Thermal decomposition process in algaenan of Botryococcus braunii race L. Part 2: Molecular dynamics simulations using the ReaxFF reactive force field

This paper reports ReaxFF MD simulation results on pyrolysis of a molecular model of the algaenan Botryococcus braunii race L biopolymer, specifically, ReaxFF predictions on the pyrolysis of prototypical chemical structures involving aliphatic chain esters and aldehydes. These preliminary computational experiments are then used to analyze the thermal cracking process within algaenan race L biopolymers. The simulations indicate that the thermal decomposition of the algaenan biopolymer is initiated by the cleavage of a C–O bond in the ester group, followed by the release of carbon dioxide. We also observe a significant, strongly temperature dependent, release of ethylene. This degradation mechanism leads to products similar to those observed in pyrolysis experiments, validating this computational approach.     

Early maturation processes in coal. Part 1: Pyrolysis mass balance and structural evolution of coalified wood from the Morwell Brown Coal seam

We have developed a theoretical approach for evaluating the maturation of kerogen-like material, involving molecular dynamic reactive modelling with a reactive force field to simulate thermal stress. Morwell Brown Coal was selected to study the thermal evolution of terrestrial organic matter (OM). To achieve this, a structural model is first constructed on the basis of literature models and analytical characterization of our samples using modern 1and 2D nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and elemental analysis. Then, artificial maturation of the coal is performed at low conversion in order to obtain quantitative and qualitative detailed evidence for the structural evolution of the kerogen upon maturation. The chemical changes include defunctionalization of carboxyl, carbonyl and methoxy functional groups, coupled with an increase in cross linking in the residual matured kerogen. Gaseous and liquid hydrocarbons, essentially CH₄, C₄H₈ and C₁₄₊ hydrocarbons, are generated in low amount, merely via cleavage of the lignin side chain.     

Irreversible evolution of tectono-magmatic processes at the Earth and Moon: Petrological data

The tectono-magmatic evolution of the Earth and Moon started after the solidification of their magmatic “oceans”, whose in-situ crystallization produced the primordial crusts of the planets, with the composition of these crusts depending on the depths of the “oceans”. A principally important feature of the irreversible evolution of the planetary bodies, regardless of their sizes and proportions of their metallic cores and silicate shells, was a fundamental change in the course of their tectono-magmatic processes during intermediate evolutionary stages. Early in the geological evolution of the Earth and Moon, their magmatic melts were highly magnesian and were derived from mantle sources depleted during the solidification of the magmatic “oceans”; this situation can be described in terms of plume tectonics. Later, geochemically enriched basalts with high concentrations of Fe, Ti, and incompatible elements became widespread. These rocks were typical of Phanerozoic within-plate magmatism. The style of tectonic activity has also changed: plate tectonics became widespread at the Earth, and large depressions (maria) started to develop at the Moon. The latter were characterized by a significantly thinned crust and basaltic magmatism. These events are thought to have been related to mantle superplumes of the second generation (thermochemical), which are produced (Dobretsov et al., 2001) at the boundary between the liquid core and silicate mantle owing to the accumulation of fluid at this interface. Because of their lower density, these superplumes ascended higher than their precursors did, and the spreading of their head parts resulted in active interaction with the superjacent thinned lithosphere and a change in the tectonic regime, with the replacement of the primordial crust by the secondary basaltic one. This change took place at 2.3–2.0 Ga on the Earth and at 4.2–3.9 Ga on the Moon. Analogous scenarios (with small differences) were also likely typical of Mars and Venus, whose vast basaltic plains developed during their second evolutionary stages. The change in the style of tectonic-magmatic activity was associated with important environmental changes on the surfaces of the planets, which gave rise to their secondary atmospheres. The occurrence of a fundamental change in the tectono-magmatic evolution of the planetary bodies with the transition from depleted to geochemically enriched melts implies that these planets were originally heterogeneous and had metal cores and silicate shells enriched in the material of carbonaceous chondrites. The involvement of principally different material (that had never before participated in these processes) in tectono-magmatic processes was possible only if these bodies were heated from their outer to inner levels via the passage of a heating wave (zone) with the associated cooling of the outermost shells. The early evolutionary stages of the planets, when the waves passed through their silicate mantles, were characterized by the of development of super-plumes of the first generation. The metallic cores were the last to melt, and this processes brought about the development of thermochemical super-plumes.     

