Basalt Content Research Articles

Disseminated sulphides in basalts from the northern Central Indian Ridge: implications on late-stage hydrothermal activity

This study examined the mineralogy and mineral chemistry of disseminated sulphides (mainly chalcopyrite-pyrite) in partly altered basalts from the northern Central Indian Ridge, Indian Ocean in order to understand the role of hydrothermal alterations and infer possible sulphide formation history. Pyrite and chalcopyrite are dominant sulphide minerals and generally associated with the oxide phases including magnetite and often ilmenite. Close association of sulphide and oxide minerals suggests that they are paragenetically related. Sulphides also occur as late impregnated veins cutting through the basaltic hosts. The chemical compositions of pyrite (avg. Fe 46.3 wt%, S 53.7 wt%) and chalcopyrite (avg. Cu 34.4 wt%, Fe 30.7 wt%, S 34.7 wt%) are almost uniform, while the secondary ilmenite often shows MnO enrichment (up to 3.0–3.4 wt%). The associated altered minerals typically resemble the greenschist facies mineral assemblages—e.g. chlorite±epidote. Evidence of albitisation and silicification suggests low-temperature hydrothermal alteration processes. This is supported by the bulk Au content (up to 60 ppb) of host-altered basalts with pyrite mineralisation. Au is usually associated with late-stage pyrites and thus related with low-temperature hydrothermal activity. Close to the dredge location, tectonic activity around the Vityaz megamullion might have promoted hydrothermal circulation and subsequent alteration of the mineral constituents in basalts, eventually inducing the formation of late-stage disseminated sulphide minerals in these rocks.

Controls on thallium uptake during hydrothermal alteration of the upper ocean crust

Hydrothermal circulation is a fundamental component of global biogeochemical cycles. However, the magnitude of the high temperature axial hydrothermal fluid flux remains disputed, and the lower temperature ridge flank fluid flux is difficult to quantify. Thallium (Tl) isotopes behave differently in axial compared to ridge flank systems, with Tl near-quantitatively stripped from the intrusive crust by high temperature hydrothermal reactions, but added to the lavas during low temperature reaction with seawater. This contrasting behavior provides a unique approach to determine the fluid fluxes associated with axial and ridge flank environments. Unfortunately, our understanding of the Tl isotopic mass balance is hindered by poor knowledge of the mineralogical, physical and chemical controls on Tl-uptake by the ocean crust.Here we use analyses of basaltic volcanic upper crust from Integrated Ocean Drilling Program Hole U1301B on the Juan de Fuca Ridge flank, combined with published analyses of dredged seafloor basalts and upper crustal basalts from Holes 504B and 896A, to investigate the controls on Tl-uptake by mid-ocean ridge basalts and evaluate when in the evolution of the ridge flank hydrothermal system Tl-uptake occurs.Seafloor basalts indicate an association between basaltic uptake of Tl from cold seawater and uptake of Cs and Rb, which are known to partition into K-rich phases. Although there is no clear relationship between Tl and K contents of seafloor basalts, the data do not rule out the incorporation of at least some Tl into the same minerals as the alkali elements. In contrast, we find no relationship between the Tl content and either the abundance of secondary phyllosilicate minerals, or the K, Cs or Rb contents in upper crustal basalts. We conclude that the uptake of Tl and alkali elements during hydrothermal alteration of the upper crust involves different processes and/or mineral phases compared to those that govern seafloor weathering. Furthermore, a correlation between the Tl and S concentrations of upper crustal basalts from Holes U1301B, 504B and 896A indicates that Tl is primarily incorporated into secondary sulfides. Given that some of these secondary sulfides formed as a result of microbial sulfate reduction, microbial action is at least indirectly responsible for Tl-uptake.Thallium-enrichment of ridge flank basalts requires a Tl-bearing fluid and physical, chemical and microbial conditions that favor secondary sulfide formation. Uptake of Tl occurs in reducing environments in the background rocks away from fluid flow pathways during early ‘open’ circulation of oxidizing seawater but more pervasively throughout the system during later ‘restricted’ circulation of reducing fluids. The Tl-isotope system is therefore a useful tracer of the fluid flux through both the ‘open’ and ‘restricted’ ridge flank hydrothermal regimes.

