene carbonate platform comprises more than 1 km thick carbonate sequence and overlies a metamorphic basement. The southeastern part of the atoll comprises a fault-controlled graben system, which was formed during the Cenozoic rifting stage of the South China Sea. Most of the faults trend NE-SW and E-W and terminate at or slightly above the top of Middle Miocene strata. Atolls and abundant organic reefs initiated on the positive relief and closely mimicked the underlying topography during the Early Miocene. Shallow-water carbonates continued growing through Middle Miocene to present times. Regional uplift led to subaerial exposure, termination of platform growth and karstification during the Miocene. We also reveal a number of fluid-flow features such as vertical sub-bottom venting features (chimneys and pipes), chaotic reflection zones, which provide the first evidence of active fluid venting in the area of Zhongsha atoll. The Neogene sedimentation history of Zhongsha atoll further provide an important paleoenvironmental context for future scientific drilling to better constrain the evolution of Asia Monsoon. • First documentation of seismic stratigraphy and deposition of Zhongsha atoll (Macclesfield Bank), South China Sea. • Reefs and lagoons developed during the post-rift phase, whose onset is marked by a turning point around the time of the formation of reflector T50. • Three drowning events are identified to tentatively imply three episodes of fast sea floor spreading in the study region.

Evidence of ridge propagation in the eastern Gulf of Mexico from integrated analysis of potential fields and seismic data

Integrated analysis of gravity, magnetic, and seismic data reveals two phases of spreading in the eastern Gulf of Mexico (GOM) including two distinct spreading centers, suggesting a major ridge reorganization during the opening of the eastern part of the GOM. Ridge propagation between the two spreading episodes explains the following observations: 1) the drastic asymmetry in the oceanic domain of northeastern GOM, 2) the presence of two distinct crustal zones with dramatically different thickness and physical properties, and 3) the observed seismicity within the oceanic domain that is not aligned with any known tectonic structure. The initial Late Jurassic spreading center (~160 Ma) resulted in thin (~5 km) and uniform oceanic crust with a fast compressional velocity (7 km/s). Based on our analysis, the estimated full spreading rate of this older spreading event is less than 1 cm/yr. The spreading regime changed in Early Cretaceous around 150 Ma, resulting in a propagation (i.e., jump) of the spreading center. The new spreading episode was characterized by a change in spreading direction and increased magma supply as it produced thicker (up to 9 km) oceanic crust with a typical two-layered structure. Despite the increase in magmatic material, the full rate of this younger spreading event estimated from our analysis is only slightly faster (1.1 cm/yr assuming that spreading ceased at 137 Ma). The later conclusion is consistent with the morphology of the spreading centers mapped by seismic data. Our analysis shows that recent deep crustal earthquakes in the middle of the Gulf of Mexico are aligned with the boundary between the two identified distinct oceanic zones, referred here as a pseudofault.

The metamorphic evolution and tectonic significance of the Sumdo HP–UHP metamorphic terrane, central-south Lhasa Block, Tibet

Abstract The Lhasa terrane, forming one of the main tectonic components of the Himalayan–Tibetan orogen, has received a lot of attention as it records multiple episodes of plate spreading, subduction and collision within the realm of the Paleo-Tethys Ocean. A review of the mineralogical, petrological, geochemical and geochronological data of eclogites, associated blueschists and garnet-bearing mica schists from the Sumdo high- and ultrahigh-pressure metamorphic (HP/UHP) complex in the central/southern part of the Lhasa terrane, is present here so that the origin and tectono-metamorphic evolution of this important suture can be deduced. By re-evaluating the original published P – T conditions for the metamorphic rocks of the Sumdo Complex, we consider that the Sumdo Complex has experienced low temperature HP/UHP metamorphic conditions, characteristic of fast subduction (and exhumation) in a typical oceanic subduction zone setting. The original wide spread in the maximal peak P – T conditions could be reduced in size due to thus far unknown inconsistencies in the usage of applied geothermobarometric techniques. The remaining spread in the maximal P – T conditions ( c. 200°C/10 kbar) of the HP/UHP regions can be explained by a mechanism that the rocks from individual tectonic slices were subducted to different depths and followed by juxtaposition on their way back to the surface. A re-consideration of the isotopic ages of eclogites from the Sumdo Complex demonstrates that the opening of the Paleo-Tethys Ocean, located in between the two major components of the Lhasa terrane, was initiated prior to c. 280 Ma and the eclogite facies metamorphism is likely to be of late Permian ( c. 260 Ma) to early Triassic age (245–225 Ma), recording different ages of subduction from individual slices of the oceanic crust. The closure of the Paleo-Tethys Ocean resulted, no earlier than 210 Ma, in the final collision between the northern and southern Lhasa blocks. This final collision event may have been triggered by the initial subduction of the Bangong–Nujiang Tethys Ocean in the north.