Dauphiné twinning and texture memory in polycrystalline quartz. Part 1: Experimental deformation of novaculite

Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with time-of-flight neutron diffraction and hard synchrotron X-rays, analyzing diffraction data with the Rietveld method. Similar texture patterns are observed as described previously but the new results establish a profound influence of temperature and document that twinning initiates at stresses less than 50 MPa. Possibilities of using Dauphiné twinning as a paleopiezometer in quartz-bearing rocks are discussed.     

Acyclic isoprenoid biomarkers and evolution of biosynthetic pathways in green microalgae of the genus Botryococcus

Acyclic isoprenoids were among the earliest lipids on Earth and today > 30,000 isoprenoid-derived compounds are known, testifying to the remarkable diversification in isoprenoid biosynthetic pathways over time. Many of the isoprenoids have proven to be useful biomarkers in geochemical studies and evidence from sedimentary studies has the potential to provide a timeline for the evolution of different types of isoprenoid biosynthesis. A single green microalgal species termed Botryococcus braunii has been recognised as a major contributor of organic matter to sediments as old as the Precambrian. Modern studies of the taxonomy of B. braunii using molecular biology techniques have shown that the major clades identified from 18S rRNA gene sequences correspond to races A, B, L and S, which are defined on the basis of their hydrocarbon composition. The biosynthetic pathways by which C₃₀–C₃₇ botryococcenes are produced by the B race have now been shown to be due to a duplication of the squalene synthase gene, followed by subsequent changes to the genes, such that one pathway leads to the production of the C₃₀ botryococcene and the other to squalene. Both products are then methylated to produce botryococcenes and methylated squalenes having higher carbon numbers. The mode of biosynthesis of lycopadiene in race L is unclear, but may involve coupling of two C₂₀ phytyl diphosphates. From an examination of the geological record of botryococcenes and lycopadiene it seems likely that these pathways probably evolved early in the Eocene (ca. 55 Ma) and thus are more recently evolved than the genes for highly branched isoprenoid (HBI) alkenes first produced by diatoms about 92 Ma ago. Botryococcane produced from botryococcenes and a monoaromatic hydrocarbon produced from lycopadiene-related lipids, presumably under anoxic conditions, show promise as age diagnostic biomarkers. In view of these results, it seems likely that the Botryococcus species recorded in sediments predating the Eocene lacked the ability to produce botryococcenes or lycopadiene, but nonetheless still contained polymeric non-isoprenoid alkyl chains in the form of an algaenan which on preservation gave rise to a multitude of organic rich rocks.     

Geodynamics of the Early Precambrian,Part 1: Volcanism and associated mantle processes

The work is dedicated to most important abiotic processes of the Early Precambrian, effect of which is recorded in continental crust, and to complementary processes in subcontinental mantle. We intend to figure out when a certain process was triggered first in the past and what indications suggest its further activity, evolution and possible cessation in subsequent geological history. Considerations are based on described natural objects characterizing particular geological events and enabling the cause-and-effect interpretation in order to understand different viewpoints known from publications. Considered in the work are the early Precambrian greenstone belts and ophiolites, island-arc systems and ecologites, magmatism unconnected with subduction zones (rifting-related, plateau basalts, dykes, kimberlites) and anorthosites representing a group of heterochronous intrusions of complicated genesis. Main considerations are premised with a brief review of the earliest geodynamic phenomena associated with meteorite impacts by termination of the planetary accretion.     

