The dilemma of the Jiaodong gold deposits: Are they unique?

The ca. 126e120 Ma Au deposits of the Jiaodong Peninsula, eastern China, define the country＇s largest gold province with an overall endowment estimated as＆gt;3000 t Au. The vein and disseminated ores are hosted by NE-to NNE-trending brittle normal faults that parallel the margins of ca. 165e150 Ma, deeply emplaced, lower crustal melt granites. The deposits are sited along the faults for many tens of kilometers and the larger orebodies are associated with dilatational jogs. Country rocks to the granites are Pre-cambrian high-grade metamorphic rocks located on both sides of a Triassic suture between the North and South China blocks. During early Mesozoic convergent deformation, the ore-hosting structures developed as ductile thrust faults that were subsequently reactivated during Early Cretaceous ＂Yan-shanian＂intracontinental extensional deformation and associated gold formation. 〈br〉 Classification of the gold deposits remains problematic. Many features resemble those typical of orogenic Au including the linear structural distribution of the deposits, mineralization style, ore and alteration assemblages, and ore fluid chemistry. However, Phanerozoic orogenic Au deposits are formed by prograde metamorphism of accreted oceanic rocks in Cordilleran-style orogens. The Jiaodong de-posits, in contrast, formed within two Precambrian blocks approximately 2 billion years after devolati-lization of the country rocks, and thus require a model that involves alternative fluid and metal sources for the ores. A widespread suite of ca. 130e123 Ma granodiorites overlaps temporally with the ores, but shows a poor spatial association with the deposits. Furthermore, the deposit distribution and mineral-ization style is atypical of ores formed from nearby magmas. The ore concentration requires fluid focusing during some type of sub-crustal thermal event, which could be broadly related to a combination of coeval lithospheric thinning, asthenospheric upwelling, paleo-Pacific plate subduction, and seismicity along the continental-scale Tan-Lu fault. Possible ore genesis scenarios include those where ore fluids were produced directly by the metamorphism of oceanic lithosphere and overlying sediment on the subducting paleo-Pacific slab, or by devolatilization of an enriched mantle wedge above the slab. Both the sulfur and gold could be sourced from either the oceanic sediments or the serpentinized mantle. A better understanding of the architecture of the paleo-Pacific slab during Early Cretaceous below the eastern margin of China is essential to determination of the validity of possible models.     

Permian Fusuline Fauna from the Lower Part of the Lugu Formation in the Central Qiangtang Block and its Geological Implications

A Kubergandian （Kungurian） fusuline fauna from the lower part of the Lugu Formation in the Cuozheqiangma area,central Qiangtang Block is described.This fusuline fauna belongs to the Southern Transitional Zone in palaeobiogeography,and is characterised by the presence of the distinctive bi-temperate genus Monodiexodina and many genera common in lower latitude Tethyan areas such as Parafusulina and Pseudodoliolina.The occurrence of Monodiexodina in the fauna confirms that the seamount-type carbonates of the Lugu Formation did not originate from the Palaeotethys Ocean,but rather from a branch of the Neotethys Ocean after the rifting of the Qiangtang Block from the Tethys Himalaya area in the Artinskian.     

Skeletal Microstructures of the Chiton Ischnochiton hakodadensis and a Comparison with the Cambrian Halkieria

Halkieria is an Early Cambrian fossil genus with proposed phylogenetic affinities ranging from stem group lophotrochozoan to stem-group aculiferan. Skeletal similarities are often cited as evidence in support of a mollusk interpretation for Halkieria and related Cambrian fossils. The skeletal microstructures of the polyplacophoran mollusk （chiton） Ischnochiton hakodadensis, which bears perinotum elements resembling sclerites of halkieriids and other coeloscleritophoran small shelly fossils （SSFs）, were studied to evaluate the interpretations. There are both similarities and differences between chiton skeletal structures and halkieriid sclerites： 1） the head valve of L hakodadensis and the dorsal shell of Halkieria evangelista share a similar pattern of fine concentric growth lines, but halkieriid dorsal shells lack other polyplacophoran valve characteristics, including V-shaped indentation, radiate ribs; 2） the arrangement of I. hakodadensis perinotum elements in three zones is somewhat similar to the arrangement pattern of halkieriid sclerites; 3） the inner perinotum scales of L hakodadensis （-200 μm in diameter） have a base and a blade, remarkably similar in morphology to halkieriid palmate sclerites （-400 μm in diameter）. However, I. hakodadensis perinotum scales are nearly solid whereas halkieriid sclerites are hollow. These observations add a microstructural dimension to the skeletal comparison between mollusks and halkeriids, and may prove to be useful in resolving the phylogenetic affinity of Halkieria and the Halwaxiidae.     

