大兴安岭白音诺尔铅锌矿控矿构造研究与找矿预测   总被引：4，自引：1，他引：3  

牛树银  孙爱群  郭利军  王宝德  胡华斌  刘建明 《大地构造与成矿学》2008,32(1):72-80

成矿物质来源及控矿因素是矿床学研究的前沿课题。过去人们认为成矿物质主要源于含矿围岩的萃取。因此,找矿重点是寻找矿源层。但是,更多的事实表明,成矿物质主要来自深源,通过地幔热柱多级演化迁移至地壳,并在幔枝构造较好的控矿构造空间聚集成矿。本文探讨了大兴安岭中南段的成矿作用,总结了该区的主要控矿构造,指出了不同级别构造对成矿的控制作用,并预测了不同级别的成矿靶区。  相似文献   

中国边缘海域及其邻区的岩石层结构与构造分析   总被引：3，自引：0，他引：3  

胥颐  郝天珧  李志伟  刘建华 《地学前缘》2008,15(3):55-63

利用中国边缘海域近年的地震层析成像结果,根据速度异常和各向异性分析东海、黄海和南海北部的岩石层结构和构造,讨论中朝块体和扬子块体在黄海内部的拼合边界(黄海东部断裂带)、东海陆架盆地上地幔异常与岩石层形成演化、南海北部地壳底部高速层的成因及地幔活动等问题。分析表明,黄海东部与朝鲜半岛之间存在一个深部构造界限(大致对应于黄海东部断裂带),分界两侧Pn波速度各向异性存在明显差异,反映不同构造应力和断裂剪切运动作用下的岩石层地幔变形特征。东海陆架下方的低速异常揭示了张裂盆地形成时期的地幔活动痕迹,表明中、新生代期间发生过地幔上涌并造成岩石层减薄,菲律宾海板块向西俯冲引发的地幔活动对东海陆架岩石层的形成、演化产生明显的影响。南海北部岩石层厚度较大并且温度相对偏低,地幔异常仅限于局部地区,估计南海北部大陆边缘的地壳底部高速层形成于张裂发生之前,或者是地壳形成时期壳幔分异时的产物。南海中央海盆的扩张不仅导致地壳拉张,软流层物质上涌,而且也造成岩石层地幔减薄甚至缺失。  相似文献   

幔源CO_2释出机理、脱气模式及成藏机制研究进展   总被引：10，自引：0，他引：10  

鲁雪松  宋岩  柳少波  洪峰  付晓飞 《地学前缘》2008,15(6):293

针对幔源CO2如何从地幔岩浆中脱出并进入沉积地层中形成CO2气藏聚集这一关键问题,总结了国内外研究进展和前缘方向。研究表明,地幔深部的碱性玄武岩浆和碱性岩浆才是深部流体和CO2等挥发份大量赋存、渗滤和释出的场所。浅成侵入岩、次火山岩和火山通道等是CO2释放和聚集的有利位置,岩浆期后和岩浆衰弱期的热液活动阶段是CO2大量释放和聚集的有利时期。幔源CO2进入沉积盆地中具有3种脱气模式,即沿岩石圈断裂直接脱气模式、热流底辟体脱气模式和壳内岩浆房-基底断裂组合脱气模式。CO2的固有物化性质决定其运移相态多样,具有运移和聚集过程同步的特征。只有在满足大量的化学消耗及地层水或原油的溶解和耗散之后才能形成CO2有效聚集。幔源CO2成藏和分布主要受岩浆气源体和气源断裂体系的控制。今后,在超临界CO2及其对油气运移聚集的作用、CO2与深大断裂及火山岩的关系、CO2脱气运移机制、CO与常规烃类油气的耦合差异成藏机制等方面仍需要进一步的研究和探索。  相似文献   

(ϖμ/ϖT) P of the lower mantle     

Yanbin Wang  Donald J. Weidner 《Pure and Applied Geophysics》1996,146(3-4):533-549

