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1.
Laurence Hopkinson Stephen Roberts Richard Herrington Jamie Wilkinson 《Contributions to Mineralogy and Petrology》1999,137(4):342-350
Silica occurs in abundance in a variety of hydrothermal samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal mound,
26°N Mid-Atlantic Ridge. The water content, trace element chemistry, and mineralogy of crystalline silica from 15 different
samples have been examined by vibrational spectroscopy and probe microanalysis. The samples are from: shallow subsurface ferric
iron oxyhydroxide silica deposits (n=4), a fragment of an active white smoker chimney (n=1), anhydrite bearing hydrothermal breccias (n=2), pyrite silica breccias (n=3), and silicified wall rock breccias (n=5). Length-fast chalcedony occurs in association with variable quantities of ferric iron oxyhydroxides in hydrothermal breccias
from the mound flanks, within shallower subsurface chert samples, and within white smoker chimney walls. Samples from the
anhydrite zone contain textures which are suggestive of an origin involving replacement of anhydrite. Samples taken from TAG
1 and 5 from below the anhydrite zone contain no chalcedony. Instead they contain subhedral quartz crystals which show oscillatory
zoning in aluminium. Two types of crystalline silica namely, type A and type B quartz, are defined on the basis of the infrared
spectra in the OH region from 3200 cm−1 to 3600 cm−1. The type A quartz occurs beneath the anhydrite zone at TAG 1 and 5. We propose a model that relates specific varieties of
crystalline silica to different thermal and chemical environments within the mound interior. Length-fast chalcedony occurs
in an outer low temperature envelope across the top and sides of the mound. The common association between length-fast chalcedony
and ferric iron oxyhydroxides suggests that chalcedony crystallization is favoured where catalysis by ferric iron can occur.
The apparent suppression of fibrous silica at the expense of single quartz crystals with increasing depth is attributed to
differing growth rates and degrees of supersaturation of silica-bearing solutions with increasing temperature within the mound.
The transition from type A to type B single crystal growth is interpreted to occur at temperatures approaching ˜360 °C due
to decreasing solubility of aluminium in quartz, so that aluminium is rendered unavailable for type A valence compensation.
Received: 10 September 1998 / Accepted: 6 July 1999 相似文献
2.
Christopher T. Perry 《Sedimentology》1999,46(1):33-45
Micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms. These are referred to as 'destructive micrite envelopes' and have long been recognized as reflecting an important early diagenetic process. Recent analysis of sediments collected from back-reef environments at Discovery Bay, north Jamaica, however, has demonstrated 'envelope' formation on the surfaces of carbonate grains, clearly distinct from the micrite filling of microborings. Such constructive envelopes occur almost exclusively in sediments from grass-bed environments and are always intimately associated with 'biofilms' comprising abundant mucilage, cyanobacteria, bacteria and diatoms. It is suggested that these envelopes represent a product of both biologically mediated micrite precipitation (occurring within the biofilm mucilage and around the biofilm components, i.e. cyanobacteria and diatoms) and associated trapping of carbonate mud and fine-grained sediment. Their recognition only within grass-bed sediments may enable their use as a diagnostic feature of grass-bed environments or vegetation-stabilized substrates in the rock record. 相似文献
3.
N. N. Mozgova Yu. S. Borodaev T. V. Stepanova G. A. Cherkashev E. A. Zhirnov 《Lithology and Mineral Resources》2000,35(1):1-18
Primary sulfides from cores of holes 957M, 957C, and 957H drilled during the ODP Leg 158 on the active hydrothermal TAG mound
(Mid-Atlantic Ridge, 26°08′ N) were examined for the concentration of several elements. Based on 262 microprobe analyses,
it has been established that the sulfides are characterized by an extremely heterogeneous distribution of noble metals (Au,
Ag, Pt, and Pd) and several associated elements (Hg, Co, and Se). Noble metals are arranged in the following order in terms
of decreasing abundance, i.e., concentration level above the detection limit (the number of analyses containing the specific
element is given in parentheses): Au (65), Ag (46), Pt (21), and Pd (traces). The associated trace elements make up the following
series: Co (202), Hg (132), and Se (49). Main carriers of the “invisible” portion of noble metals are represented by pyrite
(Au, Hg), marcasite and pyrite (Ag, Co), sphalerite and chalcopyrite (Pt, Pd), and chalcopyrite (Se). The noble metal distribution
in sulfides reveals a lateral zonality: the maximal concentration and abundance of Au in chalcopyrite (or Pt and Ag in chalcopyrite
and pyrite) increase from the periphery (Hole 957H) to the center (holes 957C and 957M) of the hydrothermal mound, while the
Au distribution in pyrite displays a reversed pattern. The Co distribution increases with depth. This work discusses the vertical
zonality in the distribution of elements mentioned above and their response to the evolution of ore genesis. 相似文献
4.
