Research achievements of the Qinghai-Tibet Plateau based on 60 years of aeromagnetic surveys

The Qinghai-Tibet Plateau (also referred to as the Plateau) has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources. This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements, which mainly include the followings. (1) The boundaries between the Plateau and its surrounding regions have been clarified. In detail, its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan (Wudu)-Kangding Fault. Meanwhile, the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary. (2) The Plateau is mainly composed of four orogens that were stitched together, namely East Kunlun-Qilian, Hoh-Xil-Songpan, Chamdo-Southwestern Sanjiang (Nujiang, Lancang, and Jinsha rivers in southeastern China), and Gangdese-Himalaya orogens. (3) The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks. Therefore, it exhibits the characteristics of unstable orogenic basement. (4) The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones. Therefore, it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice. (5) A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau, indicating a giant deep thermal-tectonic zone. (6) A dual-layer magnetic structure has been revealed in the Plateau. It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending. They overlap vertically and cross horizontally, showing the flyover-type geological structure of the Plateau. (7) A group of NW-trending faults occur in eastern Tibet, which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet. (8) As for the central uplift zone that occurs through the Qiangtang Basin, its metamorphic basement tends to gradually descend from west to east, showing the form of steps. The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it. The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west. The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas. Up to now, 19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin. (9) A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing (or mineralization) anomalies have been discovered. Additionally, the formation and uplift mechanism of the Plateau are briefly discussed in this paper.©2021 China Geology Editorial Office.     

川南柏香田地区早志留世石牛栏组风暴沉积的发现及意义

通过野外实测剖面和镜下薄片观察,于通过野外实测剖面和镜下薄片观察,在川南柏香田剖面早志留世石牛栏组下部发现一套风暴沉积,具有侵蚀底面、砾屑层、粒序层理、丘-洼状交错层理、沙纹层理以及风暴与平静天气形成的沉积物互层等风暴沉积特征。理想风暴沉积序列由6个沉积单元组成,根据剖面不同沉积单元间的排列组合,将其划分为4种风暴沉积序列,各序列间存在一定继承性,由下向上表现为远源型风暴向近源型风暴的转变、风暴强度逐渐增强的过程。结合更靠扬子东南缘的深水剖面重力流沉积的缺乏,可以推断早志留世石牛栏期研究区的沉积模式为碳酸盐缓坡。结合风暴的形成机制以及石牛栏组风暴沉积的发育特征可知（尤其是正粒序层理和典型丘状交错层理）：研究区早志留世处于中低纬度的古地理位置,可为上扬子区古气候及古扬子海盆演化提供依据;上扬子区早志留世同期异相地层存有争议,风暴沉积特征为石牛栏组、小河坝组、罗惹坪组等地层提供等时性对比标尺;川南早志留世石牛栏组沉积环境意见不一,风暴沉积为其碳酸盐岩缓坡环境提供证据资料。通过总结前人对风暴岩物性认识,结合上扬子区同期地层油气地质条件,可提供油气勘探新途径。川南柏香田剖面早志留世石牛栏组下部发现一套风暴沉积,发育侵蚀底面、砾屑层、粒序层理、丘-洼状交错层理、沙纹层理以及风暴与平静天气形成的沉积物互层等风暴沉积特征。理想风暴沉积序列由6个沉积单元组成,根据剖面不同沉积单元间的排列组合,将其划分为4种风暴沉积序列,各序列间存在一定继承性,由下向上表现为远源型风暴向近源型风暴的转变、风暴强度逐渐增强的过程。结合更靠扬子东南缘的深水剖面中重力流沉积的缺乏,可以推断早志留世石牛栏期研究区的沉积模式为碳酸盐缓坡。结合风暴的形成机制以及石牛栏组风暴沉积的发育特征可知（尤其是正粒序层理和典型丘状交错层理）：研究区早志留世存于中低纬度的古地理位置,可为上扬子区古气候及古扬子海盆演化提供依据;上扬子区早志留世同期异相地层存有争议,风暴沉积特征为石牛栏组、小河坝组、罗惹坪组等地层提供等时性对比标尺;川南早志留世石牛栏组沉积环境意见不一,风暴沉积为其碳酸盐岩缓坡环境提供证据资料;总结前人对风暴岩物性认识,结合上扬子区同期地层油气地质条件,提供油气勘探新途径。     

