Formation Of Igneous Rocks Research Articles

Reconstruction of the Sakhalin marginal paleobasin by geological and petrochemical data

The structural and compositional volcanosedimentary complexes and igneous rocks of the Sakhalin marginal paleobasin as well as the geodynamic setting were described. The Sakhalin marginal paleobasin was formed in Sakhalin Island and the adjacent water areas at the end of the Early Cretaceous-start of the Late Cretaceous. The paleobasin was a part of the Kula Plate separated from the ocean along with spreading zones and oceanic volcanic islands by the Sea of Okhotsk microcontinent and the Jurassic-Early Cretaceous Sheltinga volcanic island arc. The petrochemical features and geodynamic setting of the igneous rock formation testify to the fact that magma-generating tectonomagmatic structures of the epioceanic Sakhalin marginal paleobasin continued functioning after its isolation under intensive terrigenous sedimentation. The Sakhalin marginal paleobasin had a heterogeneous basement composed of oceanic and continental crust blocks of the Earth. The paleobasin completed its development in the Paleogene.

Age of nephrite-bearing dikes of the Uzunkyr Belt (South Urals): Local U-Pb isotope analysis of zircon and Sr-Nd isotope data of rock-forming minerals

Through local U-Pb isotope analysis of zircon and Sir-Need data on rock-forming minerals, the age of nephrite-bearing monzonite-diorite dikes of the Uzunkyr Belt has been determined. The derived datings coincide with known geological events that took place in the Phanerozoic on the territory of the South Urals. Xenogenic zircons prove the participation of the Upper Ordovician units in the tectonic structure of the studied area. Devonian zircons are associated with assimilation of subvolcanic rocks which are middle and basic in composition and whose formation time correlates with the appearance of the subduction zone with the Magnitogorsk island arc above it. Early Carboniferous datings indicate the relationship between dike formation and formation of the continental arc-shaped structure to which the Syrostan massif (monzodiorite-granite formation) belongs. The age range of the Uzunkyr nephrite-bearing dikes coincides with that of intrusives (350–336 Ma) of the Magnitogorsk Belt, where formation of gabbro series was also changed by formation of subalkali and alkali igneous rocks. According to the analogous data on zircon datings from metamorphic rocks of the Il’menogorskii Complex, the given territory later evolved as a whole.

Relationship between topological order and glass forming ability in densely packed enstatite and forsterite composition glasses

The atomic structures of magnesium silicate melts are key to understanding processes related to the evolution of the Earth's mantle and represent precursors to the formation of most igneous rocks. Magnesium silicate compositions also represent a major component of many glass ceramics, and depending on their composition can span the entire fragility range of glass formation. The silica rich enstatite (MgSiO(3)) composition is a good glass former, whereas the forsterite (Mg(2)SiO(4)) composition is at the limit of glass formation. Here, the structure of MgSiO(3) and Mg(2)SiO(4) composition glasses obtained from levitated liquids have been modeled using Reverse Monte Carlo fits to diffraction data and by density functional theory. A ring statistics analysis suggests that the lower glass forming ability of the Mg(2)SiO(4) glass is associated with a topologically ordered and very narrow ring distribution. The MgO(x) polyhedra have a variety of irregular shapes in MgSiO(3) and Mg(2)SiO(4) glasses and a cavity analysis demonstrates that both glasses have almost no free volume due to a large contribution from edge sharing of MgO(x)-MgO(x) polyhedra. It is found that while the atomic volume of Mg cations in the glasses increases compared to that of the crystalline phases, the number of Mg-O contacts is reduced, although the effective chemical interaction of Mg(2+) remains similar. This unusual structure-property relation of Mg(2)SiO(4) glass demonstrates that by using containerless processing it may be possible to synthesize new families of dense glasses and glass ceramics with zero porosity.

Design and Study of PDC Bit for Igneous Rock Formation of Santanghu

Based on the geological configuration and formation lithology of igneous rock stratum of Santanghu, optimized design methods of PDC (polycrystalline diamond compact) bit are used to design PDC bit crown shape, cutting angle, the distribution of cutters and hydraulic structure, etc. Especially, these methods, which are design methods of gentle crown profile, spiral blade, high-density distribution of cutters, suitable back rake angle, and hydraulic structures which are more flexible nozzles of asymmetric arrangement and deeper fluid course layout, are fit for high hardness, multiple interbed and high abrasiveness of the igneous rock formation. The bit designed in this paper has turned out to be much better in the experiment of Horse 36 well of Santanghu.

