沈积岩石学

沈积学,在二十世纪初叶始渐起而为地质学中之新支,近数十年来随着石油工业之发达,而日趋蓬勃;一变昔日仅以岩石性质研究为沈积原因之解说,而侧重沈积作用及沈积环境之     

Evaporites,brines and base metals: Low‐temperature ore emplacement controlled by evaporite diagenesis

Salt beds and salt allochthons are transient features in most sedimentary basins, which through their dissolution can carry, focus and fix base metals. The mineralisation can be subsalt, intrasalt or suprasalt, and the salt body or its breccia can be bedded or halokinetic. In all these evaporite‐associated low‐temperature diagenetic ore deposits there are four common factors that can be used to recognise suitably prepared ground for mineralisation: (i) a dissolving evaporite bed acts either as a supplier of chloride‐rich basinal brines capable of leaching metals, or as a supplier of sulfur and organics that can fix metals; (ii) where the dissolving bed is acting as a supplier of chloride‐rich brines, there is a suitable nearby source of metals that can be leached by these basinal brines (redbeds, thick shales, volcaniclastics, basalts); (iii) there is a stable redox interface where these metalliferous chloride‐rich waters mix with anoxic waters within a pore‐fluid environment that is rich in organics and sulfate/sulfide/H₂S; and (iv) there is a salt‐induced focusing mechanism that allows for a stable, long‐term maintenance of the redox front, e.g. the underbelly of the salt bed or allochthon (subsalt deposits), dissolution or halokinetically maintained fault activity in the overburden (suprasalt deposits), or a stratabound intrabed evaporite dissolution front (intrasalt deposits). The diagenetic evaporite ‐ base‐metal association includes world‐class Cu deposits, such as the Kupferschiefer‐style Lubin deposits of Poland and the large accumulations in the Dzhezkazgan region of Kazakhstan. The Lubin deposits are subsalt and occur where long‐term dissolution of salt, in conjunction with upwelling metalliferous basin brines, created a stable redox front, now indicated by the facies of the Rote Faule. The Dzhezkazgan deposits (as well as smaller scale Lisbon Valley style deposits) are suprasalt halokinetic features and formed where a dissolving halite‐dominated salt dome maintained a structural focus to a regional redox interface. Halokinesis and dissolution of the salt bed also drove the subsalt circulation system whereby metalliferous saline brines convectively leached underlying sediments. In both scenarios, the resulting redox‐precipitated sulfides are zoned and arranged in the order Cu, Pb, Zn as one moves away from the zone of salt‐solution supplied brines. This redox zonation can be used as a regional pointer to both mineralisation and, more academically, to the position of a former salt bed. In the fault‐fed suprasalt accumulations the feeder faults were typically created and maintained by the jiggling of brittle overburden blocks atop a moving and dissolving salt unit. A similar mechanism localises many of the caprock replacement haloes seen in the diapiric provinces of the Gulf of Mexico and Northern Africa. Evaporite‐associated Pb–Zn deposits, like Cu deposits, are focused by brine flows associated with both bedded and halokinetic salt units or their residues. Stratabound deposits, such as Gays River and Cadjebut, have formed immediately adjacent to or within the bedded salt body, with the bedded sulfate acting as a sulfur source. In allochthon/diapir deposits the Pb–Zn mineralisation can occur both within a caprock or adjacent to the salt structure as replacements of peridiapiric organic‐rich pyritic sediments. In the latter case the conditions of bottom anoxia that allowed the preservation of pyrite were created by the presence of brine springs and seeps fed from the dissolution of nearby salt sheets and diapirs. The deposits in the peridiapiric group tend to be widespread, but individual deposits tend to be relatively small and many are subeconomic. However, their occurrence indicates an active metal‐cycling mechanism in the basin. Given the right association of salt allochthon, tectonics, source substrate and brine ponding, the system can form much less common but world‐class deposits where base‐metal sulfides replaced pyritic laminites at burial depths ranging from centimetres to kilometres. This set of diagenetic brine‐focusing mechanisms are active today beneath the floor of the Atlantis II Deep and are thought to have their ancient counterparts in some Proterozoic sedex deposits. The position of the allochthon, its lateral continuity, and the type of sediment it overlies controls the size of the accumulation and whether it is Cu or Pb–Zn dominated.     