We estimate (/T) _P of the lower mantle at seismic frequencies using two distinct approaches by combining ambient laboratory measurements on lower mantle minerals with seismic data. In the first approach, an upper bound is estimated for |(/T) _P | by comparing the shear modulus () profile of PREM with laboratory room-temperature data of extrapolated to high pressures. The second approach employs a seismic tomography constraint ( lnV _S / lnV _P ) _P =1.8–2, which directly relates (/T) _P with (K _S /T) _P . An average (K _S /T) _P can be obtained by comparing the well-established room-temperature compression data for lower mantle minerals with theK _S profile of PREM along several possible adiabats. Both (K _S /T) and (/T) depend on silicon content [or (Mg+Fe)/Sil of the model. For various compositions, the two approaches predict rather distinct (/T) _P vs. (K _S /T) _P curves, which intersect at a composition similar to pyrolite with (/T) _P =–0.02 to –0.035 and (K _S /T) _P =–0.015 to –0.020 GPa/K. The pure perovskite model, on the other hand, yields grossly inconsistent results using the two approaches. We conclude that both vertical and lateral variations in seismic velocities are consistent with variation due to pressure, temperature, and phase transformations of a uniform composition. Additional physical properties of a pyrolite lower mantle are further predicted. Lateral temperature variations are predicted to be about 100–250 K, and the ratio of ( lnp/ lnV _S ) _P around 0.13 and 0.26. All of these parameters increase slightly with depth if the ratio of ( lnV _S / lnV _P ) _P remains constant throughout the lower mantle. These predicted values are in excellent agreement with geodynamic analyses, in which the ratios ( ln / lnV _S ) _P and ( / lnV _S ) _P are free parameters arbitrarily adjusted to fit the tomography and geoid data.  相似文献   

Dynamics of the mid-ocean ridge plate boundary: Recent observations and theory     

Yongshun John Chen 《Pure and Applied Geophysics》1996,146(3-4):621-648

The global mid-ocean ridge system is one of the most active plate boundaries on the earth and understanding the dynamic processes at this plate boundary is one of the most important problems in geodynamics. In this paper I present recent results of several aspects of mid-ocean ridge studies concerning the dynamics of oceanic lithosphere at these diverging plate boundaries. I show that the observed rift valley to no-rift valley transition (globally due to the increase of spreading rate or locally due to the crustal thickness variations and/or thermal anomalies) can be explained by the strong temperature dependence of the power law rheology of the oceanic lithosphere, and most importantly, by the difference in the rheological behavior of the oceanic crust from the underlying mantle. The effect of this weaker lower crust on ridge dynamics is mainly influenced by spreading rate and crustal thickness variations. The accumulated strain pattern from a recently developed lens model, based on recent seismic observations, was proposed as an appealing mechanism for the observed gabbro layering sequence in the Oman Ophiolite. It is now known that the mid-ocean ridges at all spreading rates are offset into individual spreading segments by both transform and nontransform discontinuities. The tectonics of ridge segmentation are also spreading-rate dependent: the slow-spreading Mid-Atlantic Ridge is characterized by distinct bulls-eye shaped gravity lows, suggesting large along-axis variations in melt production and crustal thickness, whereas the fast-spreading East-Pacific Rise is associated with much smaller along-axis variations. These spreading-rate dependent changes have been attributed to a fundamental differences in ridge segmentation mechanisms and mantle upwelling at mid-ocean ridges: the mantle upwelling may be intrinsically plume-like (3-D) beneath a slow-spreading ridge but more sheet-like (2-D) beneath a fast-spreading ridge.  相似文献   

初论地幔热柱与成矿——以冀西北金银多金属成矿区为例   总被引：22，自引：8，他引：14  

李红阳  阎升好  王金锁  张建珍  王国富 《矿床地质》1996,15(3):249-256

作者通过对冀两北金、银多金属矿化集中区成矿规律和物探航磁、重力及遥感信息的综合研究,提出冀西北地区存在一个超越内蒙地轴与燕山褶皱带两个不同历史大地构造单元之上的中生代地幔热柱构造。文中例举了地幔热梓构造标志特征,探讨了地幔热柱构造地质作用（超变质作用、岩浆作用、成矿作用）及其时空演化规律,建立了地幔热柱构造的壳幔成矿模式。  相似文献   

天然火山作用探测华北下地壳组成、结构及其形成过程     

郑建平  平先权  苏玉平  汤华云  马强  魏颖 《地质学报》2022,96(9):2998-3011

与中上地壳相比，对下地壳组成、结构的认识受限于样品的获取，然而天然火山作用携带的下地壳捕虏体可以为了解下地壳提供关键样品。华北克拉通是世界上最古老的克拉通之一，显生宙以来的火山作用携带有丰富的下地壳捕虏体，为探测华北下地壳组成、结构及其形成过程提供了可能。通过对这些捕虏体定深、定性及定年的综合研究，构建了以信阳，莒南，汉诺坝和女山等典型地区为代表的下地壳组成、结构剖面模型。这些剖面表明，华北克拉通下地壳具有分层的特点，且上老下新，暗示可能与底侵作用有关。其中捕虏体的锆石U- Pb年龄和Hf同位素的研究，揭示了该克拉通下地壳复杂的形成与演化过程：最古老的组成部分可能老至~4. 0 Ga冥古宙，此后经历了3. 80~3. 65 Ga古太古代的再造作用，2. 8~2. 5 Ga 新太古代和2. 3~1. 8 Ga 古元古代的增生与再造共存，同时还经历了显生宙以来包括462~220 Ma，140~90 Ma和47~45 Ma的增生与再造事件。  相似文献   