Oblique strike-slip motion off the Southeastern Continental Margin of India: Implication for the separation of Sri Lanka from India

The ocean floor in the Bay of Bengal has evolved after the breakup of India from Antarctica since the Early Cretaceous. Recent geophysical investigations including updated satellite derived gravity map postulated two phases for the tectonic evolution of the Bay of Bengal, the first phase of spreading occurred in the NW-SE direction forming its Western Basin, while the second phase occurred in the N-S direction resulting in its Eastern Basin.Lack of magnetic data along the spreading direction in the Western Basin prompted us to acquire new magnetic data along four tracks (totaling ∼3000 km) to validate the previously identified magnetic anomaly picks. Comparison of the synthetic seafloor spreading model with the observed magnetic anomalies confirmed the presence of Mesozoic anomalies M12n to M0 in the Western Basin. Further, the model suggests that this spreading between India and Antarctica took place with half-spreading rates of 2.7–4.5 cm/yr.The trend of the fracture zones in the Western Basin with respect to that of the Southeastern Continental Margin of India (SCMI) suggests that SCMI is an oblique transform margin with 37° obliquity. Further, the SCMI consists of two oblique transform segments separated by a small rift segment. The strike-slip motion along the SCMI is bounded by the rift segments of the Northeastern Continental Margin of India and the southern margin of Sri Lanka.The margin configuration and fracture zones inferred in its conjugate Western Enderby Basin, East Antarctica helped in inferring three spreading corridors off the SCMI in the Western Basin of the Bay of Bengal. Detailed grid reconstruction models traced the oblique strike-slip motion off the SCMI since M12n time. The strike-slip motion along the short northern transform segment ended by M11n time. The longer transform segment, found east of Sri Lanka lost its obliquity and became a pure oceanic transform fault by M0 time. The eastward propagation of the Africa-Antarctica spreading center initiated the anticlockwise separation of Sri Lanka from India by M12n time. Seafloor spreading south of Sri Lanka due to the India-Antarctica spreading episode and the simultaneously occurring strike-slip motion east of Sri Lanka restricted this separation resulting in a failed rift. Thus Sri Lanka with strike-slip motion to its east, failed rift towards west, continental extension to its north and rifting to its south behaved as a short lived microplate during the Early Cretaceous period and remained attached to India thereafter.

Multiple peaks patterns of epidemic spreading in multi-layer networks

The study of epidemic spreading on populations of networked individuals has seen recently a great deal of significant progresses. A common point in many of past studies is, however, that there is only one peak of infected density in each single epidemic spreading episode. At variance, real data from different cities over the world suggest that, besides a major single peak trait of infected density, a finite probability exists for a pattern made of two (or multiple) peaks. We show that such a latter feature is distinctive of a multilayered network of interactions, and reveal that a two peaks pattern may emerge from different time delays at which the epidemic spreads in between the two layers. Further, we show that the essential ingredient is a weak coupling condition between the layers themselves, while different degree distributions in the two layers are also helpful. Moreover, an edge-based theory is developed which fully explains all numerical results. Our findings may therefore be of significance for protecting secondary disasters of epidemics, which are definitely undesired in real life.

Arab-Madagascan brachiopod dispersal along the North-Gondwana paleomargin towards the Western Tethys Ocean during the Early Toarcian (Jurassic)

