Paleomagnetic Constraints on Mineralization Age of the Nansatsu-type Gold Deposits in Southern Kyushu, Japan     

Tetsuichi TAKEDA  Nobutaka SHIMADA  Hirotomo UENO 《Resource Geology》2001,51(3):239-248

Abstract: Two mineralization stages, stage I and stage II, have been identified from textural, mineralogical and crosscutting relationships in gold ore from the Nansatsu-type gold deposits of Kasuga, Iwato and Akeshi. Mineralization age of each stage in each deposit was determined with paleomagnetic methods on 432 specimens from 312 oriented samples. As results, mineralization ages of stage I of each deposit fall in the same period, the reversed polarity subchron of 4.18–3.58 Ma, and those of stage II are limited in the normal and reversed polarity subchrons of 3.58–3.22 Ma. Contrasting with previous results based only on K-Ar ages, our conclusion shows that these Nansatsu-type gold deposits were formed contemporaneously.  相似文献   

新疆东天山泥盆纪火山岩岩石学特征及其形成的大地构造环境   总被引：1，自引：0，他引：1  

肖渊甫  茅燕石 《矿物岩石》1992,12(2):34-42

新疆东天山地区泥盆纪火山活动频繁,火山岩广泛发育。火山岩系由钙碱系列(占75％)石英安山岩、英安岩、玄武岩、碱长流纹岩以及大量的火山碎屑岩,和拉斑玄武系列(约占25％)的石英拉斑玄武岩,少量橄榄拉斑玄武岩组成。岩石普遍富含Na_2O,SiO_2,而贫MgO,K_2O,以CaO,属钠质型和普通型。稀有元素配分型式具“三隆起”特征,过渡族元素呈明显的“W”形态,稀土元素为铕平坦或略具亏损的轻稀土富集型。据研究,火山岩由南至北具明显的钾元素地球化学极性。反映其板块构造环境为一俯冲带倾向北的陆壳型岛弧。  相似文献   

Development of grabens and associated fault-drags: An experimental study     

Sugata Hazra 《Journal of Earth System Science》1995,104(3):489-498

Experiments on extensional faulting were performed with semi-brittle talc-sand beds resting on a ductile clay base. The experiments show that the development of graben in the talc-sand beds is controlled by the deformation in the ductile basement. Graben-like structures form only when there is a non-uniform stretching in the basement. Uniform extension at the basement level fails to produce any such structures. Grabens initiate as large synclinal structures (sag). The sag is generated either by a downward flexing of the talc-sand bed on a ductile basement or by non ****-uniform thinning of beds. Listric master faults bounding the grabens intersect the basement at high angles. The master faults that initiate as curved shear planes rotate further with continued extension. At the initial stage, the graben structures are associated with normal drags, and with progressive deformation, drag patterns change from normal to a reverse one.  相似文献   

Seismogenic destruction of the Kamenka medieval fortress, northern Issyk-Kul region, Tien Shan (Kyrgyzstan)     

Andrey M. Korjenkov  J. Ramon Arrowsmith  Christopher Crosby  Ernes Mamyrov  Lyubov A. Orlova  Irina E. Povolotskaya  Kubatbek Tabaldiev 《Journal of Seismology》2006,10(4):431-442

A paleoseismological study of the medieval Kamenka fortress in the northern part of the Issyk-Kul Lake depression, northern Tien Shan in Kyrgyzstan, revealed an oblique slip thrust fault scarp offsetting the fortification walls. This 700 m long scarp is not related to the 1911 Kebin Earthquake (Ms 8.2) fault scarps which are widespread in the region. As analysis of stratigraphy in a paleoseismic trench and archaeological evidence reveal, it can be assigned to a major twelfth century a.d. earthquake which produced up to 4 m of oblique slip thrusting antithetic to that of the nearby dominant faults. The inferred surface rupturing earthquake apparently caused the fortress destruction and was likely the primary reason for its abandonment, not the Mongolian–Tatar invasions as previously thought.  相似文献   

