黔北铝土矿含矿岩系的沉积时代研究

通过对黔北铝土矿含矿岩系下伏灰岩中丰富的筵类化石和含矿岩系中大量的植物化石的鉴定和研究。结合对黔北地区沉积旋回和古气候的分析,认为黔北铝土矿含矿岩系的下伏灰岩为黄龙组地层。而上覆于黄龙组之上的铝土岩系,其沉积时代应为早二叠世马平组沉积期的晚期,层位相当于Pseudoschwagerina化石带。     

Red clay deposits on the Chinese Loess Plateau during 11.0–2.6?Ma and its implications for long-term evolution of East Asian monsoon

Loess and red clay on the Chinese Loess Plateau have produced a detailed history of the East Asia monsoon for the past eight million years. Recently, a well-conserved red clay sequence was discovered at Shilou on the eastern edge of Chinese Loess Plateau, extending the monsoon history back to approximately 11 Ma. By comparing lithologic features, particle size distribution, magnetic susceptibility and deposition rate of Shilou red clay sequence, the paleomonsoon evolution from 11 to 2.6 Ma can be divided into four stages: largely fluctuated stage (11.0–8.0 Ma), relatively strengthened period (8.0–6.5 Ma), extremely changed stage (6.5–4.9 Ma) and further intensified period (4.9–2.6 Ma). The new evidence indicates that variation of paleomonsoon has close relationship with uplifting of the Tibetan Plateau and ongoing global cooling and the consequent expansion of ice sheets during 11.0–2.6 Ma.     

Zircon U–Pb ages and O–Nd isotopic composition of basement rocks in the North Qinling Terrain, central China: evidence for provenance and evolution

The Qinling Group was previously interpreted as the oldest Precambrian basement unit of the North Qinling Terrain, recording its formation and early crustal evolution. The Qinling Group consists predominantly of gneisses, amphibolites, and marbles, which underwent multi-phase deformation and metamorphism. In order to better constrain the provenance and tectonic setting of this group and the evolution of the North Qinling orogenic belt, in situ U–Pb dating and oxygen isotopic analysis of zircons in combination with whole-rock geochemistry and Sr–Nd isotope analysis was performed on the two dominant rock types, amphibolite and felsic gneiss. Felsic gneisses exhibit enrichment of LREEs and LILEs (Rb, Ba, Th, K, Pb), negative Eu anomalies and depletion of HFSEs (Nb, Ta, P, Ti). The rocks have slightly elevated δ¹⁸O values (6.5–9.3 ‰) and initial ε _Nd values of ?4.6 corresponding to two-stage Nd model age of 1.99 Ga. Amphibolites are also enriched in LILEs and LREEs and depleted in Nb and Ta and have homogeneous δ¹⁸O values (5.0–6.0 ‰), but higher initial ε _Nd values (2.8–3.3) and younger two-stage Nd model ages (1.29–1.24 Ga) compared to the gneisses. The zircon age record indicates that the gneisses and amphibolites were formed in a ~960 Ma volcanic arc environment rather than in a rift setting as previously suggested. A major metamorphic event took place during the Early Paleozoic. Based on the age spectrum of detrital zircons, the Qinling Group is interpreted as an autonomous geological unit, which was mainly derived mostly from 1,000 to 900 Ma old granitoid rocks. The North Qinling Terrain can be regarded as a remnant of the Grenville orogenic belt with an early Neoproterozoic evolution different from that of the North and South China blocks.     

塔中古溶洞见证晚奥陶世抬升幅度

塔中隆起区上奥陶统良里塔格组灰岩与桑塔木组砂—粉砂岩之间为不整合接触,昭示着这两个组沉积期之间存在一次历时约百万年的区域性构造抬升事件。中古31井良里塔格组三段的4 125.6～4 133.9 m井段为垮塌型溶洞沉积,洞顶距良里塔格组二段顶部190.6 m,溶洞中角砾状充填物主要来自良里塔格组洞壁本身的礁相灰岩,且见数厘米厚的暗河流水沉积纹层,未发现源于其它时代的颗粒混杂其间。这一事实指证了溶洞的形成和充填时代均为良里塔格组沉积之后、桑塔木组覆盖之前的晚奥陶世凯迪中期。具溶蚀力的淡水潜流带的深度一般不低于周围的海平面,由此可推断出该井区这次抬升出海平面之上的高度,即使忽略良里塔格组顶部可能经地表剥蚀的良里塔格组一段,抬升出水面部分至少也应该有190 m,藉生态地层学恢复洞壁礁灰岩沉积时的海水深度约为30 m±,因此总抬升幅度至少能达到220 m。     

