西藏亚东-谷露裂谷带运动特征的InSAR研究

亚东-谷露裂谷等南北向分布的大型地堑在青藏高原新生代构造演化中发挥着重要作用,该研究对理解青藏高原中南部地堑在第四纪构造演化的地位具有重要意义。基于欧空局Envisat卫星2003~2008年SAR数据,利用SBAS时序InSAR技术,去除地形、大气、轨道等因素的影响,获取亚东-谷露裂谷带及邻区的LOS速度场,并反演亚东-谷露裂谷带的滑动速率和闭锁深度。结果表明,亚东-谷露裂谷带南段与北段具有相同的倾滑速率,均为1 mm/a;其闭锁深度南段为31 km,北段为22 km;其断层倾角南段为52°,北段为40°,与地质结果一致。     

2008年10月当雄MW6.3级地震断层参数的InSAR反演及其构造意义

2008年10月6日在西藏当雄发生了M_W6.3地震.我们从一对降轨ENVISAT ASAR资料获得了这次地震的同震位移场,通过同震位移场的反演确定了发震断层参数.并且应用一维变异理论评估了InSAR结果中的误差协方差矩阵,直接用于评价断层反演参数的不确定性水平.结果表明,此次地震发生于羊易盆地东缘的次级断层,走向178°,倾角58°,倾向近正西,以正断层运动为主,兼具少量右旋走滑分量,且资料的误差水平对反演结果的影响不大.这次地震引起震中位置地表下沉至少30 cm,似乎是亚东-谷露裂谷带北段的羊易地堑下沉的表现.     

Late Quaternary activity of the Pajarito fault, Rio Grande rift of northern New Mexico, USA

The Pajarito fault forms the western margin of the Rio Grande rift in north-central New Mexico, and lies adjacent to Los Alamos National Laboratory, a major Federal research facility. Vertical displacement on this normal fault over the past 1.2 Ma has created a 50- to 120-m-high fault scarp on Bandelier Tuff (1.2 Ma), yielding a long-term average slip rate of ca. 0.1 mm/yr. In support of a Laboratory-wide seismic hazards assessment, we excavated 14 trenches in the Pajarito fault zone to determine the age of the most recent displacement event, the recurrence interval between events, the displacement per event, and the variability in slip rate and recurrence through time. The large number of trenches was required by the large height of the fault scarp and the complexity of the fault zone. Only about half the trenches contained significant thicknesses of Holocene deposits, but in those trenches there was clear evidence for an early-to-mid-Holocene displacement event. The previous event was at least 20–40 ka, and the average recurrence interval over the past ca. 300 ka was about 20–40 kyr. We infer that much of the structural relief across this fault developed soon after eruption of the Bandelier Tuff between 1.0 and 1.2 Ma, and that slip rate slowed considerably after that time.     

Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly (G ^h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G ^h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault (F1) or the southeast boundary of Alxa block is in accord with the western change belt of G ^h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault (F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.     

羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩地球化学特征及其构造意义

羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩主要由中基性火山碎屑岩及熔岩组成,火山岩地球化学研究表明,其主元素表现为高TiO_2和低TiO_2两种特征,球粒陨石标准化稀土配分模式为LREE富集型.MORB标准化的微量元素配分型式为大洋隆起型,显示岩浆形成于板内裂谷构造环境.Sr、Nd、Pb同位素地球化学研究表明火山岩显示明显的亏损地幔源区特征.综合研究表明直根尕卡一带二叠纪栖霞期火山岩形成于大陆边缘拉张构造(或陆缘始裂谷)环境,岩浆起源于地幔,属地幔柱作用的产物.     

国外大陆裂谷构造研究现状及展望

大地构造学是现今地质学研究的热门学科,大陆裂谷构造属于大地构造的研究范畴。本文从裂谷沉积作用与成矿的简单联系和由于先存下地壳组构对大陆裂谷构造的影响两方面介绍了国外对大陆裂谷研究的情况。作者指出：大地构造学的研究需借助假定的模式或实验模型,但不能局限于其中;大地构造学的各个研究领域都存在着挑战,地质学的研究需要进一步完善。     

箕状断陷湖盆不同构造区带成岩作用特征及差异性研究:以东营凹陷沙河街组为例

东营凹陷在沙河街组沉积期为北陡南缓的箕状断陷湖盆,凹陷内可进一步细分为陡坡带、缓坡带、洼陷带及中央背斜带。在沙河街组成岩演化过程中发育了多种类型的成岩作用,主要包括压实作用、压溶作用、溶解作用、胶结作用等。不同构造区带成岩作用具有明显的差异性,具体表现为:压实作用总体表现为早期压实影响较大,后期较小,但不同构造区带差异明显;胶结作用在不同构造区带碳酸盐胶结胶物含量不同。不同粘土矿物在不同构造区带含量及转化深度不同;溶蚀作用在不同构造区带发育深度不同,从而导致次生孔隙带发育深度均明显不同。不同构造区带成岩作用的差异性导致不同构造区带成岩相带类型、特征不同。详细研究这种差异性对于寻找岩性油气藏具有重要的理论价值和实际意义。     

