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1.
The Godzilla Megamullion,the largest oceanic core complex on the earth: a historical review 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Yasuhiko Ohara 《Island Arc》2016,25(3):193-208
The Godzilla Megamullion is the largest known oceanic core complex (OCC) on the Earth, located in the Parece Vela Basin in the Philippine Sea. In this article, the history of Godzilla Megamullion study is reviewed for the first time, dividing it into three major phases: (i) the early studies done before Japan's extended continental shelf survey program; (ii) the studies during Japan's extended continental shelf survey program that discovered the OCC; and (iii) the studies by the post‐discovery cruises. The early studies included an interpretation of US nautical chart of the southwestern Pacific and the site surveys for Deep Sea Drilling Project cruises (DSDP Legs 6, 31 and 59). The early studies recognized the presence of the Parece Vela Rift, the extinct spreading axis of the Parece Vela Basin, and established the currently accepted model that the Philippine Sea evolved with eastward progression of backarc spreading and arc migration. The modern understanding of the Parece Vela Basin comes from Japan's extended continental shelf survey program. The program revealed the ultramafic petrology as well as a two‐stage evolution model of the basin. Following these results, the discovery of the Godzilla Megamullion was made in 2001. The studies by the post‐discovery cruises further revealed important characteristics of the OCC, such as the presence of abundant plagioclase‐bearing peridotite and the systematic temporal changes in both deformation microstructures and composition of plagioclase and amphibole in gabbroic mylonites and ultramylonites. Zircon U–Pb ages of gabboric and leucocratic rocks indicate that the terminal phase of Parece Vela Basin spreading was with a significant decline in spreading rate and asymmetry accompanying formation of the Godzilla Megamullion. The estimated denudation rate of the OCC was approximately 2.5 cm/yr; significantly slower than the previous estimate based on poorly constrained magnetic data. 相似文献
2.
A new Lower Triassic (Induan) Jerus Limestone locality in northwest Pahang,Peninsular Malaysia: Conodont fauna,depositional and tectonic settings 下载免费PDF全文
下载免费PDF全文 Ian Metcalfe 《Island Arc》2016,25(2):126-136
Limestones exposed north of Raub, Pahang, Malaysia, and sandwiched between the Bentong‐Raub Suture Zone and the westernmost margin of the Sukhothai Arc terrane, yield a late Dienerian (late Induan) conodont fauna. The co‐occurrence of Neospathodus dieneri Sweet (morphotypes 1, 2 and 3) and Neospathodus pakistanensis Sweet represents the Neospathodus dieneri morphotype 3 sub‐zone of the Neospathodus dieneri Zone. The sampled limestones are interpreted as the northwards extension of the Jerus Limestone which crops out near Cheroh and Jerus villages, significantly extending the known outcrop of the Jerus Limestone northwards. The Jerus Limestone is interpreted as hemipelagic and formed in a foredeep or forearc setting on top of the accretionary complex formed by eastwards subduction of the Palaeo‐Tethys during the Lower to Middle Triassic. 相似文献
3.
New insights on the origin of troctolites from the breakaway area of the Godzilla Megamullion (Parece Vela back‐arc basin): The role of melt‐mantle interaction on the composition of the lower crust 下载免费PDF全文
下载免费PDF全文 The troctolites and olivine‐gabbros from the Dive 6 K‐1147 represent the most primitive gabbroic rocks collected at the Godzilla Megamullion, a giant oceanic core complex formed at an extinct spreading segment of the Parece Vela back‐arc basin (Philippine Sea). Previous investigations have shown that these rocks have textural and major elements mineral compositions consistent with a formation through multistage interaction between mantle‐derived melts and a pre‐existing ultramafic matrix. New investigations on trace element mineral compositions basically agree with this hypothesis. Clinopyroxenes and plagioclase have incompatible element signatures similar to that of typical‐MORB. However, the clinopyroxenes show very high Cr contents (similar to those of mantle clinopyroxene) and rim having sharply higher Zr/REE ratios with respect to the core. These features are in contrast with an evolution constrained by fractional crystallization processes, and suggest that the clinopyroxene compositions are controlled by melt‐rock interaction processes. The plagioclase anorthite versus clinopyroxene Mg#[Mg/(Mg + FeTot)] correlation of the Dive 6 K‐1147 rocks shows a trend much steeper than those depicted by other oceanic gabbroic sections. Using a thermodynamic model, we show that this trend is reproducible by fractionation of melts assimilating 1 g of mantle peridotite per 1 °C of cooling. This model predicts the early crystallization of high Mg# clinopyroxene, consistent with our petrological observation. The melt‐peridotite interaction process produces Na‐rich melts causing the crystallization of plagioclase with low anorthite component, typically characterizing the evolved gabbros from Godzilla Megamullion. 相似文献
4.
