0.6～2.0GPa压力下部分熔融角闪辉长岩的纵波波速

利用超声波透射-反射法,测量了0.6～2.0 GPa、最高1 085℃条件下角闪辉长岩的纵波波速(vp),详细统计了部分熔融阶段实验产物组分的体积百分含量,利用矿物含量和弹性参数,计算了角闪辉长岩的纵波波速.实验测量和理论计算显示了较一致的vp-t关系,即高压下角闪辉长岩的vp随温度升高先缓慢降低,在温度约800～900℃后转而大幅下降.实验产物显示,样品在温度达812℃(0.6 GPa)、865℃(1.0 GPa)和919℃(2.0 GPa)后发生矿物脱水和部分熔融,熔体含量随温度升高显著增加.熔体是导致高温阶段岩石vp快速降低的主要原因.在初熔阶段vp随熔体增加而降低尤为显著,可能是初熔时矿物脱水生成的自由水及含水量高的熔体,以微细熔体薄膜浸润矿物边界或裂隙所导致.     

http://www.sciencedirect.com/science/article/pii/S1674987112001570

The supercontinent cycle,by which Earth history is seen as having been punctuated by the episodic assembly and breakup of supercontinents,has influenced the rock record more than any other geologic phenomena,and its recognition is arguably the most important advance in Earth Science since plate tectonics.It documents fundamental aspects of the planet’s interior dynamics and has charted the course of Earth’s tectonic,climatic and biogeochemical evolution for billions of years.But while the widespread realization of the importance of supercontinents in Earth history is a relatively recent development,the supercontinent cycle was first proposed thirty years ago and episodicity in tectonic processes was recognized long before plate tectonics provided a potential explanation for its occurrence.With interest in the supercontinent cycle gaining momentum and the literature expanding rapidly,it is instructive to recall the historical context from which the concept developed.Here we examine the supercontinent cycle from this perspective by tracing its development from the early recognition of long-term episodicity in tectonic processes,through the identification of tectonic cycles following the advent of plate tectonics,to the first realization that these phenomena were the manifestation of episodic supercontinent assembly and breakup.     

Pendleian (early Serpukhovian) marine carbonates from SW Spain: sedimentology,biostratigraphy and depositional model

The San Antonio–La Juliana tectono‐sedimentary unit contains the only Namurian marine carbonates in the southwestern part of the Iberian Peninsula. The analysis of this unit is fundamental in understanding the sedimentary evolution and tectonic movements which operated during the Namurian in this area. Using foraminifera the succession has been assigned to two biozones (Zones 17 and 18), both occurring in the Pendleian (early Namurian). Seven stratigraphic sections have been analysed: San Antonio, Burjadillo, Lavadero de la Mina, Cornuda, Lozana, Caridad and Via Crucis. The stratigraphic succession of the San Antonio–La Juliana Unit consists of olistolites in the basal part, with common debris‐flow deposits (mainly of carbonates, with minor siliciclastic rocks), and turbidites, all of them embedded in shales. These rocks, interpeted as slope deposits, pass up into shallow‐water platform facies, with sediments characteristic of the inner platform and tidal flats. Above these rocks, terrigenous deltaic deposits occur. Thus, the stratigraphic sections show an overall shallowing‐upward trend. The isolation of some outcrops, and the duplication and absence of some parts of the stratigraphic succession are explained by tectonic movements. Overall, tectonic factors seem to be the main control rather than glacio‐eustatic or autocyclic processes, and sedimentation took place in a strike‐slip regime. Copyright © 2004 John Wiley & Sons, Ltd.     

Petrogenesis of Tertiary Continental Intra-plate Lavas from the Westerwald Region, Germany

Tertiary volcanic rocks from the Westerwald region range frombasanites and alkali basalts to trachytes, whereas lavas fromthe margin of the Vogelsberg volcanic field consist of morealkaline basanites and alkali basalts. Heavy rare earth elementfractionation indicates that the primitive Westerwald magmasprobably represent melts of garnet peridotite. The Vogelsbergmelts formed in the spinel–garnet peridotite transitionregion with residual amphibole for some magmas suggesting meltingof relatively cold mantle. Assimilation of lower-crustal rocksand fractional crystallization altered the composition of lavasfrom the Westerwald and Vogelsberg region significantly. Thecontaminating lower crust beneath the Rhenish Massif has a differentisotopic composition from the lower continental crust beneaththe Hessian Depression and Vogelsberg, implying a compositionalboundary between the two crustal domains. The mantle sourceof the lavas from the Rhenish Massif has higher ²⁰⁶Pb/²⁰⁴Pband ⁸⁷Sr/⁸⁶Sr than the mantle source beneath the Vogelsbergand Hessian Depression. The 30–20 Ma volcanism of theWesterwald apparently had the same mantle source as the QuaternaryEifel lavas, suggesting that the magmas probably formed in apulsing mantle plume with a maximum excess temperature of 100°Cbeneath the Rhenish Massif. The relatively shallow melting ofamphibole-bearing peridotite beneath the Vogelsberg and HessianDepression may indicate an origin from a metasomatized portionof the thermal boundary layer. KEY WORDS: continental rift volcanism; basanites; trachytes; assimilation; fractional crystallization; partial melting     

