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981.
Autochthonous inheritance of zircon through Cretaceous partial melting of Carboniferous plutons: the Arthur River Complex,Fiordland, New Zealand 总被引:1,自引:0,他引:1
Andrew J. Tulloch Trevor R. Ireland David L. Kimbrough William L. Griffin Jahandar Ramezani 《Contributions to Mineralogy and Petrology》2011,161(3):401-421
TIMS and SHRIMP U–Pb analyses of zircons from Milford Orthogneiss metadiorite (P = 1–1.4 GPa; T ≥ 750°C) of the Arthur River Complex of northern Fiordland reveal a bimodal age pattern. Zircons are predominantly either
Paleozoic (357.0 ± 4.2 Ma) and prismatic with oscillatory zoning, or Cretaceous (133.9 ± 1.8 Ma) and ovoid with sector or
patchy zoning. The younger age component is not observed overgrowing older grains. Most grains of both ages are overgrown
by younger Cretaceous (~120 Ma) metamorphic zircon with very low U and Th/U (0.01). We interpret the bimodal ages as indicating
initial igneous emplacement and crystallisation of a dioritic protolith pluton at ~357 Ma, followed by Early Cretaceous granulite-facies
metamorphism at ~134 Ma, during which a significant fraction (~60%) of the zircon grains dissolved, and subsequently reprecipitated,
effectively in situ, in partial melt pockets. The remaining ~40% of original Paleozoic grains were apparently not in contact
with the partial melt, remained intact, and show only slight degrees of Pb loss. Sector zoning of the Cretaceous grains discounts
their origin by solid state recrystallisation of Paleozoic grains. The alternative explanation—that the Paleozoic component
represents a 40% inherited component in an Early Cretaceous transgressive dioritic magma—is considered less likely given the
relatively high solubility of zircon in magma of this composition, the absence of 134 Ma overgrowths, the single discrete
age of the older component, equivalent time-integrated 177Hf/176Hf compositions of both age groups, and the absence of the Cambrian-Proterozoic detrital zircon that dominates regional Cambro-Ordovician
metasedimentary populations. Similar bimodal Carboniferous-Early Cretaceous age distributions are characteristic of the wider
Arthur River Complex; 8 of 12 previously dated dioritic samples have a Paleozoic component averaging 51%. Furthermore, the
age and chemical suite affinity of these and several more felsic rocks can be matched with those of the relatively unmetamorphosed
Carboniferous plutonic terrane along the strike of the Mesozoic margin in southern Fiordland, also supporting the in situ
derivation of the Carboniferous “inherited” component. 相似文献
982.
栉孔扇贝(Chlamys farreri) 血细胞类型及抗菌力的研究 总被引:1,自引:0,他引:1
用2种方法将栉孔扇贝血细胞分为2大类透明细胞、颗粒细胞.吉姆萨染色观察,透明细胞的细胞质中颗粒很少,细胞核圆形,居中,细胞质较少,核质比大;颗粒细胞比透明细胞大且多,染色深,但核质比小,在细胞质中有颗粒,有些颗粒细胞具双核.密度梯度离心结果,透明细胞主要位于上层,颗粒细胞则大部分位于下层.吞噬力、抗菌活力、溶菌活力及活性氧检测结果表明,颗粒细胞均强于透明细胞. 相似文献
983.
利用新三维地震资料对松南-宝岛凹陷反转构造带发育特征、形成期次进行研究,并从构造背景及力学机制两个方面探讨反转构造的成因机制。研究结果表明,松南-宝岛凹陷反转构造带主要发育一系列"上凸下凹"的大型褶皱背斜,伴生NWW向弱走滑断裂构造和NNW向张剪构造。反转构造及其伴生构造符合NEE右旋剪切应力场特征,形成时间与东沙运动一致,表明该反转构造带可能受晚中新世南海东北部东沙运动产生的右旋走滑应力场作用控制。反转构造有利于研究区圈闭的重建和改造,对琼东南盆地东部新区油气运移和重新优选分配的认识,具有重要的油气地质意义。 相似文献
984.
羟化酶是细菌降解烷烃的关键酶,本文以南极低温降解菌Shewanella sp.NJ49为研究对象,通过硫酸铵沉淀、超滤浓缩及葡聚糖凝胶Sephadex G-75柱层析方法,分离纯化NJ49的羟化酶,获得了单一羟化酶组分,研究了温度、p H、表面活性剂和盐度等环境因素对NJ49羟化酶酶活活性影响。结果表明,羟化酶组分由α、β、γ三个亚基组成,分子质量分别为56,45和36 k D。NJ49最适产酶条件为:温度15℃、p H7.2、盐度55;不同类型表面活性剂对酶的活性影响效应不一,两性离子表面活性剂、阳离子表面活性剂、非离子表面活性剂对酶活没有作用,阴离子表面活性剂+非离子表面活性剂混和剂和阳离子表面活性剂+非离子表面活性剂混和剂能提高羟化酶的活性。 相似文献
985.
The present paper focuses on heat and mass exchange processes in methane hydrate fragments during in situ displacement from the gas hydrate stability zone (GHSZ) to the water surface of Lake Baikal. After being extracted from the methane hydrate deposit at the lakebed, hydrate fragments were placed into a container with transparent walls and a bottom grid. There were no changes in the hydrate fragments during ascent within the GHSZ. The water temperature in the container remained the same as that of the ambient water (~3.5 °С). However, as soon as the container crossed the upper border of the GHSZ, first signs of hydrate decomposition and transformation into free methane gas were observed. The gas filled the container and displaced water from it. At 300 m depth, the upper and lower thermometers in the container simultaneously recorded noticeable decreases of temperature. The temperature in the upper part of the container decreased to –0.25 °С at about 200 m depth, after which the temperature remained constant until the water surface was reached. The temperature at the bottom of the container reached –0.25 °С at about 100 m depth, after which it did not vary during further ascent. These observed effects could be explained by the formation of a gas phase in the container and an ice layer on the hydrate surface caused by heat consumption during hydrate decomposition (self-preservation effect). However, steady-state simulations suggest that the forming ice layer is too thin to sustain the hydrate internal pressure required to protect the hydrate from decomposition. Thus, the mechanism of self-preservation remains unclear. 相似文献
986.