Thermal evolution of organic matter in source rocks — Experimental and scanning electron microscopic studies

Five major forms (lamellar, banded, crack-like, disseminated and segregated encrustation) of organic matter distribution in source rocks have been revealed under scanning electron microscope by using the heavy metal staining technique. The degree of organic impregnation is related to the amount of liquid hydrocarbons in the rocks, and from this relationship a rough estimation of organic matter can be made on the basis of electron microscopic observations. In conjunction with experimental studies it has been found that the distribution forms of organic matter are a function of its maturity in the process of thermal evolution and accordingly some microscopic criteria can be developed for the assessment of source rocks.     

Biogeochemical processes in a clay formation in situ experiment: Part C - Organic contamination and leaching data

Data interpretation of the Porewater Chemistry (PC) experiment at the Mont Terri Rock Laboratory has led to unexpected observations of anaerobic microbial processes which caused important geochemical perturbations of the Opalinus Clay water in the borehole. The increases of acetate to 146 mg C/L, of DIC to 109 mg C/L and of CH₄ to 0.5 mg C/L were unexpected and could not be explained without the presence of a C source in the system. The organic C fuelling the observed microbial activity was until then unknown. Leaching tests were performed on several polymers used for the fabrication of the PC equipment to identify the source of organic matter (OM). Polyethylene (PE) appears to be very inert and does not release detectable concentrations of dissolved organic C (DOC) (<1 ppb) into the water. Polyurethane (PU) leaches out a dozen different organic compounds accounting for only 13 μg DOC/g PU. Under the conditions of the leaching tests, 1 g of polyamide (PA, Nylon) also releases ∼512 μg of the plasticizer N-Butyl-Benzene-Sulfonamide (NBBS). Soaking tests with polyethylene samples immersed in acetone under conditions similar to those used to remove grease spots on the porous PE filter prior to installation showed that acetone could have been trapped in the PE filter, corresponding to an initial concentration of 1.5 g acetone/L of water. However, the accumulated amount of organic C taken into account from all these components was insufficient to satisfactorily explain the observed microbially mediated reducing perturbation. Finally, large amounts of dissolved organic C were found to be released in the system by the jelly polymer filling the reference compartment of the pH and E_h electrodes permanently installed over 5 years in flow-through cells on the water circulation loop of the PC experiment. Glycerol was further identified by chromatographic analysis as the main organic compound released by the electrodes. From the analysis results, as well as from the geochemical calculations, the most likely primary organic C source fuelling the microbial perturbation was glycerol released from the polymeric gel filling the reference electrodes (1.6 g glycerol/electrode). Other sources, such as acetone, may also have contributed to microbial processes, but only to a minor extent.     

Growth of the Namche Barwa Syntaxis and associated evolution of the Tsangpo Gorge: Constraints from structural and thermochronological data

The eastern syntaxis of the Himalaya, Namche Barwa, is dominated by a north-plunging antiform which began to decompress/grow at approximately 4 Ma. New fission-track analyses on both apatite and zircon, combined with previous geochronological ages, indicate that the Namche Barwa Dome also extended laterally while growing vertically. Zircon fission-track ages range from 17.6 to 0.2 Ma and have a strong relationship to the main faults of the region, including the Tertiary Tsangpo Suture, with the younger ages inside the fault bounds towards the syntaxis core on the Indian Plate and the older ages away from the fault. Apatite ages reveal that the dome has grown laterally and now impinges over the older faulted margin onto the Asian Plate. The dome is traversed by the Tsangpo which has followed the trace of the Suture for over 1300 km from its source to the entrance of the dome near Dania. As the Tsangpo crosses the dome it departs from the Suture but rejoins it some 60 km northeastwards. We construe that the Suture has been displaced by the growing antiform and as a consequence, the antecedent river has been “dragged” in a left-lateral sense along the exhuming north-plunging dome. Restoring the Suture to its position prior to 4 Ma reveals a path of the Tsangpo eastwards across the present southwestern position of the Namche Barwa indentation. This geometric reconstrunction implies that the Tsangpo and the Brahmaputra were always one and the same river. In addition, the Tsangpo was tectonically forced into juxtaposition with a tributary of the Jiali-Parlung which it probably then captured. The capture was due to tectonic forcing, in the last 4 Ma, rather than headward retreat of the paleo-Brahmaputra as has been previously suggested.     

Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study

The structure of deuterated jarosite, KFe₃(SO₄)₂(OD)₆, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH)₆] octahedra and [SO₄] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, α = α₀ + α₁ T, where α₀ = 1.01 × 10⁻⁴ K⁻¹ and α₁ = −1.15 × 10⁻⁷ K⁻². On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together.     

Thermal decomposition of serpentine during coseismic faulting: Nanostructures and mineral reactions

This paper reports a detailed characterization of an antigorite-bearing serpentinite, deformed at seismic slip-rate (1.1 m/s) in a high-velocity friction apparatus. Micro/nanostructural investigation of the slip zone (200 μm thick) revealed a zonal arrangement, with a close juxtaposition of horizons with significantly different strength, respectively consisting of amorphous to poorly-crystalline phases (with bulk anhydrous composition close to starting antigorite) and of highly-crystalline assemblages of forsterite and disordered enstatite (200 nm in size and in polygonal-like nanotextures). The slip zone also hosts micro/nanometre sized Cr-magnetite grains, aligned at low angle with respect to the slipping surface and inherited from the host serpentinite.Overall observations suggest that frictional heating at asperities on the slipping surface induced a temperature increase up to 820–1200 °C (in agreement with flash temperature theory), responsible for serpentine complete dehydration and amorphization, followed by crystallization of forsterite and enstatite (under post-deformation, static conditions). The results of this study may provide important keys for the full comprehension of the mechanical behaviour and of the possible geodynamical role of serpentinite-hosted faults through the seismic cycle.     

Experimental growth of quartz in petroleum environment. Part I: Procedures and Fluid Trapping

The quartz-water-oil-gas system has been experimentally studied with the objective of investigating the trapping of petroleum and aqueous inclusions in quartz at different water/oil (W/O) ratios (0/100, 5/95, 10/90, 20/80, 50/50, 100/0). Experiments were carried out in both a gas-pressure autoclave (GPA) under CH₄ pressure control, up to 250°C and 212 bar, and in a fluid-pressure autoclave (FPA) up to 350°C and 400 bar. High p-T conditions have notably allowed the growth of quartz at high oil saturation levels (W/O ratios from 10/90 to 50/50). Petroleum inclusions have been synthesised inside quartz microfractures (W/O ratios from 0/100 to 50/50; 209-350°C; 175-400 bar), and also inside quartz overgrowths (W/O ratios from 10/90 to 50/50; 289-350°C; 350-400 bar). Aqueous inclusions have been synthesised in presence of oil inside quartz microfractures from 185°C-163 bar up to 400°C-400 bar, and inside quartz overgrowth from 277°C-330 bar. Synthesised petroleum inclusions are representative of the parent oil up to 250°C. At 350°C, evidence of a cracking process has been observed with the consequent formation of methane. The segregation of the oil/gas/water column inside the GPA autoclave may also have prevented methane diffusion into the water phase when oil is present. This experimental approach shows that the trapping of fluid inclusions and the formation of quartz cement, under conditions of high oil saturation, have not been suppressed or prevented.     

Four-dimensional transform fault processes: progressive evolution of step-overs and bends

Many bends or step-overs along strike–slip faults may evolve by propagation of the strike–slip fault on one side of the structure and progressive shut-off of the strike–slip fault on the other side. In such a process, new transverse structures form, and the bend or step-over region migrates with respect to materials that were once affected by it. This process is the progressive asymmetric development of a strike–slip duplex. Consequences of this type of step-over evolution include: (1) the amount of structural relief in the restraining step-over or bend region is less than expected; (2) pull-apart basin deposits are left outside of the active basin; and (3) local tectonic inversion occurs that is not linked to regional plate boundary kinematic changes. This type of evolution of step-overs and bends may be common along the dextral San Andreas fault system of California; we present evidence at different scales for the evolution of bends and step-overs along this fault system. Examples of pull-apart basin deposits related to migrating releasing (right) bends or step-overs are the Plio-Pleistocene Merced Formation (tens of km along strike), the Pleistocene Olema Creek Formation (several km along strike) along the San Andreas fault in the San Francisco Bay area, and an inverted colluvial graben exposed in a paleoseismic trench across the Miller Creek fault (meters to tens of meters along strike) in the eastern San Francisco Bay area. Examples of migrating restraining bends or step-overs include the transfer of slip from the Calaveras to Hayward fault, and the Greenville to the Concord fault (ten km or more along strike), the offshore San Gregorio fold and thrust belt (40 km along strike), and the progressive transfer of slip from the eastern faults of the San Andreas system to the migrating Mendocino triple junction (over 150 km along strike). Similar 4D evolution may characterize the evolution of other regions in the world, including the Dead Sea pull-apart, the Gulf of Paria pull-apart basin of northern Venezuela, and the Hanmer and Dagg basins of New Zealand.     

