Igneous Rock Types Research Articles

Analysis of bead wear in diamond wire sawing considering the rock properties and production rate

Predicting the wear rate of diamond beads in the diamond wire sawing process is one of the most important factors in the optimized design and cost estimation of quarrying. This paper aims to predict the wear rate of diamond beads as one of the principal performance criteria in dimension stone quarrying. Saw operating parameters and mechanical and physical properties of rock are the most effective factors on diamond bead wear. In the same working conditions (at constant operating parameters), the wear rate of diamond wire saw is strongly affected by the production rate, and the characteristics of rock. In this study, the uniaxial compressive strength, Schmiazek abrasivity factor, Mohs hardness, and Young’s modulus were selected as the main physical and mechanical properties of rock. The 11 types of igneous rocks were cut in the laboratory using a diamond wire saw and a fully instrumented cutting platform. During the cutting process, the wear rate of diamond beads were determined after each cutting test. The wear rate of diamond bead and rock characteristics were evaluated using simple and multiple curvilinear regression analysis, and prediction models were developed. The developed models were validated by considering the t-test, F-test, correlation coefficient and the plots of predicted versus actual values. The results indicated that the wear rate of diamond beads can be reliably predicted using the developed model.

A multi-isotope approach towards constraining the origin of large-scale Paleoproterozoic B-(Fe) mineralization in NE China

Borate ore deposits occur predominantly in Phanerozoic evaporative sedimentary environments but are scarce in Precambrian strata. However, massive B- and Mg-rich borate deposits are abundant in the Paleoproterozoic strata of Northeast (NE) China. In addition, several of these borate deposits are dominated by Fe (e.g., >60% Fe2O3 content in the Wengquangou deposit). To constrain the origin of these unusual deposits, we obtained B, Fe, and Mg isotope data on the wall rocks and ores of the Mg-rich Houxianyu borate deposit and the Fe-rich Wengquangou borate deposit in NE China. The δ11B values of the borate deposits (10.7±4.4‰, n=15) are higher than most types of igneous and non-evaporative sedimentary rocks, suggesting that B is of evaporative sedimentary origin. However, the borate deposits have a limited range of δ56Fe values near 0‰ (0.05±0.18‰, n=24), which is similar to igneous rocks and thus points to a magmatic origin for the Fe. The δ26Mg values of the ores and associated rocks (−0.52±0.34‰, n=24) are intermediate between Mg-rich carbonate rocks and igneous rocks, suggesting a mixed sedimentary and magmatic origin for the Mg. Regional metamorphism and intense deformation modified the deposits significantly by promoting metasomatic alteration of the igneous rocks and evaporite minerals, thus resulting in mixing of magmatic and sedimentary-evaporative sources as well as recrystallization of the sedimentary borate precursors to metamorphic borate minerals. Hence, the B, Fe, and Mg isotope data together with geological and mineralogical observations indicate that formation of the Paleoproterozoic B-(Fe) deposits in NE China involved a three-stage process: enrichment of B and Mg by evaporative sedimentation, introduction of Fe and additional Mg by volcanism, and modification by regional metamorphism/metasomatism.

Geochemistry and petrogenesis of Late Carboniferous igneous rocks from southern Mongolia: Implications for the post-collisional extension in the southeastern Central Asian Orogenic Belt

Late Carboniferous is a critical period in terms of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). In this study, we report the petrology, geochronology and geochemistry of Late Carboniferous mafic to felsic rocks from southern Mongolia, to better characterize the Late Carboniferous magmatism in the southeastern CAOB. Three types of igneous rocks have been identified, including diabase dykes, porphyritic granites and quartz monzonite dykes. LA-ICP MS zircon U-Pb dating of these rocks shows that the diabase dykes and porphyritic granites were simultaneously emplaced at 306Ma. The quartz monzonite dykes were subsequently emplaced at 300Ma. The diabases belong to the high-K calc-alkaline series and show strong enrichment of large ion lithophile elements (LILE; e.g., Rb, Ba and Sr) and depletion in high field strength elements (HFSE; Nb, Ta and Ti), with enriched mantle isotopic signature (εNd(t)=−2.6 to +0.5). They were likely derived from the partial melting of metasomatized sub-continental lithospheric mantle (SCLM) and experienced variable degrees of crustal contamination. The porphyritic granites are characterized by high SiO2 contents, strong negative Eu anomalies with low εNd(t) values of −3.0 to −2.7, suggesting that they were derived from crustal anatexis and experienced strong fractional crystallization. Compared with the porphyritic granites, quartz monzonites display lower SiO2 contents, weaker negative Eu anomalies with higher and more variable εNd(t) values (−0.3 to +4.2). This indicates that the quartz monzonites were probably generated by the mixing of crust- and mantle-derived magmas. The petrographic and geochemical data suggest that all the mafic to felsic rocks in the southern Mongolia formed in a post-collisional extensional setting.