Magnetism, entropy, and the first nano-machines

Abstract The efficiency of bio-molecular motors stems from reversible interactions ∼ k B T; weak bonds stabilizing intermediate states (enabling direct conversion of chemical into mechanical energy). For their (unknown) origins, we suggest that a magnetically structured phase (MSP) formed via accretion of superparamagnetic particles (S-PPs) during serpentinization (including magnetite formation) of igneous rocks comprising the Hadean Ocean floor, had hosted motor-like diffusion of ligand-bound S-PPs through its ‘template’-layers. Ramifications range from optical activity to quantum coherence. A gentle flux gradient offers both detailed-balance breaking non-equilibrium and asymmetry to a magnetic dipole, undergoing infinitesimal spin-alignment changes. Periodic perturbation of this background by local H-fields of templatepartners can lead to periodic high and low-template affinity states, due to the dipole’s magnetic degree of freedom. An accompanying magnetocaloric effect allows interchange between system-entropy and bath temperature. We speculate on a magnetic reproducer in a setting close to the submarine hydrothermal mound-scenario of Russell and coworkers that could evolve bio-ratchets.

南部北上帯古期岩類のＬＡ‐ＩＣＰ‐ＭＳ Ｕ‐Ｐｂジルコン年代

The Japanese Islands have grown through the formation of igneous rocks and accretionary prism caused by subduction of oceanic plates. However, the timing of the initiation of the subduction is not well defined. The South Kitakami Belt (SKB) in NE Japan is the best field to solve this problem. Here, basement igneous rocks are covered by successions of Ordovician to Early Cretaceous beds (450-100 Ma). We obtained LA-ICP-MS U-Pb zircon ages from the following localities. Along the Yakushigawa-Valley section in the northeastern part of the SKB, we examined the ages of (1) trondhjemite of the Kagura Complex of basement igneous rocks, (2) felsic tuff of the Koguro Formation conformably covering the Kagura Complex, and (3) Yakushigawa Formation covering the Koguro Formation and lying under the Silurian Odagoe Formation. In the Ohasama area in the northwestern part of the SKB, we examined the age of (4) Nameirizawa Formation, which probably lies below the Silurian Orikabetoge Formation. Moreover, we examined the ages of four samples from the Hikami Granite body in the central part of the SKB. The ages of trondhjemite (08331-5: 466±6 Ma) of the Kagura Complex and felsic tuff (08331-4b: 457±10 Ma) of the Koguro Formation indicate that the subduction of an oceanic plate had already started at 466 Ma, and that the Koguro Formation is the oldest age-known formation of the SKB. The tuffaceous sandstone of the Yakushigawa Formation (08331-3) has detrital zircons with the youngest age cluster of around 425 Ma, and is probably a Silurian formation. The tuffaceous sandstone of the Nameirizawa Formation (08331-9) has detrital zircons with the youngest age cluster of around 430 Ma. The formation is probably a Silurian formation and is correlated with the Yakushigawa Formation. Precise ages of around 412 Ma were obtained from the Hikamiyama body of the Hikami Granitic Rocks (08330-1,-3,-4), clearly suggesting that at least some parts of the body are not pre-Silurian basement.

中央ヨーロッパ，カルパティア・パンノニア地域における中新世の大規模な火成活動について—北東部のマグマ発生および分化メカニズム—

Large-scale igneous activity characterised the development of the Carpathian-Pannonian Region, Central Europe from Late Cretaceous to Pleistocene times, with a peak of activity during the Miocene. The magmatism is considered to have been caused by the closure of the Tethys Sea and consequent collision between the African and Eurasian plates, but the exact mechanism for magmageneration is still a matter of debate. In order to get a better understanding of magmageneration and differentiation processes, a new set of bulk chemical data, including trace and rare earth elements has been presented on igneous rocks from the NE part. Together with published data, igneous rocks from the three regions of the research area (Tokaj-Slanske Mts., Great Plain and Transcarpathia) cover a wide spectrum of the calc-alkaline series and reveal close similarities in both petrography and geochemistry. No significant spatial differences could be revealed in terms of major element chemistry but Nb and Zr trends slightly differ in Tokaj-Slanske Mts. -Great Plain and Transcarpathia. Felsic rocks formed mainly at the earlier stages, the most mafic sample at the latest stage of the igneous activity. Alkali basaltic activity (generally characterising the development of the Carpathian-Pannonian Region from 11.7 Ma) has not been observed at the NE part. The results of crystallization and mixing calculations on igneous rocks from the area of research show that geochemical characteristics of most rocks cannot be explicitly explained by crystallization processes alone and they reflect the involvement of various (upper crustal, lower crustal, upper mantle and alkali basaltic) source materials through magma mixing, assimilation and contamination. The different spatial Nb and Zr trends may be interpreted as the outcome of mainly crustal contamination in the case of rocks from Transcarpathia, as opposed to the joint effects of upper crustal contamination and the involvement of alkali basaltic magma in the case of rocks from the Tokaj-Slanske Mts. Thus, alkali basaltic magma may have been involved in the formation of calc-alkaline igneous rocks not only as heat source, but in the case of basaltic rocks, also as material.

