大别山地震波速度剖面的重力拟合及花岗岩带

笔者对穿越大别山造山带的六安—大冶宽角反射地震剖面进行了重力拟合。拟合结果表明严格按宽角反射地震速度换算成的密度剖面所产生的是一个重力高,它反映出大别山是一个穹隆,与实测大别山重力低大相径庭。只有将位于大别山山根上,南北大别之间设置一个从地表直达莫霍界面的巨大低密度体,重力曲线才能得到很好的拟合。这个低密度体应为近北西走向的花岗岩带。它与反射地震剖面上石镇透明反射地震带位置吻合,但宽度远较反射地震透明带为大。重力曲线的拟合进一步说明,在华北陆块与扬子陆块碰撞后的白垩纪时,大别山出现一个伸展期,在这个时期,大别山穹隆形成,并伴随有大规模花岗岩的侵入,超高压变质岩从地壳中下部折返到地表。研究说明,联合应用反射地震、宽角反射地震和重力,进行综合解释是必要的,可以得到更令人信服的地质结论。     

青海东昆仑成矿带综合选区研究

笔者通过改进先前提出的基于专家证据权重法的成矿远景区划与评价方法的不足之处,重新对青海东昆仑地区Au、Cu和Co3矿种进行成矿远景区划与评价,将各矿种的远景区按成矿潜力大小划分为A、B、C三级。在此基础上,提出了将多个单矿种远景区合成综合成矿远景区的评价方法和手段,最终圈定出青海东昆仑的综合远景区25个,并对它们也按成矿潜力大小划分为A、B、C三级。从青海东昆仑地区已知Au、Cu、Co矿床(点)在各综合远景区内的数量和规模分布情况来看,结果令人满意。青海东昆仑地区的综合选区研究成果可望为该区进一步找矿工作部署提供部分科学依据。     

鲁西地区太古宙绿岩带硫铁矿床地质特征及成矿机制

鲁西地区新太古代雁翎关组由科马提岩、角闪质岩石、变粒岩和含铁石英岩等组成 ,其原岩为一套超镁铁质镁铁质火山熔岩及火山碎屑沉积的表壳岩建造 ,经历了三期区域变质作用 ,变质程度达低角闪岩相 ,是华北地台上一个典型的绿岩带。鲁西花岗岩绿岩带中分布有大小黄铁矿脉数十条之多 ,呈层状、透镜状或脉状沿片麻理方向展布 ,硫品位 3 .79%～ 3 1.6% ,伴生有用组分Fe、Ni、Ag等。通过对绿岩、矿体和矿石特征、S、Fe分布及变质成矿作用等方面的研究 ,证实绿岩中含有丰富的S、Fe、Ni等造矿元素 ,认为绿岩既是赋矿岩石亦是矿源层 ,矿床属变质热液叠加的变质火山沉积型硫铁矿床。     