Black Sea coast line is a hazardous region especially in winter due to the dominant wave action. Therefore, rubble mound breakwaters protected with armourstone used as ship shelters are vital structures especially for the fishermen. The deterioration of the armourstone with time in the form of abrasion and disintegration may result in the failure of the breakwater. In this study, the properties of the armourstone taken from an andesite quarry and used in the Hisarönü rubble mound breakwater were studied both in field and laboratory in order to assess their qualities and long-term durabilities. Based on the in situ observations and laboratory tests, the andesite is found to be generally marginal rock. CIRIA/CUR, RDIs, RERS and Wet-Dry strength ratio classifications are in good agreement with the in situ observations and the results of the laboratory tests. However, RDId, Average Pore Diameter and Saturation Coefficient classifications cannot correctly predict long-term durability of the armourstone. Field studies reveal that block size of the andesite in the quarry increases with depth due to the increase in spacing of the cooling joints of the rock. 相似文献
5.
Third dimension of a presently forming VMS deposit: TAG hydrothermal mound, Mid-Atlantic Ridge, 26°N
ODP drilling of the active TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge provided the first insights into the
third dimension of a volcanic-hosted massive sulfide (VMS) deposit on a sediment-free mid-ocean ridge. Sulfide precipitation
at this site started at least 20,000 years ago and resulted in the formation of a distinctly circular, 200-m diameter, 50-m-high
pyritic mound and a silicified stockwork complex containing approximately 3.9 million tonnes of sulfide-bearing material with
an average of 2.1 wt% Cu and 0.6 wt% Zn in 95 samples collected from 1–125 m below the seafloor. The periodic release of high-temperature
hydrothermal fluids at the same location for several thousand years with intermittent periods of hydrothermal quiesence is
the dominating process in the formation of the TAG hydrothermal mound. Distinct geochemical, mineralogical and isotopic zonation
as well as a complex assemblage of sulfide-anhydrite-quartz bearing breccias can be related to this process. Geochemical depth
profiles indicate extremely low base and trace element concentrations for the interior of the mound, which clearly contrasts
with published analyses of samples collected from the surface of the TAG mound. This is explained by continued zone refining
during which metals were mobilized from the interior of the mound by upwelling, hot (>350 °C) hydrothermal fluids. Mixing
of these fluids with infiltrating ambient seawater subsequently caused redeposition of metals close to the mound-seawater
interface. The sulfur isotopic composition of bulk sulfides (+4.4 to +8.2‰δ34S; average +6.5‰) is unusually heavy when compared to other sediment-free mid-ocean ridge deposits and implies the introduction
of heavy seawater sulfur to the hydrothermal fluid. The slight increase in sulfur isotope ratios with depth and distinct variations
between early, disseminated sulfides related to wallrock alteration, and massive as well as late vein sulfides indicates widespread
entrainment of seawater deep into the system. Fluid inclusion measurements in quartz and anhydrite reveal high formation temperatures
throughout the TAG mound (up to 390 °C) at one time with an overall increase in trapping temperatures with depth. Lower formation
temperatures close to the paleo-seafloor indicate local entrainment of seawater into the mound. Formation temperatures for
a central anhydrite-bearing zone range from 340–360 °C and are slightly lower than the exit temperature of hydrothermal fluids
presently venting at the Black Smoker Complex (360–369 °C). Fluid inclusions in quartz and anhydrite from the stockwork zone
are characterized by formation temperatures higher than 375 °C, indicating conductive cooling of the hydrothermal fluids or
mixing with ambient seawater prior to venting. Formation temperatures for quartz from an area of extremely low heat flow at
the western side of the mound reach up to 390 °C, implying that this area was once part of a high-temperature hydrothermal
upflow zone. The low heat flow and the absence of anhydrite within this part of the mound are strong indications that the
recent pulse of high-temperature hydrothermal activity is not affecting this area and provides evidence for significant changes
in the fluid flow regime underneath the deposit between hydrothermal cycles.
Received: 16 November 1998 / Accepted: 19 August 1999 相似文献
6.
The Taipinghu Bridge is an important project, and the safety of rock masses of its foundation is very crucial. This article analyzes the potential causes of the deformation of the rock masses of the bridge foundation, and uses the Fast Lagrangian Analysis of Continua to analyze the geologic model. The simulating process shows that no mater in the excavating process or in the loading process the rock masses are suit for the engineering. The modeling and analyzing process can be used for reference. 相似文献
7.