短周期仪器记录在远震分析中的应用     

许康生 《地震地磁观测与研究》1992,13(2):15-19

地震泼由多种频率成份组成,在其传播过程中。由于地球介质的滤波作用,随着传播距离的增大。高频成份逐渐被衰减。周期越大的成份传播越远。因此,在地震观测上,不同频带的地震仪用于观测不同震中距范围的地震,使仪器较好地响应,就我国台网而言,短周期仪用于地方震、近震的监测,中长周期仪和长周期仪用于远震,极远震的监测,其中长周期仪偏重于记录极远震。但作者在实际分析工作中注意到,短周期仪的记录应用于远震,极远震的分析,显示出独特的作用,充分挖掘和利用短仪资料,将会更加丰富远震、极远震的震相资料。本文以高台地震台的资料为依据,从震中距和震级角度,与中长仪和长仪作比较,对短仪记录远震、极远震的震相及特征作了统计分析与初步探讨,并对新疆地区“影区”地震S波的记录、日本地区地震_PPcP等震相的出现提出了现象的存在,给出了相应的观测结果,以待步一步研究。  相似文献   

Na depletion in modern adakites via melt / rock reaction within the sub-arc mantle     

X.L. Xiong  B. Xia  J.F. Xu  H.C. Niu  W.S. Xiao 《Chemical Geology》2006,229(4):273-292

Interaction between slab-derived melt and mantle peridotite and the role of slab melt as a metasomatizing agent in the sub-arc mantle is being increasingly recognized. Adakite, the slab melt erupted on the surface, usually exhibits anomalously high MgO, CaO, Cr and Ni contents that indicate interaction with mantle peridotitite. Here we note that Cenozoic adakites have Na₂O contents below 5.8 wt.% with ∼95% samples lower than 5.0 wt.%, and are generally depleted in this component relative to experimental basalt partial melts (mostly beyond 5.0 wt.% and up to 9.0 wt.% Na₂O) produced under 1.5-3.0 GPa conditions that are most relevant to adakite production. We interpret the adakite Na depletion to be also a consequence of the melt / rock reaction that takes place within the hot mantle wedge. During ascent and reaction with mantle peridotite, primary adakite melts gain mantle components MgO, CaO, Cr and Ni but lose Na₂O, SiO₂ and perhaps K₂O to the mantle, leading to Na-rich mantle metasomatism. Selective assimilation of predominately mantle clinopyroxene, some spinel and minor olivine at high T/P has been considered to be an important process in producing high-Mg adakites from primary low-Mg slab melts [Killian, R., Stern, C. R., 2002. Constraints on the interaction between slab melts and the mantle wedge from adakitic glass in peridotite xenoliths. Eur. J. Mineral. 14, 25-36]. In such a process, Na depletion in the assimilated melt is the result of dilution due to the increase in melt mass. Phase relationships in the reaction system siliceous melt + peridotite and quantitative calculation suggest that assimilation of mantle clinopyroxene, olivine and spinel and fractional crystallization of sodic amphibole and orthopyroxene, under conditions of moderate T/P and increasing melt mass, is also an important process that modifies the composition of adakites and causes the Na depletion.  相似文献   

Mantle plumes from top to bottom   总被引：5，自引：0，他引：5  

Norman H. Sleep 《Earth》2006,77(4):231-271

Hotspots include midplate features like Hawaii and on-axis features like Iceland. Mantle plumes are a well-posed hypothesis for their formation. Starting plume heads provide an explanation of brief episodes of flood basalts, mafic intrusions, and radial dike swarms. Yet the essence of the hypothesis hides deep in the mantle. Tests independent of surface geology and geochemistry to date have been at best tantalizing. It is productive to bare the current ignorance, rather than to dump the plume hypothesis. One finds potentially fruitful lines of inquiry using simple dynamics and observations. Ancient lithospheric xenoliths may reveal heating by plumes and subsequent thermal equilibration in the past. The effect at the base of the chemical layer is modest 50-100 K for transient heating by plume heads. Thinning of nonbuoyant platform lithosphere is readily observed but not directly attributable to plumes. The plume history in Antarctica is ill constrained because of poor geological exposure. This locality provides a worst case on what is known about surface evidence of hotspots. Direct detection of plume tail conduits in the mid-mantle is now at the edge of seismic resolution. Seismology does not provide adequate resolution of the deep mantle. We do not know the extent of a chemically dense dregs layer or whether superplume regions are cooler or hotter than an adiabat in equilibrium with the asthenosphere. Overall, mid-mantle seismology is most likely to give definitive results as plume conduits are the guts of the dynamic hypothesis. Finding them would bring unresolved deep and shallow processes into place.  相似文献