Conditions and processes during metamorphic and igneous petrogenesis

Processes such as nucleation and crystal growth, chemical diffusion, crystal dissolution and deformation fundamentally impact on the mineral content, mineral chemistry and texture of a rock. Studies on the nature and rates of these processes in rocks (e.g. Carlson 2002), their interplay (e.g. Baxter and DePaolo 2004; Selverstone 2005) and their dependence on changes in pressure, temperature and chemical environment with time (e.g. Gaidies et al. 2008) are required to better understand metamorphic and igneous petrogenesis. Recent advances in the development of analytical and experimental techniques allow for the integration of microstructure analyses of rocks and minerals with chemical and isotopic investigations at unprecedented high resolution (Keller et al. 2008). Combined with novel theoretical and computational capabilities, the natural record preserved in geological materials can now be studied through more realistic simulations of mineral reactions in rocks accounting for fundamental thermodynamic, kinetic and mechanic principles (e.g. Schmid et al. 2009). Quantitative knowledge of the conditions and processes that control mineral formation in rocks is essential for a better understanding of the close relationship between the bulk properties of rocks and the way solid Earth responds to changes in external forces. It can be expected that this knowledge will help developing a successively more realistic picture of the dynamics of our planet considering for instance the relevance of the extent of mineral reactions in rocks for catastrophic rock failure such as seismogenic slip (e.g. John et al. 2009). This special issue originates from the session “Controls on metamorphic processes” held at the European Geosciences Union General Assembly 2008 in Vienna. It extends the original focus of this session on metamorphic petrogenesis to conditions and processes also fundamental for igneous rock formation and covers a broad spectrum of topics ranging from fluid-rock interactions on the outcrop scale to intracrystalline chemical diffusion and nucleation. Eight papers are included that address various themes relevant for a better understanding of metamorphic and igneous petrogenesis. Habler et al. (2009) investigate the interplay of deformation, chemical equilibration and mineral reaction during Cretaceous metamorphism in polymetamorphic rocks from the Austroalpine Matsch Unit west of the Tauern Window in the European Eastern Alps. Based on detailed studies of mineral chemistry and rock microstructure, different mechanisms of interrelated deformation and chemical reequilibration could be identified. Habler et al. conclude that understanding the mechanisms of the mutual interrelation between deformation and equilibration is required to deduce thermobarometrical constraints from deformed metamorphic rocks. In order to derive estimates for the pressure and temperature conditions and timescales of polymetamorphism in the Wolz Complex (Eastern European Alps, Austria), Bestel et al. (2009) combine garnet isopleth thermobarometry with chemical diffusion modelling. The authors infer that during the Permian metamorphic event the rocks of the Wolz Complex were exposed to temperatures ranging from 570 to 610°C for about 10 to 20 Ma. F. Gaidies (*) Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada e-mail: fgaidies@earthsci.carleton.ca

A comment on “Tectonic evolution of the Hengshan–Wutai–Fuping complexes and its implication for the Trans-North China Orogen”