Joint inversion of P- and S-receiver functions and dispersion curves of Rayleigh waves: The results for the Central Anatolian Plateau

The P- and S-wave receiver functions and dispersion curves of the fundamental Rayleigh wave are used to study the lithosphere within the Central Anatolian Plateau. The results for eight broadband seismic stations are presented. It is established that within the plateau, the crust with a thickness of about 35 km is underlain by the mantle lid with its bottom at a depth of about 60 km. The velocities of longitudinal (Vp) and shear (Vs) waves in this layer are at most 7.6 and 4.5 km/s, respectively, and the Vp/Vs ratio is close to 1.7 (i.e., by 6% lower than in the standard IASP91 and PREM models). Such a low velocity ratio is characteristic of rocks having high orthopyroxene content. Beneath the high-velocity mantle lid, the S-wave velocity decreases to 4.0–4.2 km/s and the Vp/Vs ratio is close to its standard value (1.8). At most stations, the P-wave receiver functions do not contain seismic phase P410s, which is formed at the global seismic boundary at a depth of 410 km. The seismic boundary at a depth of 410 km is related to the olivine-spinel phase transformation, and its absence can indicate the anomalously low olivine content and high basalt content. This anomaly is probably associated with the subduction of a large amount of oceanic crust during the closure of the Tethys. The results of the study overall indicate the high informativity of the used method.

Mechanical Property for the Combining Yarn of BF/GF and Polypropylene

In order to study the mechanical property for the combining yarn of BF/GF and polypropylene, 8 groups of combining yarn were designed and prepared. Through testing the mechanical property of the yarns, the affection of some parameters on the property of the yarns was analyzed. And following conclusions can be gotten. For BF/polypropylene combining yarn, when the fiber content of basalt is about 50.7%, the mechanical property of the yarn is the best. When the fiber content of basalt is about 43.7%, the mechanical property of the yarn is the worst. For GF/polypropylene combining yarn, the optimal and worst ratio is 55.42% and 44.4%, respectively.

Carbon dioxide emission to Earth’s surface by deep-sea volcanism

Large amounts of CO 2 are transferred from Earth’s interior to the surface by volcanism. On a geological time scale, the rate of CO 2 emission has controlled the evolution of Earth’s atmosphere and climate, as well as the dynamic processes that take place in the mantle and core. The total rate of natural CO 2 emission from Earth has been estimated on the basis of CO 2 fl ux from arc, mid-ocean-ridge, and hotspot volcanism. However, previous estimates have overlooked the CO 2 emitted from a recently discovered type of volcanism—petit-spot volcanism—that occurs on the deep-sea fl oor. Here, we measure the CO 2 and H 2 O contents of glassy basalts produced by petit-spot volcanism and estimate the initial contents to be >5 wt% and 1.0–1.1 wt%, respectively. Based on these values and magma fl ux of petitspot volcanism, we show that the rate of CO 2 emission from petitspot volcanoes (2.7–5.4 × 10 11 g CO 2 yr –1 ) is a few percent of the CO 2 emissions from arc and mid-ocean-ridge volcanism, and up to ~14% of that from hotspot volcanism. Thus, the contribution to the carbon cycle on Earth of the large amounts of CO 2 that have been emitted from the deep-sea fl oor by petit-spot volcanism has not previously been recognized.