QUATERNARY FOLDING OF THE XIHU ANTICLINE BELT ALONG FORELAND BASIN OF NORTH TIANSHAN

Tianshan is one of the longest and most active intracontinental orogenic belts in the world. Due to the collision between Indian and Eurasian plates since Cenozoic, the Tianshan has been suffering from intense compression, shortening and uplifting. With the continuous extension of deformation to the foreland direction, a series of active reverse fault fold belts have been formed. The Xihu anticline is the fourth row of active fold reverse fault zone on the leading edge of the north Tianshan foreland basin. For the north Tianshan Mountains, predecessors have carried out a lot of research on the activity of the second and third rows of the active fold-reverse faults, and achieved fruitful results. But there is no systematic study on the Quaternary activities of the Xihu anticline zone. How is the structural belt distributed in space?What are the geometric and kinematic characteristics?What are the fold types and growth mechanism?How does the deformation amount and characteristics of anticline change?In view of these problems, we chose Xihu anticline as the research object. Through the analysis of surface geology, topography and geomorphology and the interpretation of seismic reflection profile across the anticline, we studied the geometry, kinematic characteristics, fold type and growth mechanism of the structural belt, and calculated the shortening, uplift and interlayer strain of the anticline by area depth strain analysis.
In this paper, by interpreting the five seismic reflection profiles across the anticline belt, and combining the characteristics of surface geology and geomorphology, we studied the types, growth mechanism, geometry and kinematics characteristics, and deformation amount of the fold. The deformation length of Xihu anticline is more than 47km from west to east, in which the hidden length is more than 14km. The maximum deformation width of the exposed area is 8.5km. The Xihu anticline is characterized by small surface deformation, simple structural style and symmetrical occurrence. The interpretation of seismic reflection profile shows that the deep structural style of the anticline is relatively complex. In addition to the continuous development of a series of secondary faults in the interior of Xihu anticline, an anticline with small deformation amplitude(Xihubei anticline)is continuously developed in the north of Xihu anticline. The terrain high point of Xihu anticline is located about 12km west of Kuitun River. The deformation amplitude decreases rapidly to the east and decreases slowly to the west, which is consistent with the interpretation results of seismic reflection profile and the calculation results of shortening. The Xihu anticline is a detachment fold with the growth type of limb rotation. The deformation of Xihu anticline is calculated by area depth strain analysis method. The shortening of five seismic reflection sections A, B, C, D and E is(650±70) m, (1 070±70) m, (780±50) m, (200±40) m and(130±30) m, respectively. The shortening amount is the largest near the seismic reflection profile B of the anticline, and decreases gradually along the strike to the east and west ends of the anticline, with a more rapidly decrease to the east, which indicates that the topographic high point is also a structural high point. The excess area caused by the inflow of external material or outflow of internal matter is between -0.34km² to 0.56km². The average shortening of the Xihubei anticline is between(60±10) m and(130±40) m, and the excess area caused by the inflow of external material is between 0.50km² and 0.74km². The initial locations of the growth strata at the east part is about 1.9~2.0km underground, and the initial location of the growth strata at the west part is about 3.7km underground. We can see the strata overlying the Xihu anticline at 3.3km under ground, the strata above are basically not deformed, indicating that this section of the anticline is no longer active.     

准噶尔盆地西北缘走滑断层特征及油气地质意义

准噶尔盆地西北缘前陆冲断带构造样式复杂多样,除规模较大的逆断层外,还发育一系列北西向的走滑断层。以高分辨率三维地震资料为基础,对断裂体系分析表明克拉玛依—百口泉地区的走滑断层可分为花状走滑断层和简单走滑断层两类,二者在成因、剖面特征等方面具有明显差别。研究结果认为走滑断层对油气的运聚成藏具有重要的双重控制作用,即能作为有效的运移通道,又能够起遮挡作用而形成圈闭。     

湘中奥陶纪锰矿带成矿特征及资源前景

湘中奥陶纪沉积锰矿带位于湖南省安化县、桃江县、宁乡县境内,呈近EW向展布,矿带内锰矿以质量好而著称。该成矿带的成锰沉积盆地受控于加里东期张性断裂系统,为一断陷盆地。盆地内发育一组NW向同沉积断裂,形成了一系列断陷槽,控制了沉积岩相的分布。锰矿主要产于盆地中心亚相的黑色页岩夹碳酸锰矿微相内。据矿带中锰矿的地质和地球化学特征以及微量元素和碳、氧、锶同位素组成,笔者认为,该锰矿属于热水沉积成因。综合对比表明,该成矿带具有良好的成矿条件和值得注意的资源潜力,有可能发展为大型锰成矿带。     

雅鲁藏布江蛇绿岩中地幔柱型岩浆作用——来自氦、氩同位素的证据

雅鲁藏布江蛇绿岩的氦、氩同位素组成分别是：蛇绿岩中变质橄榄岩的^3He/^4He比值为1．104-3．384Ra,平均为2．383Ra;玄武岩的He同位素组成比较均一,^3He/^4He平均值为5．359 Ra;辉绿岩的^3He／^4He比值变化较大,为1—5Ra。由于各岩石样品有不同程度的蚀变,造成放射性成因He的加入,因此大多数样品He同位素组成比低于亏损地幔大洋中脊玄武岩的值(MORB≈8Ra),不能真实反映源区特征。而采自吉定的辉绿岩样品^3He/^4He比值平均高达31．57Ra,与夏威夷发现的热点地幔源区的样品比值接近;分步加热法进一步测试,其高比值的He是在低温区段释放的。这种高^3He/^4He比值He的捕获,表明雅鲁藏布江蛇绿岩形成时存在地幔柱型富集地幔岩浆作用。     

