Sr–Nd isotopes and geochemistry of the infrastructural rocks in the Meatiq and Hafafit core complexes, Eastern Desert, Egypt: Evidence for involvement of pre-Neoproterozoic crust in the growth of Arabian–Nubian Shield

Abstract Meatiq and Hafafit core complexes are large swells in the Eastern Desert of Egypt, comprising two major tectono‐stratigraphic units or tiers. The lower (infrastructure) unit is composed of variably cataclased gneissose granites and high‐grade gneisses and schists. It is structurally overlain by Pan–African ophiolitic mélange nappes (the higher unit). The two units are separated by a low‐angle sole thrust, along which mylonites are developed. Major and trace element data indicate formation of the gneissose granites in both volcanic arc and within‐plate settings. Nevertheless, all analyzed gneissose granites and other infrastructural rocks, exhibit low initial ratios (Sr_i) (<0.7027), positive ε_Nd(t) (+4.9 to +10.3) and Neoproterozoic Nd model age (T_DM) (592–831 Ma for the gneissose granite samples). Although these values are compatible with other parts of the Arabian– Nubian Shield considered to be juvenile, the ε_Nd(t) values and several incompatible element ratios of the gneissose granites are too low to be derived from a mantle source without contribution from an older continental crust. Our geological, Sr–Nd isotopic and chemical data combined with the published zircon ages indicate the existence of a pre‐Neoproterozoic continent in the Eastern Desert that started to break up at ca 800 Ma. Rifting and subsequent events caused the formation of oceanic crust and emplacement within‐plate alkali basalts in the hinterland domains of the old continent. The emplacement of basaltic magma might have triggered melting of lower crust in the old continent and resulted in emplacement of the within‐plate granite masses between 700 Ma and 626 Ma. The granite masses and other rocks in the old continent have been subjected to deformation during the over‐thrusting of Pan–African nappes, probably because of the oblique convergence between East and West Gondwanaland. Rb–Sr isotopes of the gneissose granites in both Meatiq and Hafafit core complexes defines an isochron age of 619 ± 25 Ma with Sr_i of 0.7009 ± 0.0017 and mean squares of weighted deviates = 2.0. We interpret this age as the date of thrusting of the Pan–African nappes in the Eastern Desert. Continued oblique convergence between East and West Gondwanaland could have resulted in the formation northwest–southeast‐trending Meatiq and Hafafit anticlinoriums.     

鞍本地区鞍山式铁矿区地质构造

鞍本地区,从太古宙到新生代地层齐全。其中有鞍山式铁矿、菱镁矿、煤、粘土矿等沉积矿产,有古基底构造和盖层构造,有径向裂谷构造和纬向地粮构造。特别是在鞍山狭小范围内出现多期回归性垂直运动,蔚为地质构造奇观。所有这些都体现了两极挤压构造运动史。     

黄陵断隆北部太古界花岗岩-绿岩地体的发现

属于扬子地台基底的黄陵断隆北部太古界混合奥长花岗岩及其残留围岩——王家湾群所组成的地体,是一个遭受了斜长角闪岩相变质的花岗岩-绿岩地体。本区上太古界酸性侵入岩体是白岗岩-奥长花岗岩套(AT岩套)。绿岩带中的超镁铁质岩是含SiO_2稍高的辉岩质科马提岩。     

试论陕西省黄陵矿区洛河砂岩水水质分布规律

洛河砂岩水是黄陵矿区供水水源中的唯一水质水量合乎要求的含水层。经过对洛河砂岩水水质的分析研究,发现洛河砂岩水水质分布有一定的规律性,具体表现为：溶解性固体、Na＋含量、SO4^2-含量、Cl-含量在浅部较低,深部则有所增大;水质类型浅部为HCO3-Ca型,深部为HCO3-Na·Ca型;在动态变化上,呈现出随着开采时间的延续,溶解性固体、Na＋、SO4^2-含量逐渐变小,Ca2＋含量逐渐增大的趋势。强调在开发煤炭、石油时,一定要对洛河砂岩水加以保护。使其更好的为矿区建设服务。     

鄂尔多斯盆地南部奥陶系天然气成藏条件分析

对鄂南奥陶系风化壳天然气成藏的烃源条件、储集层形成机理和圈闭特征的研究认为,早奥陶世,黄陵古隆起分割秦岭坳拉槽与华北海,并在古隆起北侧形成蒸发台地斜坡云坪相膏云岩沉积。加里东运动期,黄陵古隆起随同鄂尔多斯盆地整体抬升,其北坡不同层位膏云岩、含膏白云岩差异溶蚀形成各类孔隙型储集层,并以探井钻遇的蜂窝状膏溶细晶白云岩、针孔状膏溶白云岩和膏溶角砾白云岩为代表广泛分布。海西-印支期,黄陵古隆起处于有利于接受秦岭坳拉槽运移流体的部位,目前已在其南北两翼发现较多的含沥青古油藏显示。古油藏中的石油在晚侏罗-早白垩世高古地温热演化阶段转化成天然气,可为富县斜坡提供充足的天然气源。米脂坳陷致密岩性带为风化壳天然气聚集提供了区域圈闭条件,从而使富县-甘泉地区成为天然气勘探的有利场所。     