构造强烈改造型盆地——来自杉松岗盆地的证据

通过对杉松岗盆地构造变形的研究与分析,总结并提出构造强烈改造型盆地的概念。构造强烈改造型盆地主要特征表现为盆地的原生状态遭到毁灭性的破坏,盆地的现存岩貌是构造改造的结果而非原始的有序堆积;各种构造岩和构造煤的广泛发育是构造强烈改造型盆地的重要物质记录;混杂堆积构成的宏观有序、微观无序的叠堆构造是构造强烈改造型盆地的主要控煤构造。     

Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province)

The Zagros fold-and-thrust belt of SW-Iran is among the youngest continental collision zones on Earth. Collision is thought to have occurred in the late Oligocene–early Miocene, followed by continental shortening. The High Zagros Belt (HZB) presents a Neogene imbricate structure that has affected the thick sedimentary cover of the former Arabian continental passive margin. The HZB of interior Fars marks the innermost part of SE-Zagros, trending NW–SE, that is characterised by higher elevation, lack of seismicity, and no evident active crustal shortening with respect to the outer (SW) parts. This study examines the brittle structures that developed during the mountain building process to decipher the history of polyphase deformation and variations in compressive tectonic fields since the onset of collision. Analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors. Various strike–slip, compressional, and tensional stress regimes are thus identified with different stress fields. Brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of corresponding stress fields, considering the folding process. Results indicate that in the studied area, the main fold and thrust structure developed in a general compressional stress regime with an average N032° direction of σ₁ stress axis during the Miocene. Strike–slip structures were generated under three successive strike–slip stress regimes with different σ₁ directions in the early Miocene (N053°), late Miocene–early Pliocene (N026°), and post-Pliocene (N002°), evolving from pre-fold to post-fold faulting. Tensional structures also developed as a function of the evolving stress regimes. Our reconstruction of stress fields suggests an anticlockwise reorientation of the horizontal σ₁ axis since the onset of collision and a significant change in vertical stress from σ₃ to σ₂ since the late stage of folding and thrusting. A late right-lateral reactivation was also observed on some pre-existing belt-parallel brittle structures, especially along the reverse fault systems, consistent with the recent N–S plate convergence. However, this feature was not reflected by large structures in the HZB of interior Fars. The results should not be extrapolated to the entire Zagros belt, where the deformation front has propagated from inner to outer zones during the younger events.     

A geomorphic framework for understanding the surface archaeological record in arid environments

The Narcao and Cixerri basins in Southwestern Sardinia are east-west trending basins of Oligocene age. Recent geological mapping, combined with structural and stratigraphical analyses, support the proposed hypothesis that these basins were very open growth synclines confined within a structural high, delimited by northwest trending dextral strike slip faults. Previously the basins have been interpreted as fault-bounded grabens. The newer revised interpretation is consistent with the existence of NNW trending dextral strike-slip dynamic, related to a north-south shortening which has generated reverse faulting and tight folds in the underlying, pre-synclinal evolution, Eocene succession. This deformation, along with an interfering sub-orthogonal thrust and fold system which affects the Mesozoic sequence, was traditionally linked to the Pyrenean Orogenesis. The Oligocene–Aquitanian shortening, which resulted in the growth synclines and strike-slip faulting, is consistent with the structural development recognized in north-central Sardinia; there structures related to the collision between continental margins that resulted in the Northern Apennines are well documented. Therefore, the Oligocene tectonics of Southwestern Sardinia also must be related to the collision event between the Southern Europe margin (i.e. a crustal sector corresponding to the future Corsica-Sardinia block) and the Adria Plate, which generated the Northern Apennines. Conversely, the previous E-W shortening- related structures must be related to Pyrenean tectonics.     

A structural synthesis of the Proterozoic Arabian-Nubian Shield in Egypt

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 – 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime.     

A lithospheric model to interpret focal properties of intermediate and shallow shocks in central greece

Summary An attempt has been made to interpret the striking difference, in focal properties, between the intermediate and shallow earthquakes in Central Greece and an observed time sequence of these shocks by a lithospheric model. This model consists of a lithospheric slab descending from the Ionian to the Aegean and a back-arc expanding Aegean lithosphere. Thrust faulting near the top surface of the slab, caused by the sinking of the slab, triggers spreading and normal faulting in the back-arc Aegean region.