Constraints on Variscan granite emplacement in north-east Bavaria,Germany: further clues from a petrogenetic study of the Mitterteich granite     

Wolfgang Siebel 《International Journal of Earth Sciences》1995,84(2):384-398

Petrochemical and Rb-Sr, K-Ar and Sm-Nd isotopic data presented for the Mitterteich granite provide information on whole rock and mineral compositional characteristics, intrusion and cooling history, and protolith nature and put further constraints on the Variscan magmatic evolution in north-east Bavaria.The compositional characteristics classify the Mitterteich granite as a peraluminous (monzo-)granite (SiO₂ 67.3–73.5 wt.% ). Values for K₂O/Na₂O (> 1.2 and Al₂O₃/(CaO + N₂O + K₂O) (>1.1) are in the range of S-type granites. The rare earth elements show fractionated chondrite-normalized patterns (La _N /Yb _N =24–19) with negative Eu anomalies (Eu _N /Eu _N ^*=0.35–0.19). The micas have restricted ranges of major element composition, but reveal notable variations in trace element concentrations. Different biotite fractions of single specimens show a trend to lower concentrations of compatible elements in the finer fraction which can be explained as a result of asynchronous growth during the fractionation process. The PT conditions of crystallization of the magma based on muscovite and biotite is 600–640°C at 3 kbar. Regression of the whole rock samples gives an isochron corresponding to a ⁸⁷Rb-⁸⁷Sr age of 310 ± 7 Ma, initial ⁸⁷Sr/⁸⁶Sr of 0.7104±0.0010 (2 errors) and MSWD =0.03. Muscovite and biotite yield concordant K-Ar ages between 310 and 308 Ma, indicating a fast cooling rate of the granite intrusion. _{Nd T310}values average –4.2±1.0. Nd model ages of 1.4 Ga suggest a source region of mid-Proterozoic age.The Rb-Sr isochron age and initial Sr ratio of the Mitterteich granite are indistinguishable from those of the adjacent Falkenberg granite, establishing a genetic link. However, the K-Ar mica ages suggest that the Mitterteich granite must have undergone a faster uplift or cooling history than Falkenberg. Confronted with the geochronological record of granite emplacement in north-east Bavaria, the new results substantiate the view of three key periods of magmatic activity around 330–325, 315–305 and 290 Ma.  相似文献   

Comparison of the nonlocal transport characteristics of a series of one-dimensional oceanic boundary layer models     

A. James Kettle 《Ocean Modelling》2005,8(4):301-336

Seven one-dimensional oceanic boundary layer models are investigated to assess the possible nonlocal transport characteristics of mass and heat in the upper ocean. The dynamical models have been chosen from the diffusion and bulk types currently in use plus two modifications of the transilient type that have been used extensively for atmospheric work by Stull. The models are forced using wind speed and insolation conditions recorded during a 9-day oceanographic cruise near Bermuda in March 1993 during the decline of the spring bloom. The attenuation of sunlight in the upper ocean is calculated using a full spectral model for downwelling irradiance. The vertical heat transport characteristics are reported and compared. A series of spectral diagnostic tests (Green's function analysis, process spectra, and overall mixing lengths) reveal significant differences in the vertical transport characteristics of the models that are not observed in commonly used diagnostics such as sea surface temperature or mixed layer depth. Age spectra (or modal time since last surface contact) are calculated from Green's functions and reveal how a water mass can be cut off from the surface within a short time period. The large differences in the vertical mixing characteristics of the upper ocean boundary layer models have potential implications on the vertical distributions of short-lived chemical tracers and phytoplankton.  相似文献   

Age and Growth of <Emphasis Type="Italic">Sillago aeolus</Emphasis> in Okinawa Island,Japan     

Md.?Habibur?RahmanEmail author  Katsunori?Tachihara 《Journal of Oceanography》2005,61(3):569-573

In a study of the age and growth of Sillago aeolus, a total of 414 fish were collected from December 2000 to March 2002, around Okinawa Island. Ages of 403 specimens were determined by otoliths. Monthly changes in the percentage of otoliths with an opaque zone in the outer margin indicated that an opaque ring formed once a year, occurring between February and May. The rings can therefore be defined as annual rings. Ages of females were estimated to be 0+ to 4+, while those of males were 0+ to 2+. The von Bertalanffy growth curves were well fitted to age-standard length data of males and females, as follows: Male: L_t = 209.6 [1 − exp{−0.70 (t + 0.58)}]. Female: L_t = 297.7 [1 − exp{−0.42 (t + 0.61)}].  相似文献   

细鳞鯻年龄与生长的研究   总被引：2，自引：0，他引：2  

张健东  宋蓓玲  陈刚 《海洋科学》2002,26(7):62-66

选用胸鳍覆盖处的鳞片作为细鳞(鱼剌)(Therapon jarbua(Forssk(a)l))的年龄鉴定材料,其年轮形成时期主要在2～4月.体长与鳞径呈线性关系.体长-体重关系为W=3.8891×10-2L2.8761.vonBertalanffy生长方程适合描述其体长和体重的生长,生长参数为L∞=35.9cm,W∞=1153.7g,k=0.2376,t0=-0.2115.体重生长在4.41a具一拐点,此时体重生长速度达到最大.  相似文献   