This study investigates atmospheric responses to the directions of surface wind over the Kuroshio front in the East China Sea, using wintertime satellite-derived data sets. Composite maps of sea surface temperature, wind speed, precipitation, turbulent heat flux, surface wind divergence, and the curl of wind vectors above the atmospheric boundary layer are depicted based on the classification of intense northeasterly (along the front) and northwesterly (across the front) winds over the East China Sea. When northeasterly winds prevail, considerable precipitation occurs on the offshore side of the Kuroshio front, in contrast to periods when northwesterly winds prevail. First, the northeasterly winds strengthen above the front because of the downward transfer of momentum from the fast-moving air at higher levels and/or an adjustment of sea level pressure over the oceanic front, although the process by which the influence of the Kuroshio penetrates beyond the marine atmospheric boundary layer remains unclear. Second, a cyclonic vortex forms above the marine atmospheric boundary layer (at 850-hPa height) on the offshore side of the front, and thereafter, surface wind convergence via Ekman suction (hence, enhanced precipitation) occurs over the East China Sea shelf breaks. The northeasterly winds blow over the East China Sea when the Aleutian Low retreats to the east and when high sea level pressure covers the northern Sea of Japan. 相似文献
987.
988.
Natasha Khan Khaista Rehman Sajjad Ahmad Jamil Khokher M. Iqbal Hajana M. Hanif 《Marine Geophysical Researches》2016,37(3):207-228
In this study, seismic data from two wells (Pak G2-1 and Indus Marine-1C) and age diagnostic larger benthic foraminifera (LBF) within drill cuttings has been used for the first time to identify depositional sequences within the carbonates in the Offshore Indus Basin, Pakistan. The Offshore Indus is tectonically categorized as a passive continental margin where carbonates occur as shelf carbonates in the near offshore and on volcanic seamounts in deeper waters. Seismic data analysis has indicated the presence of minor faults and carbonate buildups above the igneous basement in the south. Patterns of the seismic reflections enabled definition of three seismic facies units identified as: Unit 1 basement, represented by chaotic, moderate amplitude reflection configuration; while parallel bedding and the drape of overlying strata is typical character of Unit 2, carbonate mound facies. The younger Miocene channels represent Unit 3. The diagnosis of Alveolina vredenburgi/cucumiformis biozone confirmed the Ilerdian (55–52 Ma) stage constituting a second order cycle of deposition for the Eocene carbonates (identified as Unit 2). The carbonate succession has been mainly attributed to an early highstand system tract (HST). The environmental conditions remained favorable leading to the development of keep-up carbonates similar to pinnacle buildups as a result of aggradation during late transgressive system tract and an early HST. The carbonate sequence in the south (Pak G2-1) is thicker and fossiliferous representing inner to middle shelf depths based on fauna compared to the Indus Marine-1C in the north, which is devoid of fossils. Three biozones (SBZ 5, SBZ 6 and SBZ 8) were identified based on the occurrence of LBF. The base of the SBZ 5 zone marks the larger foraminifera turnover and the Paleocene–Eocene (P–E) boundary. The LBF encountered in this study coincides with earlier findings for the P–E boundary. Our findings indicate that the entire Ilerdian stage ranges from 55.5 to 52 Ma that was the episode of warmer water conditions on the carbonate shelves leading to the diversification of K-strategist larger foraminifera. The larger foraminiferal assemblage encountered in this study confirms the findings. The possible indication of stratigraphic-combination traps, revealed as reflection terminations, make carbonate mounds in the south a potential exploration target. 相似文献
989.
根据榧螺螺旋部的差异可将其分为两种不同的形态类型,类型Ⅰ(MorphotypeⅠ)的个体螺旋部陷入体螺层中,其壳顶与前部数螺层愈合;类型Ⅱ(MorphotypeⅡ)的个体螺旋部高出壳顶,缝合线明显,此类型可明确鉴定为伶鼬榧螺(Oliva mustelina)。本研究通过线粒体COⅠ和16SrRNA基因序列的分析对两种形态类型的榧螺进行了分子鉴定。结果表明:两种形态类型的榧螺含有共享的单倍型;不同形态类型间的遗传距离和同一形态类型内的遗传距离重叠;两者的单系性在系统发育分析中没有得到显现,而是共同构成一个单系。因此,两种形态类型的个体均为伶鼬榧螺。类型Ⅰ可能是伶鼬榧螺中一种少见的有别于典型个体的形态变异类型。 相似文献
990.
In 1991, a digital seismic monitoring network was installed in Iceland with a digital seismic system and automatic operation. After 20 years of operation, we explore for the first time its nationwide performance by analysing the spatiotemporal variations of the completeness magnitude. We use the Bayesian magnitude of completeness (BMC) method that combines local completeness magnitude observations with prior information based on the density of seismic stations. Additionally, we test the impact of earthquake location uncertainties on the BMC results, by filtering the catalogue using a multivariate analysis that identifies outliers in the hypocentre error distribution. We find that the entire North-to-South active rift zone shows a relatively low magnitude of completeness Mc in the range 0.5–1.0, highlighting the ability of the Icelandic network to detect small earthquakes. This work also demonstrates the influence of earthquake location uncertainties on the spatiotemporal magnitude of completeness analysis. 相似文献