Research on extraction of FeO and TiO<sub>2</sub> contents of the Sinus Iridum region based on optical remote sensing data

The extraction of iron and titanium contents of lunar surface is of great importance to both researches of origin and development of the Moon and exploitation and utilization of lunar resource. Iron and titanium contents extracted by various optical data are always different, it is necessary to obtain these contents through multiple optical data and analyze these results. This paper makes use of data from different optical periods (OP1B, OP2C) of Moon Mineralogy Mapper (M3) onboard Chandrayaan-1 and two calibrated data sets (pc1, pc2) of Interference Imaging Spectrometer (IIM) onboard Chang’E-1 to extract iron and titanium contents of the Sinus Iridum region. The results are as followed: FeO peak value obtained by OP1B and OP2C is 17.80wt% and 17.60wt% respectively, which is higher than pc1’s 15.80wt% and pc2’s 14.00wt%. FeO average value achieved by OP1B and OP2C is 16.91wt% and 16.79wt% respectively, higher than pc1’s 14.11wt% and pc2’s 13.46wt%. 0wt%-4wt% titanium contents percentage acquired by OP2C is 74.46%, higher than pc1’s 54.66% and pc2’s 62.46%, while OP1B’s is 37.55%. TiO2 average value obtained by OP1B and OP2C is 5.35 wt% and 3.16wt% respectively. TiO2 average value achieved by pc1 and pc2 is 4.25wt% and 3.65wt% respectively. Very low and low titanium basalt of the Sinus Iridum area nearly approach 50% and 40% respectively, which mainly locate on Im1 and Im2 units. High titanium basalt that account for nearly 10% percentage locates on EIm unit. On the whole, titanium content of basalt obtained by optical data show a unimodal distribution, low titanium basalt dominates, which differs from the bimodal distribution of the samples’ titanium. Iron and titanium contents of the Sinus Iridum’s basalt, with its age become younger, present a growing tendency. Among the four data sets, the photometric calibration of pc2 data is the best, the precision of photometric calibration of pc1 is rather low, the reflectance of various optical periods of M3 differs, and the precision of photometric calibration of M3 data from different optical periods needs to be improved.

Comparison between Composite Column Using Limestone and Basalt Concrete

This research is conducted to study the experimental behavior of composite steel-concrete columns with basalt additives. Various percentages of basalt are added to the concrete mixes to investigate its effect on the total axial compressive capacity of the columns. Expected failure scenarios of the columns are: concrete compressive failure, buckling of steel section, and de-bonding between steel and concrete sections. A conventional limestone composite column was used as base mix. The results of the study indicate a significant improvement in structural behavior and strength of the columns by increasing the percentage of basalt content.

Volcano: nature and culture, by James Hamilton. Reaktion Books, London, 2012. No. of pages: 208. Price: UK£14.95. ISBN 978-1-86189-917-0 (paperback)

Books with simple titles like volcano or volcanoes are well known to the geologist (e.g. Francis, 1976; Lopes, 2010). Here is another one, but it is a somewhat out of the ordinary. Volcanoes are the subject, but their geological aspects are subservient to the history of their artistic depiction and influence. The production of what is a paperback for a large pocket (about 210 × 148 mm) is on high quality paper and the many reproductions of (mostly) paintings are in colour, many at full page. These are uniquely fascinating and make me wonder why a photograph of a recent eruption (Kilauea?) was chosen for the cover, making it look like any other book on volcanoes. The text is well written, readable and full of information that will be new to most geologists. Only when Hamilton talks geology, rarely and briefly, might we be critical; for example, “… the crust first developed a rigid surface roughly 2.5 billion years ago” (p. 29); reference to Vesuvius as atypical is without adequate explanation as to why (p. 32); “Low viscosity lava is low in silica and high in basalt content” (p. 39); and so on. But Hamilton's book shouldn't be read for its petrological and tectonic whimsies. It is the illustrations that take centre stage and the text supports them at every step. Many of the paintings inspire awe. Vesuvius and Etna dominate paintings from the 18th Century and earlier, being readily accessible to the European cognoscenti. A visit to Vesuvius, including an obligatory walk to the crater, may or may not have coincided with volcanic activity, but it still fascinated even if painted in repose. Artistic license, based on eyewitness accounts and earlier paintings, could produce even more magnificent renditions. This license led to restorations of the destruction of Pompeii and Herculaneum ranging from the Gothic (p. 95) to the fanciful (pp. 111, 117). The works of native Icelandic artists included paintings in a starkly different style from European artists (e.g. p. 152) that are no less fascinating. Asides on British scientists and naturalists are many; for example, Joseph Banks climbed Hekla in 1772 (p. 53). But Hamilton seems to think that eruption forecasting is a modern attainment; I don't think many modern experts in the field would make such a confident pronouncement except within broad limits. And Hamilton has as much a weakness for the numerical as any scientist; “It would be meaningless to quote” the statistics of the Mt St Helens eruption of 1980 (p. 165), but he then proceeds to do so! One interesting aside, De la Beche's Jamaican slave plantation has long been a slight embarrassment to modern geologists. That J. M. W. ‘Turner had financial interests in West Indian slavery in the 1810s and early 1820s’ (p. 90) demonstrated to me that involvement was broader among the moneyed classes than I had suspected. This book is not written for geologists per se, but will appeal particularly to them. As I found, it will make its way to the popular science shelves in bookshops rather than the art and history sections, so it will be easy to find. And its many beautiful and breath-taking images will make it a ‘dipper’, pulled off the shelf just to enjoy these great geological spectacles.

