Mosaic desert pavement influences water infiltration and vegetation distribution on fluvial fan surfaces

Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content, gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (i_int), steady-state infiltration rate (i_sat) and infiltration time (T) averaged 1.19 cm/min^-0.5, 0.64 cm/min, 0.13 cm/min and 12.76 min, respectively. Where the pavement layer was scalped, the S, i_int, and i_sat increased by 0.27 cm/min^-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+) and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions.     

Mantle dynamics of the Paleoproterozoic North China Craton: A perspective based on seismic tomography

We investigate the mantle dynamics beneath the North China Craton (NCC) and surrounding regions based on a synthesis of recent P-wave mantle tomographic data down to depths of 600–800 km and their correlation with the surface geological features, with particular reference to the Paleoproterozoic tectonic events associated with the incorporation of the NCC within the Columbia supercontinent amalgam. From the tomographic images, we identify a hot corridor in the mantle transition zone beneath the central region of the Western Block of the NCC sandwiched between two cold corridors. This scenario is similar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomaly in the lowermost mantle under the Pacific and suggests that the cold regions might represent slab graveyards which provide the fuel for the plumes rising from the center. A tomographic transect along the collisional suture of the NCC with the Columbia supercontinent, covering the Yinshan-Ordos Blocks in the Western Block through the Central Orogenic Belt and into the Eastern Block of the NCC reveals a ca. 250 km thick lithospheric keel below the Ordos Block defined by a prominent high-velocity anomaly. We identify slab break-off and asthenospheric upwelling in this region and suggest that this process probably initiated the thermal and material erosion of the tectosphere beneath the Eastern Block from the Paleoproterozoic, which was further intensified during the Mesozoic when a substantial part of the sub-continental mantle lithosphere was lost. We visualize heat input from asthenosphere and interaction between asthenosphere and overlying carbonated tectosphere releasing CO₂-rich fluids for the preservation of ultra-high temperature (ca. 1000 °C) metamorphic rocks enriched in CO₂ as well as high-pressure mafic granulites as a paired suite in this region. We also identify a hot swell of the asthenosphere rooted to more than 200 km depth and reaching up to the shallow mantle in the tomographic section along 35°N latitude at a depth of 800 km. This zone represents a cross-section through the southern part of the NCC. The surface distribution of Paleoproterozoic Xiong’er lavas and mafic dykes in this region would indicate that this region might have evidenced similar upwellings in the past. Our study has important implications in understanding the evolution of the NCC and suggests that the extensive modification of the mantle architecture and lithospheric structure beneath one of the fundamental Precambrian nuclei of Asia had a prolonged history probably dating from the Paleoproterozoic suturing of the NCC within the Columbia supercontinent amalgam.     

Theoretical analyses of acidization dissolution front instability in fluid‐saturated carbonate rocks

This paper presents an instability theory that can be used to understand the fundamental behavior of an acidization dissolution front when it propagates in fluid‐saturated carbonate rocks. The proposed theory includes two fundamental concepts, namely the intrinsic time and length of an acidization dissolution system, and a theoretical criterion that involves the comparison of the Zhao number and its critical value of the acidization dissolution system. The intrinsic time is used to determine the time scale at which the acidization dissolution front is formed, while the intrinsic length is used to determine the length scale at which the instability of the acidization dissolution front can be initiated. Under the assumption that the acidization dissolution reaction is a fast process, the critical Zhao number, which is used to assess the instability likelihood of an acidization dissolution front propagating in fluid‐saturated carbonate rocks, has been derived in a strictly mathematical manner. Based on the proposed instability theory of a propagating acidization dissolution front, it has been theoretically recognized that: (i) the increase of the mineral dissolution ratio can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (ii) the increase of the final porosity of the carbonate rock can destabilize the acidization dissolution front, while the increase of the initial porosity can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (iii) the increase of the mineral dissolution ratio can cause an increase in the dimensionless propagation speed of the acidization dissolution front; (iv) the increase of the initial porosity can enable the acidization dissolution front to propagate faster, while the increase of the final porosity can enable the acidization dissolution front to propagate slower in the acidization dissolution system. Copyright © 2012 John Wiley & Sons, Ltd.     

Storm Deposits of the Sinian Zhangqu Formation in Northern Anhui — An Upward Shallowing Carbonate Sequence1

Abstract This paper studies, for the first time, the storm deposits of a carbonate sequence in the Sinian Zhangqu Formation in northern Anhui. In the formation, a great number of calcareous trider sponge spicules were discovered in a distal storm turbidity sequence, which have provided further evidence for the correlation of the Sinian Systems in North and South China from a view point of palaeontology.     

JCXA——733型电子探针快速半定量分析程序

在近代科学技术发展前缘之一的微束分析中,电子探针X射线显微分析仪是目前相当活跃的微区微量物质成份分析的设备.六十年代初期,电子探针开始被应用于地质领域进行矿物成份分析,至今它已成为矿物岩石学,地球化学、矿床综合评价及综合利用等众多科研课题研究的重要手段.我们使用的JCXA-733型电子探针装配的是美国DEC公司PDF-11型电子计算机,RX02双软盘驱动装置、LA-36型宽行打字机,RT-1l操作系统     

岩溶在古地理研究中的作用——“关于古地理研究中若干原则问题的商榷”一文的补充及讨论

本文从现代、地史时期岩溶剥蚀速度及岩溶铝土矿的形成等方面探讨岩溶在古地理研究中的重大作用,从而提出稳定地区“缺失”某一时期地层,并非该时期为陆;而是前期仍有沉积,后期才真正上升为陆,遭受剥蚀。     

湘西南采金“信”的地质解释

在湘西南民间开采脉金的活动中,人们积累了很多识别金富集的标志,简称“信”。本文收集列举了25种“信”,并相应地作了地质解释,评估了含金情况。从金的地球化学特性,论述了“信”与金富集的内在联系。     

焦耳效应标定高温卡尔维微量热计

根据热流式量热计的Tian氏方程,用焦耳效应标定高温卡尔维微量热计。用偏差法得到的灵敏度值与积分法测得的值一致。用回归曲线对灵敏度实验值进行拟合,利用计算机求得灵敏度—温度回归曲线,得到了室温至700℃的全部灵敏度值,从而即可使用微量热计测量此温度范围内的未知样品热效应。     

北京市区冬季大气气溶胶空气动力学尺度谱分布的研究

本文讨论了北京市区冬季大气气溶胶空气动力学尺度的各种谱分布,发现平均粒子谱为单峰型,而平均表面积谱和平均质量谱则通常为三峰型。但是,表面积谱和质量谱随时间变化明显。 三峰型质量谱与国外给出的城市双峰型质量谱差别显著,揭示了我国目前城市气溶胶污染所具有的一种带普遍性的重要特性。     

5—10月全球热带和副热带200hPa多年平均环流的研究(一)——行星尺度环流系统

本文用近13年200hPa高空风资料得到了夏半年(5—10月)逐月平均全球热带风场,发现如下一些主要结果: (1)在亚洲地区对流层上部反气旋存在两个中心;一个在青藏高原上空;一个在伊朗和阿富汗地区。两者的演变不同。伊朗高压的北推和撤退都比青藏高原上的早。北美墨西哥高压的变化在时间上与伊朗高压很相似。 (2)北太平洋中部高空槽(TUTT)出现在5—10月,8月份最强,位置最北;北大西洋中部高空槽出现在5—9月,7—8月最强。 (3)南半球冬季有三个主要的长波脊和长波槽,分别位于大陆以西和以东海区。