Five hundred million years of punctuated addition of juvenile crust during extension in the Goochland Terrane,central Appalachian Piedmont Province     

Aaron J. Martin  Irene Kadel-Harder  Brent E. Owens  Kouki Kitajima  Scott D. Samson  Sanjeet K. Verma 《International Geology Review》2020,62(5):523-548

ABSTRACT

The Goochland Terrane is an enigmatic crustal block in the Appalachian Piedmont Province of central Virginia, USA. Sparse exposures of terminal Mesoproterozoic and late Neoproterozoic igneous rocks in the central Goochland Terrane offer the opportunity to investigate both the continental affinity of the terrane during the Proterozoic Eon and the timing and mechanisms of crustal growth. We apply multiple geochemical tools to these rocks: tectonic discrimination using whole-rock major and trace element abundances; whole-rock Sm-Nd isotopes; O, U-Pb, and Lu-Hf isotope analyses of spots in zircon; and measurement of O isotopes in multi-grain quartz separates. Eruption of the Sabot Amphibolite protolith is difficult to date, but we tentatively assign an age of 552 ± 11 Ma. Goochland Terrane continental crust first separated from the mantle prior to ca. 1050–1010 Ma intrusion of the Montpelier Anorthosite and the State Farm Gneiss protolith. The granitic magma that became the State Farm Gneiss protolith could have been derived entirely from partial melting of this initial Goochland Terrane crust. In contrast, the magmas that became the Montpelier Anorthosite, Neoproterozoic granitoid, and the Sabot Amphibolite were mixtures of mantle melt and preexisting Goochland Terrane crust. This production of juvenile continental crust occurred during continental extension and, eventually, rifting. The timing and compositions of terminal Mesoproterozoic magmatism in the Goochland Terrane closely match those in the nearby Blue Ridge Province. Although the compositions of the Neoproterozoic magmas in the two regions are similar, intrusion and possibly eruption occurred about 10 M.y. later in the Goochland Terrane.  相似文献   

Matrices of type 3 ordinary chondrites—primitive nebular records     

Hiroko Nagahara 《Geochimica et cosmochimica acta》1984,48(12):2581-2595

Petrologic studies were made on the fine-grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype. The matrix minerals, in order of abundance, are olivine (Fo₉₉ to Fo₉), enstatite or bronzite, augite or subcalcic augite, albite, Fe-Ni metal, troilite, magnetite, spinel (MgAl₂O₄), chromite, and calcite. Fe- and Mg-rich fluffy particles and albite-like particles are also major constituents. The chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium, showing that the matrix materials were hardly heated after their formation. Textural relationships indicate that magnesian olivine was formed after Ca-pyroxene, followed by intermediate to iron-rich olivine. Intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions. The observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules. They were mostly the products of condensation and reaction among solids and/or between solids and the ambient gas mostly at low temperatures, and thus they contain records of primitive processes in the nebula. In order to explain the presence of olivines more iron-rich than Fo₅₀, the presence of free SiO₂ or a high activity of SiO₂ in the gas is necessary, which was not shown in previous thermochemical calculations. Mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites, indicating that they were formed at different oxygen fugacities. The rims of chondrules, and surrounding matrix materials, must have accreted onto chondrules during turbulent movements of the nebula.  相似文献   

Simultaneous In Situ Analysis of Carbon and Nitrogen Isotope Ratios in Organic Matter by Secondary Ion Mass Spectrometry          下载免费PDF全文

Akizumi Ishida  Kouki Kitajima  Kenneth H. Williford  Michael L. Tuite  Takeshi Kakegawa  John W. Valley 《Geostandards and Geoanalytical Research》2018,42(2):189-203

An in situ measurement method for simultaneous determination of carbon and nitrogen isotope ratios in organic matter was developed by secondary ion mass spectrometry with a spatial resolution of ~ 12 μm. Secondary ion intensities of ¹²C^?₂, ¹²C¹³C^?, ¹²C¹⁴N^? and ¹²C¹⁵N^? were simultaneously measured by three Faraday cups and one electron multiplier. Ions of ¹²C₂H^? were measured to monitor hydride interferences and to correct for mass bias. The analytical precisions of δ¹³C and δ¹⁵N values of a reference material (UWLA‐1 anthracite) were 0.16‰ and 0.56‰, respectively (2s). A negative correlation was observed between the mass bias of carbon and ¹²C₂H^?/¹²C^?₂ ratios of examined reference materials. In contrast, there was no correlation between mass bias and hydrogen concentration for nitrogen. The δ¹³C_VPDB and δ¹⁵N_Air values of twenty‐two individual globules of organic matter, found in carbonate rock of the 1878 Ma Gunflint Formation, were determined by the new procedure, ranging from ?33.8‰ to ?33.3‰ and +4.2‰ to 5.8‰, respectively. Means of δ¹³C_VPDB and δ¹⁵N_Air values, ?33.5 ± 0.25‰ and +5.2 ± 0.81‰, are consistent with reported values from bulk sample analysis within analytical precision.  相似文献   

Evolution of the composition of seawater through geologic time, and its influence on the evolution of life   总被引：2，自引：2，他引：0  

