我国优质锰矿的勘查方向

优化锰矿是国家战略资源和紧缺矿种，也是近期地质勘查的主要目标矿种之一。锰矿地质勘查进展和勘查评价技术以及锰矿选冶技术的进步拓展了优质锰矿的勘查工作领域。我国优质锰矿仍有较大的资源潜力。从优质锰矿成矿地质背景，成锰条件，地质工作程度和找矿潜力分析，提出5个重要的找矿远景区作为近期优质锰矿的勘查方向。     

Variations in the distribution of magma in the lower crust and at the Moho beneath the East Pacific Rise at 9°-10°N

Measurements of the seafloor deformation under ocean waves (compliance) reveal an asymmetric lower crustal partial melt zone (shear velocity less than 1.8 km/s) beneath the East Pacific Rise axis between 9° and 10°N. At 9°48′N, the zone is less than 8 km wide and is centered beneath the rise axis. The zone shifts west of the rise axis as the rise approaches the westward-stepping 9°N overlapping spreading center discontinuity and is anomalously wide at the northern tip of the discontinuity. The ratio of the compliance determined shear velocity to the compressional velocities (estimated by seismic tomography) suggests that the melt is well-connected in high-aspect ratio cracks rather than in isolated sills. The shear and compressional velocities indicate less than 18% melt in the lower crust on average. The compliance measurements also reveal a separate lower crustal partial melt zone 10 km east of the rise axis at 9°48′N and isolated melt bodies near the Moho beneath four of the 39 measurement sites (three on-axis and one off-axis). The offset of the central melt zone from the rise axis correlates strongly with the offset of the overlying axial melt lens and the inferred center of mantle melting, but its shape appears to be controlled by crustal processes.     

Water-weakened lower crust and its role in the concentrated deformation in the Japanese Islands

The nature and origin of the concentrated deformation zone along the Japan Sea coast (NKTZ: Niigata-Kobe tectonic zone) was investigated by carefully analyzing the GPS data and qualitatively modeling the lower crust in NKTZ. It was concluded that this deformation zone is not a plate boundary between the Amurian plate (AMU) and the North America plate but is rather an internal deformation zone near the eastern margin of AMU. The data previously obtained on the conductivity anomalies in the lower crust and the ³He/⁴He ratios suggest that the concentrated deformation in NKTZ results from the lower crust in NKTZ being weakened by a high water content. The high water content is thought to result from the dehydration of subducting slabs. NKTZ has a higher water content in the lower crust than other regions do because there is no Philippine Sea plate (PHS) seismic slab beneath NKTZ. In other regions, it is estimated that the mantle wedge above the seismic Philippine Sea slab prevents the water dehydrated from the slab from rising to the lower crust, and that the lithosphere within PHS itself prevents the water dehydrated from the Pacific plate from rising up through it.     

Temporal aspects of the abrasion of microphytic crusts under grain impact

Wind‐tunnel simulations of the response of two moss crusts to grain impact indicate that, given sufficient time, these surfaces will deteriorate under very low wind velocities only slightly above u_*t for the loose, saltating grains. In parallel with these experiments, the frequency distributions of ultimate strength and penetration energy were determined for each of the two crust types via penetrometry. Pohlia was found to be stronger than Tortula; but, even so, both of these crusts had ultimate strengths 20–350 times higher than the force delivered by a single grain impacting each surface at a velocity of 1 ms^?1. In comparison, the modulus of deformation and penetration energy data were very similar for the two surface types, especially for the weakest areas of crust development. This observation is in accord with the wind‐tunnel simulations that also found no consistent difference in the response of these two crust types to impact. In comparison with crusts formed by clay and salt, fibrous microphytic crusts are morphologically complex and typically weak. The notable elasticity of these surfaces does reduce the force of grain impact, and thereby provides some protection against rupture. One of the central conclusions of this study suggests that not only is the particle kinetic energy at impact important in crust breakdown, but also tiny fractures at points of localized stress concentration contribute to a progressive reduction in the integrity of the filament net. In some of the experiments conducted as part of this study, up to 50 or more minutes of constant bombardment was required to produce small abrasion marks on selected areas of the microphytic crust. This study prepares a foundation for future experiments needed to examine the breakdown of complex crusts formed in nature. Copyright © 2002 John Wiley & Sons, Ltd.     