In a recent issue of Precambrian Research (vol. 170, pp. 73–87), Wang (2009) published a paper entitled ‘Tectonic evolution of the Hengshan–Wutai–Fuping complexes and its implication for the Trans-North China Orogen, in which he proposes that (1) the formation of arc-related igneous rocks in the Hengshan and Wutai Complexes formed by northwest-directed subduction, not by (south)east-directed subduction; and (2) the Wutai granitoids were the products of an intra-oceanic island arc, not formed in a continent-derived arc. However, we consider both the structural and geochemical approaches Wang (2009) adopted to determine the polarity of the subduction and the tectonic setting of the Wutai granitoids are inappropriate or invalid. Firstly, all his structural observations used to determine the polarity of subduction are restricted to the Zhujiafang and Longquanguan ductitle shear zones, both of which developed at the late stage. It is unreliable to use kinematic indicators from these later structures to infer the polarity of the pre-collisional subduction. Secondly, Wang (2009) assumed that the initial positive ɛ(Nd) values (+0.5 to +4.5) of the Wutai granitoids indicate their generation directly from a mantle source, forming in an intra-oceanic arc. Such an interpretation is incorrect because the positive ɛ(Nd) values of the Wutai granitoids merely indicate that the igneous protoliths of these granitoids originated from a depleted mantle source, not the Wutai granitoids themselves. As the products of the earliest arc magmatism in the Wutai arc, the Wutai granitoids could not be generated directly from a mantle source but must have been derived by partial melting of juvenile crust.

CRETACEOUS RIDGE SUBDUCTION ALONG THE LOWER YANGTZE RIVER BELT, EASTERN CHINA

The Lower Yangtze river belt is one of the most important metallogenic belts in China. The mechanisms responsible for ore genesis and the formation of related Cretaceous igneous rocks, such as adakite, A-type granitoid, and Nb-enriched basalt, remain controversial. Mesozoic granitoids in the Lower Yangtze river belt were mostly formed in the Early Cretaceous (140–125 Ma), and three granitoid belts—the inner, the south, and the north—have been defined according to petrological and geochemical characteristics. Previously, based mainly on negative eNd and high initial Sr isotope values, the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust, both of which require crustal thickening. Mesozoic crustal thickening, however, is not supported by the development of extensional basins in the region. From the Late Jurassic to Cretaceous, eastern China was closely associated with subduction of the Pacific plate in the south and the Izanagi plate in the north. The midocean ridge (MOR) between these two plates was drifting toward and likely subducting under the Lower Yangtze river belt. A ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt. Partial melting of subducting young, hot oceanic slabs close to the ridge formed adakitic rocks. The negative eNd values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle, and/or crustal materials through AFC process. A slab window opened during ridge subduction as indicated by A-type granitoids in the center of the inner belt. Nb-enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths.

Formation of the adakite-like granitoid complex and porphyry copper-gold deposit in Shaxi from southern Tancheng-Lujiang fault belt: A clue to the West Pacific plate subduction

On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geochemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.

ＣＯ２地中貯留のナチュラルアナログ―松代での地化学調査―

Environmental assessments and safety control during and after CO2 injection are essential for CO2 geological storage, and we are required to evaluate long-term environmental changes and safety. However, long-term changes are difficult to detect directly because the leakage of CO2 is expected to be small and the evaluation is, sometimes, requested to cover more than 1,000 years. To solve this problem, a natural-analogue study, which inquires into environmental changes at present through a comparison with past geological phenomena, is one possible approach. When the Matsushiro earthquake swarm began in 1965, a large volume of subsurface water accompanied by CO2 gas was discharged along fracture zones. A natural-analogue study on the CO2 discharge during the earthquake swarm should be helpful to create a scenario of leakage and a guideline for the safety of CO2 geological storage. Surveys of the CO2 content in soil gas and CO2 flux emissions from the surface were carried out with carbon isotope ratio measurements to understand the current state at Matsushiro, and to make a conceptual model for environmental assessments and safety control. From geological and geophysical points of view, it is said that deep water gushing out from the surface caused the swarm of earthquakes. As this deep water is still gushing out, we planned to measure CO2 concentrations in soil gas and CO2 flux to examine present CO2 activities at Matsushiro. Because CO2 in the soil is also produced by activities of microbes, however, we decided to measure the isotope ratio of the carbon to distinguish CO2 in deep groundwater origin from that produced by microbes. We selected five survey lines and three survey areas based on previous geochemical measurements and fissure distribution during the earthquake swarm, and measured CO2 concentration in soil, CO2 flux, and isotope ratio. Although there were survey points on the thick fan deposit where CO2 concentration in the soil and CO2 flux were high, the isotope ratio indicated that the carbon is produced by the activity of microbes. On the other hand, the isotope ratio of the samples collected from the thin fan deposit area shows deep subsurface water as the origin. An investigation well was drilled into the basement. Subsurface water samples were collected near the bottom of the well in the igneous rock formation. Geochemical analyses and carbon isotope ratio measurements show higher concentrations of chloride and abiogenic CO2, indicating that groundwater of a deep origin with CO2 is still rising. We are now making a conceptual model of hydrogeological history at the next step. This natural analogue study of CO2 seepage could indicate the importance of understanding shallow hydrogeological characteristics in a CO2 storage field.

