Did the Altyn Tagh fault extend beyond the Tibetan Plateau?

The pre-Miocene northeastern termination of Altyn Tagh fault is a critical outstanding problem for understanding the mechanics of Cenozoic deformation resultant from the Indo-Asian collision and mechanisms of Tibetan Plateau formation. Structures beyond the widely accepted NE end of the Altyn Tagh fault, near the town of Yumen, are needed in order to accommodate strike-slip deformation related to plate-like lateral extrusion tectonics, but structures with the necessary slip magnitudes and histories have not been identified. We report on a series of newly recognized and documented E to ENE-striking faults within the Alxa block, NE of the Tibetan Plateau, that are visible on remotely sensed images and confirmed by field studies. These structures are demonstrably left-lateral faults based on offset geology and kinematic indicators such as striae and s-c fabrics in fault gouge. The faults have post-Cretaceous offsets of at least tens to possibly > 150 km, but limited post-Miocene displacement, constrained by offset sedimentary basins. These characteristics suggest that strike-slip faults of the Alxa region have a similar structural history as the central-eastern Altyn Tagh fault and can provide a mechanism for accommodating Oligocene-Early Miocene extrusion along the Altyn Tagh fault.     

Late Mesozoic and Cenozoic wrench tectonics in eastern Australia: Insights from the North Pine Fault System (southeast Queensland)

The North Pine Fault System (NPFS) in SE Queensland belongs to a series of NNW-striking sinistral faults that displaced Paleozoic to Cenozoic rock units in eastern Australia. We have studied the geometry and kinematics of the NPFS by utilizing gridded aeromagnetic data, digital elevation models, and field observations. The results indicate that all segments of the NPFS were subjected to sinistral reverse strike-slip faulting. Restorations of displaced magnetic anomalies indicate sinistral offsets ranging from ∼3.4 to ∼8.2 km. The existence of a (possibly) Late Triassic granophyre dyke parallel to one of the fault segments, and the occurrence of NNW-striking steeply dipping strike-slip and normal faults in the Late Triassic-Early Cretaceous Maryborough Basin, indicate that the NPFS has likely been active during the Mesozoic. We propose that from Late Cretaceous to early Eocene, NNW-striking faults in eastern Australia, including the NPFS, were reactivated with oblique sinistral-normal kinematics in response to regional oblique extension associated with the opening of the Tasman and Coral Seas. This interpretation is consistent with the modeled dominant NNE- to NNW-directed horizontal tensional stress in the Eocene. The latest movements along the NPFS involved sinistral transpressional kinematics, which was possibly related to far-field contractional stresses from collisional tectonics at the eastern and northern boundaries of the Australian plate in the Cenozoic. This sinistral-reverse oblique kinematics of the NPFS in the Cenozoic is in line with ∼ESE to ENE orientations of the modeled maximum horizontal stress in SE Queensland.     

Late Cenozoic sedimentary process and its response to the slip history of the central Altyn Tagh fault,NW China

The ENE-striking Altyn Tagh fault (ATF), extending along the northern edge of the Ti-betan Plateau, is one of the major important strike-slip faults, and has been known as one of the key areas to debate the eastward extrusion and crustral shortening models of the Tibetan Plateau during and after India-Asia collision. This paper mainly presents new evidence of Late Cenozoic sedimentary process to reconstruct the slip history of the ATF during the Late Cenozoic. Field measurements and laboratory analyses of the sedimentary characteristics in the Late Cenozoic basins in the central Altyn Tagh fault suggest that Late Cenozoic sedimentary sequence should be divided into three units according to facies changes. The paleo-topography reconstruction shows that the sedimentarion in these basins was tightly related with the fault, indicating that the ATF has experienced at least three stages of strike slipping in the Late Cenozoic. New geological data from the Late Cenozoic sedimentary basins and the formation of the present Suo’erkuli basin provide evidence for the displacement of the fault. The result shows that the 80–100 km left-lateral strike-slip displacement of the fault has been accumulated in the Late Cenozoic.