金在地壳、岩石和沉积物中的丰度

金在地壳，岩石和沉只物中的丰度一直是地球化学研究和金矿勘查中非常重要的参数。随着20世纪80年代金分析测试技术的突破性进展以及目前积累的大量可靠的金的分析数据，发现引用20世纪70年代前发表的有关金的地壳丰度和金在岩石，沉积物中的平均含量作为衡量标准已不适宜。根据近15年来发表的大量有关金在地壳，岩石和沉积物中含量的文献，结合作者在地壳与岩石研究中积累的金的大量可靠数据，综合给出金的地壳丰度为1.0ng/g，出露出壳丰度为0．8ng/g，金在岩石，火成岩，沉积岩和变质岩中的平均含量分别为0．9，0．6，1．0和1．0ng/g，金在中国水纱沉积物，泛滥平均沉积物，浅海沉积物和土壤中的平均含量分别为1．4，1．6，1．2和2．0ng/g。这种对金在地壳，岩石和沉积物中丰度值的新认识，对地球化学理论研究，勘查地球化学甚至金的矿产勘查工作都有重大意义。     

华南上地壳速度分布与基底、盖层构造研究

对华南地区有代表性的几条宽角地震剖面进行了研究,利用初动到时资料拟合剖面地带地壳上部详细的速度分布,结合其他地球物理资料与地质资料对地壳基底和沉积盖层的构造进行了综合解释. 结果表明,浙-闽-粤东部地区在地壳基底上分布一系列中生代火山岩断陷盆地,火山岩盖层厚度变化为1000-4000m. 浙西-皖南以及湘-赣地区地壳基底起伏较大,盖层主要为古生界,并发育许多受基底形态与边界断裂控制的小型中生代白垩纪盆地. 华南西部的楚雄盆地为一构造复杂的深坳陷,其中侏罗-白垩系的厚度超过10km,并被分割为东部斜坡和西部坳陷两个单元,而西部坳陷又被一中央隆起分割为东、西两个更次级的凹陷. 区内一些主要的断裂构造在速度等值线图上均有明显的反映,如东部的江绍断裂、莲花山断裂和吴川-四会断裂以及西部的程海断裂和绿汁江断裂都是重要的构造分界,此外众多的基底断裂多是盆地与隆起的边界.     

伽师强震群区上地壳三维速度层析成像

以伽师强震群为中心布设了一个50km60km范围的三维人工地震透射临时台阵，接收来自不同方位的8次爆破激发产生的地震波；利用所记录到的莫霍界面临界反射P 波、S波走时，采用模型不分块反演技术，重建台阵下方上地壳三维P，S波速度扰动图象，以及vp/vs扰动分布图象；并结合伽师震群的地震活动分布，对该震群的成因进行了分析．结果表明，研究区上地壳存在明显的不均匀性．自12ｋｍ 深度开始，在与震群震中相应的位置上，明显出现沿北北西向的高Ｐ波速度块体，在它的周围为相对低速分布，这种结构上的差异是伽师强震群发生的最直接原因；vp/vs在相同的位置上为高值分布，则表明由于介质相对软弱可能造成震源体抗剪强度下降．这可作为伽师强震群发震特点的一种解释．      

中国大陆及其邻域的瑞利波群速度分布图象与地壳上地幔速度结构

利用中国数字化地震台网（CDSN）11个台站和周边地区的11个IRIS数字化地震台站记录的长周期面波资料，用多重滤波方法测定了在647条不同路径上周期从10～92ｓ的基阶瑞利波群速度频散曲线．采用Dimtar Yanovskaya方法，反演得到北纬18～54、东经70～140范围内，25个中心周期的群速度分布图象．结果表明:在10～15.9s周期范围内，群速度分布存在着明显的横向不均匀性．其分区分块特征与大地构造单元有着密切的对应关系，两个明显的低速区域分别位于塔里木盆地和东海及北部邻域；从21～33ｓ逐渐显示出深部构造块体的格局；在36.6～40ｓ周期附近的群速度分布图象中，十分清晰地显示出中国大陆岩石圈结构的分区特征，南北地震带、青藏高原、华北、华南块体及东北地块的边界非常明显．本文给出了沿30N、38N 纬线和沿90E、120E 经线剖面的群速度随周期分布图象．在这些剖面上，较明显地展示出中国大陆及其邻域地壳上地幔速度结构的基本特征．各构造块体的深部速度结构差异较大，在青藏高原东部地区的地壳中部存在局部低速区域；塔里木盆地、扬子地台的上地幔速度较高，显示出稳定地台特征；华北平原上地幔低速层的埋深浅、厚度大；东海及日本海的上地幔速度较低，这可能与菲律宾板块下插产生的摩擦热与喜山期以来受强烈拉张有密切的关系．