Tsuyoshi Komiya  Takafumi Hirata  Kouki Kitajima  Shinji Yamamoto  Takazo Shibuya  Yusuke Sawaki  Tomoko Ishikawa  Degan Shu  Yong Li  Jian Han 《Gondwana Research》2008,14(1-2):159

The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO₂ content (pCO₂) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO₂ condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO₂ through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates.  相似文献   

Further characterization of carbonaceous materials in Hayabusa‐returned samples to understand their origin     

Masayuki Uesugi  Motoo Ito  Hikaru Yabuta  Hiroshi Naraoka  Fumio Kitajima  Yoshinori Takano  Hajime Mita  Yoko Kebukawa  Aiko Nakato  Yuzuru Karouji 《Meteoritics & planetary science》2019,54(3):638-666

Carbonaceous materials in the sample catcher of the Hayabusa spacecraft were assigned as category 3 particles. We investigated the category 3 particles with a suite of in situ microanalytical methods. Possible contaminants collected from the cleanrooms of the spacecraft assembly and extraterrestrial sample curation center (ESCuC) were also analyzed in the same manner as category 3 particles for comparison. Our data were integrated with those of the preliminary examination team for category 3 particles. Possible origins for the category 3 particles include contamination before and after the operation of the Hayabusa spacecraft.  相似文献   

Implications for the low latitude cloud formations from solar activity and the quasi-biennial oscillation     

Peng K. Hong  Hiroko Miyahara  Yusuke Yokoyama  Yukihiro Takahashi  Mitsuteru Sato 《Journal of Atmospheric and Solar》2011,73(5-6):587-591

We examined the effect of the 11-year solar cycle and quasi-biennial oscillation (QBO) on the ～27-day solar rotational period detected in tropical convective cloud activity. We analyzed the data of outgoing longwave radiation (OLR) for AD1979–2004, dividing into four different cases by the combination of high and low solar activities in terms of the 11-year variation, and easterly and westerly stratospheric winds associated with QBO. As a result, ～27-day variation has been most significantly detected in high solar activity period around the Indo-Pacific Warm Pool. Based on correlation analysis, we find that solar rotation signal can explain 10–20% of OLR variability around the tropical warm pool region during the high solar activity period. The spatial distribution has been, however, apparently different according to the phases of QBO. It is suggested that the 11-year solar cycle and stratospheric QBO have a possibility to cause large-scale oceanic dipole phenomena.  相似文献   

Waveform characteristics of deep low-frequency earthquakes: time-series evolution based on the theory of the KM₂O-Langevin equation     

Minoru Takeo  Hiroko Ueda  Yasunori Okabe  Masaya Matsuura 《Geophysical Journal International》2006,165(1):87-107

  相似文献   

New discoveries in dynamics of an M8 earthquake-phenomena and their implications from the 2003 Tokachi-oki earthquake using a long term monitoring cabled observatory   总被引：1，自引：0，他引：1  

Hitoshi Mikada  Kyohiko Mitsuzawa  Hiroyuki Matsumoto  Tomoki Watanabe  Shigehiko Morita  Riyo Otsuka  Hiroko Sugioka  Toshitaka Baba  Eiichiro Araki  Kiyoshi Suyehiro 《Tectonophysics》2006,426(1-2):95

At the 2003 Tokachi-oki earthquake of M8, seafloor phenomena such as a generation process of tsunami, seafloor uplifts, turbidity current, etc., were observed using a cabled observatory installed on the seafloor. The turbidity current was observed as a benthic storm caused presumably by the mainshock. The seafloor uplifts were observed at the mainshock and continuously after the mainshock. The uplifts were 0.35, 0.37, and 0.12 m for epicentral distances of 25.5, 31.4, and 81.7 km, respectively. After the mainshock, a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock. In this paper, we first show what was observed using the cabled observatory installed right above the focal area of the earthquake, and then we discuss to summarize these phenomena associated with the earthquake, its possible causes, and future directions in long term monitoring of seismogenic processes.  相似文献   

Array observation of background atmospheric waves in the seismic band from 1 mHz to 0.5 Hz     

K. Nishida  Y. Fukao  S. Watada  N. Kobayashi  M. Tahira  N. Suda  K. Nawa  T. Oi  T. Kitajima 《Geophysical Journal International》2005,162(3):824-840

  相似文献   

Terrestrial heat flow at Hirabayashi on Awaji Island, south-west Japan   总被引：1，自引：0，他引：1  

Taku Kitajima  Yoji Kobayashi  Ryuji Ikeda  Yoshihisa Iio  Kentaro Omura 《Island Arc》2001,10(3-4):318-325

Abstract Terrestrial heat flow at Hirabayashi in Awaji Island, south-west Japan, was investigated using the deep borehole penetrating through the Nojima Fault, which was activated during the 1995 Hyogo-ken Nanbu earthquake, by measuring the thermal conductivity of basement rocks. Using the temperature logging data, the value of terrestrial heat flow in Hirabayashi was found to be 56.6 ± 5.2 mW/m². The relationship between cut-off depth of aftershocks of the Hyogo-ken Nanbu earthquake in Hirabayashi and terrestrial heat flow are discussed. The cut-off depth roughly corresponds to isotherms of 300°C.  相似文献