Multiple approaches, mainly focused on assessing the depositional environments, paleotemperature, chronostratigraphical and paleobiogeographical data, morphometrical analyses and the study of the internal structure of spiriferinide brachiopods assigned to the genus Calyptoria, have revealed that this brachiopod fauna migrated from their Arab-Madagascan homeland along the North-Gondwana paleomargin into the peri-Iberian epicontinental platform system, in the same well-known spreading episode suffered by the Arab-Madagascan Bouleiceras ammonite fauna over the worldwide-distributed early Toarcian platforms. This brachiopod fauna has been so far overlooked as potential Arab-Madagascan immigrant fauna, as it was integrated together with diverse assemblages well-established in the peri-Iberian basins. Dispersal of Calyptoria stock was conditioned by the interplay of several factors, such as the tectonic framework, the development of epicontinental seas on both Tethyan margins, the early Toarcian transgression, the prevailing ocean current pattern, and their limited ability for dispersal. The revised chronostratigraphical framework of this dispersal episode reveals the coincidence with the thermal maximum recorded prior to the Early Toarcian Mass Extinction Event (ETMEE) in the westernmost Tethys Ocean. The concurrence of these factors played a significant role in the Calyptoria spreading, showing an inter-tropical distribution between 0° and 30° in both hemispheres. The taxonomical updating performed in the light of the current systematic trends support this adaptive strategy carried out by Calyptoria species, consisting of a sudden and practically synchronous dispersal without outstanding morphological changes instead of the diverse evolution of different brachiopod taxa in response to the environmental changes related to the ETMEE. Updating and rearranging of the species attributed to the genus Calyptoria suggest a new systematic scheme for several former attributions, supporting that lower Toarcian occurrences of L. undulata from westernmost Tethyan areas belong to Calyptoria, thus pointing towards the dispersal from the Northern peri-Gondwana seas to the westernmost Tethyan epicontinental platforms. Similar adaptive strategies were linked to other extinction events, supporting a possible pattern in the response of certain brachiopod populations to such biotic crises.

Temporal phylogeography of Yersinia pestis in Madagascar: Insights into the long-term maintenance of plague.

BackgroundYersinia pestis appears to be maintained in multiple, geographically separate, and phylogenetically distinct subpopulations within the highlands of Madagascar. However, the dynamics of these locally differentiated subpopulations through time are mostly unknown. To address that gap and further inform our understanding of plague epidemiology, we investigated the phylogeography of Y. pestis in Madagascar over an 18 year period.Methodology/Principal findingsWe generated whole genome sequences for 31 strains and discovered new SNPs that we used in conjunction with previously identified SNPs and variable-number tandem repeats (VNTRs) to genotype 773 Malagasy Y. pestis samples from 1995 to 2012. We mapped the locations where samples were obtained on a fine geographic scale to examine phylogeographic patterns through time. We identified 18 geographically separate and phylogenetically distinct subpopulations that display spatial and temporal stability, persisting in the same locations over a period of almost two decades. We found that geographic areas with higher levels of topographical relief are associated with greater levels of phylogenetic diversity and that sampling frequency can vary considerably among subpopulations and from year to year. We also found evidence of various Y. pestis dispersal events, including over long distances, but no evidence that any dispersal events resulted in successful establishment of a transferred genotype in a new location during the examined time period.Conclusions/SignificanceOur analysis suggests that persistent endemic cycles of Y. pestis transmission within local areas are responsible for the long term maintenance of plague in Madagascar, rather than repeated episodes of wide scale epidemic spread. Landscape likely plays a role in maintaining Y. pestis subpopulations in Madagascar, with increased topographical relief associated with increased levels of localized differentiation. Local ecological factors likely affect the dynamics of individual subpopulations and the associated likelihood of observing human plague cases in a given year in a particular location.

THE CALLOVIAN UNCONFORMITY AND THE OPHIOLITE OBDUCTION ONTO THE PELAGONIAN CARBONATE PLATFORM OF THE INTERNAL HELLENIDES

The carbonate-platform-complex and the oceanic formations of the central Pelagonian zone of the Hellenides evolved in response to a sequence of plate tectonic episodes of ocean spreading, plate convergence and ophiolite obduction. The biostratigraphies of the carbonate platform and the oceanic successions, show that the Triassic-Early Jurassic platform was coeval with an ocean where pillow basalts and radiolarian cherts were being deposited. After convergence began during late Early- Jurassic - Middle Jurassic time, the oceanic leading edge of the Pelagonian plate was subducted beneath the leading edge of the oceanic, overriding plate. The platform subsided while a supra-subduction, volcanic-island-arc evolved. Biostratigraphic and geochemical evidence shows that the platform and the oceanic floor, temporarily became subaerially exposed during Callovian time. This “Callovian event” is suggested to have taken place as oceanic lithosphere first made compressional, tectonic contact with the carbonate platform, initiating a basal detachment fault, along which the platform was thrust upwards. The central Pelagonian zone became an extensive land area that was supplied with laterite from an ophiolite highland. A similar emergence of Vardar ophiolite most likely took place in the Guevgueli area. The Callovian emergence shows that the initial ophiolite obduction onto the platform took place about 25 million years before the final emplacement of the ophiolite during Valanginian time.