Constraints from melt inclusions and their host olivines on the petrogenesis of Oligocene-Early Miocene Xindian basalts, Chifeng area, North China Craton

The geochemical characteristics of melt inclusions and their host olivines provide important information on the processes that create magmas and the nature of their mantle and crustal source regions. We report chemical compositions of melt inclusions, their host olivines and bulk rocks of Xindian basalts in Chifeng area, North China Craton. Compositions of both bulk rocks and melt inclusions are tholeiitic. Based on petrographic observations and compositional variation of melt inclusions, the crystallizing sequence of Xindian basalts is as follows: olivine (at MgO > ~5.5 wt%), plagioclase (beginning at MgO = ~5.5 wt%), clinopyroxene and ilmenite (at MgO 6 wt%), indicate that Xindian basalts are possibly derived from a pyroxenite source rather than a peridotite source. In the CS-MS-A diagram, all the high MgO melt inclusions (MgO > 6.0 wt%) project in the field between garnet + clinopyroxene + liquid and garnet + clinopyroxene + orthopyroxene + liquid near 3.0 GPa, further suggesting that residual minerals are mainly garnet and clinopyroxene, with possible presence of orthopyroxene, but without olivine. Modeling calculations using MELTS show that the water content of Xindian basalts is 0.3–0.7 wt% at MgO = 8.13 wt%. Using 20–25 % of partial melting estimated by moderately incompatible element ratios, the water content in the source of Xindian basalts is inferred to be ≥450 ppm, much higher than 6–85 ppm in dry lithospheric mantle. The melting depth is inferred to be ~3.0 GPa, much deeper than that of tholeiitic lavas (<2.0 GPa), assuming a peridotite source with a normal mantle potential temperature. Such melting depth is virtually equal to the thickness of lithosphere beneath Chifeng area (~100 km), suggesting that Xindian basalts are derived from the asthenospheric mantle, if the lithospheric lid effect model is assumed.

The influence of hybridization on impact damage behavior and residual compression strength of intraply basalt/nylon hybrid composites

Low-velocity impact and compression after impact (CAI) tests were performed to investigate the impact behavior of hybrid composite laminates reinforced by basalt-nylon intraply fabrics. The purpose of using this hybrid composite is to combine the good mechanical property of basalt fiber as a brittle fiber with the excellent impact resistance of nylon fiber as a ductile fiber. Five different types of woven fabric with different contents of nylon (0%, 25%, 33.3%, 50% and 100%) were used as reinforcement. The effect of nylon/basalt fiber content on impact parameters, impact damage behavior and CAI strength was studied at different nominal impact energy levels (16, 30 and 40J). The results indicate that at low impact energy, hybridization and variation in basalt/nylon fiber content cannot improve the impact performance of composite plates. With increasing impact energy, the impact performance becomes more and more dependent on the content of nylon and basalt.