Geodynamic evolution of a forearc rift in the southernmost Mariana Arc

The southernmost Mariana forearc stretched to accommodate opening of the Mariana Trough backarc basin in late Neogene time, erupting basalts at 3.7–2.7 Ma that are now exposed in the Southeast Mariana Forearc Rift (SEMFR). Today, SEMFR is a broad zone of extension that formed on hydrated, forearc lithosphere and overlies the shallow subducting slab (slab depth ≤ 30–50 km). It comprises NW–SE trending subparallel deeps, 3–16 km wide, that can be traced ≥ ∼30 km from the trench almost to the backarc spreading center, the Malaguana‐Gadao Ridge (MGR). While forearcs are usually underlain by serpentinized harzburgites too cold to melt, SEMFR crust is mostly composed of Pliocene, low‐K basaltic to basaltic andesite lavas that are compositionally similar to arc lavas and backarc basin (BAB) lavas, and thus defines a forearc region that recently witnessed abundant igneous activity in the form of seafloor spreading. SEMFR igneous rocks have low Na₈, Ti₈, and Fe₈, consistent with extensive melting, at ∼23 ± 6.6 km depth and 1239 ± 40°C, by adiabatic decompression of depleted asthenospheric mantle metasomatized by slab‐derived fluids. Stretching of pre‐existing forearc lithosphere allowed BAB‐like mantle to flow along the SEMFR and melt, forming new oceanic crust. Melts interacted with pre‐existing forearc lithosphere during ascent. The SEMFR is no longer magmatically active and post‐magmatic tectonic activity dominates the rift.     

A model for the state of brittle failure of the western Trans-Mexican Volcanic Belt

The Trans-Mexican Volcanic Belt (TMVB) is an igneous arc built above the Middle America subduction zone. Its western section is being extended orthogonally to its axis by several arrays of active normal faults with a combined length of 450 km and including up to 1.5 km of throw. Until now, intra-arc extension in the TMVB has been considered the result of either rifting or retreat of the Rivera and Cocos plates. Observations worldwide and numerical models, however, appear to contradict these ideas. Continental extension in convergent margins takes place where the upper plate moves away from the trench, and the subduction zone is only weakly coupled with the overlying plate. In western Mexico, neither of these relationships applies. A new numerical model presented here is able to explain satisfactorily the state of brittle failure of the TMVB. The model embodies the first-order physics of the northern Middle America subduction zone, and its boundary conditions are consistent with the convergence history of the Rivera and North America plates. Modelling results show that periods of accelerated subduction between the Rivera and North America plates give rise to an increase in suction force under the fore arc. The over-riding plate then bends downwards, building up tensional stress inside the volcanic arc. Failure of the arc follows within 1 million years of pulse initiation. Analysis of the results shows that the steep subduction angle of the Rivera slab, the relief of the volcanic plateau, and the thermal weakening of the lower crust facilitated the failure of the arc. The model demonstrates that a highly coupled subduction zone can cause extension, albeit limited, in the over-riding plate.     

Orderliness of Hydrocarbon Accumulation Distribution in Rift Basins of Eastern China

The Cenozoic rift basins in eastern China show a clear temporal and spatial zonation and episodic tectonic evolution, which control their episodic hydrocarbon generation and zonal accumulation. In this paper, based on the study of depositional architecture, hydrocarbon migration system and dynamic evolution in the rift basins, combinations of hydrocarbon accumulation elements were analyzed using sequence stratigraphy. Hydrocarbon distribution in system tracts with different sequence orders was further studied. And we summarized stacking patterns and horizontal combination relationships for different types of reservoirs, such as lithological, tectonic-lithological, tectonic and stratigraphical reservoirs which can be observed from depression center to basin margin. The result reveals that various scales of pools exhibit significant distribution and evolution orderliness in different pool-forming units, i.e., depositional systems, plays and depressions. The regular distribution of various scales of pools is closely related to tectonic evolution and depositional filling in the rift basins. The result can be applied to the fine petroleum exploration in rift basins in eastern China. It will promote the scientific prediction and evaluation of reservoir types and their spatial distribution, lead to the active shifts of exploration targets in different zones, and thus support the stable progress of fine exploration in mature exploration areas.