冲击反循环钻进工艺在大直径钻孔灌注桩施工中的应用     

钟兴吉  潘学森  郑文丽  赵德成 《吉林地质》2006,25(3):49-50

主要介绍了冲击反循环钻进工艺原理、适用范围、特点以及在工作中的应用效果等.  相似文献   

安宁河断裂带晚第四纪运动特征及模式的讨论   总被引：12，自引：1，他引：12       下载免费PDF全文

何宏林  池田安隆 《地震学报》2007,29(5):537-548

安宁河断裂带是中国西南地区一条重要的地震活动断层， 地方志记载公元1536年曾发生过震级大于7级的破坏性地震. 详细的断裂地貌航片解译和野外调查表明， 安宁河断裂带除具有主要的左旋走滑断层活动外，还兼有重要的逆冲运动分量. 根据冲沟和阶地面的位错量及其热释光测年结果估计，该断裂带晚更新世以来平均左旋走滑速率为3~7 mm/a. 根据滑移方向与断层走向的关系，推测跨安宁河断裂带东西向由于逆冲断层运动造成的挤压缩短速率约为1.7~4.0 mm/a； 简单分解鲜水河断裂带上的滑动速率，估计分配在大凉山断裂带上的滑动速率与安宁河断裂带上的大致相当，约为3~7 mm/a. 此外，根据野外调查结果，并结合最近青藏高原构造动力学研究的新认识， 建立了安宁河断裂带的动力学模型，认为安宁河断裂带是一条逆冲走滑断裂带. 其下盘（西盘）主动向南东方向下插，造成了上盘（东盘）向北西方向的上冲运动.   相似文献   

泵吸反循环砂石泵不返水原因分析与防治     

谭维信 《地质与勘探》1998,34(3):58-59

从水力学角度分析了泵吸反循环砂石泵不返水的主要原因,并结合生产实践提出了相应的处理措施。  相似文献   

Fidelity and time resolution of the magnetostratigraphic record in Siwalik sediments: high-resolution study of a complete polarity transition and evidence for cryptochrons in a Miocene fluviatile section     

Wolfgang Rösler  & Erwin Appel 《Geophysical Journal International》1998,135(3):861-875

The Surai Khola section in southwest Nepal, a 5000 m continuously exposed record of fluvial sedimentation since Middle Miocene, was revisited for high-resolution magnetostratigraphy in sequences with expected cryptochrons and reversals of the geomagnetic field. Polarity intervals with durations of a few tens of thousands of years are recorded as zones of stable palaeomagnetic directions. Polarity transitions are recorded as zones with complex demagnetization behaviour of specimens in the sedimentary column. Almost antiparallel palaeoremanence directions, residing in different haematite phases in the same specimens, could generally not be separated properly by thermal demagnetization. Differing demagnetization paths for neighbouring specimens during a reversal suggest that measured transitional directions are not true geomagnetic field directions, but rather are generated by the superposition of variable amounts of at least two almost antiparallel components of magnetization. Accompanying studies of recent river sand deposits demonstrate that these sediments acquire a true depositional remanent magnetization (DRM) with considerable inclination errors and scattered directions for individual specimens.  相似文献   

武汉白沙洲长江大桥百米长桩成孔技术与施工实践          下载免费PDF全文

李世京  廖光华 《探矿工程》1998,(3):10-11

介绍了百米长桩的施工方法、施工设备、护孔技术,并就深孔实施泵吸反循环的可行性、主要技术措施以及强风化岩层的糊钻问题进行了分析。  相似文献   

Repacking practice for G-3 engineering driller power unit with drive shaft of dual channel reverse circulation     

Lihong ZHU  Kun YIN  Qingyan WANG  Yong HUANG 《世界地质(英文版)》2008,11(1)

In order to satisfy operating requirements for constant core drilling technology in reverse circulation with hollow-through DTH,the power unit of G-3 engineering driller was ameliorated. The new one with dual channel drive shaft, achieved the perfect assemble with transmission structure of the original power unit. It could interconvert according to need by using two sets of drive shafts with direct and reverse circulation. The repacked G-3 engineering driller carried on experiment in the field test in Luanchuan molybdenum mine of Henan, whose effect was very good.  相似文献