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    1. 深地震反射剖面揭露青藏高原陆-陆碰撞与地壳生长的深部过程
    GAO Rui, ZHOU Hui, GUO Xiaoyu, LU Zhanwu, LI Wenhui, WANG Haiyan, LI Hongqiang, XIONG Xiaosong, HUANG Xingfu, XU Xiao
    地学前缘    2021, 28 (5): 320-336.   DOI: 10.13745/j.esf.sf.2021.8.10
    摘要157)   HTML25)    PDF(pc) (14121KB)(315)    收藏

    印度板块与亚洲板块的碰撞使喜马拉雅-青藏高原隆升,地壳增厚和生长扩展。探测青藏高原深部结构,揭露两个大陆如何碰撞,碰撞如何使大陆变形的过程,是全球关切的科学奥秘。深地震反射剖面探测是打开这个科学奥秘的最有效途径之一。20多年来,运用这项高技术探测到青藏高原巨厚地壳的精细结构,攻克了难以得到下地壳和Moho清晰结构的技术瓶颈,揭露了陆陆碰撞过程。本文在探测研究成果基础上,从青藏高原南北-东西对比,再到高原腹地,系统地综述了青藏高原之下印度板块与亚洲板块碰撞-俯冲的深部行为。印度地壳在高原南缘俯冲在喜马拉雅造山带之下,亚洲板块的阿拉善地块岩石圈在北缘向祁连山下俯冲,祁连山地壳向外扩展,塔里木地块与高原西缘的西昆仑发生面对面的碰撞,在高原东缘发现龙日坝断裂而不是龙门山断裂是扬子板块的西缘边界,高原腹地Moho 薄而平坦,岩石圈伸展垮塌。多条深反射剖面揭露了在雅鲁藏布江缝合带下印度板块与亚洲板块碰撞的行为,印度地壳不仅沿雅鲁藏布江缝合带存在由西向东的俯冲角度变化,而且其向北行进到拉萨地体内部的位置也不同。在缝合带中部,显示印度地壳上地壳与下地壳拆离,上地壳向北仰冲,下地壳向北俯冲,并在俯冲过程发生物质的回返与构造叠置,使印度地壳减薄,喜马拉雅地壳加厚。俯冲印度地壳前缘与亚洲地壳碰撞后沉入地幔,处于亚洲板块前缘的冈底斯岩基与特提斯喜马拉雅近于直立碰撞,冈底斯下地壳呈部分熔融状态,近乎透明的弱反射和局部出现的亮点反射,以及近于平的Moho都反映出亚洲板块南缘的伸展构造环境。

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    2. 俄罗斯-蒙古地学断面地壳模型的地质-地球物理资料综合研究
    Evgeny Kh. TURUTANOV, Evgeny V. SKLYAROV, Valentina V. MORDVINOVA, Anatoly M. MAZUKABZOV, Viktor S. KANAYKIN
    地学前缘    2021, 28 (5): 260-282.   DOI: 10.13745/j.esf.sf.2021.3.10
    摘要879)   HTML15)    PDF(pc) (7300KB)(116)    收藏

    地学断面是指地壳的垂直剖面,主要通过对地质和地球物理资料的综合分析来揭示构造带的性质及其空间关系。横断面的研究所采用的数据基本包括100 km宽区域地质图、上地壳的地质剖面图、重磁图(沿横断面的重磁剖面图)以及地壳的地震波速度、密度和其他地球物理属性的剖面图。这些数据被用于构建综合的数据剖面图(结果图),以展示各种地球动力学条件下(裂谷、海洋、碰撞带、造山盆地、大陆地台和岩浆弧,包括安第斯岛弧、活动大陆边缘、海沟、弧前和弧后盆地)的特定的岩石组构。本项目的研究目标是根据研究区现存的地质和地球物理数据的综合解释,统一图例,建立研究区深部剖面,以确定地体的空间关系及其在板块构造方面的地球动力学性质。
    前人已分别对东西伯利亚南部和蒙古境内的多个地体进行了构造划分,并对它们的地球动力学性质和时空关系进行了分析。研究结果显示该系列地体为早古生代、中晚古生代和晚古生代—早中生代的岛弧和微大陆。此外,研究还识别出了中—晚古生代和晚古生代—早中生代安第斯型活动大陆边缘、晚古生代—早中生代被动大陆边缘和早白垩世裂谷。与岛弧和安第斯型活动大陆边缘相关的岩体被推覆至相邻大陆和微陆块上,部分推覆宽度可达150 km。目前已开展泥盆纪到晚侏罗世时期蒙古-鄂霍次克海地区的古地球动力学重建。
    “非地槽”型花岗岩类岩浆作用在板块构造方面找到了直接且合理的解释,其中泥盆纪—石炭纪和二叠纪—三叠纪岩浆作用区域对应于安第斯型活动大陆边缘,中—晚侏罗世岩浆作用则与西伯利亚/蒙古-中国大陆板块碰撞有关。碰撞岩浆作用中亚碱性(地幔)元素的存在及其所在的构造区域在很大程度可以说明蒙古-鄂霍次克海闭合后,巨厚大陆岩石圈下曾经发生过持续的大洋裂谷活动(地幔热点)。在早白垩世时期,大陆裂谷活动影响到了同一时期正在发生的大陆汇聚作用。
    西伯利亚南部边界大部分具有安第斯型活动大陆边缘性质,这也是蒙古—鄂霍次克缝合线沿线蛇绿岩数量较少的原因。因为当汇聚大陆一个具有安第斯类型的活动边缘,而另一个具有被动边缘时,前者的大陆地壳会最终逆冲到后者之上,并因此破坏掉先前出露的蛇绿杂岩体。部分被破坏的蛇绿岩块是俯冲带保留下来的海山残余,其可能成为增生-俯冲楔体的混沌复合体的一部分。然而,由于快速俯冲作用,这种楔形体在晚二叠世—早侏罗世的积累并不是西伯利亚活动边缘的典型特征。
    沿地学断面综合的地质和地球物理资料分析表明,亚洲大陆是在显生宙时期由部分前寒武纪微陆块构造拼贴而成的。前寒武纪地块间存在不同宽度的已变形且剥蚀强烈的显生宙火山弧,它们也被归类为特定地体。