Nature of the Martian uplands: Effect on Martian meteorite age distribution and secondary cratering

Abstract— Martian meteorites (MMs) have been launched from an estimated 5–9 sites on Mars within the last 20 Myr. Some 80–89% of these launch sites sampled igneous rock formations from only the last 29% of Martian time. We hypothesize that this imbalance arises not merely from poor statistics, but because the launch processes are dominated by two main phenomena: first, much of the older Martian surface is inefficient in launching rocks during impacts, and second, the volumetrically enormous reservoir of original cumulate crust enhances launch probability for 4.5 Gyr old rocks. There are four lines of evidence for the first point, not all of equal strength. First, impact theory implies that MM launch is favored by surface exposures of near‐surface coherent rock (≤102 m deep), whereas Noachian surfaces generally should have ≥102 m of loose or weakly cemented regolith with high ice content, reducing efficiency of rock launch. Second, similarly, both Mars Exploration Rovers found sedimentary strata, 1–2 orders of magnitude weaker than Martian igneous rocks, favoring low launch efficiency among some fluvial‐derived Hesperian and Noachian rocks. Even if launched, such rocks may be unrecognized as meteorites on Earth. Third, statistics of MM formation age versus cosmic‐ray exposure (CRE) age weakly suggest that older surfaces may need larger, deeper craters to launch rocks. Fourth, in direct confirmation, one of us (N. G. B.) has found that older surfaces need larger craters to produce secondary impact crater fields (cf. Barlow and Block 2004). In a survey of 200 craters, the smallest Noachian, Hesperian, and Amazonian craters with prominent fields of secondaries have diameters of ˜45 km, ˜19 km, and ˜10 km, respectively. Because 40% of Mars is Noachian, and 74% is either Noachian or Hesperian, the subsurface geologic characteristics of the older areas probably affect statistics of recognized MMs and production rates of secondary crater populations, and the MM and secondary crater statistics may give us clues to those properties.

A Study on the Evaluation of Excavation Rate and Geological Condition through the TBM Excavation Index

The rapid excavation with TBMs is an ultimate dream to tunnelers in the world. In order to establish a useful and practical guide several ideas and concepts have been proposed up to the present. For example, there are the Tarkoy's Total Hardness (1975), Sanio's relation between rolling and penetration forces (1985), the Estimated Rock Strength by Fukui and Okubo et al. (1996), the Specific Energy in Rock Drilling by K. Ryoke et al. (1998), the Torque Variation by T. Aoki (1999), β-value by Hashizume (2000), etc. Considering the papers in the past, the authors propose the concept of the TBM Excavation Index (TEI) so as to generalize the relationship between excavation rate and variation in geological condition. This concept came from the analyses of three TBM applications to sedimentary, metamorphic, and igneous rock formations. The proposed index is based on dividing the total TBM's workload into the primary fragmentation for excavation and the secondary fragmentation for the other activities. And it is calculated with torque, thrust and penetration, excluding any uncertain constants. In conclusion, the standard deviation of 0.2 in the TBM Excavation Index clearly suggests the remarkable variation in geology, and when the standard deviation exceeds 0.2, excessive cutter wear occurs due to hard rock with low brittleness and less cracks and TBM operation is forced to be halted due to the instability of a face and its vicinity.