松潘-甘孜造山带地壳速度结构

位于川西地区的奔子栏——唐克深地震测深剖面以NNE走向穿越松潘——甘孜造山带．根据人工地震记录分析得到的震相走时和相关的振幅信息，确定了该剖面二维P波地壳速度结构．剖面的地壳结构可分为5层，其中第1，2，3层为上地壳；第4，5层为下地壳．上地壳中部普遍存在低速异常带，但龙日坝以北，这一低速带与其上覆的低速基底合为一体．同时，沿剖面的地壳速度结构具有较强的横向变化．据此，可将剖面分为4段，即甘孜——理塘断裂以南、甘孜——理塘断裂至鲜水河断裂、鲜水河断裂至龙日坝断裂和龙日坝断裂以北. 这与区域构造划分基本一致． 地壳厚度沿测线从南西向北东逐渐减薄，即从金沙江畔的62 km减小到黄河附近的52 km． 根据PmP震相分析，莫霍界面深度在鲜水河断裂两侧没有明显变化．全剖面的地壳平均速度较低，为6.30 km/s．奔子栏——唐克剖面揭示了该地区的造山带型地壳上地幔结构特征．鲜水河断裂带位于剖面的中部，该地区的上地壳速度为正异常，而下地壳和上地幔顶部存在负异常．笔者认为，这是一类有利于强震孕育和发生的深部构造环境．      

东秦岭商丹地区蛇绿岩中的角闪石研究

东秦岭蛇绿岩主要分布在北秦岭南缘、商丹断裂带以北的狭窄地带,断续逶迤呈带状作近东西向展布。分布于商丹地区的蛇绿岩是东秦岭蛇绿岩带的重要组成部分并具有代表性。 本文着重论述了商丹地区蛇绿岩中广泛分布的主要造岩矿物之一,角闪石的主要特征组份、微量元素、晶胞参数、阳离子占位度等成因矿物学特点。并据此说明了该蛇绿岩中的角闪石属于区域正变质的产物;形成的物质来源具有同源性,原岩为超镁铁质-镁铁质的岩浆岩和火山熔岩;形成的热力学条件基本相同,变质程度为绿帘角闪岩相或角闪岩相,变质温度为610℃左右,压力大于5×10~8Pa。 此外,根据商丹地区蛇绿岩中角闪石成因矿物学特征之相同性所提供的信息表明,东秦岭蛇绿岩带是华北和扬子两个板块俯冲、碰撞的构造边界变质带。     

Middle Paleozoic paleomagnetism of east Kazakhstan: post-Middle Devonian rotations in a large-scale orocline in the central Ural–Mongol belt

In order to test different hypotheses concerning the Paleozoic evolution of the Ural–Mongol belt (UMB) and the amalgamation of Eurasia, we studied Middle Devonian basalts from two localities (11 sites) and Lower Silurian volcanics, redbeds, and intra-formational conglomerates from three localities (20 sites) in the Chingiz Range of East Kazakhstan. The Devonian rocks prove to be heavily overprinted in the late Paleozoic, and a high-temperature, presumably primary, southerly, and down component is isolated at only four sites from a homoclinal section. Most Silurian redbeds are found to be remagnetized in the late Paleozoic; in contrast, a bipolar near-horizontal remanence, isolated from Silurian volcanics, is most probably primary as indicated by positive tilt and conglomerate tests. Analysis of paleomagnetic data from the Chingiz Range shows that southward-pointing directions in Ordovician, Silurian, and Devonian rocks are of normal polarity and hence indicate large-scale rotations after the Middle Devonian. The Chingiz paleomagnetic directions can be compared with Paleozoic data from the North Tien Shan and with the horseshoe-shaped distribution of subduction-related volcanic complexes in Kazakhstan. Both paleomagnetic and geological data support the idea that today's strongly curved volcanic belts of Kazakhstan are an orocline, deformed mostly before mid-Permian time. Despite the determination of nearly a dozen new Paleozoic paleopoles in this study and other recent publications by our team, significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late Paleozoic. However, the paleomagnetic results from the Chingiz Range and the North Tien Shan indicate that these areas show generally coherent motions with Siberia and Baltica, respectively.