Parameterisation of orographic cloud dynamics in a GCM

A new parameterisation is described that predicts the temperature perturbations due to sub-grid scale orographic gravity waves in the atmosphere of the 19 level HadAM3 version of the United Kingdom Met Office Unified Model. The explicit calculation of the wave phase allows the sign of the temperature perturbation to be predicted. The scheme is used to create orographic clouds, including cirrus, that were previously absent in model simulations. A novel approach to the validation of this parameterisation makes use of both satellite observations of a case study, and a simulation in which the Unified Model is nudged towards ERA-40 assimilated winds, temperatures and humidities. It is demonstrated that this approach offers a feasible way of introducing large scale orographic cirrus clouds into GCMs.     

Fatigue-Damage Evolution Characteristics of Interbeded Marble Subjected to Dynamic Uniaxial Cyclic Loads

In this work, uniaxial fatigue tests combined with post-test X-ray computed tomography (CT) scanning were conducted on marble samples with different interbed orientations, in order to reveal the anisotropic damage evolution characteristics during rock failure. The dynamic elastic modulus, damping ratio, fatigue deformation, damage evolution, accumulative damage modeling and crack pattern were systematically analyzed. The testing results indicate that the interbed structure in marble affects the damage evolution and the associated dynamic mechanical behaviors. The damage curve in “S” style indicates three-stage trend, namely, initial damage stage, steady damage stage and the accelerated damage stage. The damage index during cyclic deformation for marble presents obvious discrepancy. In addition, a fatigue damage prediction models was employed numerically as double-term power equations based on the experimental data. It is found that the selected damage model is suitable in modeling the rapid damage growth in the early and final stage of rock fatigue lifetime. Moreover, post-test CT scanning further reveals the anisotropic damage characteristics of marble, the crack pattern in the fractured sample is controlled by the interbed structure. What is more, the most striking founding is that the fracture degree is in consistent with the damage accumulation within the steady damage stage. Through a series of damage mechanical behavior analysis, the internal mechanism of the effect of interbed orientation on damage evolution of marble is firstly documented.

     

The suitability of apatite as an age indicator by the uranium-lead isotope method

Experimental data obtained for 14 samples from the granitic terrain surrounding the Barberton Mountain Land in the Republic of South Africa is used to demonstrate that the common accessory mineral, apatite, is suitable for age measurements by the U-Pb isotope method and may in many cases be a more reliable age indicator than the co-existing zircon. The ages calculated for apatite separated from the granitic rocks are in most cases concordant or nearly so (the biggest difference between two uranium-lead ages exhibited being less than 7%); while the ages calculated for co-existing zircon are mostly grossly disconcordant. It is proposed that the theoretical explanation for this observation is found in the crystal chemical stability of the apatite structure as compared to that of zircon. Zircon is probably much more susceptible to loss of members of the U-Pb decay system especially when metamict.     

Interlaboratory calibration experiments using the polychaetous annelid Capitella capitata

An interlaboratory calibration experiment was conducted at three laboratories to test two sources of variation associated with bioassay experiments, variation due to the experimenter and to the natural seawater. Twenty-eight day static (with frequent media renewal) bioassays exposing the polychaete Capitella capitata to cadmium were conducted with synthetic and natural seawaters. Test results varied between the three laboratories; however, the variations are most probably explained by the shipment of the experimental animals to the participating laboratories.     

Combining pixel and object based image analysis of ultra-high resolution multibeam bathymetry and backscatter for habitat mapping in shallow marine waters

Habitat mapping data are increasingly being recognised for their importance in underpinning marine spatial planning. The ability to collect ultra-high resolution (cm) multibeam echosounder (MBES) data in shallow waters has facilitated understanding of the fine-scale distribution of benthic habitats in these areas that are often prone to human disturbance. Developing quantitative and objective approaches to integrate MBES data with ground observations for predictive modelling is essential for ensuring repeatability and providing confidence measures for habitat mapping products. Whilst supervised classification approaches are becoming more common, users are often faced with a decision whether to implement a pixel based (PB) or an object based (OB) image analysis approach, with often limited understanding of the potential influence of that decision on final map products and relative importance of data inputs to patterns observed. In this study, we apply an ensemble learning approach capable of integrating PB and OB Image Analysis from ultra-high resolution MBES bathymetry and backscatter data for mapping benthic habitats in Refuge Cove, a temperate coastal embayment in south-east Australia. We demonstrate the relative importance of PB and OB seafloor derivatives for the five broad benthic habitats that dominate the site. We found that OB and PB approaches performed well with differences in classification accuracy but not discernible statistically. However, a model incorporating elements of both approaches proved to be significantly more accurate than OB or PB methods alone and demonstrate the benefits of using MBES bathymetry and backscatter combined for class discrimination.     