Experiment Study of BFRP Bars’ Mechanical Properties

The testing rule of mechanical properties of material can be established and the mechanical performance can be found by studying the basic mechanical properties of BFRP bars. Using the opressive sleeve anchor developed by the researchers,tensile tests of BFRP bars are carried out according to the national standards of “GFRP bar tensile test methods”.The BFRP bar’s force-deformation curve is linear before the force-deformation relationship is destroyed,therefore,referring to steel wire or steel cable,the BFRP bar’s reliable strength is suggested to be approximately 80% of its ultimate tensile strength. The BFRP bar’s tensile elastic modulus is related to the content of basalt fiber.The tensile elastic modulus increases with the increase of the basalt fiber’s content and the content increases when the BFRP bar’s diameter becomes longer, so the tensile elastic modulus increases with the increase of its diameter. Compared with steel, the BFRP bar is obviously superior in the aspects of tensile strength, corrosion resistance ,etc,therefore to use the BFRP bar in reinforced concrete structures insead of steel is feasible.

Specific characteristics of coating glazes based on basalt

Investigations in this paper has been carried out in order to define the correlation between specific characteristics of coating glazes based on basalt, fired faience and appearance and the quality of the ceramic product surface. The paper presents the initial results of research on possibilities for utilisation of basalt from the locality “Vrelo” – Kopaonik Mountain (Serbia) for producing the opaque glaze.From frits with different basalt content (25%, 30%, 35%, and 60%) with addition of water and 5% of the kaolin “Zetlizer”, the liquid glazes-suspensions were made (G-1/25, G-2/30, G-3/35, and G-4/60). The primary fired biscuit-shaped faience was used for applying the glazes by dipping, pouring and brushing methods. The further firing process of glazes took place in a laboratory tunnel furnace, under the following operating parameters: temperature T=980°C and retention time t=3h (hours).The initial investigation has shown that the basalt from the locality Vrelo is suitable for obtaining applicable glazes, bringing the attractive and decorative colours to the surfaces of the faience ceramics. The best results were achieved by adding the iron pigments.

Wear Behavior of Basalt Filled Low Density Polyethylene Composites

The friction and wear performance of pure LDPE and 10%, 30%, 50% and 70% basalt filled (by wt) LDPE composite were comparatively evaluated under dry sliding conditions. Wear tests were carried out at room temperature under 5, 10 and 20N loads and at 0.5, 1.0 and 1.5 m/s sliding speeds. The coefficients of friction of the composites were significantly influenced with increase in basalt content. Friction coefficient of the LDPE was getting decreased from 0.51 to 0.13 with increase in basalt content, depending on applied loads and sliding speeds. The results show that the wear rates for pure LDPE and basalt filled composites increase with increasing loads and sliding speeds. The wear rates of the basalt filled composites were significantly affected from the basalt content. Wear rates of the LDPE was decreased from 2.596 × 10−3 to 6.8 × 10−5 mm3/m with increase in basalt content, depending on applied loads and sliding speeds.

Slurry erosion behaviors of basalt filled low density polyethylene composites

In this study, slurry erosion behaviors of basalt filled low density polyethylene composites were investigated. Pure low density polyethylene and four different compositions of the composites 10 wt.%, 30 wt.%, 50 wt.% and 70 wt.% basalt were used in the study. Slurry wear, tensile strain, hardness and fracture toughness tests were performed on the samples. Samples turns in the abraded slurry media including 50 wt.% Al 2O 3 with nominal particle size of 500 μm and the erosion tests of pure low density polyethylene and basalt filled composites were performed at the contact angles of 15°, 30°, 45°, 60°, 75° and 90° for 30 min. in 3 periods at 500 rpm turning speed (1 m/s speed). It was observed that erosion rate have no effect up to 30 wt.% basalt content. Wear resistance of the composites including over 30 wt.% basalt were micro structural examination of the worn samples showed that the basalt particles on the worn surface can be sustained by matrix. Basalt particles were worn more slowly than that of the matrix. The more the basalt content in the basalt filled low density polyethylene resulted to the lower the tensile strength, tensile strain and fracture toughness, and the higher the hardness. The slurry erosion rate of the basalt filled low density polyethylene composites was getting sharply increase above 30 wt.% basalt content above 60° contact angle.