陶正章 《中国地球化学学报》1991,10(3):288-293,T003
The carat is the unit of weight for diamonds and other gemstones.It corresponds to the average weight of the seeds of a leguminous tree.What kind of tree is this?We have studied the samples from Ethiopia,Egypt,Cyprus and the United States.The tree is neither“Kuara“nor“Locust“（Robina pseudoacacia Linn.）,but rather Carob(Ceratonia Siliqua).In Ethiopia,as called by local inhabitants,“Kuara“is a species of Erythrina-E.brucei rather than E.abyssinica.As might be expected,using the seeds as a means of weighing an extremely valuable commodity is not very scientific.Before 1907,at various times and in various countries,there were at least twenty-three stan-dards for the carat ranging from 187.00mg to 215.990mg.The metric carat equal to 200mg was proposed in Paris in 1907.It was adopted in the United States on July1,1913 and now is the world-accepted standard.But in reality,the standard of the carat is still confused with respect to its usage throughout the world .This is why the author reiterates that the standard of the car-at should be integrated with the metric system. 相似文献
8.
The catastrophic Shikotan earthquake of October 4 (5), 1994, occurred in the Pacific Ocean. Its focus was located 80 km eastward of Shikotan Island. The stress state of the Earth’s crust in this area was estimated by the method of the cataclastic analysis of the whole range of the earthquake mechanisms. The performed reconstruction of the parameters of the current stress state of the Earth’s crust and the upper mantle in the area of the Southern Kuril Islands made it possible to establish that this area is characterized, on the one hand, by the presence of extensive areas of steady behavior of the stress tensor parameters and, on the other hand, by the presence of local sections of anomalously fast changes in these parameters. 相似文献
9.
The Taipinghu Bridge is an important project，and the safety of rock masses of its foundation is very crucial．This article analyzes the potential causes of the deformation of the rock masses of the bridge foundation，and uses the Fast Lagrangian Analysis of Continua to analyze the
geologic model． The simulating process shows that no mater in the excavating process or in the loading process the rock masses are suit for the engineering．The modeling and analyzing process can be used for reference． 相似文献
10.
INTRODUCTIONIn comparison with studies on the geochemistryof the REE and trace elements of the Emeishan Per-mian basalts ,there has been onlyli mited research onthe platinum group elements ( PGE) . Preli minarystudies have been carried out on the PGE geochemis-try of the basalts in the Emeishan area ( QingyingPower Station profile) and Xinjie area (Zhang andLi ,1998) ,andinthe Shuicheng and Weining areasinGuizhou (Li et al .,2003) . There are no PGEanaly-sis data of the basaltsin… 相似文献
11.
12.
Guan Shaozeng 《《地质学报》英文版》1989,63(3):281-296
Since the coexistence of the Cretaceous and Palaeocene was ascertained in the Hengyang Basin of Hunan in the middle of the 1960's, the Cretaceous and Tertiary boundary has been discussed in several papers, but it still remains controversal. The points at issue are the connotation, stratigraphical position and lateral correlation of the Dongtang (or Chejiang) Formation. 相似文献
13.
Doklady Earth Sciences - An attempt to provide a new explanation for the change in the geodynamic regime in the Early Cretaceous is presented below. It accounts for data on a number of global... 相似文献
14.
A simple mechanical model explaining the long-period (about 100-year) variations in the Earth’s rotational velocity is proposed. This model takes into account the gravitational interaction of the mantle with the solid core of the Earth and the fact that the core rotation leads that of the mantle. Well-known Earth parameters provide estimates of the gravitational torque that support the proposed model. The mathematical problem involved reduces to the classical problem of a nonlinear oscillator exposed to a constant torque. The well-known parameters of the core-mantle system result in a stable equilibrium and a stable limiting cycle on the phase cylinder of this oscillator. This equilibrium corresponds to a single angular velocity for the mantle and solid core, with no long-period oscillations in the length of the day. The limiting cycle corresponds to the core rotation leading the mantle rotation. In this case, the ellipsoidality of the gravitationally interacting bodies provides a periodic interchange of kinetic angular momentum between the mantle and solid core that results in long-period variations in the length of the day. The proposed model does not support the formerly widespread opinion that the core rotates more slowly than the mantle. 相似文献
15.