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    3. Natural mineral photoelectric effect: mineral non-classical photosynthesis
    LU Anhuai, LI Yan, DING Hongrui, WANG Changqiu, XU Xiaoming, LIU Feifei, LIU Yuw
    地学前缘    2020, 27 (5): 300-.   DOI: 10.13745/j.esf.sf.2020.12.3
    摘要203)      PDF(pc) (1024KB)(119)    收藏
    Under the ever-present solar radiation, photosynthetic organisms on Earth evolved structurally-sophisticated photosynthetic systems. However, little attention has been paid to the inherent impact of sunlight illumination on the inorganic minerals widespread on the Earth surface. We discovered for the first time the solar energy conversion system of the “mineral coatings” on the Earth's surface ( aka  “mineral membrane”), which exerts potential oxygen-production and carbon-sequestration functions on the Earth surface. Our finding shed a light on the photoelectric effect and non-classical photosynthesis involving natural semiconducting minerals. In this contribution, we studied the semiconducting property and photoelectron energy of typical minerals in the “mineral membrane”, focusing primarily on the photoelectric effect in and oxygen-production/carbon-sequestration function of ferromanganese oxides, as well as relevant geological records. We propose that birnessite, goethite and hematite, the semiconducting minerals commonly found in the “mineral membrane”, can perform sensitive and stable photon-to-electron conversion under solar radiation.  The non-classical mineral photosynthetic function we put forth is as follows: Solar energy utilization by inorganic minerals resembles photosynthesis in regarding to oxygen evolution and carbon fixing, and the “mineral membrane” may take part in both photocatalytic water-oxidation reaction and transformation of atmospheric CO 2  into marine carbonate. In addition, minerals might as well have promoted photosynthesis in photosynthetic organisms. During the water-oxidation reaction, the inorganic cluster Mn 4 CaO 5  of photosystem II cycles through redox intermediates that are analogous to birnessite both in structure and component. Thus, it is fair to postulate that birnessites could play a role in the initiation of the photosynthesis in cyanobacteria, as minerals could weaken the hydrogen bond strength and alter water properties, thus facilitating water oxidation and photosynthesis. This observation offers further insights into the molecular mechanism of mineral participation in photosynthesis in photosynthetic organisms.
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    4. Core value of the Chengjiang fauna: formation of the animal kingdom and the birth of basic human organs
    SHU Degan, HAN Jian
    地学前缘    2020, 27 (6): 382-412.   DOI: 10.13745/j.esf.sf.2020.10.28
    摘要670)   HTML835)    PDF(pc) (25271KB)(178)    收藏

    Well known for its abundant and extraordinary soft-tissue fossils, the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth. The large-scale survey and exploration of the fauna by Chinese paleontologists, partly in collaboration with international scientists, over the past 30 years can be broadly divided into three stages. In the first decade since 1984 (1984-1994), a large number of invertebrates, including basal animals and the protostomes of the early animal tree were discovered, but the subkingdom Deuterostomia was completely unknown. Then in the second decade (1995-2005), the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals (TPTEA, including basal animals, protostomes and deuterostomes), for the first time. In the third decade (after 2005), the academic community began to think about the internal relationships between the formation of TPTEA and the multi-episode Cambrian explosion, leading to the new hypothesis of the three-episode Cambrian explosion. The Chengjiang fauna is important for deciphering the fauna structure, paleoecological environment, and so on. However, its core academic values mainly rest on two aspects. Firstly, The Chengjiang fauna, as the main phase witness of the Cambrian explosion, has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time. The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion: a step-wise divergent evolution of animals, from basal to highly advanced groups, lasting about 40 million years. In the first phase, it gave birth to a bulk of basal animals (including some now extinct “animal” groups) in the latest Ediacaran, probably including some pioneer protostomes. The second phase took place in the first epoch of the Cambrian period (Terreneuvian), giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals. The third phase proceeded in Cambrian Epoch 2 (represented by the Chengjiang fauna), which not only maintained the prosperity of basal animals and protostomes, but also, more importantly, gave birth to all the main phyla of the subkingdom Deuterostomia. Thus, the rudimental framework of the whole TPTEA has been shaped, with the termination of the major innovation events of the Cambrian explosion. Here, we discussed the evolutionary properties of Ediacaran biota, small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups. The order Myllokunmingiida is the only known oldest vertebrate, while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes; Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates; and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes. The second core value of the Chengjiang fauna is of profound humanistic and philosophical significance: the discoveries of the ‘first gill openings’, ‘first brain’, ‘first vertebrae’ and ‘first heart’ provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s “The Descent of Man”. In addition, the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.

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