Water distribution across the mantle transition zone and its implications for global material circulation

Various methods for inferring the water distribution in Earth's mantle are reviewed including geochemical and geophysical methods. The geochemical approach using the water contents of basalts shows that the water content in the source regions of ocean island basalt is generally larger than that of the source region of mid-ocean ridge basalt, but the location of the source regions of ocean island basalts is poorly constrained. Geophysical approaches have potential of providing constraints on the spatial distribution of water but their usefulness depends critically on the sensitivity of geophysical observations to water content relative to other factors, in addition to the resolution of geophysical observations. Existing experimental data on the influence of water on seismologically observable properties and on electrical conductivity are reviewed. Frequently used seismological observations such as the anomalies in seismic wave velocities and of the topography on the mantle discontinuities are only weakly sensitive to water content but more sensitive to other factors such as the major element chemistry and temperature for a typical range of water contents. In contrast, electrical conductivity is highly sensitive to water content and only modestly sensitive to other factors such as temperature, oxygen fugacity and major element chemistry. Models of electrical conductivity–depth profiles are constructed where the influence of hydrogen and iron partitioning among coexisting minerals and of the depth variation in oxygen fugacity are incorporated. It is shown (i) that the electrical conductivity varies more than two orders of magnitude for a plausible range of water content in the mantle (~ 10 ppm wt to ~ 1 wt.%) and (ii) that if water content is constant with depth, there will be a drop in electrical conductivity at ~ 410-km. Although the resolution is not as high as seismological observations, geophysically inferred electrical conductivity distributions generally show higher conductivity in the mantle transition zone than the upper mantle, suggesting that the water content in the transition zone is higher than that in the upper mantle with some lateral variations. Implications of inferred water distribution are discussed including the possible partial melting near 410-km and its role in global water circulation.

The Determining Role of Inorganic Particles on Physical and Mechanical Properties of Reinforced Polyethylene Composites

The interactions between basalt chosen as a reinforcement material and low-density polyethylene (LDPE) chosen as a matrix material in polymer matrix composite (PMC) were investigated in this study. A variety of mechanical tests were performed on the resultant composites, which had appropriate compositions. Tensile, flexural, density, and hardness tests have been carried out, and the relationship between the basalt content and properties were examined. Energy Dispersive Spectrometer (EDS) and Scanning Electron Microscopy (SEM) facilities were applied on surfaces of composites. The addition of basalt increases the flexural strength, elastic modulus, density, and hardness while decreasing the tensile strain to fracture, toughness, and fracture energy.

Geochemical identification of impactor for Lonar crater, India

Abstract— The only well‐known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ?0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI‐mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ?2 Am2/Kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral‐shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe2O3 (by ?1.5 wt%), MgO (?1 wt%), Mn (?200 ppm), Cr (?200 ppm), Co (?50 ppm), Ni (?1000 ppm) and Zn (?70 ppm), and low Na2O (?1 wt%) and P2O5 (?0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na2O and P2O5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume.

Chemical Composition and Mechanical Properties of Basalt and Glass Fibers: A Comparison

The geometrical and mechanical properties and chemical composition of different basalt and glass fibers have been investigated. Tensile tests were performed on short basalt fiber made by melt blowing, glass fiber and three different types of continuous basalt fibers made by spinneret method. The chemical composition was evaluated by plasma atomic emission spectroscopy. The geometrical and mechanical properties of continuous basalt and glass fibers were similar to each other in terms of diameter, tensile strength and modulus. Short basalt fibers had considerably lower average diameter and mechanical performance with relatively high standard deviation. The SiO2 and Al2 O3 content of basalt fibers showed correlation with tensile properties of fibers. Results revealed that continuous basalt fibers were competitive with glass fibers and short basalt fibers were weaker in terms of quality and mechanical properties. It was observed that the joint SiO 2 and Al2O3 content of basalt and glass fibers showed correlation with tensile properties of fibers.