Petrology and Geochemistry of Igneous Rocks in Zarinkamar Area, NE of Shahrood, Iran

Zarinkamar area is located in northeast of Shahrood, northeast of Iran, between latitudes of 36°37’ - 36°42’ and longitudes of 55°07’ - 55°12’. Different types of igneous rocks have an outcrop on the region. Intrusive igneous rocks include a type of syenite with aegirine pyroxene and the other includes quartz from 5 to 20 percent. Moreover, aegirine syenite, ordinary syenite, and quartz syenite have been injected into Karaj Formation with an age of middle to early Eocene. Also, some parts of trachyte magma have given rise to produce trachyte outcrops after passing the crust and current flows. Studying major and rare elements shows that a magma separation has been caused by separation smelting or a crystal separation. These magmas are alkaline and shoshonites and they have been originated in a continental rift. The magma of Zarinkamar region has been combined with acidic continent crust as it rose to the surface. High amount of Th, and Rb and low amount of Ti, P, Sr, and Ba can prove this hypothesis.

The Role of Fluids in the Formation of Rare Earth Element Deposits

Fluids play an important role in the formation of many rare earth element (REE) deposits. Groundwater and hydrothermal fluids can transport these elements and with changes in fluid composition or properties, the REEs can be removed from solution by adsorption or precipitation of REE-rich minerals. Currently, REEs are primarily produced from two types of ore deposits, ion adsorption clay deposits (located in southern China) and carbonatites. Ion adsorption clay deposits in southern China form by lateritic weathering of underlying granites. Groundwater is responsible for the mobilization, transport, and deposition of the REEs in forming these ore deposits. Carbonatites are a relatively rare type of igneous rock that contain the highest concentrations of REEs of any igneous rocks. Ore-grade REE enrichment in carbonatites can result from crystallization of REE mineral phases directly from the magma or by hydrothermal processes. One carbonatite-related REE ore deposit, the Mount Weld deposit (Australia), was formed by lateritic weathering of the underlying carbonatite.

Appendix Geochronology in Myanmar (1964–2017)

This Appendix summarizes the published isotopic age data for Myanmar up to early 2017. It is intended as a resource for geoscientists to stimulate future investigations. A variety of age dating methods have been applied in Myanmar since the mid-1960s, when Searle & Ba Than Haq (1964) published ages of rocks from the Mogok area data based on their uranium contents. During the 1970s the K–Ar and Rb–Sr methods were applied to date biotite, muscovite and amphibole and aggregates of these minerals (‘whole-rock method’), mainly of granitic rocks. In the K–Ar dating method the original sample was split into two halves. One half of the sample was analysed for K and the second half of the sample for Ar. Ideally the K–Ar isotope data document the closure temperatures when the magmatic minerals stabilized, such as biotite (250–350°C), muscovite (300–400°C) and hornblende (450–500°C), the results being used to date the solidification of an igneous rock. In practice K–Ar age data were often ambiguous due to resetting of the magmatic Ar and K isotope system by later tectonic and metasomatic events. However, it was found that the isotopes of Rb and Sr in magmatic minerals were more stable and not so affected by later events. Dating of intrusion of magma could be derived from the linear plot of the ratios of 87Sr/86Sr v. 87Rb/86Sr from a collection of related igneous rock types from a locality to plot an ‘isochron age’. In addition, the initial 87Sr/86Sr ratios gave an indication of the source of an igneous rock. 87Sr/86Sr ratios less than 0.705 suggested a mantle origin, while higher 87Sr/86Sr ratios indicated crustal contaminations of some nature. The analysis of Rb and Sr isotopes, major oxides and trace elements …