Isolated Archosaur teeth from the green sandstone capping the Coralline Limestone (Bagh Group) of the Narmada valley: Evidence for the presence of pre‐Late to Late Maastrichtian abelisaurids in India 下载免费PDF全文
下载免费PDF全文 Guntupalli V.R. Prasad Vishal Verma Pooja Grover Rajkumari Priyadarshini Ashok Sahni Ranjit S. Lourembam 《Island Arc》2016,25(6):410-420
Recent field prospecting in the Cretaceous sequences of the lower Narmada valley has led to the discovery of three isolated archosaur teeth from the upper part of marine Cretaceous rocks of the Bagh Group. The specimens were recovered by surface prospecting from an oyster‐bearing green sandstone bed occurring at the top of the Coralline Limestone (Coniacian) from a site near Phutibawri village, Dhar District, Madhya Pradesh, India. Of the three teeth recovered from this horizon, two are identified with abelisaurid dinosaurs and the third one with an indeterminate crocodile. The abelisaurid teeth conform to the premaxillary and maxillary tooth morphology of Majungasaurus and Indosuchus. Earlier reports of abelisaurid dinosaurs from India are from the Upper Cretaceous (Maastrichtian) Lameta Group of Jabalpur, Pisdura (Central India) and Balasinor (Western India) and Upper Cretaceous (Late Maastrichtian) Kallamedu Formation (South India). As no associated age diagnostic fossils are found, the specimens described here are considered to represent pre‐Late to Late Maastrichtian age based on the known ages of the underlying and overlying formations. The new finds, therefore, document stratigraphically the oldest occurrence of abelisaurid dinosaurs known from the Indian subcontinent. 相似文献
5.
念青唐古拉山作为青藏高原东南缘重要山古冰川分布区,受季风影响,各区域冰川变化特征差异明显。论文通过Landsat TM/ETM+/OLI资料、ASRTMGDEM与气象数据,采用比值—阈值法、目视解译和VOLTA模型,结合实地考察,对1990—2020年间念青唐古拉山中段北坡边坝地区现代冰川进退状况、面积变化、冰储量变化以及冰川变化对气候变化响应特征进行研究。结果表明：① 1990—2020年5条冰川(玉贡拉冰川、玛拉波冰川、祥格拉冰川、孔嘎冰川、贡日—庚东冰川)末端高程逐渐升高,面积和冰储量分别减少30.38 km2和4.64 km3,总体缩减并呈现加速趋势。② 冰川冰储量减少0.14~1.92 km3,总体变化率为0.40%·a-1。2020年上述5条冰川储量占1990年冰川储量的比例分别为0.70、0.99、0.98、0.91和0.82,显示出冰川规模越大,在短时间尺度的变化量越小。③ 气象数据分析显示,1990—2020年研究区冰川变化受气温升高主导,平均气温变化率为0.51 ℃。水热组合呈现温度升高—降水减少,且在最后10 a日益显著,预测未来冰川变化仍受气温控制并呈加速退缩趋势。④ 区域对比研究表明,念青唐古拉山冰川面积变化总体呈退缩状态,但各区域冰川变化特征差异明显。同时,不同研究方法对同一冰川区冰储量模拟结果相差较大,相对误差范围为34.45%~115.49%,精确的冰储量可对比研究方法仍有待进一步研究。 相似文献
6.