The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics

The Palinpinon geothermal field, Negros Island, Philippines is a high-temperature, liquid-dominated geothermal system in an active island-arc volcanic setting. This paper presents a regional context for the Palinpinon geology, discusses the petrogenetic evolution of magmatism in the district and assesses the genetic relationships between intrusion and geothermal circulation. The oldest rock formation, the Lower Puhagan Volcanic Formation (Middle Miocene), is part of a volcanic sequence that is traceable throughout the Visayas region and is related to subduction of the Sulu Sea oceanic basin in a southeasterly direction beneath the Sulu arc. Late Miocene to Early Pliocene times mark a period of regional subsidence and marine sedimentation. A thick sequence of calcareous sediments (Okoy Formation) was deposited during this period. Magmatism in Early Pliocene to Recent times coincided with commencement of subduction at the Negros–Sulu Arc. This produced basaltic andesites and andesites belonging to the Southern Negros and Cuernos Volcanic Formations. During this time the Puhagan dikes and the Nasuji Pluton intruded Middle Miocene, Late Miocene and Early–Late Pliocene formations. Based on radiogenic ( 40Ar/ 39Ar) dating of hornblende, the Puhagan dikes are 4.1–4.2 Ma and the Nasuji Pluton 0.3–0.7 Ma. This age difference confirms these intrusions are not genetically related. The Early Pliocene age of the Puhagan dikes also confirms they are not the heat source for the current geothermal system and that a much younger intrusion is situated beyond drill depths. Igneous rock formations in southern Negros are the products of regional island-arc magmatism with medium K, calc-alkaline, basaltic to dacitic compositions. Their adakitic affinity implies that the melting of subducted oceanic basalt has influenced magmatism in this region. Considering the regional tectonic history the most likely scenarios for the generation of slab melts are: (1) during the Middle Miocene, by the melting of relatively young (<20 Ma) oceanic crust; (2) during Early Pliocene times, by the initiation of subduction along the Negros–Sulu Trench; and (3) during Late Pliocene times, by the melting of young (<10–20 Ma) oceanic crust. The adakitic composition of the magmas at Palinpinon has promoted the formation of a porphyry copper-style magmatic–hydrothermal system that is comparable to mineralised porphyry deposits elsewhere in the Philippines.

The recognition of adakite-type gneisses in the North Dabie Mountain and its implication to ultrahigh pressure metamorphic geology

Adakite[1] is an igneous rock generated by the partial melting of subducting ocean slab in an island arc setting. Meanwhile, residuals of the slab-melting are transformed to eclogite or garnet-amphibolite during a slab subduction process. This note reports the adakite-type grey gneisses discovered in the North Dabie Mountain. These adakitic rocks are characterized by high Al2O3,(14.97%–17.56%), Sr (545–941 gm/g), Sr/Y (44.71–218.98), La/Yb (16.70–97.50), and low Y (3.32–12.19 μg/g), Yb (0.31–1.34 μg/g), Sc (0.92–4.2 μg/g), as well as positive Sr anomaly but absent or positive Eu anomaly. They are different from the low aluminum grey gneisses with low Al2O3 (13.73%–14.38%), Sr (262–409 μg/g), Sr/Y (6.46–15.97) and La/Yb (1.90–22.60), high Y(21.79–36.24 μg/g), Yb (2.00–5.59 μg/g), Sc (8.30%–12.70%), and negative Sr, Eu anomaly in the North Dabie Mountain. The adakite-type grey gneisses in the North Dabie Mountain were most probably formed by the partial melting of subducting ocean slab before the Indo-Chinese epoch. We suggest that the subducting of an ocean slab took place prior to the incorporation between the Yangtze and North China plates in the Indo-Chinese epoch, resulting in formation of adakite-type igneous rocks and some ultrahigh pressure eclogites related to the subducted ocean slab. Therefore, besides the ultrahigh pressure metamorphism of the Indo-Chinese epoch, some ultrahigh pressure ecoglits were most likely formed prior to the Indo-Chinese epoch in the Dabie Mountain. In addition, the adakite-type grey gneisses with arc origin occur in the North Dabie Mountain, inferring that the Yangtze plate subducted down below the North China plate and the main suture zone between the two plates was likely along the southern side to the North Dabie Mountain.

