The initiation and development of metamorphic foliation in the Otago Schist, Part 2: evidence from quartz grain-shape data

Shape, size and orientation measurements of quartz grains sampled along two transects that cross zones of increasing metamorphic grade in the Otago Schist, New Zealand, reveal the role of quartz in the progressive development of metamorphic foliation. Sedimentary compaction and diagenesis contributed little to the formation of a shape‐preferred orientation (SPO) within the analysed samples. Metamorphic foliation was initiated at sub‐greenschist facies conditions as part of a composite S1‐bedding structure parallel to the axial planes of tight to isoclinal F1 folds. An important component of this foliation is a pronounced quartz SPO that formed dominantly by the effect of dissolution–precipitation creep on detrital grains in association with F1 strain. With increasing grade, the following trends are evident from the SPO data: (i) a progressive increase in the aspect ratio of grains in sections parallel to lineation, and the development of blade‐shaped grains; (ii) the early development of a strong shape preferred orientation so that blade lengths define the linear aspect of the foliation (lineation) and the intermediate axes of the blades define a partial girdle about the lineation; (iii) a slight thinning and reduction in volume of grains in the one transect; and (iv) an actual increase in thickness and volume in the survivor grains of the second transect. The highest‐grade samples, within the chlorite zone of the greenschist facies, record segregation into quartz‐ and mica‐rich layers. This segregation resulted largely from F2 crenulation and marks a key change in the distribution, deformation and SPO of the quartz grains. The contribution of quartz SPO to defining the foliation lessens as the previously discrete and aligned detrital quartz grains are replaced by aggregates and layers of dynamically recrystallized quartz grains of reduced aspect ratio and reduced alignment. Pressure solution now affects the margins of quartz‐rich layers rather than individual grains. In higher‐grade samples, therefore, the rock structure is characterized increasingly by segregation layering parallel to a foliation defined predominantly by mica SPO.     

内蒙古白乃庙金矿含金石英脉LA-ICP-MS锆石U-Pb测年及其地质意义

为了厘定内蒙古白乃庙金矿床的成矿时代,对矿区主要含金石英脉中热液蚀变锆石进行了LA-ICP-MS U-Pb测年。结果表明,锆石热液蚀变特征明显,具有清晰的核—幔—边结构,锆石核、幔均为岩浆锆石或变质锆石,热液蚀变增生边呈自形—半自形结构,Th/U值集中于0.2~0.5之间,测年数据为421.4~447.6Ma,认为金矿形成时代为志留纪。从区域成矿规律分析,初步认为白乃庙金矿床的形成与早古生代古亚洲板块向华北地块强烈俯冲引起的构造—岩浆活动密切相关。     

A multi‐method approach to dating the burial and skeleton of Kiacatoo Man,New South Wales,Australia

Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd.     

Ore Genesis and Tectonic Significance of the Xiaojiashan Tungsten Deposit,Eastern Tianshan,Xinjiang, China: Evidence from Geology,Fluid Inclusions,and Stable Isotope Geochemistry

The Xiaojiashan tungsten deposit is located about 200 km northwest of Hami City, the Eastern Tianshan orogenic belt, Xinjiang, northwestern China, and is a quartz vein‐type tungsten deposit. Combined fluid inclusion microthermometry, host rock geochemistry, and H–O isotopic compositions are used to constrain the ore genesis and tectonic setting of the Xiaojiashan tungsten deposit. The orebodies occur in granite intrusions adjacent to the metamorphic crystal tuff, which consists of the second lithological section of the first Sub‐Formation of the Dananhu Formation (D₂d ₁²). Biotite granite is the most widely distributed intrusive bodies in the Xiaojiashan tungsten deposit. Altered diorite and metamorphic crystal tuff are the main surrounding rocks. The granite belongs to peraluminous A‐type granite with high potassic calc‐alkaline series, and all rocks show light Rare Earth Element (REE)‐enriched patterns. The trace element characters suggest that crystallization differentiation might even occur in the diagenetic process. The granite belongs to postcollisional extension granite, and the rocks formed in an extensional tectonic environment, which might result from magma activity in such an extensional tectonic environment. Tungsten‐bearing quartz veins are divided into gray quartz vein and white quartz veins. Based on petrography observation, fluid inclusions in both kinds of vein quartz are mainly aqueous inclusions. Microthermometry shows that gray quartz veins have 143–354°C of T_h, and white quartz veins have 154–312°C of T_h. The laser‐Raman test shows that CO₂ is found in fluid inclusions of the tungsten‐bearing quartz veins. Quadrupole mass spectrometry reveals that fluid inclusions contain major vapor‐phase contents of CO₂, H₂O. Meanwhile, fluid inclusions contain major liquid‐phase contents of Cl^?, Na⁺. It can be speculated that the ore‐forming fluid of the Xiaojiashan tungsten deposit is characterized by an H₂O–CO₂, low salinity, and H₂O–CO₂–NaCl system. The range of hydrogen and oxygen isotope compositions indicated that the ore‐forming fluids of the tungsten deposit were mainly magmatic water. The ore‐forming age of the Xiaojiashan deposit should to be ~227 Ma. During the ore‐forming process, the magmatic water had separated from magmatic intrusions, and the ore‐bearing complex was taken to a portion where tungsten‐bearing ores could be mineralized. The magmatic fluid was mixed by meteoric water in the late stage.     