论扬子地块西缘元古宙铁氧化物铜金型矿床与大地构造演化

探讨和总结了扬子地块西缘大地构造演化、元古宙重大构造-岩浆事件与铁氧化物铜金型(IOCG)矿床关系,以促进对深部隐伏IOCG矿床勘查和新技术研发。在新太古界-古元古界小溜口岩组顶部和不整合面之下,含矿层状-似层状碱性方解石钠长石岩中锆石SHRIMP U-Pb年龄为2520±14 Ma,这种似层状铜矿床和其上不整合面型Cu-Co-AuAg-REE-Fe矿体,以云南东川因民铁铜矿床深部小溜口岩组中铜矿床为代表。总体上,IOCG矿床与扬子地块大地构造演化之间关系为:(1)扬子地块于东川运动(中条运动/Hudsonian Orogeny,1800 Ma)形成了陆壳基底。在中元古代初期(1700±50 Ma)发生了地幔热物质上涌侵位的构造-岩浆事件,导致古扬子地块发生裂解并形成裂谷构造和大陆裂谷盆地。在近东西向大陆裂谷盆地发育初期,构造动力学特征为火山地堑式断陷成盆。在碱性铁钠质基性岩、铁钾质粗面岩和铁质辉绿辉长岩形成过程中,形成了第一期IOCG矿床成岩成矿高峰期(1650±50 Ma),以云南大红山IOCG矿床为代表。(2)在裂谷盆地成熟发育期,构造动力学特征为裂陷沉降成盆。因民期和黑山期两次地幔热物质上涌侵位,导致了构造-岩浆-成岩成矿事件发生。在铁钠质基性火山岩、铁钾质粗面岩、水下火成碳酸岩、火山喷溢-火山热水喷流沉积相等形成过程中,形成了第二期IOCG矿床的成岩成矿高峰期(1500±50 Ma),以云南迤纳厂IOCG矿床为代表。(3)在小黑箐运动/满银沟运动(格林威尔造山期,1000 Ma±),扬子地块南缘形成了近南北向洋壳俯冲和陆缘侧向挤压收缩体制,碱性铁质辉长岩-辉绿岩体上涌侵位,伴随同构造期脆韧性剪切带形成和沉积盆地构造反转,形成区域性不整合面(小黑箐运动/满银沟运动)和后期沉积型-火山沉积型铁矿床,为IOCG矿床第三期成岩成矿高峰期(1000±100 Ma)。以白锡腊深部和新塘IOCG矿床为代表,形成IOCG矿床和IOCG矿床的叠加成岩成矿。(4)晋宁-澄江期为多重构造体制耦合与转换格局,扬子地块内部和陆缘具有造山带-沉积盆地-深部地幔柱上涌侵位,深部地幔柱上涌侵位形成的碱性铁质辉长岩具有OIB源区特征,形成了第四期IOCG矿床的成岩成矿高峰期(800±50 Ma),以四川拉拉IOCG矿床受碱性铁质辉长岩侵位与叠加成岩成矿为代表。在澄江期"盆→山"耦合与转换,IOCG矿床和东川型铜矿中进一步发生了盆地流体叠加改造富集(810~700 Ma)。     