A simple method for quantitative analysis of elements by WD-XRF using variable dilution factors in fusion bead technique for geologic specimens

A common approach in the quantitative analysis of geological samples by X-ray fluorescence is to establish calibration lines for elements of interest by using several reference materials (RMs) and/or the combination of RMs and pure chemicals. Herein, we introduce an alternative to use only two RMs, to establish a calibration application. Variation of the dilution factor is employed to generate a dynamic range of concentrations for each RM and to evenly furnish the calibration lines to analyze certain matrices. A wide range of dilution factors were employed from 2–54 times dilution (with respect to the flux to sample ratios). Calibration lines for the major elements including: Si, Al, Ca, Fe, Mg, Na, Mn, and Ti show an extremely high level of linearity with all elements. R2 values greater than 0.9990 were obtained for each analyzed element. The calibration application was validated by checking against a variety of geological RMs including petroleum and carbonate rich shale (SGR-1), Muscovite rich marine shale (SBC-1), metamorphic rock (SDC-1), carbonatite (COQ-1), and types of igneous rocks (GSP-2, BCR-2, AGV-2, QLO-1, and W-2). Mixtures of Alumina and Silica (ARG-1 and ARG-2) and pure SiO2 beads were also analyzed to further check the application. Rigorous statistical analysis on the RMs confirms the reliability of the calibration application for the employed matrices. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of I- and S-type granite parent material mineralogy and geochemistry on soil fertility: A multivariate statistical and Gis-based approach

This study provides new insights into the effects of a parent material on inherent soil fertility. We describe the mineralogy and geochemistry of I- and S-type granites and their effect on soil fertility under similar environmental conditions in Borborema Province, NE Brazil, using standard mineralogical, geochemical and soil analyses as well as multivariate analysis and geographic information system approaches. We hypothesized that soils derived from I-type granites will develop higher natural fertility than those derived from S-type granites. The mineralogy and chemistry of the two different granitic parent materials have a profound effect on soil fertility. The S-type and I-type granites have different mineralogical compositions: the S-type granites have higher concentrations of silica, and the I-type granites contain larger concentrations of mafic and accessory minerals, mainly amphibole and apatite. Geophysical field measurements show different magnetic susceptibilities: for example, the I-type granites have substantial higher magnetic properties than the S-type granites. Soils derived from the I-type granites have higher natural fertility than soils derived from the S-type granites. Principal component, cluster and discriminant analyses (95% accuracy) were effective tools to discriminate among soils developed from different granites. Spatial distribution maps are suitable soil fertility management tools to guide and support soil fertility management decisions for improved soil- and crop-specific fertilization. These findings have wider implications in large parts of the tropics (South America, sub-Saharan Africa, India, SE and East Asia and Australia), which are underlain by igneous and metamorphic rock types, including S- and I-type granites, and where effective management tools are needed to increase the nutrient use efficiencies for increased productivity of food, fodder and energy crops.

Black box in red: porphyry in space and time

ABSTRACTPorphyry, a specific type of igneous rock, highly appreciated because of its purple tone, remains throughout western history a central feature in strategies of political representation: Roman and Byzantine emperors, as well as medieval kings and modern leaders have assessed it in the course of the execution of their rule. They all drew on the long and distinct symbolical tradition of the use of porphyry. However, the significance of the precious material also derived from a unique history of exploitation, distribution and workmanship that endowed porphyry with an exclusive spatial connotation. This paper indicates this history in the exemplary case of the four porphyry sarcophagi of the Norman kings and Holy Roman emperors in Palermo Cathedral.