东海6种石首鱼的年龄鉴定与生长特性的研究   总被引：1，自引：0，他引：1  

兰永伦  罗秉征 《海洋与湖沼》1995,26(S1):108-114

利用1985年9月 - 1988年10月长江口近海采集到的6种石首鱼的标本，以及1981年和1982东海作业区收集到的部分石首鱼标本，用且石切片机，对6种石首鱼的耳石进行切片试验，以确定6种石首鱼且石的最佳切片方法;并进行年龄鉴定。运用幂函数方程、von Bertalanffy生长方程和季节生长方程对6种石首鱼的生长特性进行分析和比较。结果表明，体长和体重的相关参数在不同种之间差异性显著，生长速度与极限体长（L_∞）和极限体重（W_∞）成正相关，生长速度的时间分布由K值决定。季节生长的冬滞点（WP）和耳石暗带的形成时间是一致的。  相似文献   

Age and growth in olive ridley seaturtles (Lepidochelys olivacea) from the North-central Pacific: a skeletochronological analysis     

George R. Zug  Milani Chaloupka  & George H. Balazs 《Marine Ecology》2006,27(3):263-270

The olive ridley is the most abundant seaturtle species in the world but little is known of the demography of this species. We used skeletochronological data on humerus diameter growth changes to estimate the age of North Pacific olive ridley seaturtles caught incidentally by pelagic longline fisheries operating near Hawaii and from dead turtles washed ashore on the main Hawaiian Islands. Two age estimation methods [ranking, correction factor (CF)] were used and yielded age estimates ranging from 5 to 38 and 7 to 24 years, respectively. Rank age‐estimates are highly correlated (r = 0.93) with straight carapace length (SCL), CF age estimates are not (r = 0.62). We consider the CF age‐estimates as biologically more plausible because of the disassociation of age and size. Using the CF age‐estimates, we then estimate the median age at sexual maturity to be around 13 years old (mean carapace size c. 60 cm SCL) and found that somatic growth was negligible by 15 years of age. The expected age‐specific growth rate function derived using numerical differentiation suggests at least one juvenile growth spurt at about 10–12 years of age when maximum age‐specific growth rates, c. 5 cm SCL year⁻¹, are apparent.  相似文献   

OSL dating of sediments from deserts in northern China   总被引：2，自引：0，他引：2  

Sheng-Hua Li  Yong-Ye Chen  Bo Li  Jimin Sun  Li-Rong Yang 《Quaternary Geochronology》2007,2(1-4):23-28

Aeolian samples from deserts in northern China were studied using the optically stimulated luminescence (OSL) of quartz and potassium (K) feldspar separates. K-feldspar has shown advantages over quartz for dating samples younger than 100 years, due to its more homogeneous equivalent dose (D_e) values, higher internal dose rate and higher luminescence sensitivity to dose. Without additional measurements, the luminescence characteristics of quartz obtained in D_e determination procedures can be used to reveal the source material and/or quartz thermal history for the deserts in northern China. The results indicated that the duration of paleosol formation in desert areas reflects regional paleoenvironments.  相似文献   

Century-scale variability in late-summer rainfall events recorded over seven centuries in subannually laminated lacustrine sediments, White Pass, British Columbia     

Jaclyn M.H. Cockburn  Scott F. Lamoureux 《Quaternary Research》2007,67(2):193-203

Formation of annually laminated sediments in Summit Lake, White Pass, British Columbia is controlled by runoff generated by snowpack and glacier melt and major rainfall events. The 700-yr varve record is divided into two subannual series (early and late) based on sedimentological criteria and sedimentary structures within each varve. A comparison of recent subannual laminae with nearby meteorological records supports the interpretation they are formed by river discharge events generated by major snow and glacier melt events and large late-summer rainfall events. A significant correlation exists between the late subannual thickness series and the size of the largest rainfall events in late summer. The long record indicates there was an abrupt increase in the thickness and frequency of major rainfall-induced sedimentary events at the end of the seventeenth century. In addition, the frequency of laminae generated by early runoff events also increased. However, early subannual varve thickness component remains statistically the same as the thickness prior to the end of the seventeenth century. This suggests the change in varve thickness at this time is due to increases in major late-summer rainfall frequency rather than increased sediment availability caused by regional Little Ice Age glacier advances.  相似文献   

Sequence framework of two different kinds of margins and their response to tectonic activity during the Middle-Late Triassic, Ordos Basin     

YANG MingHui  LIU ChiYang  ZHENG MengLin  LAN ChaoLi  TANG Xuan 《中国科学D辑(英文版)》2007,50(Z2):203-216

  相似文献   

Solar and anthropogenic imprints on Lake Masoko (southern Tanzania) during the last 500 years   总被引：1，自引：0，他引：1  

Yannick Garcin  David Williamson  Laurent Bergonzini  Olivier Radakovitch  Annie Vincens  Guillaume Buchet  Joël Guiot  Simon Brewer  Pierre-Etienne Mathé  Amos Majule 《Journal of Paleolimnology》2007,37(4):475-490

The Masoko crater-lake in southern Tanzania provides a continuous record of environmental changes covering the last 500 years. Multi-proxy studies were performed on a 52 cm sediment core retrieved from the deepest part of the lake. Magnetic, organic carbon, geochemical proxies and pollen assemblages indicate a dry climate during the ‘Little Ice Age’ (AD 1550–1850), confirming that the LIA in eastern Africa resulted in marked and synchronous hydrological changes. However, the direction of response varies between different African lakes (low versus high lake-levels), indicating strong regional contrasts that prevent the clear identification of climate trends over eastern Africa at this time. Inferred changes in Masoko lake-levels closely resemble the record of solar activity cycles, indicating a possible control of solar activity on the climate in this area. This observation supports previous results from East African lakes, and extends this relationship southward. Finally, anthropogenic impact is observed in the Masoko sediments during the last 60 years, suggesting that human disturbance significantly affected this remote basin during colonial and post-colonial times.  相似文献