新疆东准噶尔卡拉麦里蛇绿岩带研究现状

新疆东准噶尔卡拉麦里蛇绿岩带是一条重要的蛇绿岩带,其所代表的古大洋是中亚古生代构造框架中一个非常重要的构造单元。对于该带归属何古板块之间的缝合带存在着截然不同的认识,对卡拉麦里蛇绿岩前身洋盆俯冲闭合年限也存在多种观点。根据对前人研究资料的综合,简要地论述了该断裂带是准噶尔洋俯冲消亡的遗迹,其闭合年限在350Ma左右。     

安徽铜陵地区幔源镁铁质团块研究及其地质意义

幔源岩石包体研究,是认识上地幔岩石圈物质组成、幔源岩浆演化及壳幔动力学过程的重要手段。铜陵地区小铜官山石英二长闪长岩中发育有微粒闪长质包体,并且这些微粒闪长质包体中不均匀地分布着镁铁质团块,三者的形成过程可视为铜陵地区岩浆演化的缩影,为了解本区深部岩浆作用过程提供了有力的证据。在前人研究的基础上,笔者借助电子探针、扫描电镜、电镜能谱和二次飞行时间离子探针(Tof-SIMS)对产于铜陵地区微粒闪长质包体中的镁铁质团块进行了详细的研究,首次获得了一套精确的矿物化学资料和元素分布图,总结了镁铁质团块的特征,并讨论了本区的深部岩浆作用过程。矿物学研究表明,镁铁质团块中的角闪石和辉石均已发生了不同程度的透闪石化和阳起石化蚀变,蚀变过程中,从镁钙闪石到镁角闪石,再到透闪石,随着Si的增加,角闪石呈现出Mg的富集和Ti、Al贫化的特点。团块中的富Cr磁铁矿、Ti磁铁矿和少量的铝直闪石指示了其具有深源性。Tof-SIMS元素分布图显示,透闪石主要由Al、Si、Ca、Sc、V、Cr、Mn、Cu和Sr元素组成,透辉石主要由Si、Mg、Ca、Cu和Rb组成。在铜陵地区,上地幔部分熔融形成一套玄武岩浆,受岩浆底侵作用影响,玄武岩浆上侵,进入下地壳深位岩浆房,与下地壳硅镁层发生同化混染作用,形成一套轻度演化的中基性(辉长质)玄武岩浆,镁铁质团块就是这类中基性玄武岩浆直接结晶形成的。后受构造作用影响,这类中基性玄武岩浆上侵到中地壳岩浆房(12~16 km),与中地壳的变质岩系发生同化混染和结晶分异作用形成一套中性闪长质岩浆,微粒闪长质包体就是这套闪长质岩浆发生结晶分异作用而形成的。镁铁质团块和微粒闪长质包体清楚地解释了铜陵地区深部岩浆作用过程,并有力地证明了铜陵地区中地壳的闪长质岩浆来源于下地壳的壳幔混源岩浆。     

黑龙江张家湾岩体锆石U-Pb年龄与地球化学及其地质意义

通过对兴蒙造山带东段小兴安岭-张广才岭地区张家湾岩体石英闪长岩、正长花岗岩进行的锆石LA-ICP-MS U-Pb年龄分析测试、岩石地球化学的各项分析测试,综合分析研究表明,石英闪长岩形成于早侏罗世(176.2±1.8Ma),具浆混花岗岩特点,属壳幔混合成因;正长花岗岩形成于中侏罗世(166±2.2Ma),具"S"型花岗岩的地球化学属性,属壳源熔融成因。结合该区大地构造背景,认为张家湾岩体很可能是环太平洋增生地体的佳木斯板块与西侧的张广才岭地块碰撞造山作用形成。     