Distribution of igneous rocks in China revealed by aeromagnetic data

After several decades of aeromagnetic surveys, the measured data now cover nearly the entire Chinese continent and part of the China Sea. These data were first applied in this research and could provide important insights into the distribution of igneous rocks beneath the earth’s surface. Because different types of igneous rocks have a magnetic difference and produce distinct aeromagnetic anomalies on aeromagnetic ΔT image with reduction to the pole or other data calculating maps. By analyzing more than 240 thousand magnetic susceptibility data points and aeromagnetic anomalies of known igneous rocks in the Chinese continent, it was determined that mafic-ultramafic rocks commonly have a high magnetic susceptibility and cause linear and strong positive aeromagnetic anomalies. Intermediate-felsic rocks have a stable and low magnetic susceptibility and show a flat gradient variation and regular shape. Volcanic rocks have large variability in regard to magnetic susceptibility and romance; therefore, the aeromagnetic anomalies are always random or show variation within a planar area and decrease rapidly when an upward continuation is applied. Following the aeromagnetic data and calculating the maps of the vertical first order derivative and the tilt derivative, and combining this information with known outcrops of igneous rocks, we renewed the boundaries of 82 known mafic-ultramafic rocks, 228 known intermediate-felsic rocks and 131 known volcanic rocks. In addition, we newly mapped concealed igneous rocks of 203 mafic-ultramafic rocks, 2322 intermediate-felsic rocks and 494 volcanic rocks. The igneous rocks can be identified as nine ultra-mafic belts, 10 mafic belts (or regions), 27 intermediate-felsic belts and eight volcanic blocks. The results indicate that the mafic-ultramafic rocks are mainly distributed in Tibet, Erenhot of Inner Mongolia and northern Qilian and the smaller zones in the western Kunlun, Tianshan, western Junggar, eastern Tibet, Maqin in Gansu and the Ailao Mountain (Mtn.) areas. The mafic rocks are mostly outcropped in northern Tibet, southwestern Sanjiang, Kangdian in Sichuan, Baise and Rongjiang in Guangxi, Yinjiang in Guizhou, Dabashan Mtn., Southern Dabie Mtn, Bangbu in Anhui, Qiemo in Xinjiang. The intermediate-felsic rocks are mainly located in the orogenic system and rarely within the craton. Volcanic rocks are widely developed in eastern and western China such as the circumference of Songliao Basin, Erlian Basin, the southern Yellow Sea - Subei Basin, Bohai Bay Basin, eastern Zhejiang, the circumference of Hainan Island, southern Sichuan - northern Yunan, central Tibet, the Bachu area in Tarim Basin, Junggar Basin and Turpan-Hami Basin.

Paleozoic collisional and intraplate granitoids of the Baikal area: comparative geochemistry and petrogenesis

Early Paleozoic granitoids of autochthonous and allochthonous facies in the Baikal area (Ol’khon Island, Khamar-Daban Ridge) are in close spatial association with gneisses, migmatites, and plagiogranites and are usually confined to granite–gneiss domes. They are virtually not subjected to magmatic differentiation. Formation of granitoids of the Solzan massif and Sharanur complex lasted 26–28 Myr, which might be considered an indicator of collisional granitoid magmatism. Collisional granitoids of different provinces have a series of indicative features: They are peraluminous and highly potassic and are enriched in crustal elements (Rb, Pb, and Th) but sometimes have low contents of volatiles. In contrast to collisional magmatism, petrogenesis of intraplate granitoids does not depend on the composition and age of the enclosing rocks. The geochemical evolution of intraplate granitoid magmatism in the Baikal area is expressed as an increase in contents of F, Li, Rb, Cs, Sn, Be, Ta, Zr, and Pb and a decrease in contents of Ba, Sr, Zn, Th, and U during the differentiation of multiphase intrusions. The geochemical diversity of these granitoids formed both from crustal and from mantle sources and as a result of the mantle–crust interaction, might be due to the effect of plume on the geologic evolution of intraplate magmatism. The wide range of compositions and geochemical types of igneous rocks (from alkali and subalkalic to rare-metal granitoids) within the Late Paleozoic Baikal magmatism area suggests its high ore potential.