     

Segmentation along Strike-Slip Faults Revisited

Fault segmentation and fault steps and their evolution are relevant to the dynamics and size of earthquake ruptures, the distribution of fault damage zones and the capacity of fault seal. Furthermore, segment interactions and coalescence are the fundamental processes for fault growth. To contribute to this end, we investigated the architecture of strike-slip faults by combining field observations in the Valley of Fire State Park, Nevada, and the published data sets. First, we studied the trace complexity for 49 faults with offsets ranging from 12 m to 460 km. We established that the number of fault steps (hence fault segments) per unit length is correlated to the maximum fault offset by a negative power law. The faults have longer segments and fewer steps when their offsets increase, indicating the progressive growth, smoothening and simplification of the fault traces as a function of the offset, as proposed by previous investigators. Second, we studied the dimensions of the segments and steps composing ~20 of the previous fault systems. The mean segment length, mean step length and mean step width are all correlated to the maximum fault offset by positive power laws over four orders of magnitude of the offset. In addition, the segment length distributions of four of the faults with offsets ranging from 80 m to 100 km are all lognormal, with most of the segment lengths falling in the range of one to five times the maximum offset of the faults. Finally, the fault steps have an approximately constant length-to-width ratio indicating that, regardless of their environment, strike-slip faults have a remarkable self-similar architecture probably due to the mechanical processes responsible for fault growth. Our data sets can be used as tools to better predict the geometrical attributes of strike-slip fault systems with important consequences for earthquake ruptures, the distribution and properties of fault damage zones, and fault sealing potential.     

Late Cenozoic faulting in SW Bulgaria: Fault geometry,kinematics and driving stress regimes. Implications for late orogenic processes in the Hellenic hinterland

We investigate the geometry and kinematics of the faults exposed in basement rocks along the Strouma River in SW Bulgaria as well as the sequence of faulting events in order to place constraints on the Cenozoic kinematic evolution of this structurally complex domain. In order to decipher the successive stress fields that prevailed during the tectonic history, we additionally carried out an analysis of mesoscale striated faults in terms of paleostress with a novel approach. This approach is based on the P–T axes distribution of the fault-slip data, and separates the fault-slip data into different groups which are characterized by kinematic compatibility, i.e., their P and T axes have similar orientations. From these fault groups, stress tensors are resolved and in case these stress tensors define similar stress regimes (i.e., the orientations of the stress axes and the stress shape ratios are similar) then the fault groups are further unified. The merged fault groups after being filled out with those fault-slip data that have not been incorporated into the above described grouping, but which present similar geometric and kinematic features are used for defining the final stress regimes. In addition, the sequence of faulting events was constrained by available tectonostratigraphic data.Five faulting events named D1, D2, D3, D4 and D5 are distinguished since the Late Oligocene. D1 is a pure compression stress regime with σ₁ stress axis trending NNE-SSW that mainly activated the WNW-ESE to ENE-WSW faults as reverse to oblique reverse and the NNW-SSE striking as right-lateral oblique contractional faults during the Latest Oligocene-Earliest Miocene. D2 is a strike-slip − transpression stress regime with σ₁ stress axis trending NNE-SSW that mainly activated the NNW-SSE to N-S striking as right-lateral strike-slip faults and the ENE-WSW striking faults as left-lateral strike-slip ones during the Early-Middle Miocene. D3 extensional event is associated with a NW-SE to WNW-ESE extension causing the activation of mainly low-angle normal faults of NE-SW strike and NNE-SSW to NNW-SSE striking high-angle normal faults. D4 is an extensional event dated from Late Miocene to Late Pliocene. It activated NNW-SSE to NW-SE faults as normal faults and E-W to WNW-ESE faults as right-lateral oblique extensional faults. The latest D5 event is an N-S extensional stress regime that dominates the wider area of SW Bulgaria in Quaternary times. It mainly activated faults that generally strike E-W (ENE-WSW and WNW-ESE) normal faults, along which fault-bounded basins developed. The D1 and D2 events are interpreted as two progressive stages of transpressional tectonics related to the late stages of collision between Apulia and Eurasia plates. These processes gave rise to the lateral extrusion of the Rhodope and Balkan regions toward the SE along the Strouma Lineament. The D3 event is attributed to the latest stage of this collision, and represents the relaxation of the overthickened crust along the direction of the lateral extrusion. The D4 and D5 events are interpreted as post-orogenic extensional events related to the retreat of the Hellenic subduction zone since the Late Miocene and to the widespread back-arc Aegean extension still prevailing today.     

