滇西思茅盆地景谷地区曼岗组石英颗粒表面特征及其指示意义

石英具有硬度大和化学稳定性高的特点,其颗粒表面特征能很好的反映沉积环境,通过扫描电镜观察石英表面微细特征是判别沉积环境行之有效的方法。思茅盆地白垩系曾一度被认为是陆相水成沉积,笔者通过野外识别及室内基础研究发现,景谷地区下白垩统曼岗组具有风成沉积特征,需对该套地层开展石英颗粒表面特征的系统研究来进一步确定其沉积相,研究结果表明:研究区曼岗组石英颗粒表面具有明显的风成特征,磨圆度高,普遍发育典型的蝶形撞击坑、新月形撞击坑、毛玻璃化表面,存在沙漠漆,极易与水成特征相区别;而其较强的溶蚀作用与沉淀作用则显示了当时干旱炎热的气候条件。在风成沉积确定的基础上,笔者再结合典型沉积构造,粒度分析、岩性特征等沉积特征进行综合分析,认为研究区曼岗组应属沙漠沉积。     

Improvement and Application of the Similarity Saltation Model: Wind-Tunnel Experimental Investigation and Numerical Simulation of the Vertical Sand Mass Flux Distribution in the Saltation Layer

Based upon comparisons between published experimental data and simulated results on the vertical sand flux distribution in the saltation layer, Shao’s similarity saltation model has been greatly improved by correcting the average vertical particle lift-off velocity and using a more suitable universal roughness length. By the improved model, the vertical sand flux profile over the bare, dry and loose uniform sandy surface, which is quite representative of real desert surfaces, can be reproduced very well. Meanwhile, the surface transport rate and the characteristic and average saltation heights have been simulated and analyzed in detail, disclosing their relationships with friction velocity, particle size and roughness length, and the possible underlying mechanisms. Besides, the average particle lift-off velocity and the average mean vertical aerodynamic action upon the ascending particle, which determine the saltation process, are explicitly expressed by parameters involved in the similarity model, and their relationships with friction velocity, particle size and roughness length are also described concisely. The corrected average particle lift-off velocity makes it possible to investigate the characteristic particle trajectory, whose initial velocity equals the average lift-off velocity, so as to estimate the average particle against surface impacting velocity and the average aerodynamic action upon the saltation process.     

Sedimentary records of the late Early Cretaceous compressional setting in the South China block: A case study of the Xingning Basin,Guangdong Province

Recently, some scholars have proposed that the South China Block (SCB) was controlled by a compressive tectonic regime in the middle–late Early Cretaceous, challenging the belief that the SCB was under an extensional setting during the Cretaceous. The Early Cretaceous tectonic setting constraint in the SCB can offer vital insight to clarify the Mesozoic subduction history of the Paleo-Pacific. Therefore, to determine the SCB tectonic regime during the Early Cretaceous, this study investigated sedimentary rocks from the Lower Cretaceous Heshui Formation in the Xingning Basin, a foreland basin located in the southeastern SCB. Provenance analysis was performed using sandstone modal analysis, sandstone geochemical characteristics, and detrital zircon geochronology. Based on the results, we discussed basin sediment sources and the SCB tectonic regime during the Early Cretaceous. The results showed that the maximum Heshui Formation depositional age was 103 Ma ± 1.6 Ma in the Early Cretaceous Albian. Detrital framework modes and geochemical characteristics of sandstone indicated that Heshui Formation's source rocks were granites and sedimentary rocks. The detrital zircon U–Pb ages could be classified into two major and four subordinate age populations. The Wuyi Terrane to the north and southeast coastal regions to the east were the primary potential Heshui Formation source areas. However, the lower and upper sandstones are different in the peak ages, ~437 and ~146 to 104 Ma, respectively, indicating that the major source area shifted from the Wuyi Terrane to the southeastern coastal regions during the late Early Cretaceous. The sandstone modal analysis results indicated that the source area comprised mainly collisional–orogenic material. The SCB was under a compressive tectonic regime during the late Early Cretaceous and this compression action continued until at least 103 Ma ± 1.6 Ma.     

二连盆地中部白垩系赛汉组碎屑锆石U-Pb年代学及地质意义

正砂岩型铀矿是世界上最重要的铀矿床类型,亦是我国铀矿勘查的主攻方向。二连盆地位于中亚造山带,是我国北方砂岩型铀矿的主攻和重点突破地区。近年来,随着找矿勘查工作的深入,在盆地中部先后发现了巴彦乌拉、赛汉高毕和哈达图等多个古河道型砂岩型铀矿床,实现了铀矿找矿的重大突破(张金带,2016)。这些矿床产于盆地中部,主     

Sedimentary and drainage evolution of the Condamine Valley Transition Zone (eastern Australia)