三峡库区黄陵背斜形成机理及与滑坡群关系

黄陵背斜、秭归向斜是三峡地区构造地质研究热点之一,前人将其划归于秦岭造山带的组成部分,认为是东西向构造后期改造的结果;分布于此区的仙女山断裂是否穿越长江也是争论的焦点问题之一.这些问题的解决对澄清研究区地质灾害分布特征具有重要意义.笔者在前人研究的基础上,从沉积学、构造地质学角度,在大量野外地质研究工作的基础上,提出了新的看法:黄陵背斜、秭归向斜、当阳向斜、仙女山断裂同属统一的构造体系,其形成和演化与中国东西部构造格局的变迁一致,黄陵背斜具有断层相关褶皱的特点,秭归向斜具有前陆挠曲型盆地构造属性;仙女山断裂形成之初具有传递断层的属性,后期又经历了引张、挤压演化过程,不存在跨越长江向北延伸的问题;受秭归向斜沉降幅度以及东西向构造与南北向构造复合影响,在研究区形成3个滑坡聚集区,分别为贾家店滑坡聚集区、八字门向家店滑坡聚集区、兴山县城附近滑坡聚集区.     

黄陵基底穹隆北部石墨矿床成矿物质来源的地球化学约束

在黄陵基底穹隆北部已发现的几个大鳞片晶质石墨矿区中采取少量新鲜石墨样品(含少量大理岩围岩)进行了矿石岩相学及地球化学测试,通过相应分析、图解,探讨其成矿物质来源。该区石墨矿石赋存于黄凉河岩组(Pt1h)一套孔兹岩系内,主要矿石类型为石墨片岩及石墨片麻岩。根据其主微量元素及碳同位素分析,恢复矿石原岩为一套含炭质的(砂)泥质沉积岩,其固定碳质绝大多数来源于有机物而不是大理岩中的无机碳。根据矿层的元素组成及古地史证据,推测黄凉河岩组的蚀源区以野马洞岩组(Ar2y,拉斑玄武质)为主,东冲河片麻杂岩(Ar2D,花岗质)次之,而不是前人认为的单一"以花岗质岩石为蚀源区"。从供给源到成矿母岩的演化过程中,发生了强烈的地球化学变化,而不只是物质简单的机械转移。     

Lateral Inhomogeneity of Basement Layer in Three Gorges Region of Changjiang River (Yangtze River)

Seismic tomography from the Pg wave data along the non-longitudinal profile in the Three Gorges Region is presented in this paper.The seismic tomography method,and the acquisition and analysis of seismic travel time are broadly outlined.The tomography of basement reveals a great amount of significant information and shows that the low-velocity zone is due to the lithologic difference and the fault fracture zone.It also demonstrates that there exist three high-velocity zones with v>6.4 km/s at the basement; the largest of zones which strikes north-south is located at the southwestern side of Huangling Anticlinorium and extends into the anticlinorium northward.The other two high-velocity zones are,respectively,situated at the eastern side of the anticlinorium and the western side of the profile.The high-velocity zones are inferred to originate from the upwelling of material with high-velocity from deep crust.     

长江三峡地区基底层横向不均匀性

对三峡地区的Ｐｇ波非纵观测资料用地震层析成象方法进行了计算处理并对解释结果作了分析。简要阐述了地震析成象处理方法，地震走时数据的采集与分析等。基底面成象图给出了许多有意义的信息；该测区低速区的开矿要起因于岩性的差异及断层破碎带；基底面上存在３个ｖ〉６．４ｋｍ／ｓ的高速度区，面积最大的一个大体呈南北走向，位于黄陵背斜西南侧、向北进入背斜区，另两个分别位于黄陵背斜东则与测区西侧。     

粤西黄岭岩组片麻状花岗质岩石的剪切深熔机理

粤西黄岭岩组片麻状花岗质岩石属于云开地块的基底岩系(2600Ma～1700Ma)。自下而上发育3种均造样式：下部透入性剪切变形带；中部平直均匀变形带；上部为揉皱带。应变分析表明，近水平分层剪切作用以及剪切应变带的向上迁移形成了上述不同构造样式，化学分析显示不同构造样式的花岗质岩石具有陆壳改造S型花岗岩特点。它们可能是形成于浅海一半深海的碎屑原岩在原地或准原地剪切深熔的结果。剪切深熔深度约13km～15km，峰期变形在2000Ma～1700Ma。