从地壳上地幔构造看洋陆转换作用

根据近年来全球地壳上地幔探测的成果,分析了洋陆转换、地壳和岩石圈加厚的作用过程。洋陆转换作用可分为以下五个演化阶段：① 同大洋扩张期的地壳增厚;② 海沟发生与早期俯冲;③ 俯冲带成熟与沟弧盆体系形成;④ 俯冲带汇聚和位移;⑤ 陆—岛碰撞和陆壳连接。同大洋扩张期的地壳增厚作用指发生在被动大陆边缘的地质作用。包括沉积作用,岩浆底侵作用,下地壳和岩石圈地幔压裂,形成海沟等。海沟形成后陆缘转变为主动大陆边缘,大地构造机制转换为板块俯冲作用。成熟期的洋—陆转换作用特征是海盆扩张和板块俯冲造成的洋壳缩短取得平衡。弧后盆地和弧后边缘海的打开,表明俯冲带进入完全成熟的阶段。洋脊俯冲之后过成熟期的洋—陆转换作用,其特征是海盆逐渐缩小而且板块俯冲带汇聚。这里既有密集的俯冲带又有短期打开的边缘海岭;俯冲带不断位移,既可后撤也可前冲;俯冲板块经常发生断裂和拆沉。过成熟期的板块俯冲结果是边缘海微板块的萎缩。经过陆—岛碰撞,岛弧地壳增厚,与大陆板块连为一体,成为大陆内部的一个构造单元,即显生宙的“古洋—陆转换带”。     

内蒙古科尔沁右翼中旗地区孟恩陶勒盖岩体成因研究

内蒙古东部科尔沁右翼中旗地区孟恩陶勒盖岩体由二长花岗岩、 花岗闪长岩、 英云闪长岩组成,属于高钾钙碱性岩系。岩石具有SiO₂较高（平均为72.03%）,富碱并相对富K₂O（K₂O/Na₂O平均为1.08）,Mg^#较低（平均为0.30）,铝饱和指数（A/CNK）较高（平均为1.08）的特点。在ACF图解中,岩石投影在S型花岗岩中,标准矿物中普遍出现刚玉分子,岩石中可见白云母,个别可见石榴石,应属S型花岗岩范畴。岩石稀土总量较低（∑ REE平均为120.76×10^-6）,轻、 重稀土分馏明显（（La/Yb）_N=3.2～32.5）,有变化较大的负铕异常（0.2～0.8）;在微量元素蜘蛛网图上,强烈富集大离子亲石元素（如Rb、 Ba）,高场强元素（如Ti）强烈亏损,在微量元素与上陆壳标准化及（La/Yb）_N-δEu图解中,物源属于壳源。岩体Sr的含量平均为176.57×10^-6,小于300×10^-6,Yb含量平均为1.3×10^-6,小于2×10^-6,属于喜马拉雅型花岗岩,源岩可能为含石榴石和斜长石的高压麻粒岩相,形成于加厚地壳部分熔融的结果,其形成的压力可能为0.8～1.5 GPa。在R₁-R₂图解、 Yb-Ta图解中,岩石均投影在同碰撞环境。因此,该岩体是中三叠世挤压背景下同碰撞壳源S型花岗岩,为华北板块与西伯利亚板块碰撞上限的约束提供了资料。     

甘蒙北山地区下石炭统绿条山组 时代修正及其构造意义

甘肃—内蒙古北山地区位于中亚造山带中段,其晚古生代洋盆最终闭合时间倍受关注且久有争议。早石炭世是该区洋陆转换的关键时期之一,下石炭统下部绿条山组与下伏的下、中泥盆统之间的角度不整合被认为是该区构造隆升的主要证据之一。但由于研究程度限制,绿条山组的时代尚有争议,一定程度上制约了该区构造演化的深入分析。北山北部甜水井北与碎石山剖面绿条山组火山岩的LA-ICP-MS锆石U-Pb年龄分别为296.8±3.5Ma与311.1±3.2Ma,产出晚石炭世巴什基尔期(Bashkirian)菊石Gastrioceras和Branneroceras,时代应修订为晚石炭世—早二叠世早期。研究区下泥盆统—上石炭统沉积充填及生物群落特征表明该区可能在晚石炭世由大陆边缘浅海演化至裂谷盆地,上石炭统与下、中泥盆统之间的角度不整合代表洋陆转化造成的长时间隆升剥蚀。