The basal succession of the Condamine Valley, which overlays the boundary between the Surat and Clarence-Moreton basins (eastern Australia), contains a clay-rich horizon ‘the Transition Zone’ that marks a pronounced unconformity between the Jurassic Walloon Coal Measures and the Quaternary Condamine Alluvium. This paper provides insights into the tectonic and drainage evolution of the Condamine Valley through integrated analysis of U–Pb ages of detrital zircon from three samples (494 concordant analyses), stable oxygen isotope analysis on eight authigenic clay samples, X-ray fluorescence of primary and trace elements, and hyperspectral mineral analysis from two drill cores (Lone Pine 17 and Daandine 164). The Transition Zone is interpreted to consist of both weathered Jurassic sediments and Cenozoic clay deposits. Two sequential cycles of erosion, deposition and pedogenesis, related to geomorphological and climatic conditions are recognised. Distinctive oxygen isotope signatures of the two weathering fronts demonstrated an initial Early Cretaceous phase (δ¹⁸O?=?11.9–15.7‰ VSMOW) associated with laterisation and possible uplift, followed by Paleogene (δ¹⁸O?=?16.4–17.3‰ VSMOW) silcretisation of reworked Jurassic sediments. Detrital zircon geochronology yielded Jurassic maximum constraints for the age of deposition of three samples that are indistinguishable within error, the oldest of which (163?±?8?Ma from the lateritic profile) corresponds to the age of the underlying Walloon Coal Measures. The two overlaying samples from a silcrete profile and granular alluvium yielded overlapping yet younger ages of 150?±?6?Ma and 156?±?9?Ma, respectively. Vitrinite reflectance used as a proxy for the thermal condition of the coal strata enabled an estimated 2–3?km of burial and subsequent (likely Early Cretaceous) uplift. Geochemical insights from the Condamine Valley correspond to broad-scale climatic and tectonic conditions, suggesting that ‘transition zone equivalents’ and corresponding groundwater dynamics may occur in similar sedimentary settings throughout eastern Australia.     

Growth and provenance of a Paleozoic subduction complex in the Broken River Province,Mossman Orogen: evidence from detrital zircon ages

A Paleozoic subduction complex dominates the Mossman Orogen developed at the northern extremity of the Tasmanides, eastern Australia. Its southern part, displayed in the Broken River Province, is characterised by dismembered ocean-plate stratigraphy in which turbidite-dominated packages and widespread tectonic mélange development are characteristic. The Broken River complex is characterised by formations with quartzose sandstone alternating with those largely formed of sandstone of more labile character. The two compositional groups are considered to reflect separate, age-significant sedimentary regimes, but their ages have hitherto been poorly constrained. With the use of 1082 concordant detrital zircon ages from 13 samples we provide age control for the complex and track its sedimentary provenance. Of quartzose units, the Tribute Hills Arenite and Pelican Range Formation are late Cambrian–Early Ordovician, and the Wairuna Formation is Middle to Late Ordovician, in age. The more labile units (Greenvale, Perry Creek and Kangaroo Hills formations) are collectively of late Silurian–mid-Devonian age. Development of the complex spanned some 130 Myr. Continent-derived sediment involved in accretion of much the complex, from mid-Ordovician to mid-Devonian, was largely sourced from a nearby magmatic arc of late Cambrian–Devonian age, now represented by granitoid plutons of the Macrossan and Pama igneous associations. An older far-field Pacific-Gondwana sediment source is characteristic of early-phase (late Cambrian–Early Ordovician) accretion, in common with sedimentary units of this age generally developed in the Tasmanides. We consider the complex to have grown largely by underplating that positioned younger components beneath those that are older, with out-of-sequence thrust interleaving of these components occurring late in the accretionary history. A Late Devonian contractional folding and cleavage development (Tabberabberan orogenesis) is uniformly expressed across the entire complex and reflects an abrupt change in plate engagement with imposition of a compressional stress regime.     

中天山基底与塔里木克拉通的构造亲缘性

中天山基底与塔里木克拉通的构造亲缘性问题涉及中亚大地构造单元的划分,倍受学术界关注.在诸多学者的研究基础上,特别是塔里木北缘物质成分和年代学成果基础上,通过区域地质调查,对托克逊县干沟与和静县阿拉沟两地的前南华纪地层序列及其岩石组合进行了专门研究,并筛选出4件浅变质砂岩样品做碎屑锆石U-Pb测年研究,获得165组年龄数据.结果表明,发育在中天山地区的前南华纪地层序列、岩石组合、地层接触关系、沉积环境与塔里木北缘的基本一致,可比性好,揭示了二者之间密切的构造亲缘性.其Th/U比值密集分布在0.4～4.0,表明岩浆锆石占绝大多数.锆石U-Pb测年产生了4个年龄峰值,分别为950Ma、1 550Ma、1 920Ma和2 480Ma,表明中天山较好地保存了元古代的4次重大构造-岩浆活动信息.这些年龄峰值在塔里木陆块均有对应岩浆体的发育,也与塔里木周缘的前寒武纪年龄谱吻合,进一步佐证了中天山基底与塔里木克拉通曾经是一个统一块体的认识.结合区域构造分析,认为中天山陆块是在南华纪以来,逐渐从塔里木克拉通拉张裂离出来的;伴随早古生代天山洋的俯冲,一个奥陶纪-志留纪火山弧发育在这个裂离的中天山陆块之上.     