The use of lithic raw materials during the Upper Paleolithic in eastern China: A focus on microblade industries

During the Upper Paleolithic, many sites with microblade industries were distributed across northeastern China and the North China Plain in eastern China. Based on the composition of lithic raw materials (LRMs) and the site distributions of microblade industries, this study defined five territories of human groups in two regions of China: 1) the western Changbai Shan Mountains (Mount Paektu) and Song-Nen Plain in northeastern China and 2) the southern Yanshan Mountains, Yi-Shu River Basin, and western Huang-Huai Plain in the North China Plain. In northeastern China, high-quality LRMs, including various types of igneous rock and obsidian, were used in combination with local LRMs such as flint and agate. Based on the distribution range of high-quality LRMs, the territories of human groups in that region are estimated at 300–450 km. It is believed that residential systems were established for the long-distance transport of LRMs and the long-distance movement of human groups. One such system included microblade technology based on biface and flake-blade reduction systems. In contrast, the territory of human groups in the North China Plain was small, with an area estimated at 100–230 km. Given the numerous small sites in that region, it is believed that human groups moved frequently within their territories because they were highly mobile and dependent on local LRM sources (e.g., flint) near their occupation sites. Human groups might have employed various microcore reduction systems to produce microblades, even from limited LRMs. Preliminary conclusions suggest that the divergent activities of late Upper Paleolithic human groups in eastern China could reflect variations in regional economic strategies and ecological environments between the Last Glacial Maximum and the Younger Dryas.

A rock-surface microweathering index from Schmidt hammer R-values and its preliminary application to some common rock types in southern Norway

An index of the degree of rock-surface microweathering based on Schmidt hammer R-values is developed for use in the field without laboratory testing. A series of indices – I2 to In, where n is the number of successive blows with the hammer – is first proposed based on the assumption that the R-values derived from successive impacts on the same spot on a weathered rock surface converge on the value characteristic of an unweathered surface of the same lithology. Of these indices, the I5 index, which measures the difference between the mean R-value derived from first and fifth impacts as a proportion of the mean R-value from the fifth impact, is regarded as optimal: use of fewer impacts (e.g. in an I2 index) underestimates the degree of weathering whereas use of more impacts (e.g. in an I10 index) makes little difference and is therefore inefficient and may also induce an artificial weakening of the rock. Field tests of these indices on weathered glacially-scoured bedrock outcrops of nine common metamorphic and igneous rock types from southern Norway show, however, that even after ten impacts, successive R-values fail to approach the values characteristic of unweathered rock surfaces (e.g. bedrock from glacier forelands and road cuttings). An improved *I5 index is therefore preferred, in which the estimated true R-value of an unweathered rock surface is substituted. Weathered rock surfaces exposed to the atmosphere for ~10,000years in southern Norway exhibit *I5 indices of 36–57%, values that reflect a similarly high degree of weathering irrespective of the rock type.

Deformation and Strength Characteristics of Simulat ed Columnar Jointed Rock Mass under Conventional Triaxial Compression Tests

The columnar jointed rock mass is a type of extrusive igneous rock. Correctly understanding the deformation and strength characteristics of columnar jointed rock mass under triaxial stress condition is essential for hydropower station and underground cavern excavation. As it is difficult to obtain the mechanical properties of columnar jointed rock mass by field tests, conventional triaxial compression tests were carried out on simulated columnar jointed rock mass specimens with different dip angles between the direction of principal stress and the column prisms. The changes of Young's modulus and peak compressive strength with dip angle β were obtained. The results indicate that the Young's modulus and peak compressive strength increase with confining pressure for the same group of specimens. However, under the same confining pressure, the curves of Young's modulus and peak strength versus dip angle resemble a “decreasing-order shape”, that is, the Young's modulus and peak strength decrease with dip angle β from 0° to 45°, reach minimum values at β = 45°, and then remain relatively constant with the increase of dip angle. Furthermore, four typical failure modes of columnar jointed rock mass specimens under triaxial compression condition are summarized based on the test results. Their failure mechanisms are also discussed.

