Forceful Emplacement of Granitic Plutons in an Extensional Tectonic Setting:Syn-kinematic Plutons in the Yagan-Onch Hayrhan Metamorphic Core Complex

It is generally considered that granitic plutons are forcefully emplaced in a compressional setting and permissively emplaced in an extensional setting. This paper, however, shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhan metamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by (1) concentric distribution of the rock units, (2) a strain pattern with strong strains on the margins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shortening of the host rocks within the aureole. The strain analysis for the host rocks shows that the host-rock ductile shortening, i.e. forceful emplacement, provides about 16-24% of the emplacement space for the present plutons. All these suggest that forceful emplacement occurs not only in a compressional tectonic setting, but also in an extensional setting. This study further demonstrates the significance of the multiple emplacement of granitic plutons and provi     

准噶尔盆地东北缘构造特征、演化及与油气的关系

通过“建造”与“改造”特征的综合分析，划分了准噶尔盆地东北缘的构造带：早古生代（1－2）陆缘逆冲带；晚古生代（D1）混杂岩浆碰撞带；晚古生代（D1）火山岩浆岛弧挤带；晚古生代（D2－3）弧后盆地褶皱带；晚古生代（C1－P2）陆缘盆地褶皱带以及中生代前陆盆地平缓背斜带等6个构造带。自古生代以来，曾发生了两次拉张－碰撞（闭合）－推覆的演化过程，均表现为“北挤南拉”和“北老南新”的构造迁移，直到二叠纪末期，相当于晚海西期构造运动，全区发生大规模褶皱变形和挤压推覆。最后依据构造特征和演分分析结果，笔建议在双井子级盆地褶皱带具备良好石油地质条件的有利油气区做进一步工作。     

汝城地区晚中生代火山岩地球化学特征及其对源区属性的指示

湘东南汝城地区发育一套由基性玄武岩和中酸性安山质-英安质岩石组成的火山岩建造,属于低钾拉斑系列,该火山岩系中两个玄武岩的K-Ar年龄分别为124.5±2.5Ma和127.6±1.9Ma,属晚侏罗—早白垩世产物。在主、微量元素上两者成分存在明显差异。其中安山质-英安质岩石具有高MgO特征,属高MgO岩石,LILE富集、Nb-Ta、Sr-P亏损强烈,(La/Yb)N=6.7～7.9,Eu*/Eu=0.74～0.85,具岛弧型微量元素配分型式,87Sr/86Sr(t)=0.71079～0.71118,εNd(t)=-7.64～-8.16,与adakites高Mg岩石有着明显的差别,可能是富集岩石圈地幔熔融后直接分异的产物;玄武岩LILE富集,Nb-Ta富集,(La/Yb)cn=4.0～4.3,Eu*/Eu=1.00～1.16,具OIB型微量元素配分型式,87Sr/86Sr(t)=0.70812～0.70832,εNd(t)=0.48～1.03,其源区具二元混合趋势,其源区可能是富集型岩石圈地幔端员与亏损的软流圈地幔端员的混合产物。汝城地区晚中生代玄武岩和高Mg安山质-英安质岩石源区属性的限定及其相互的空间依存关系表明该区晚中生代时有着较薄的岩石圈厚度,处于岩石圈伸展减薄的大地构造背景。     

燕山及邻区中新生代挤压与伸展的转换和成矿作用

通过燕山及邻区中新生代区域性不整合界面、断裂演化、盆地演化、变质核杂岩和岩浆活动等地质事实论述了燕山及邻区中新生代挤压与伸展的转换过程及其与区域成矿作用的关系。认为燕山及邻区中新生代的构造演化过程是在前中生代华北克拉通岩石圈基础上发育起来的克拉通内（陆内）成盆沉积与挤压变形的交替演化过程，在这一构造演化过程中，存在中三叠世末（老虎沟组或杏石口组前，峰值年龄≥215Ma)、早侏罗世末（海房沟组或九龙山组前，峰值年龄≥178Ma)、晚侏罗世末（义县组或东岭台组前，峰值年龄≥135Ma）、白垩纪末（古近系前，峰值年龄65Ma)、古近纪末（新近系前，峰值年龄25Ma)5个挤压作用时期。5个挤压期在时间上相对较短，期间为早中三叠世、晚三叠世－早侏罗世、中晚侏罗世、白垩纪、古近纪、新近纪至第四纪6个时间较长，相对和缓或伸展的成盆沉积期一一隔开。在时间上，主成矿期与强烈伸展期相对应；在空间上外生矿产受伸展地所控制，内生矿产的分布受盆地间隆起带控制。总体上，挤压作用由强变弱，伸展作用由弱变强。伸展作用持续的时间长，挤压作用持续时间相对较短。挤压作用和伸展作用交替出现，挤压机构和伸展构造间互发育，成矿作用与挤压和伸展的转换存在着密切的成生联系。     