青藏高原东缘湖相沉积和黄土高原黄土沉积磁化率与粒度相关性对比*

为探讨构造稳定地区(如黄土高原)和构造活跃地区(如青藏高原东缘)粉尘沉积物中磁化率(SUS)与粒度的相关性及其对环境事件的指示意义,本次研究分析了黄土高原蓝田剖面黄土—古土壤样品和青藏高原东缘湖相沉积样品的粒度和磁化率记录。黄土高原黄土—古土壤沉积SUS与2~10 μm粒度组分最强正相关,青藏高原东缘湖相沉积的SUS与2~10 μm粒度组分最强负相关,反映2~10 μm粒度组分为黄土高原和青藏高原乃至亚洲干旱—半干旱地区连续稳定敏感的背景沉积组分。黄土高原黄土—古土壤沉积的SUS与32~63 μm粒度组分最强负相关,青藏高原东缘湖相沉积的SUS与32~63 μm粒度组分最强正相关,反映32~63 μm粒度组分不仅是黄土高原尘暴事件沉积的敏感指标,也是青藏高原东缘湖相沉积记录的地震事件敏感指标。SUS与粒度组分的相关性在青藏高原东缘地区地震事件层开始部分高于结束部分,也较好地反映地震事件为研究区添加新鲜沉积物后随地形地貌恢复逐步减少的过程。SUS与粒度组分相关性也受当地物源的影响。     

Estimation of hydraulic permeability considering the micro morphology of rocks of the borehole YAXCOPOIL-1 (Impact crater Chicxulub,Mexico)

Internal surface, formation factor, Nuclear Magnetic Resonance (NMR)-T2 relaxation times and pore radius distributions were measured on representative core samples for the estimation of hydraulic permeability. Permeability is estimated using various versions of the classic Kozeny–Carman-equation (K–C) and a further development of K–C, the fractal PaRiS-model, taking into account the internal surface. In addition to grain and pore size distribution, directly connected to permeability, internal surface reflects the internal structure (“micro morphology”). Lithologies could be grouped with respect to differences in internal surface. Most melt rich impact breccia lithologies exhibit large internal surfaces, while Tertiary post-impact sediments and Cretaceous lithologies in displaced megablocks display smaller internal surfaces. Investigations with scanning electron microscopy confirm the correlation between internal surface and micro morphology. In addition to different versions of K–C, estimations by means of NMR, pore radius distributions and some gas permeability measurements serve for cross-checking and calibration. In general, the different estimations from the independent methods and the measurements are in satisfactory accordance. For Tertiary limestones and Suevites bulk with very high porosities (up to 35%) permeabilites between 10⁻¹⁴ and 10⁻¹⁶ m² are found, whereas in lower Suevite, Cretaceous anhydrites and dolomites, bulk permeabilites are between 10⁻¹⁵ and 10⁻²³ m².     

江苏镇江韦岗铁矿区深部找矿前景分析

镇江韦岗铁矿是一个已经勘查开发数十年的老矿山,目前保有资源储量保证程度已达严重危机。分析矿区成矿地质条件和矿床特征,铁矿体主要分布在碳酸盐岩层与中酸性侵入岩的接触带上,铁矿体普遍磁性强,且在地表形成一定规模的磁异常,梯度北陡南缓,向南有规则地递减呈梯形散开,说明矿体有一定的延伸。深部已施工的见矿钻孔和井中磁测异常对应,反映矿区深部-200m～-800m找矿前景良好。     