Potential alkali silica reactivity of various rock types in an aggregate granite quarry

Generally, alkali–silica reaction (ASR) is considered as an internal chemical reaction between the alkaline components in the cement and active silica–silicate based mineral constituents of some aggregates. The use of aggregates susceptible of ASR in concrete can cause a severe degradation of the concrete structures because of several reasons e.g. high humidity and sea saline water. Utilization of potentially alkali–silica reactive aggregates needs to conduct reliable tests for evaluating their alkali–silica reactivity. The objective of this study is to identify the potential alkali–silica reactivity of several aggregate rock types. To achieve this objective, a granite quarry which is operated to produce aggregates was selected and investigated. Six samples of five igneous rock types were collected from the mentioned site and an extensive laboratory tests consisting of petrographic examination and accelerated Bar Mortar test were conducted on these samples to assess the potential alkali–silica reactivity. According to ASTM C 1260 suggested method, three Bar Mortar tests were performed on each sample. Based on the obtained results, it was found that five samples of all six samples were considered as innocuous due to their average expansion rates which are less than 0.1%. Only one sample which was collected from the fault zone considered as reactive with average expansion rate of 0.2404% which is more than 0.2%.

Termination time of peak decratonization in North China: Geochemical evidence from mafic igneous rocks

Geophysical and petrological data indicate destruction of the cratonic lithosphere in North China in the Mesozoic, resulting in replacement of the ancient subcontinental lithospheric mantle (SCLM) by the juvenile SCLM. However, it remains to be answered when the craton destruction would have been terminated in the Mesozoic. This question is resolved by studying the two types of mafic igneous rocks with contrasting geochemical compositions from North China. The first type of mafic igneous rock shows arc-like trace element distribution patterns and enriched radiogenic Sr–Nd isotope compositions, with emplacement ages spanning from the Triassic to Early Cretaceous. The mafic magmatism is absent in a period from ~200Ma to ~135Ma, recording the thinning of cratonic lithosphere due to the westward flat subduction of the Paleo-Pacific slab beneath the North China Craton. In contrast, the second type of mafic igneous rocks exhibits oceanic island basalts (OIB)-like trace element distribution patterns and relatively depleted radiogenic Sr–Nd isotope compositions, with emplacement ages spanning from the Early Cretaceous to Cenozoic. Zircon U–Pb dating yields an age of ~121Ma for the geochemical transformation between the two types of mafic igneous rocks. This age marks a dramatic demarcation in the composition of their mantle sources. As such, the nature of mantle lithosphere in North China was changed from the ancient SCLM to the juvenile SCLM at ~121Ma. Thus, this age not only signifies the tectonic transition from the enriched mantle to the depleted mantle in the Early Cretaceous, but also dates the termination of peak decratonization in North China. Therefore, the craton destruction in the Early Cretaceous is temporally and spatially associated with the dramatic changes in the geochemical composition of mantle lithosphere.

Magnetic susceptibility anisotropy as a predictive exploration tool of metasomatic iron oxide deposits: Example from the Panj-Kuh iron ore body, NE Iran

The Panj-Kuh iron deposit, hosted by Late Eocene igneous rocks in north of central Iran, is associated with a syenitic intrusive body. Magnetic fabric investigations indicate that the Panj-Kuh pluton was emplaced within a sinistral shear zone. Corridors of sheared and metasomatized rocks show that the shear zone was active after emplacement of the pluton and in the final steps of crystallization. The sheared rocks allowed for circulation of hydrothermal fluids during cooling of the magma and caused the pervasive Na–Ca alteration. The ferrimagnetic phase in fresh syenite is mostly euhedral or subhedral magnetite, and is observed adjacent to, or as inclusion in biotite and pyroxene. Anisotropy of magnetic susceptibility (AMS) in the fresh syenite is due to preferred shape orientation of magnetite grains. In Na–Ca altered syenites, magnetite has reduced or has been totally absorbed. The alteration results in decreased bulk susceptibilities (Km) and higher anisotropy degrees (P%), accompanied by changes in the shape of magnetic susceptibility anisotropy ellipsoid. This study of the Panj-Kuh pluton suggests that AMS can be used for mapping lithology and hydrothermal alteration types. Since various types of hydrothermal alteration create, transform or destroy ferrimagnetic minerals in a mineralized system, susceptibility measurements aid mapping of igneous rock type, alteration zoning and mineralization. Integrating petrography, magnetic mineralogy, bulk magnetic susceptibility and preferred orientations of principal axes of the AMS in fresh and altered rocks can be used to generate predictive magnetic exploration models for metasomatic iron oxide deposits.