多镜头组合型全景相机两种成像模型的定位精度比较 总被引：1，自引：1，他引：0
根据多镜头组合型全景相机的严格成像机理,分析了广泛采用的全景理想成像模型系统误差的来源,推导出误差分布规律,并深入比较了严格成像模型和理想成像模型之间的差异.首先,分析了理想模型的单片物方定位误差和像方后方交会误差,理论公式表明其误差分布和物像间距及视角大小相关;其次,分析了全景立体像对的理想核线误差,并证明误差受像对间的旋转角和Z坐标影响.最后,分别采用室内、外数据对两种模型的空间后方交会、核线模型、光束法平差进行比较分析.试验结果表明,室外条件下由于物距接近于全景投影面、立体影像间旋转角较小等因素,两种模型的差异很小,且都达到了相当于1像素左右的测量精度;在狭窄的室内条件下,由于物距小、旋转角大等因素,严格模型在测量精度上明显优于理想模型. 相似文献
7.
Dolomite in caves: Recent dolomite formation in oxic, non-sulfate environments. Castañar Cave, Spain
Dolomite is a common mineral in the rock record but rare in recent superficial environments. Where it does occur, it is related to anoxic, sulfate-rich environments and microbial activity. The occurrence of some dolomite deposits in caves, however, indicates that dolomite formation is also possible in oxic, non-sulfate settings. Dolomite is forming at 17 °C and in oxic-vadose conditions on the host rocks and aragonite speleothems of the Castañar Cave, Cáceres, Spain. It appears as spheroids and dumbbells 50–300 μm in diameter that internally consist of micron-sized rhombic to rounded crystals. Initially this dolomite is Ca-rich, non-stoichiometric and poorly ordered. Mg-rich solutions allow the precipitation of metastable Mg-rich carbonates, such as huntite. This soon transforms into this Ca-rich dolomite, which later “ages” to form a more stoichiometric dolomite. These dolomites show similarities to those grown under anoxic, sulfate-rich conditions and their presence in caves provides a different setting that may contribute to the understanding of the “dolomite problem”, including their initial formation and later recrystallization processes. 相似文献
8.
T.P. Kiseleva I.S. Izmailov A.A. Kiselev E.V. Khrutskaya M.Yu. Khovritchev 《Planetary and Space Science》2008,56(14):1908-1912
Astrometric and photometric observations of major planets, their satellites and asteroids have been made with the 26-in. refractor of the Pulkovo observatory during the period from 1995 to 2006. The CCD (ST6) and photographic observations were carried out. Accurate relative position of satellites of Jupiter and Saturn have been derived. The positions of Saturn have been calculated using the theoretically predicted coordinates of satellites relative to the planet without measurements of the photographic images of the planet. Also the observations of Hale-Bopp comet and Mercury transit have been made. The 26-in. refractor has been included into the international campaign PHEMU-2003: photometric CCD observations of mutual occultations and eclipses of Galilean satellites. The light curves of the events have been obtained and parameters of the events have been determined. 相似文献
9.
Coseismic effects of water temperature based on digital observation from Tayuan well, Beijing 总被引：1，自引：0，他引：1
On the basis of digital records from Tayuan well,we study coseismic effects of water temperature caused by re-mote earthquakes.The records show that the water temperature changes are consistently following the process ofdrop-rise-recovery regardless of focal mechanism or epicentral directions.The step amplitude of water temperatureincreases with the increase of earthquake magnitude,and decreases with the decrease of epicentral distances.Theyhave rather well correlation.Water temperature rising after earthquake is influenced by water level variations.Fi-nally,the mechanisms of coseismic effects of water temperature have been discussed.Preliminary study shows thataccelerated convection and mixing of different temperature water in virtue of seismic wave are the main causes ofwater temperature drops.Seismic wave accelerates water convection,which causes warm water to move up fromdeeper part of the well and cold water to go down from the upper part.Temperature probe will detect water tem-perature drops at early stage.After the occurrence of earthquake,as the fluctuation of water level gradually quietsdown,water temperature near the probe begins to rise. 相似文献
10.
Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan 下载免费PDF全文
下载免费PDF全文 Dan Matsumoto Yuki Sawai Koichiro Tanigawa Osamu Fujiwara Yuichi Namegaya Masanobu Shishikura Kyoko Kagohara Haruo Kimura 《Island Arc》2016,25(5):369-385
We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation. 相似文献