Petrogenesis of the Piqiang mafic-ultramafic layered intrusion and associated Fe-Ti-V oxide deposit in Tarim Large Igneous Province,NW China

ABSTRACT

The Piqiang intrusion is one of the two important ma?c-ultrama?c layered intrusions that host giant Fe-Ti-V oxide deposits in the Permian Tarim Large Igneous Province, NW China. The intrusion mainly consists of gabbro, anorthosite and minor plagioclase-bearing clinopyroxenite in the marginal zone. Disseminated to massive Fe-Ti oxide ores occur as layers and lenses within the gabbro. SHRIMP zircon U-Pb results from both a gabbro from the Piqiang intrusion and a granite from the surrounding granitic dyke yield ages of ~270 Ma. Geochemically, the Piqiang silicate rocks are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), moderately depleted in high ?eld strength elements (HFSE), and have a limited range of Sr-Nd-Hf isotopic compositions. The similar mineralogy, mineral compositions, and trace element characteristics of the layered units suggest that all the rocks are co-magmatic. The parental magma is Fe-Ti-rich and is akin to the most primitive diabasic dyke which is associated with the Piqiang intrusion. Partial melting of the Tarim mantle plume with involvement of a subduction-metasomatized lithospheric mantle source best explains the geochemistry and petrogenesis of the parental magmas of the Piqiang intrusion. We propose that the lithospheric mantle source may have been metasomatized by subduction-related materials and the metasomatic enrichment of this source region which may be correlated with oceanic sediment recycling during southward subduction of the South Tianshan oceanic slab during the Early-Middle Paleozoic. Crystal settling and mechanical sorting is the predominant process responsible for the formation of the massive Fe-Ti oxide ores in the Piqiang intrusion. Central to ore formation is a combination of the protracted differentiation history of a Fe-Ti-enriched parental magma and the later addition of external H₂O from the country rocks to the slowly cooling magma chamber.     

Transmission and visualization of large geographical maps

Transmission and visualization of large geographical maps have become a challenging research issue in GIS applications. This paper presents an efficient and robust way to simplify large geographical maps using frame buffers and Voronoi diagrams. The topological relationships are kept during the simplification by removing the Voronoi diagram’s self-overlapped regions. With the simplified vector maps, we establish different levels of detail (LOD) models of these maps. Then we introduce a client/server architecture which integrates our out-of-core algorithm, progressive transmission and rendering scheme based on computer graphics hardware. The architecture allows the viewers to view different regions interactively at different LODs on the network. Experimental results show that our proposed scheme provides an effective way for powerful transmission and manipulation of large maps.     

基于ERA40资料的边界层厚度气候特征分析

为了解边界层厚度的大尺度分布及其气候循环特征,基于逐日ERA 40 再分析边界层厚度资料,采用统计学方法计算边界层厚度分4个时次的季节循环、年较差等气候特征场,对全球边界层厚度分布及其季节演变特征进行了研究。结果表明：全球较厚的边界层分布与大地形、沙漠等下垫面的分布有直接联系;陆地强边界层分布存在“08时”现象,即陆地较厚边界层中心分布在当地时间08时经线附近;在大洋上南北纬30°~40°两条纬度带内边界层厚度的月尺度内变率较大,与大气强斜压性的天气系统活跃区一致;月平均日较差的年循环特征存在着季节性南北进退的现象。研究结果对于全面认识和科学利用ERA 40逐日边界层再分析资料有一定帮助。     

油气勘探新领域:火山岩油气藏——松辽盆地大型火山岩气田发现的启示

通过观念转变和理论与技术创新,大庆油田在松辽盆地徐家围子断陷深层火山岩天然气勘探获得重大突破,使火山岩由原来的油气勘探"禁区"变为"靶区".从而带动了全国的火山岩油气勘探,促使国内油气储量的不断增长.研究表明,各类火山岩均有可能成为良好的储层.与沉积岩相比,火山岩在盆地深层具有体积大、储层物性受埋深影响小、孔渗条件好等...     