Improved correlation between the static and dynamic elastic modulus of different types of rocks

The relationship between the static and dynamic elastic modulus in rock materials has been frequently addressed in scientific literature. Overall, when it comes to the study of materials with a wide range of elastic moduli, the functions that best represent this relationship are non-linear and do not depend on a single parameter. In this study, the relationships between the static and dynamic elastic modulus of eight different igneous, sedimentary and metamorphic rock types, all of which are widely used as construction material, were studied. To this end, the elastic modulus values of 33 samples were obtained which, together with the values obtained for 24 other samples in a previous study, allowed a new relationship between these parameters to be proposed. Firstly, linear and nonlinear classical models were used to correlate static and dynamic moduli, giving R 2 of 0.97 and 0.99, respectively. A classical power correlation between static modulus and P-wave velocity has also been proposed, giving an R 2 of 0.99 and a sum of the squared differences (SSE) of 553.93. Finally, new equations relating static and dynamic modulus values have been proposed using new nonlinear expressions. These consider: (a) bulk density (R 2 = 0.993 and SSE = 362.66); (b) bulk density and total porosity of rock (R 2 = 0.994 and SSE = 332.16); and (c) bulk density, total porosity of rock and uniaxial compressive strength (R 2 = 0.996 and SSE = 190.27). The expressions obtained can be used to calculate the static elastic modulus using non-destructive techniques, in a broad range of rock materials.

Two types of the crust-mantle interaction in continental subduction zones

Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust, and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal materials and the crust-mantle interaction. This study presents a review of geochronology and geochemistry for postcollisional mafic igneous rocks from the Hong’an-Dabie-Sulu orogens and the southeastern edge of the North China Block. The available results indicate two types of the crust-mantle interaction in the continental subduction zone, which are represented by two types of mafic igneous rocks with distinct geochemical compositions. The first type of rocks exhibit arc-like trace element distribution patterns (i.e. enrichment of LILE, LREE and Pb, but depletion of HFSE) and enriched radiogenic Sr-Nd isotope compositions, whereas the second type of rocks show OIB-like trace element distribution patterns (i.e. enrichment of LILE and LREE, but no depletion of HFSE) and depleted radiogenic Sr-Nd isotope compositions. Both of them have variable zircon O isotope compositions, which are different from those of the normal mantle zircon, and contain residual crustal zircons. These geochemical features indicate that the two types of mafic igneous rocks were originated from the different natures of mantle sources. The mantle source for the second type of rocks would be generated by reaction of the overlying juvenile lithospheric mantle with felsic melts originated from previously subducted oceanic crust, whereas the mantle source for the first type of rocks would be generated by reaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts from subsequently subducted continental crust of the South China Block. Therefore, there exist two types of the crust-mantle interaction in the continental subduction zone, and the postcollisional mafic igneous rocks provide petrological and geochemical records of the slab-mantle interactions in continental collision orogens.

The origin of along-rift variations in faulting and magmatism in the Ethiopian Rift

The geological record at rifts and margins worldwide often reveals considerable along-strike variations in volumes of extruded and intruded igneous rocks. These variations may be the result of asthenospheric heterogeneity, variations in rate and timing of extension; alternatively, pre-existing plate architecture and/or the evolving kinematics of extension during breakup may exert first order control on magmatism. The Main Ethiopian Rift (MER) in East Africa provides an excellent opportunity to address this dichotomy: it exposes, along-strike, several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north. Here we perform studies of volcanic cone density and rift obliquity along strike in the MER. By synthesizing these new data in light of existing geophysical, geochemical and petrological constraints on magma generation and emplacement, we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin. The timing of rift sector development, the three-dimensional focusing of melt, and the ponding of plume material where the rift dramatically narrows, each influence igneous intrusion and volcanism along the MER. However, rifting obliquity plays an important role in localizing intrusion into the crust beneath en-echelon volcanic segments. Along-strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting, as well as the physical state of the convecting mantle at the time of breakup.