Patterns of bubble desorption during the solidification of a multicomponent melt

The desorption of bubbles during solidification of a melt occurs in processes as diverse as the making of ice cubes, the formation of igneous rocks and the casting of metals. In both the metal casting and rock formation processes, careful observation of the final solid suggests that the desorbed bubbles often form regular spatial patterns. Understanding and quantifying the mechanisms by which such patterns arise is important. In the geological context, comparison between field measurements and the predictions of a model will allow geologists to estimate in-situ magma properties. In the metal casting context, engineers would like to be able to specify mould geometries and cooling conditions to ensure that the distribution of bubbles will not compromise the strength of critical sections of the casting.In the present study, we develop a detailed mathematical model to predict the distribution of desorbed bubbles in a solidified melt. Our new model builds upon previous knowledge on this phenomenon in the geological context (Toramaru et al. 1996, 1997). We describe desorption of a dissolved gas in a semi-infinite melt, solidified by a one-dimensional heat flux. In the absence of convection, the transfer of heat and solute occurs mainly by a diffusive mechanism and the crystallization proceeds most rapidly near the cooled boundary. The crystals formed contain almost no dissolved gas and hence the concentration of gas dissolved in the melt increases progressively towards the cooled boundary. Diffusion of dissolved gas from the crystallizing zone is slow and, as a result, the local melt becomes supersaturated and gas bubbles desorb. The full equations for this coupled solidification and desorption processes are solved numerically.We find that bubbles desorb forming a sequence of layers parallel to the cooled boundary. The spacing between these bubble layers increases geometrically from the cooled boundary. We give a physical interpretation for this geometric pattern and analyse the effect of physical parameters on the layer spacing. We show that our theoretical model captures the important physical mechanisms involved in the solidification and desorption processes by comparing its predictions with available measurements from a geological formation.

Museums Dissolving Boundaries Between Science and Art

Although the traditional educational role of art museums is to teach about art objects, during the past few decades these institutions have moved toward teaching through art objects. This shift means that museums and their collections are presenting themselves as rich interdisciplinary resources for educators working with any subject matter, including earth sciences. One role that the visual arts can play in teaching earth science is that of illustrating and/or visually interpreting natural phenomena. For example, Hudson River School painter Albert Bierstadt documented the result of plate tectonics in his painting Alaska, while American Impressionist Childe Hassam interpreted igneous rock formations in Cliff Rock – Appledore. Natural materials have been used for centuries to create works of art, as seen in the gold leaf used in a Renaissance altarpiece created by Agnolo Gaddi or in beautiful jade pieces created by Chinese artisans. Scientific processes that can be studied in the visual arts include those used in glassmaking and in creating porcelain. More detailed information on the integration of earth science and art can be found on the Indianapolis Museum of Art's World Wide Web Site, http://www.ima-art.org.

Demarcating Old Rocks

GEOLOGY Crust that is greater than 3.0 billion years old is distributed in the cores of cratons (stable areas of Earth's crust); these can be found in the interiors of several continents. Identifying and correlating these cores provides clues to the rate of formation of continental crust through time and to Earth's geochemical evolution, and also reveals whether some form of plate tectonics operated early in Earth's history. Qiu et al. have identified 3.2 billion year old rocks in the Yangtze craton located in south China. Rocks of this age were thought to be restricted to the North China craton, which was joined with the Yangtze craton only 220 million years ago along a major orogenic belt (the Qinling-Dabie-Sulu suture). Separately, Bohm et al. have identified crust at least 3.5 billion years old (and perhaps from 3.8 billion years ago) along the ancient margin of the Superior Province located in Manitoba, Canada (the large craton core in eastern and central Canada). Both studies used uranium-lead dating of zircons to date directly the formation of igneous rocks and samarium-neodynium geochemical analysis of whole rocks to estimate the age of extraction of crust from the mantle.— BH Geology 28 , 11 (2000); Geology 28 , 75 (2000).

Basin‐Wide Diagenetic Patterns: Integrated Petrologic, Geochemical, and Hydrologic Considerations

The serious scholar of petrology is well aware of the discrepant level of understanding that exists between igneous and metamorphic petrogenesis and sediment diagenesis (also known as postdepositional evolution). While nucleation and crystallization theory, phase equilibria, and principles of heat and mass transport have provided guidance for scientists to understand the formation and subsequent evolution of igneous and metamorphic rocks, sedimentary petrologists seem to have been left behind in detailed, descriptive characterization, with little chemical and physical basis to unify the diagenesis of one rock unit with any other.Of course, one cannot lay blame entirely on the scientist: the study of sediment diagenesis is plagued by problems of incomplete chemical reaction, the need to characterize amorphous solids and poorly crystalline mineral phases, low temperature and pressure conditions that result in reaction kinetics dominating over thermodynamic equilibria, and a lot of fugitive water! Further complications arise because most of the samples available for extensive regional study of sediment diagenesis are those recovered during the exploration and exploitation of hydrocarbon and mineral resources. The processes that have controlled postdepositional chemical and physical evolution of such samples are undeniably nonrepresentative of those affecting the vast volumes of most sedimentary sequences.