Geology and age of the Glikson impact structure,Western Australia

The Glikson structure is an aeromagnetic and structural anomaly located in the Little Sandy Desert of Western Australia (23°59'S, 121°34′E). Shatter cones and planar microstructures in quartz grains are present in a highly deformed central region, suggesting an impact origin. Circumferential shortening folds and chaotically disposed bedding define a 19 km-diameter area of deformation. Glikson is located in the northwestern Officer Basin in otherwise nearly flat-lying sandstone, siltstone and conglomerate of the Neoproterozoic Mundadjini Formation, intruded by dolerite sills. The structure would not have been detected if not for its strong ring-shaped aeromagnetic anomaly, which has a 10 km inner diameter and a 14 km outer diameter. We interpret the circular magnetic signature as the product of truncation and folding of mafic sills into a ring syncline. The sills most likely correlate with dolerites that intrude the Boondawari Formation ～25 km to the north, for which we report a SHRIMP U?–?Pb baddeleyite and zircon age of 508?±?5 Ma, providing a precise older limit for the impact event that formed the Glikson structure.     

http://www.sciencedirect.com/science/article/pii/S1674987113000595

Magmatic oxide deposits in the～260 Ma Emeishan Large Igneous Province(ELIP),SW China and northern Vietnam,are important sources of Fe,Ti and V.Some giant magmatic Fe-Ti-V oxide deposits, such as the Panzhihua,Hongge,and Baima deposits,are well described in the literature and are hosted in layered mafic-ultramafic intrusions in the Panxi region,the central ELIP.The same type of ELIP- related deposits also occur far to the south and include the Anyi deposit,about 130 km south of Panzhihua,and the Mianhuadi deposit in the Red River fault zone.The Anyi deposit is relatively small but is similarly hosted in a layered mafic intrusion.The Mianhuadi deposit has a zircon U-Pb age of～260 Ma and is thus contemporaneous with the ELIP.This deposit was variably metamorphosed during the Indosinian orogeny and Red River faulting.Compositionally,magnetite of the Mianhuadi deposit contains smaller amounts of Ti and V than that of the other deposits,possibly attributable to the later metamorphism.The distribution of the oxide ore deposits is not related to the domal structure of the ELIP.One major feature of all the oxide deposits in the ELIP is the spatial association of oxide-bearing gabbroic intrusions,syenitic plutons and high-Ti flood basalts.Thus,we propose that magmas from a mantle plume were emplaced into a shallow magma chamber where they were evolved into a field of liquid immiscibility to form two silicate liquids,one with an extremely Fe-Ti-rich gabbroic composition and the other syenitic.An immiscible Fe-Ti-(P) oxide melt may then separate from the mafic magmas to form oxide deposits.The parental magmas from which these deposits formed were likely Fe-Ti-rich picritic in composition and were derived from enriched asthenospheric mantle at a greater depth than the magmas that produced sulfide-bearing intrusions of the ELIP.     

云南香格里拉红山铜矿石硫化物环带及地质意义

云南香格里拉县红山铜矿是三江义敦岛弧带南端重要铜矿床,颇受关注,成因认识分歧大.矿区出露上三叠统板岩、变碎屑岩和灰岩夹中基性火山岩、火山碎屑岩以及少量侵入其中的中酸性和超基性岩脉、岩株,透镜状铜硫化物矿体产在顺层状矽卡岩体内或边部,成矿后断裂明显.矿石中普遍发育以黄铁矿为核部、黄铜矿为中间带、磁黄铁矿为边部带的硫化物环带,其中核部黄铁矿呈立方体自形-半自形晶,黄铜矿呈他形晶围绕黄铁矿沉淀,磁黄铁矿呈他形分布在黄铜矿外围,内带常被外带硫化物溶蚀交代.环带从内到外硫化物先后沉淀,矿物生成顺序为黄铁矿-黄铜矿-磁黄铁矿.环带中三种硫化物矿物的REE配分曲线和微量元素蛛网图极为相似,负Eu异常显著,富集U、Th、Zr、Hf,亏损Rb、Sr、Ba,与矿区超基性岩表现出较高相似性;环带从内到外,∑REE(0.17371×10-6、1.22626×10-6、5.25925×10-6)和微量元素含量依次升高,Co/Ni和Se/Te比值降低,指示矿石硫化物沉淀过程中,可能伴随热液体系内地壳物质不断增加.环带中硫化物矿物δ34SV-CDT=3.81‰～5.23‰,具有岩浆硫源特征,δ34SV-CDT边部带磁黄铁矿 (4.47‰)＜δ34SV-CDT中间带黄铜矿(4.58‰)＜ δ34SV-CDT核部黄铁矿(4.65‰),三种硫化物间没有达到同位素平衡分馏.红山铜矿石环带结构是岩浆热液为主成矿流体中黄铁矿、黄铜矿、磁黄铁矿先后晶出成因,伴随硫化物环带的形成,热液系统从早到晚H2S和O2逸度降低或pH升高过程.     