基于氮气吸附-核磁共振-氩离子抛光场发射扫描电镜研究川西须五段泥质岩储层孔隙结构

微观孔隙作为泥质岩的有效储集空间,其孔隙结构参数是作为气藏评价及资源量估算的重要依据。本文应用氮气吸附法(NAM)、核磁共振法(NMR)、氩离子抛光及场发射扫描电镜(AIP-FESEM)研究川西须五段泥质岩微观孔隙特征,结果表明:1氩离子抛光及场发射扫描电镜在表征微观孔隙形态与类别时有一定优势,但定量表征孔隙参数时,受图像二值化阈值的影响,表征结果偏差较大,可结合氮气吸附法来定量表征其孔径大小;2核磁共振受岩石骨架影响小,能够更精细反映岩石的物性条件,可定量计算孔隙度与可动流体饱和度,但对样品的孔隙形态反映较差;3综合上述三种方法,在须五段泥质岩中可识别出一定量的纳米级中、大孔,孔径大多介于几十纳米到几百纳米之间,孔隙连通性差,孔隙度主要介于2.3%~7.4%之间,孔隙类型以粒间孔、晶间孔最发育,有机孔隙、微裂缝次之,粒内孔隙最不发育。总体而言,融合了三种技术方法能更精确、更全面地反映泥质岩孔隙结构特征,能得到更完善的储层孔隙结构参数,在定量表征泥质岩孔隙结构中具有广泛的应用前景。     

Depositional processes on oceanic island shelves – Evidence from storm‐generated Neogene deposits from the mid‐North Atlantic

Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands.     

Maximum Storm Surge Curve Due to Global Warming for the European North Sea Region During the 20th–21st Century

Computations of storm surges during the 20th century needs to incorporate globalwarming of about 0.6 °C ± 0.2 °C (IPCC, 2001). In order totake this global warming into consideration, the development of all storm surgesoccurred during the 20th century have been analysed. The study comprises determiningto what degree the storm surge curve and storm surge level depend on each other. Thisfact can be used to calculate a maximum storm surge curve and each single storm surgeevent can be summarised. The tendency of the surge and wind parameters do not showthat this maximum storm surge levels in the 20th century will occur earlier than predicted, however, the global warming of 0.6 °C will extend the duration of the mean storm surge curve.     

基于参考线圈和变步长自适应的磁共振信号噪声压制方法

核磁共振地下水探测仪的灵敏度高,接收到的纳伏级磁共振探测信号极易受到强工频谐波噪声的干扰,导致信号特征参数提取的准确度降低,影响反演解释的水文地质参数结果.为了解决这一难题,基于相关抵消的原理,针对全波磁共振信号,设计带有参考线圈的90°移相自适应噪声抵消系统,理论计算了参考线圈相对于探测线圈的距离,提出变步长LMS算法进行噪声压制.仿真结果表明,在不同的信号强度及不同的信噪比下,当信号与工频谐波干扰频谱不重合时,采用设计的自适应噪声抵消系统和变步长算法,信噪比可以提高到5.94 dB以上,初始振幅、弛豫时间特征参数的拟合误差在2.8%以内;当信号与工频谐波干扰频谱重合时,采用双向自适应滤波算法,信噪比可以达到5dB以上,初始振幅、弛豫时间特征参数的拟合误差在10%以内,可以满足实际应用的要求;实测数据处理进一步证明了方法的有效性.     

沙粒不能“远走高飞”———有关“尘暴”的一条根本原理

沙与尘虽然都是岩石物理风化的产物, 但在风力作用下, 习性截然不同。拜格诺用严格的物理实验证明, 尘粒能随风远走高飞, 而沙粒却只能在地面附近跳跃前进。从北方侵袭华北平原的所谓沙尘暴, 实质上都是尘暴。对历次重大天气事件沉积物的分析, 也完全证明了这一点。因此, 尘暴物质的源头不是来自有沙, 而是有尘的地方; 从而可以使人们采取正确的治理方法。