基于全球板块运动模型分析大西洋扩张变化

基于现代空间测量技术SLR、VLBI和GPS实测资料，解算出大西洋中脊海底扩张速率，其中北大西洋的东西向扩张速率平均为35mm/a，赤道大西洋东西向扩张速度分别为20－25mm/a，南大西洋东西向扩张速率为22－28mm/a，证实全球板块运动的存在及大西洋扩张学说，并基于全球几百万年地质模型NNR－NUVEL1A，北大西洋的东西向扩张速率平均为24．3mm/a，基于最新全球板块运动模型ITRF2000VEL，北大西洋的东西向扩张速率平均为20．8mm/a，总体上大西洋实测东西扩张速度与根据地学资料推出的地球板块运动模型和最新ITRF2000VEL模型的结果基本一致。     

Syn-orogenic extension in the Peloritani Alpine Thrust Belt (NE Sicily,Italy): Evidence from the Alì Unit

Structural and petrological analyses on the Alì Unit, in the Peloritani Thrust Belt, document the first evidence for Alpine exhumation associated with syn-orogenic extension in this part of the Calabria-Peloritani Arc. The Alì Unit displays ductile structures occurred during three Alpine deformation phases (D_a1, D_a2, D_a3). D_a1 and D_a3 developed in a contractional context, whereas D_a2 was generated in an extensional regime. The present-day tectonic contact between the Alì Unit and the overlying Mandanici Unit is interpreted as a low-angle extensional detachment responsible for the metamorphic break between the two units. Structural overprinting relationships indicate that the development of D_a2 structures and related tectonic exhumation occurred during syn-convergence extension, and were followed by further nappe stacking in the Peloritani Belt. To cite this article: R. Somma et al., C. R. Geoscience 337 (2005).     

Geometry and growth of an inner rift fault pattern: the Kino Sogo Fault Belt, Turkana Rift (North Kenya)

A quantitative analysis is presented of the scaling properties of faults within the exceptionally well-exposed Kino Sogo Fault Belt (KSFB) from the eastern part of the 200-km-wide Turkana rift, Northern Kenya. The KSFB comprises a series of horsts and grabens within an arcuate 40-km-wide zone that dissects Miocene–Pliocene lavas overlying an earlier asymmetric fault block. The fault belt is 150 km long and is bounded to the north and south by transverse (N50°E and N140°E) fault zones. An unusual feature of the fault system is that it accommodates very low strains (<1%) and since it is no older than 3 Ma, it could be characterised by extension rates and strain rates that are as low as 0.1 mm/yr and 10⁻¹⁶ s⁻¹, respectively. Despite its immaturity, the fault system comprises segmented fault arrays with lengths of up to 40 km, with individual fault segments ranging up to 9 km in length. Fault length distributions subscribe to a negative exponential scaling law, as opposed to the power law scaling typical of other fault systems. The relatively long faults and segments are, however, characterised by maximum throws of no more than 100 m, providing displacement/length ratios that are significantly below those of other fault systems. The under-displaced nature of the fault system is attributed to early stage rapid fault propagation possibly arising from reactivation of earlier underlying basement fabrics/faults or magmatic-related fractures. Combined with the structural control exercised by pre-existing transverse structures, the KSFB demonstrates the strong influence of older structures on rift fault system growth and the relatively rapid development of under-displaced fault geometries at low strains.     

中国东南部中一新生代地球动力学背景若干问题的探讨

近年来，有关中国东南部中新生代地球动力学背景的研究已取得了重要的进展，主要体现在：地幔性质、岩石圈减薄、岩石圈伸展和构造背景四个方面。研究表明，中国东南部中新生代的地幔性质主体是亏损地幔和EMⅢ型富集地幔混合，中生代以富集地幔为主，而新生代主体为亏损地幔。中国东南部晚中生代经历了岩石圈减薄，并伴生了玄武质底侵作用，具有较为复杂的岩石圈增生～减薄过程。大量事实表明中国东南部中新生代存在多期岩石圈伸展事件，侏罗纪存在局部岩石圈伸展，主要集中于内陆地区，白垩纪经历了区域性岩石圈伸展。近二十年来，中国东南部大规模岩浆的构造背景一直存在着争论，焦点在于太平洋俯冲对中国东南部产生什么的影响。从目前已有的资料来看，白垩纪地幔源区受到太平洋俯冲的影响，太平洋俯冲和玄武质岩浆底侵诱发了地壳加厚，岩石圈拆沉和软流圈上涌而导致岩石圈伸展是中国东南部主要构造背景。但是，中国东南部晚中生代以来的岩石圈伸展—减薄及其深部动力学机制是目前急需进一步深入探讨的问题。     

福建岱前山辉长岩体的地球化学特征与成因探讨

岱前山辉长岩体沿福建长乐一南澳大断裂带分布，侵位于沿海的绿片岩相和角闪岩相的变质岩中及内陆的中生代火山岩中，对其成因存在较多分歧。该岩体表现为与俯冲有关的岛弧地球化学特点，但在时间上又与古太平洋板块低角度歪斜俯冲、晚中生代的变质事件、平潭一东山变质带抬升和长乐一南澳剪切带运动在时间上基本一致。对于其成因不能简单的用拉张或碰撞加以解释，是受俯冲流体交代的上地幔，经部分熔融沿长乐一南澳断裂．应力转换带侵入。它与中国东南部出露的其它基性岩同源，但并未受到地壳的混染作用。计算结果表明，岱前山岩体经7％的部分熔融形成，其Sm、Nd含量高于原始地幔。