Magma plumbing system and seismicity of an active mid-ocean ridge volcano

At mid-ocean ridges volcanism generally decreases with spreading rate but surprisingly massive volcanic centres occur at the slowest spreading ridges. These volcanoes can host unexpectedly strong earthquakes and vigorous, explosive submarine eruptions. Our understanding of the geodynamic processes forming these volcanic centres is still incomplete due to a lack of geophysical data and the difficulty to capture their rare phases of magmatic activity. We present a local earthquake tomographic image of the magma plumbing system beneath the Segment 8 volcano at the ultraslow-spreading Southwest Indian Ridge. The tomography shows a confined domain of partial melt under the volcano. We infer that from there melt is horizontally transported to a neighbouring ridge segment at 35 km distance where microearthquake swarms and intrusion tremor occur that suggest ongoing magmatic activity. Teleseismic earthquakes around the Segment 8 volcano, prior to our study, indicate that the current magmatic spreading episode may already have lasted over a decade and hence its temporal extent greatly exceeds the frequent short-lived spreading episodes at faster opening mid-ocean ridges.

Parotid and mandibular gland secretion by red kangaroos, Macropus rufus, in response to heat stress

Salivary flow rates from ipsilateral parotid and mandibular glands were measured in conscious red kangaroos over a 70–90-min period during episodes of saliva spreading induced by heat stress. At the onset of saliva spreading, mandibular flow rose rapidly to plateau at 1.12 ± 0.10 mL min–1 for the collection intervals after the first 10 min of licking. Parotid flow increased more slowly and progressively, reaching secretion rates similar to those of the mandibular gland after 40 min of saliva spreading, exceeding mandibular flow after 70 min and showing no indication that it had reached maximum secretion at 90 min of saliva spreading. The ion concentrations of both parotid and mandibular salivas during saliva spreading were similar to those previously reported for parasympathomimetic stimulation. The low osmotic concentration of mandibular saliva relative to plasma (40%) makes it a functionally better evaporative coolant than parotid saliva, which was nearly isosmotic with plasma. The increased production of hydrogen ions associated with the increased secretion of bicarbonate by the parotid gland would tend to offset the respiratory alkalosis due to panting thereby helping to maintain acid/base balance during periods of prolonged heat stress.

Major zircon megacryst suites of the Indo-Pacific lithospheric margin (ZIP) and their petrogenetic and regional implications

Zircon megacrysts (± gem corundum) appear in basalt fields of Indo-Pacific origin over a 12,000 km zone (ZIP) along West Pacific continental margins. Age-dating, trace element, oxygen and hafnium isotope studies on representative zircons (East Australia–Asia) indicate diverse magmatic sources. The U–Pb (249 to 1 Ma) and zircon fission track (ZFT) ages (65 to 1 Ma) suggest thermal annealing during later basalt transport, with < 1 to 203 Ma gaps between the U–Pb and ZFT ages. Magmatic growth zonation and Zr/Hf ratios (0.01–0.02) suggest alkaline magmatic sources, while Ti—in—zircon thermometry suggests that most zircons crystallized within ranges between 550 and 830 °C. Chondrite-normalised multi-element plots show variable enrichment patterns, mostly without marked Eu depletion, indicating little plagioclase fractionation in source melts. Key elements and ratios matched against zircons from magmatic rocks suggest a range of ultramafic to felsic source melts. Zircon O-isotope ratios (δ18O in the range 4 to 11‰) and initial Hf isotope ratios (eHf in the range +2 to +14) encompass ranges for both mantle and crustal melts. Calculated Depleted Mantle (TDM 0.03–0.56 Ga) and Crustal Residence (0.20–1.02 Ga) model ages suggest several mantle events, continental break-ups (Rodinia and Gondwana) and convergent margin collisions left imprints in the zircon source melts. East Australian ZIP sites reflect prolonged intraplate magmatism (~85 Ma), often during times of fast-migrating lithosphere. In contrast, East Asian-Russian ZIP sites reflect later basaltic magmatism (<40 Ma), often linked to episodes of back-arc rifting and spreading, slow-migrating lithosphere and slab subduction.

Geochemistry and petrogenesis of volcanic rocks from Daimao Seamount (South China Sea) and their tectonic implications

The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6Ma) was formed 10my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr–Nd–Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a ‘Dupal’ isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6Ma. The seamount subsided rapidly (>0.12mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (<0.12mm/y). We propose that the parental magmas of SCS seamount lavas originated from the Hainan mantle plume. In contrast, lavas from contemporaneous seamounts in other marginal basins in the western Pacific are subduction-related.