With increasing high-quality geological and geophysical data it becomes clear that seismicity of the continents is characterized by linear patterns which are closely associated with tectonic features. The aim of this paper is to give reasonable interpretation for the earthquake distribution in the contiguous continent of the United States. Seismic lines and earthquake concentrated zones are defined, which reflect the characteristics of the continental seismotectonics. Similarities and differences in seismotectonics between the continental part of China and the contiguous continent of US are analysed. It is demonstrated that the spatial distribution of earthquakes can provide the information of the active structures in the earth's crust. The authors consider that the patterns of continental seismotectonics are not only controlled by the pre—existing tectonic frameworks and the current boundary dynamic conditions, but also possibly affected by dynamic factors of global tectonics at a higher level. 相似文献
16.
V. A. Zubakov 《Stratigraphy and Geological Correlation》2011,19(1):108-124
An international scientific conflict has arisen around the International Stratigraphic Scale, the main document that regulates
the rules of reading of geological records and, hence, concerns all Earth sciences. The matter of debate is the geological
time scale of 2004, developed by the International Commission on Stratigraphy, where the Quaternary system was abandoned. This ICS decision triggered a protest among Quaternary geologists, members of
INQUA, and became the subject of much controversy. This article provides a comprehensive analysis of the Quaternary problem
and proposes a reasonable scientific solution that may be appropriate for both parties. 相似文献
17.
Koroteev V. A. Chervyakovskiy V. S. Zaitseva M. V. Volchek E. N. Necheukhin V. M. 《Doklady Earth Sciences》2019,487(1):756-760
Doklady Earth Sciences - This paper reports on the first U–Pb dating of zircons from dacites of the volcanic paleo-edifice of the andesite–dacite complex of the Eastern Zone of the... 相似文献
18.
《地学前缘(英文版)》2016,7(6)
Life was limited for most of Earth's history, remaining at a primitive stage and mostly marine until about 0.55 Ga. In the Paleozoic, life eventually exploded and colonized the continental realm. Why had there been such a long period of delayed evolution of life? Early life was dominated by Archaea and Bacteria,which can survive ionizing radiation better than other organisms. The magnetic field preserves the atmosphere, which is the main shield of UV radiation. We explore the hypothesis that the Cambrian explosion of life could have been enabled by the increase of the magnetic field dipole intensity due to the solidification of the inner core, caused by the cooling of the Earth, and the concomitant decrease with time of the high-energy solar flux since the birth of the solar system. Therefore, the two phenomena could be responsible for the growth and thickening of the atmosphere and the development of land surface life. 相似文献
19.
Ar-Ar Dating on the Metallogenesis of the Dongchuang Gold Deposit in the Xiaoqinling Area 总被引：2，自引：0，他引：2
LI Qiangzhi CHEN Yanjing ZHONG Zengqiu LI Wenliang LI Shaoru GUO Xiaodong JIN BaoyiCollege of Earth Space Science Peking University Beijing Institute of Gold Geology Armed Police Force of Chin Langfang Hebei College of Earth Sciences China University of Geosciences Wuhan Hubei 《《地质学报》英文版》2002,76(4):488-493
The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lode gold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has been argued that it was formed in the Mesozoic, related isotopic age data have not been reported in previous studies. Based on detailed geological study, the authors have carried out isotopic dating on various metallogenic generations. The ore-forming process of the Dongchuang gold deposit consists of four stages: coarse-grained pyrite-bearing quartz veins (stage Ⅰ), fine-grained pyrite-quartz veinlets (stage Ⅱ), multi-sulfides (stage Ⅲ) and carbonate-quartz veinlets (stage IV). Ar-Ar dating on mineral separates of stages Ⅰ, Ⅱ and Ⅲ yields plateau ages of 142.9±2.9 Ma, 132.2±2.6 Ma and 128.3±6.2 Ma, respectively. Sericite separates from stage Ⅱ assemblage also yield an Ar-Ar isochron age of 132.6±2.7 Ma, similar to the Ar-Ar plateau age. These results suggest that the Dongchuang gold deposit was mainly formed during 143-128 M 相似文献
20.
The first results on current movements are presented for the western part of the Dzhugdzhur–Stanovoi Terrane based on GPS geodesy of a geodynamic survey area of the Upper Amur region. Processing of the GPS data resulted in a vector field of the displacement rates of points of the geodynamic survey area with zones of intense deformations. It was concluded from a comprehensive analysis of geological–geophysical data and estimates of the displacement rates that the terrane is characterized by kinematic integrity and was subjected to a complex of tectonic factors related to the evolution of the eastern segment of Baikal Rift Zone in the area of transpression interaction of the Eurasian and Amur plates. 相似文献