A genetic assessment of the taxonomic status of New Zealand mussels of the genus Xenostrobus Wilson, 1967

ABSTRACT

The genus Xenostrobus consists of small, marine and estuarine mussels that all appear similar externally. One of its estuarine species, Xenostrobus securis, with a native range in New Zealand and Australia, has become invasive in the Northern Hemisphere. No genetic data are available to determine if X. securis populations from the two countries are conspecific. Additionally, marine Xenostrobus from New Zealand have often been regarded as a species, X. neozelanicus, distinct fromthe marine Australian species X. pulex. We combined new DNA sequences with published data to assess the taxonomic status of New Zealand Xenostrobus. The data comprised 658 aligned bases of mitochondrial cytochrome c oxidase subunit I (COI) gene and 331 bases of nuclear histone H3. There was no evidence that X. securis populations from Australia and New Zealand are specifically distinct. Northern Hemisphere specimens of X. securis belonged to Australian, not New Zealand, clades in phylogenetic analyses of COI data, suggesting the former country as their more likely original source. The results confirm that X. neozelanicus and X. pulex are distinct species and for nomenclatural completeness for this taxonomic decision a lectotype is designated for Mytilus ater Zelebor in Dunker and Zelebor, 1866 DunkerW, ZeleborJ. 1866. Bericht über die von der Novara-expedition mitgebrachten Mollusken. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien. 16:909–916. [Google Scholar] [?=?Modiolus neozelanicus Iredale, 1915 IredaleT. 1915. A commentary on Suter’s ‘Manual of New Zealand Mollusca’. Transactions of the New Zealand Institute. 47:417–497. [Google Scholar]].     

Formation of the Late Permian Panzhihua plutonic-hypabyssal-volcanic igneous complex: Implications for the genesis of Fe–Ti oxide deposits and A-type granites of SW China

The Late Permian (260 Ma) Emeishan large igneous province of SW China contains numerous magmatic Fe–Ti oxide deposits. The Fe–Ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with A-type granitic rocks. The 260 Ma Panzhihua layered gabbroic intrusion hosts one of the largest magmatic Fe–Ti oxide deposits in China and is coeval with a peralkaline A-type granitic pluton. The granite has intruded the overlying Emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes. The presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks. The syenodiorites have intermediate to felsic composition with SiO₂ = 61 to 65 wt.%, MgO = 0.27 to 0.6 wt.% and CaO = 1.0 to 2.5 wt.% as compared to the granite SiO₂ = 65 to 72 wt.%, MgO = 0.1 to 0.4 wt.%, CaO = < 1.0 wt.%. Primitive-mantle-normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks. The chondrite-normalized REE patterns show Eu anomalies changing from > 1(Eu/Eu? = 1.1 to 2.6) in the gabbroic intrusion, to < 1 in the syenodiorite (Eu/Eu? = 0.75 to 0.83), granites and trachytes (Eu/Eu? = 0.55–0.87). Previously published εNd_(T) values from clinopyroxenes (εNd_(T) = + 1.1 to + 3.2) of the gabbroic intrusion match the whole-rock values of the syenodiorite (εNd_(T) = + 2.1 to + 2.5), granite and trachyte (εNd_(T) = + 2.2 to + 2.9), suggesting that all rock types originated from the same mantle source. MELTS and trace element modeling confirm that all rock types can be generated by fractional crystallization of high-Ti Emeishan basalt. The jump in SiO₂ from the gabbro to the syenodiorite is attributed to the en masse crystallization of the Fe–Ti oxides. The geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and Fe–Ti oxide deposit, the syenodiorite, granites and trachyte of the Panzhihua region, which thus form a genetically related plutonic-hypabyssal-volcanic complex. Other granite–gabbro complexes in the region likely formed in a similar manner.     

A uniform solution of the Lambert problem

A uniform method (with respect to the type of the conic section) for solving the Lambert boundary value problem is presented. It is derived by using the KS-transformation and consists in solving one nonlinear equation. It can be used either in the ordinaryx-frame (physical space) as well as in the KS-coordinates (regularized space).