第二代地质学若干问题的探讨

第二代地质学与传统地质学的差别在于物质观和运动观的不同，第二代地质学不只是把各种大地构造学说统一起来，而且把整个地质学原理大统一，一元化了，即所有的地质现象都是在气－水参与作用下岩石圈循环运动的产物，称为“岩石圈循环论”。本文着重讨论了与星系旋流，地球成长，岩石圈循环，气－水作用与造岩成矿和构造运动等有关问题。     

中国大陆及其邻区岩石层挠曲强度变化和均衡补偿机制

利用中国大陆以及最近与俄罗斯拼接的中亚地区的布格重力和地形数据，采用响应函数和互相关函数技术，结合弹性板挠曲理论，研究了中国大陆及其邻近地区（２５°Ｎ－７０°Ｎ，５０°Ｅ－１４０°Ｅ）的岩石层强度，用现代均衡的观点探讨了研究区的均衡补偿机制．研究结果表明，整个中国大陆及其邻近地区的有效弹性厚度Ｔｅ值为３５ｋｍ．其中，青藏地区Ｔｅ值为８５ｋｍ．西伯利亚西部至乌拉尔Ｔｅ值为７５ｋｍ，天山、塔里木盆地Ｔｅ值为４０ｋｍ，帕米尔高原Ｔｅ值为２５ｋｍ左右，西伯利亚中部、蒙古以及中国东北北部Ｔｅ值为４０ｋｍ，华北Ｔｅ值为２５ｋｍ，华南Ｔｅ值为４０ｋｍ．均衡补偿对于波长大于几千米的地形负荷为局部补偿，对几百公里到１１００ｋｍ的地形负荷为局部补偿和岩石层强度所支持，短波长地形负荷基本上由岩石层强度所支持．     

The lithosphere in the central-eastern Mediterranean area

The lithosphere beneath the central-eastern Mediterranean area has been investigated by the inversion of the regional dispersion relations derived from analysis of surface waves. It is possible to distinguish several types of crust with average S-wave velocities in the range 3.0–3.8 km/sec, and thicknesses varying from a minimum of about 30 km, which corresponds to the Apennines, Crete and Otranto Channel regions, to a maximum of about 51 km beneath the Ionian Sea, which can be considered as a submerged continent. Associated with these crustal features, large lateral variations have been detected in the lithosphere thickness, which varies from a minimum of about 30 km corresponding to the Tyrrhenian Sea and south of Crete to a maximum of about 130 km corresponding to south-eastern Alps and north-central Greece, while the sub-Moho S-wave velocity varies in the range 4.2–4.8 km/sec. The constraint furnished by our results to the geological-tectonic setting of the investigated area, characterized by the continent continent collision between Africa and Europe, is pointed out.Publication No. 405, P. F. Geodinamica, CNR, Roma, Italy.     

Influence of lithosphere and basement properties on the stretching factor and development of extensional faults across the Otway Basin,southeast Australia

The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults.     

Giant impacts and the initiation of plate tectonics on terrestrial planets

Earth is the only terrestrial planet with present-day lithosphere recycling through plate tectonics. However, theoretical models of mantle convection based on general considerations find that all the terrestrial planets should be operating in the stagnant lid regime, in which the planets are one-plated and there is no lithosphere recycling. The stagnant lid regime is a consequence of the strong viscosity contrast across the convective layer, and therefore the upper lid (roughly equivalent to the lithosphere) must be sufficiently weakened in order to be mobilized. Here I propose that giant impacts could have provided the upper layer weakening required for surface recycling, and hence for plate tectonics, to initiate on the early Earth. Additionally, giant impacts originated lithosphere thickness and density differences, which might contribute to the initiation of subduction. Impacts are more energetic for Earth than for Mars, which could explain the likely early existence of plate tectonics on the Earth whereas Mars never had lithosphere recycling. On the other hand, convection on Mercury and the Moon might be sluggish or even inexistent, implying a reduced influence of giant impacts on their internal dynamics, whereas there is no record of the earliest geological history of Venus, which obscures any discussion on the influence of giant impacts on their internal dynamics.     

盆山耦合与沉积盆地成因

我国的沉积盆地成因研究主要遵循盆山耦合的研究思路进行 ,关注重点为盆山体系的构造、沉积和深部结构上的耦合现象。构造耦合研究是指盆山结合带的统一变形特征 ,沉积耦合研究是通过沉积响应去重塑盆山耦合过程及相邻造山带的演化过程 ,深部结构耦合的重点是研究盆山体系在岩石圈尺度的动力学统一性。国际上相应领域的研究重点为岩石圈深部过程与近地表构造过程的耦合。国内外研究既有相同之处 ,又有差异之处。建议在未来的沉积盆地成因研究中更加开阔思路 ,采用天然实验室的工作模式 ,进行多学科综合研究。     

岩石圈流变学研究进展

岩石圈流变学的目标是研究岩石圈物质的变形、流动及其机制。７０年代以来高温高压岩石力学实验和地热研究的丰硕成果,推动了该分支学科的进展。Ｒａｎａｌｉ等（１９８７）建立了７种岩石圈流变学剖面,并论述了岩石圈的流变学分层特性。此后,一些学者对不同地区的岩石圈做了研究,获得了类似的结果,建立了岩石圈流变学分层理论。运用这一理论,能解释地球科学许多分支学科所研究的不同尺度的构造现象。因为岩石圈的结构分层和流变性质,控制了大陆构造的形成演化,尤其是大陆构造变形。最新研究表明,一系列深成构造作用,如下地壳韧性剪切、造山带演化晚期或造山期后重力塌陷和莫霍面松驰等,与下地壳软化和塑性流动密切相关,而中上地壳（或汇聚带上地幔最上部）脆性域控制了地震震源的分布     

Orogen-parallel variability in 3D seismicity distribution,Northern Apennines (Italy): Evidence for a slab tear fault?

Within the central Mediterranean geodynamic puzzle, the seismotectonic processes of the northern sector of the Apennines are still under debate. In this framework, we conducted a careful examination of seismic catalogues for five years of instrumental seismicity located in the eastern sector of the Tosco-Emiliano Apennines. In our study, we merge two separate seismic bulletins, derived from a small- and a large-aperture seismic network. The joint analysis of the seismic phases of both catalogues allows us to improve event locations and to assess their hypocentral depths. After re-location using a regional velocity model, we found that the spatial distribution of hypocenters follows characteristic patterns at the southwestern and northeastern sides of the chain. Such distribution exhibits a marked axial offset in correspondence of the Livorno-Sillaro Line (LSL), a NE-SW trending lithological discontinuity previously interpreted in terms of a transform zone. Basing on this evidence, and on additional observations related to the morphology of the area, we hypothesise the LSL to represent the shallow manifestation of a discontinuity affecting the whole lithospheric thickness, i.e. a incipient tear fault dislocating the subducting slab.     

中国东部随县─启东地带上地幔结构研究

随县─启东人工地震探测剖面长７００ｋｍ，穿越郯城─庐江深大断裂带．提取了该区莫霍界面以下上地幔中的反射界面信息，获得了上地幔的分层结构．结果表明，该区上地幔中有两个深度分别为７６ｋｍ和１００ｋｍ的界面．７６ｋｍ深度以下为一低速层，１００ｋｍ深度以下则为速度更低的低速层．该区岩石层厚度为７６ｋｍ，与华北地区相似，具有薄岩石层性质．