青藏高原西北缘盆山过渡带陡坡地貌的形成时代与成因

平均海拔大于4500 m的青藏高原,是通过高原边缘的陡坡地貌与海拔低于1500 m的周缘盆地或平原相连接的,这些围绕高原的陡坡地貌是何时、如何形成的呢？本文通过对西昆仑山中段北缘主逆冲断层上盘陡坡地貌区9件磷灰石样品的裂变径迹年龄与长度分析表明：在海拔3900～4635 m的陡坡地貌中的裂变径迹样品年龄为6.2±1.4 Ma～0.9±0.3 Ma,呈现“上新下老”的反序分布特征; 而通过热历史模拟显示约5 Ma,约3～2 Ma,约2～1 Ma 和约1 Ma该地区出现多阶段的隆升与剥露。结合前人研究成果和野外地质的观察认为,现今青藏高原西北缘陡坡地貌的形成是中新世晚期以来高原边界叠瓦状断裂系经历了约8 Ma、约5 Ma、约3～2 Ma、约2～1 Ma和约1 Ma多阶段后展式逆冲运动的结果,这为青藏高原周缘陡坡地貌的形成和青藏高原的隆升时代与型式提供了关键的热年代学约束。     

黄河兰州谷地新构造运动的初步研究

通过分析新构造运动在黄河兰州谷地的表现,证明自上新世末以来本区新构造运动强烈,相继发生过3次主要构造事件,制约和影响黄河兰州谷地的形成、发育及环境演变。新构造运动以脉动式整体抬升和差异式断块运动的方式活动,使本区自2.4Ma以来上升约800m。由于特定的地貌位置和特殊的区域地质构造,本区新构造运动完全受制于青藏高原阶段性强烈隆起。     

内蒙古呼鲁斯太石炭纪脊椎动物化石

首次记叙了发现于内蒙古阿拉善左旗呼鲁斯大地区上石炭统土坡组上部和羊虎沟组下部的鱼类鳞片，其种类与在宁夏中卫纳缪尔期地层中发现的鱼类相似，均属古鳕类（Palaeoniscoids）；同时还记述了一枚产于土坡组上部的脊椎动物牙齿化石。     

Geochronology of the Xihuashan Tungsten Deposit in Southeastern China: Constraints from Re–Os and U–Pb Dating

Xihuashan tungsten deposit is one of the earliest explored tungsten deposits in southeastern China. It is a vein type deposit genetically associated with the Xihuashan granite pluton. Here we report new dating and zircon geochemistry results. Re–Os isotopic dating for molybdenite intergrowth with wolframite in the oldest generation of the Xihuashan pluton yielded an isochron age of 157.0 ± 2.5 Ma (2σ). Zircon U–Pb laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) dating shows that the pluton crystallized at 155.7 ± 2.2 Ma (2σ). This age is similar to the molybdenite Re–Os age for the ore deposit within error. This, together with published data, suggests that the major W(Mo)‐Sn mineralization occurred between 160–150 Ma in southeastern China. These deposits constitute a major part of the magmatic‐metallogenic belt of eastern Nanlin. The lower Re content in molybdenite of the Xihuashan tungsten deposit shows crustal origin for the ore‐forming material. The limited direct contributions from the subducting slab for the tungsten mineralization in the Nanling region suggest a change of the style of the paleo‐Pacific plate beneath southeastern China.     

水汽场初值调整及其对华南降水预报贡献的研究

该文利用GMS多通道气象卫星资料推导得到的降水资料估算出的加热率, 作为非绝热的非线性正规模初始化过程中的非绝热强迫项, 进行风压场的初值调整, 再采用一个与模式中的对流参数化方案相反的逆运算方案, 进行水汽场的初值调整.以保证初始时刻按模式的物理参数化方案计算得到的加热率与由卫星推导的加热率一致. 这一方法在非绝热的非线性正规模初值化的框架中, 使初始时刻的水汽场得到调整.既实现了传统的初始化目标, 又提高了模式对降水的短时预报效果.对华南的两个个例的试验结果表明该文的方法是有效的.     

The 2020/21 Extremely Cold Winter in China Influenced by the Synergistic Effect of La Niña and Warm Arctic

In the first half of winter 2020/21,China has experienced an extremely cold period across both northern and southern regions,with record-breaking low temperatures set in many stations of China.Meanwhile,a moderate La Ni?a event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase,just prior to the 2020/21 winter.In this report,the mid?high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere,which were forced by the negative phase of Arctic Oscillation,a strengthened Siberian High,an intensified Ural High and a deepened East Asian Trough,are considered to be the direct reason for the frequent cold surges in winter 2020/21.At the same time,the synergistic effect of the warm Arctic and the cold tropical Pacific(La Ni?a)provided an indispensable background,at a hemispheric scale,to intensify the atmospheric circulation anomalies in middle-to-high latitudes.In the end,a most recent La Ni?a prediction is provided and the on-coming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.