Study of some Physical properties of basalt – clay mixes

Jordanian basalt was added to China clay on different mixes up to 60% by weight. Some of physical properties were studied. Mixes basalt showed a remarkable increase in density with increasing basalt addition. Porosity was the property greatly affected with increasing the firing temperature. Maximum reduction in porosity was observed at high firing temperature for all mixes and this will cause increase in hardness values. The different phases were determined by X–ray analysis. The expansion coefficient decreases with the increase of the basalt content. No significant differences of the heating rate are observed on the properties of the thermal expansion after firing at 1100°C for all mixes.

Variable involvements of mantle plumes in the genesis of mid-Neoproterozoic basaltic rocks in South China: A review

Ca. 825–720 Ma global continental intraplate magmatism is generally linked to mantle plumes or a mantle superplume that caused rifting and fragmentation of the supercontinent Rodinia. Widespread Neoproterozoic igneous rocks in South China are dated at ca. 825–760 Ma. There is a hot debate on their petrogenesis and tectonic affiliations, i.e., mantle plume/rift settings or collision/arc settings. Such competing interpretations have contrasting implications to the position of South China in the supercontinent Rodinia and in Rodinia reconstruction models. Variations in the bulk-rock compositions of primary basaltic melts can provide first order constraints on the mantle thermal–chemical structure, and thus distinguish between the plume/rift and arc/collision models. Whole-rock geochemical data of 14 mid-Neoproterozoic (825–760 Ma) basaltic successions are reviewed here in order to (1) estimate the primary melts compositions; (2) calculate the melting conditions and mantle potential temperature; and (3) identify the contributions of subcontinental lithosphere mantle (SCLM) and asenthospheric mantles to the generation of these basaltic rocks. In order to quantify the mantle potential temperatures and percentages of decompression melting, the primary MgO, FeO, and SiO 2 contents of basalts are calculated through carefully selecting less-evolved samples using a melting model based on the partitioning of FeO and MgO in olivine. The mid-Neoproterozoic (825–760 Ma) potential temperatures predicted from the primary melts range from 1390 °C to 1630 °C (mostly > 1480 °C), suggesting that most 825–760 Ma basaltic rocks in South China were generated by melting of anomalously hot mantle sources with potential temperatures 80–200 °C higher than the ambient Middle Ocean Ridge Basalt (MORB)-source mantle. The mantle source regions of these Neoproterozoic basaltic rocks have complex histories and heterogeneous compositions. Enriched mantle sources (e.g., pyroxenite and eclogite) are recognized as an important source for the Bikou and Suxiong basalts, suggesting that their generations may have involved recycled components. Trace elements variations show that interactions between asthenospheric mantle (OIB-type mantle) and SCLM played a very important role in generation of the 825–760 Ma basalts. Our results indicate that the SCLM metasomatized by subduction-induced melts/fluids during the 1.0–0.9 Ga orogenesis as a distinct geochemical reservoir that contributed significantly to the trace-elements and isotope inventory of these basalts. The continental intraplate geochemical signatures (e.g., OIB-type), high mantle potential temperatures and recycled components suggest the presence of a mantle plume beneath the Neoproterozoic South China block. We use the available data to develop an integrated plume-lithosphere interaction model for the ca. 825–760 Ma basalts. The early phases of basaltic rocks (825–810 Ma) were most likely formed by melting within the metasomatized SCLM heated by the rising mantle plume. The subsequent continental rift allowed adiabatic decompression partial melting of an upwelling mantle plumes at relatively shallow depth to form the widespread syn-rifting basaltic rocks at ca. 810–800 Ma and 790–760 Ma.