太行山东麓断裂带板内构造地貌反转与机制

华北克拉通前寒武纪基底可划分为东部地块、中部带和西部地块。中生代以来,华北克拉通发生减薄破坏,其破坏中心位于东部地块,而西部地块与中部带基本保持完整,其过渡带就是太行山东侧。太行山地区近乎平行发育着两条重要的断裂：太行山大断裂和太行山山前断裂,统称为太行山东麓断裂带。通过研究发现,太行山山前断裂是继承早前寒武纪构造带形成的断裂,控制着太行山与东部地块前寒武纪基底的差异,古新世以来发生板内构造地貌的负反转,构成渤海湾盆地的西界断裂。太行山大断裂则在燕山期时为重要的逆冲断裂,对太行山的隆起起着重要作用;中新世以来,伴随着山西地堑系的形成,太行山大断裂发生构造负反转,控制着一系列山间地堑的发育。新生代以来,该区构造演化特征整体表现为向西构造迁移的特点,是区域走滑伸展背景下的一种新的板内盆山关系。     

西藏古大湖成盐模式的提出与分析探讨

根据目前对青藏高原第四系及古环境研究的最新进展,提出了西藏地区盐湖成盐的模式———古大湖成盐模式,并列举了诸多具有说服力的证据,为研究盐湖矿产形成规律和进一步开发利用,促进西藏经济发展,将产生积极的影响。     

长偶极大功率可控源电磁波响应特征研究

地球物理学中关于电磁波勘探研究通常采用的是地球半空间模型.然而,对于几十公里的有限长电缆源（长偶极源）,远距离电磁波场探测必须要考虑电离层的影响,它是一个全空间问题.关于包含电离层、空气层和地球介质（我们称“地-电离层”模式）的电磁波场特征的研究在国外较少,国内几乎是空白.本文采用全空间积分方程法首先对小尺度的可控源电磁波场特征进行了研究,由于此时电离层的影响可忽略,它应该和半空间成熟的CSAMT模拟结果一致,对比结果表明,二者是一致的,验证了全空间模拟方法的可靠性和有效性.随后进行了50 km长电缆电离层和空气层高度都为100 km的“地-电离层”模式大尺度电磁波场模拟,以探讨大尺度可控源电磁波场的特征.给定频率的“地-电离层”模式电磁场的衰减曲线表明长电缆远距离电磁波场由于受电离层的作用存在衰减逐渐变小的过渡场和衰减变小的波导场.为了探讨复杂介质“地-电离层”模式电磁波特征,对“地-电离层”模式的典型地盾和地台多层介质模型进行了数值模拟,得到了偶极源长度50 km、电流200A、收发距离远达1600 km和2500 km的合理的电磁场结果.最后,对一简单含油储层结构模型进行了长偶极、大功率、远距离电磁波场响应计算.储层横向不均匀复杂结构模拟的结果表明,考虑电离层和大气层的“地-电离层”模式大尺度深层复杂介质模拟时,电磁场对深部目标体仍有很好的异常响应.