微波消解-火焰原子吸收光谱法测定石英砂中的氧化钙和氧化镁

采用微波消解-硼酸络合-火焰原子吸收光谱法测定石英砂中的氧化钙和氧化镁。样品在MK-Ⅲ型实验室微波炉上消解,消解压力为2.0 MPa、消解时间为5 m in,以硼酸络合消除氢氟酸的影响。方法已用于实际样品的测定,7次测定的相对标准偏差(RSD)小于5%,加标回收率为95.0%~104.2%。     

广西珊瑚钨锡矿床成矿年代学研究及其地质意义

珊瑚钨锡矿床位于富贺钟钨锡多金属成矿集中区的中部,是南岭钨锡多金属成矿带内典型的热液石英脉型矿床之一。本文采用白云母~(40)Ar-~(39)Ar法和石英流体包裹体Rb-Sr法,对矿床V32号含矿石英脉进行精细年代学研究,获得石英脉中白云母~(40)Ar-~(39)Ar坪年龄为101.7±0.7 Ma(MSWD=0.34),正等时线年龄为102.0±1.0 Ma(MSWD=1.17);石英流体包裹体Rb-Sr等时线年龄为106.4±3.5 Ma(MSWD=0.83)。它们在误差范围内一致,是华南地区燕山晚期成岩成矿高峰期的产物。同时通过石英包裹体H-O同位素组成的初步分析,认为成矿流体属于"再平衡岩浆水",主要来自岩浆,在矿床深部可能存在隐伏花岗岩体。该成果对研究区域成矿规律,指导类似地区的找矿勘查工作具有重要意义。     

延边开山屯花岗闪长岩-石英闪长岩体年代学、地球化学特征及对古太平洋板块俯冲作用时限的制约

近年来古太平洋构造域的构造演化备受学者关注。本文报道的延边开山屯地区花岗闪长岩-石英闪长岩体LAICP-MS U-Pb年龄表明其形成时间为早侏罗世早期(198±1Ma),所采样品可根据Zr/Hf值分为高Zr/Hf值组花岗闪长岩和低Zr/Hf值组石英闪长岩。高Zr/Hf值组花岗闪长岩起源深度浅,富集Rb、Th、U、K等大离子亲石元素(LILEs),贫Nb、Ta、Ti等高场强元素(HFSEs),具壳源岩浆的特点。低Zr/Hf值组为壳源岩浆与来自深部的亏损地幔岩浆混合而成,岩石亏损Nb、Ta、Zr、Hf、Ti等高场强元素,具有典型的弧型岩浆地球化学特征。岩体中存在细粒闪长质包体,镜下可见针柱状磷灰石。开山屯岩体属钙碱性系列岩石,结合前人资料,认为其与该地区同时代火成岩组成北-东向分布的早侏罗世活动大陆边缘型火成岩带,而位于该带西侧的小兴安岭-张广才岭地区存在同时代弧后拉张带,两者构成典型的大陆弧与弧后拉张带模型,共同揭示了早侏罗世早期古太平洋板块对东北地区的俯冲作用。     

热液矿床石英铅同位素组成及其地质意义

作者以若尔盖铀矿床为例，研究了含矿热液形成的石英脉石英的铅同位素组成，并将其作为联系母源铅同位素组成的桥梁，判别铀的来源。结果表明，矿床中石英铅同位素组成与含矿黄铁矿和中酸性构造－岩浆成因的花岗岩铅同位素组成具线性演化关系。由此提出含矿热液中的铀来自中酸性构造－岩浆岩而不是地层岩石的新见解，同时提出利用热液石英铅同位素组成判别非放射性矿床成矿元素来源的可能性。     

河北小营盘石英—碳酸盐型金矿成矿地质特征

小营盘金矿赋存在稳定的缓倾斜石英脉中，但单纯的白色石英脉仅有微弱矿化，只有经过Ｓ懊断层剪切拉张破裂和叠加铁白云石化及硫化物蚀变的石英脉才能成为矿体，金矿体的顶底面常被铁白云石蚀变岩和糜棱岩所包裹，而且部分蚀变岩的金含量也达到工业品位，石英脉与蚀变岩作用构成矿体。因此，早期金成矿作用的时代大致与铁白云蚀变同期，含金铁白云石蚀变岩的δ＾１３Ｃ值平均为－４．１３‰，Ｐｂ－Ｐｂ等时线年龄为２７１１±２３８     

内蒙古迪彦庙蛇绿岩带早石炭世闪长岩成因与古亚洲洋洋内俯冲作用

由于缺少对SSZ型蛇绿岩和洋内弧火成岩的系统研究,制约了古亚洲洋东段古生代洋内俯冲过程的进一步认识。本文报道了内蒙古迪彦庙SSZ型蛇绿岩带北部新发现的巴嘎哈尔早石炭世闪长岩。LA-ICP-MS锆石U-Pb定年显示,巴嘎哈尔闪长岩的侵位年龄为324.2±1.8 Ma,其形成时代为早石炭世末期。巴嘎哈尔闪长岩SiO₂含量为57.71%～61.24%;高铝(Al₂O₃含量为15.58%～16.68%);具有相对富钠(Na₂O含量为3.29%～4.15%)、低钾(K₂O含量为1.05%～1.69%)的特征,Na₂O/K₂O比值为2.18～3.95;MgO含量较高(3.30%～4.23%),Mg^#为47.20～51.82;贫TiO₂(0.65%～0.76%)和P₂O₅(0.14%～0.15%);稀土元素总量(ΣREE为85.19×10^-6