Thermal evolution of n- and iso-alkanes in oils. Part 1: Pyrolysis model for a mixture of 78 alkanes (C1-C32) including 13,206 free radical reactions

A mechanistic model consisting of 13,206 lumped free radical reactions has been developed to describe the thermal evolution of a mixture of 78 alkanes: all n-alkanes from C₁ to C₃₂ and 46 branched alkane model compounds from C₄ to C₃₂. The mixture was meant to represent the major part of the saturated fraction of petroleum. The rate constants used are available from the literature. The lumping together procedure is described and the model validated on the basis of several experimental results from the literature and relating to pure alkanes. The model is also compared to the saturated fraction obtained from pyrolysis of Elgin oil at 372 °C for up to 1000 h. The cracking global activation energy of n-C₁₅ as well as iso-C₁₅ is close to 69 kcal/mol in the range 200-350 °C. The implications of the model for geological reservoirs will be discussed in a following paper.     

实验矿物物理的发展现状与趋势:1.相变和状态方程、电导率、热导率

实验矿物物理是高温高压实验地球科学的重要分支学科之一,它主要是通过高温高压实验模拟地球内部的物理化学环境,并原位测定地球深部物质（矿物、岩石和熔/流体等）的相变和状态方程、电导率、热导率等物理参数,探讨地球内部的圈层结构、物质组成、地球动力学过程等地球物理性质相关的一系列重要科学问题. 综述了实验矿物物理的发展历史、近二十年的研究现状与趋势,并展望了该学科未来发展的方向、关键科学问题与面临的主要挑战.      

Thermal decarboxylation of acetate. Part I. The kinetics and mechanism of reaction in aqueous solution

In an effort to understand the kinetics of the thermal decarboxylation of acetate and the role of catalysis, a series of laboratory experiments were conducted to measure the rate constants for the decomposition of acetate (acetic acid and sodium acetate) in the presence of titanium, silica, stainless steel, gold, and magnetite. Activation energies for decarboxylation of acetic acid and acetate ion range from about 8 kcal mol⁻¹ in stainless steel vessels to 69 kcal mol⁻¹ in silica tubes. Extrapolated rate constants at 100°C for acetic acid differ by more than fourteen orders of magnitude between the experiments conducted in stainless steel and the catalytically least active titanium vessels. Gold and titanium were the least active catalysts for the acetic acid substrate, while stainless steel, silica, and magnetite showed marked catalytic effects. Methane and carbon dioxide were the predominant reaction products of most of these experiments, although mass spectrometric analyses of the gas phase revealed concentrations of carbon monoxide and hydrocarbons (apparent mass range from 29 to 56) amounting to as much as 55 mole percent of the total volatile products, depending on the catalyst. The reactions were generally first order in acetic acid or acetate ion, except for those involving the acid over silica and magnetite which were zero order. These results and the observed effects of variations in surface area are rationalized in terms of changes in the mode of surface catalysis. The mechanistic assignment is simplified by the existence of three unique straight lines on an isokinetic plot (i.e., activation enthalpy versus activation entropy) which fit all the respective first- and zeroorder reactions. The results described here provide the nucleus for the discussion in Part II of the role of acetate in the primary migration of methane and the transportation of metals in hydrothermal solutions.