扬子板块西北缘早中泥盆世构造演化：来自略阳地区踏坡组岩石学、锆石年代学和微量元素组成的约束

碧口地块北缘下中泥盆统踏坡组的物源长期被认为来自碧口地块新元古界基底——碧口岩群,但一直缺少碎屑锆石物源数据的支持。本文对略阳地区泥盆系踏坡组不同层位的3个碎屑岩样品开展了系统的岩石学、锆石岩相学及其U-Pb定年和微量元素组成研究。锆石晶体特征对比分析显示,研究样品存在两种类型的锆石:普遍发育变质增生边的碎屑锆石(剖面北段样品)和不发育变质增生边的典型岩浆成因的碎屑锆石(剖面南、中段样品)。前者显示2个年龄峰值(～2.5 Ga主峰、～2.0 Ga次峰),还形成了2473±24 Ma的上交点年龄和359±84 Ma的下交点年龄,而后者两个样品有着一致的年龄峰值(～2.0 Ga主峰、～2.5 Ga次峰和～1.39 Ga微小峰值)。3个样品的谐和年龄均大于1.3 Ga,并不能限定踏坡组的沉积时代,且均不支持其物源主要来自碧口岩群的传统认识。碎屑锆石地球化学判别图解指示它们的源岩主要为形成于造山带环境中的花岗岩类(花岗闪长岩和英云闪长岩)、基性岩和钾镁煌斑岩。基于样品中的岩屑类型,结合区域地质、古流向、锆石年龄对比和源岩判别,认为踏坡组的原始物源来自位于扬子板块北缘的太古宙—古元古代基底(鱼洞子杂岩和崆岭杂岩),并且鱼洞子杂岩在踏坡组沉积后期曾大面积出露/抬升。同时表明碧口地块可能至少在早中泥盆世就与扬子板块拼合在一起了。     

上扬子西南缘早三叠世嘉陵江组物源分析和构造环境:沉积学、重矿物电子探针和U- Pb年龄的限定

上扬子西南缘地区广泛分布峨眉山玄武岩,受其影响在中带金阳和外带荥经地区嘉陵江组发育滨岸和潮坪环境沉积物。本文在交错层理恢复的物源方向基础上,根据重矿物组成、重矿物电子探针和碎屑锆石测年结果,综合分析不同区域嘉陵江组物源区,进而探讨嘉陵江组形成的构造环境。嘉陵江组砂岩碎屑重矿物锆石、磷灰石、铬尖晶石等指示物源主要来自于岩浆岩,且自中带至外带基性岩浆岩所占比重逐渐减少。电气石电子探针分析显示,二者物源主要来自于贫锂花岗岩和变质砂岩、板岩。铬尖晶石显示,金阳地区物源来自峨眉山玄武岩和洋岛岩浆岩类岩石,荥经物源主要来自洋岛岩浆岩类岩石,个别为峨眉山玄武岩。碎屑锆石表明,嘉陵江组物源主要来自于新元古代岩浆岩和晚二叠世峨眉山玄武岩,前者经历再搬运。综合物源分析表明,嘉陵江组物源主要来自康滇古陆,岩石类型主要为峨眉山玄武岩和砂岩等。沉积序列和物源分析表明,嘉陵江组反映了沉积物蚀顶过程。结合地震资料、大火成岩省的分析成果表明,嘉陵江组形成于火山型裂谷边缘。     

河北赞皇杂岩官都群碎屑沉积岩锆石SHRIMPU-Pb定年及其地质意义

新太古代—古元古代表壳岩系在华北克拉通广泛发育,在赞皇地区也出露有较典型的中低级变质的火山-沉积岩系,即从原赞皇群解体出来的官都群,其形成时代和成因目前仍有争议。官都群的主要岩石组合为变基性火山岩(包括角闪片岩和斜长角闪岩)、大理岩、石英片岩,以及一系列长英质副片麻岩等。对其中的长英质副片麻岩进行碎屑锆石定年研究,并结合前人已报道的碎屑锆石数据可知,碎屑锆石年龄主要峰值约为2.5Ga,部分样品出现2.0～2.2Ga的峰值。变质锆石记录主要有2个范围,分别为2.48Ga左右和1.85～1.9Ga,可能代表了2期不同的构造热事件记录。结合该地区近年来的研究,可以得到如下认识:(1)样品中存在形态完好的长柱状锆石,表明是近源沉积;(2)约2.48Ga的变质记录与核部岩浆锆石的年龄(约2.5Ga)非常接近,可能代表了物源区中酸性岩体侵位后遭受的一次构造热事件,而不代表沉积岩形成后遭受变质的记录,即沉积过程晚于2.48Ga;(3)官都群至少有一部分岩石组合形成于古元古代;(4)官都群可能是不同时代、不同岩性单元拼贴而成,需要进一步解体。