沂沭大陆裂谷的生成与演化

本文从沂沭断裂带的大地构造背景、边界断裂、地貌、沉积岩相、火山和地震活动、地壳深部结构、重力、地热等的分析,说明沂沭断裂是一条中生代的裂谷,并给出了裂谷的形成机制及其演化特征     

Structural control on uranium mineralization in South China: Implications for fluid flow in continental strike-slip faults

South China is the most important uranium producer in the country. Much of the Mesozoic-Cenozoic geology of this area was dominated by NNE-trending intracontinental strike-slip faulting that resulted from oblique subduction of the paleo-Pacific plate underneath the eastern China continent. This strike-slip fault system was characterized by transpression in the early-mid Jurassic and by transtension from the latest Jurassic through Cretaceous to early Tertiary. Most uranium ore deposits in South China are strictly fault-hosted and associated with mid-late Mesozoic granitic intrusions and volcanic rocks, which formed under transpression and transtension regimes, respectively. Various data demonstrate that the NNE-trending strike-slip faults have played critical roles in the formation and distribution of hydrothermal uranium deposits. Extensive geochronological studies show that a majority of uranium deposits in South China formed during the time period of 140–40 Ma with peak ages between 87–48 Ma, coinciding well with the time interval of transtension. However, hydrothermal uranium deposits are not uniformly distributed along individual strike-slip fault. The most important ore-hosting segments are pull-apart stepovers, splay structures, extensional strike-slip duplexes, releasing bends and fault intersections. This non-uniform distribution of ore occurrences in individual fault zone reflects localization of hydrothermal fluids within those segments that were highly dilational and thus extremely permeable. The unique geometric patterns and structural styles of strike-slip faults may have facilitated mixing of deeply derived and near-surface fluids, as evidenced by stable isotopic data from many uranium deposits in South China. The identification of fault segments favorable for uranium mineralization in South China is important for understanding the genesis of hydrothermal ore deposits within continental strike-slip faults, and therefore has great implications for exploration strategies.     

河西走廊西段及邻区主要断裂（一）-晚新生代逆断层与走滑断层的地震剖面解释

基于地震剖面解释的构造分析表明，河西走廊西段及邻区发育有许多晚第三纪-第四纪的逆断层与走滑断层. 其主要类型有两种:一是与北祁连逆冲推覆作用有关的南倾逆断层，其走向北西，主要分布于北祁连山东北缘及河西走廊西南部地区；二是与阿尔金断裂活动有关的逆断层与走滑断层，主要分布于红柳峡、宽台山——合黎山地区. 这些断层与新生代始新世末期以来印-藏碰撞的远距离效应有关. 它们于晚第三纪开始活动，主要活动于第四纪时期，而且大多目前仍在活动，属于活动性断层，是河西走廊地区地震的潜发因素. 此外，它们还造成了地层的强烈变形，形成了一系列的地貌阶地和河流的水平错移.      

On the faults of western Hexi Corridor and its nearby regions, northwestern China:Thrust faults and strike-slip faults of Late Cenozoic

Introduction Hexi Corridor, a corridor extended over 1 000 km and with a strike of WNW-ESE, is locatedbetween Alxa uplift and northern Qilianshan Caledonian folding belt of northern Qinghai-Xizang(Tibet) Plateau (Figure 1). In the paper, we will discuss the regions between Altun fault and Yu-mushan of the western Hexi Corridor, where the climate is arid, which results in sparse vegetation,but abundant oil and gas resource, and being one of the most important petroleum industry base…     

Seismites in the Dasheng Group: New evidence of strong tectonic and earthquake activities of the Tanlu Fault Zone

More than 80 layers of seismites were recognized from the Early Cretaceous Dasheng Group in the Mazhan and Tancheng graben basins in the Tanlu Fault Zone, eastern China. The responsible seismic events took place about 110–100 Ma in the Early Cretaceous. The fault zone was affected at the time by strong tectonics, due to tension-related stretching and scattered squeezing by strike-slip faults. These tectonic activities induced a series of strong earthquakes with Richter magnitudes(M) of 5–8.5. The earthquakes affected saturated or semi-consolidated flood and lake sediments, and produced intra-layer deformations by several processes, including liquefaction, thixotropy, drop, faulting, cracking, filling and folding, which resulted in the formation of various soft-sediment deformation structures, such as dikes and veins of liquefied sand, liquefied breccias, liquefied homogeneous layers, load structures, flame structures, ball-and-pillow structures, boudinage, diapirs, fissure infillings, a giant conglomerate wedge, and syn-sedimentary faults. The seismites are new evidence of tectonic and seismic activities in the Tanlu Fault Zone during the Early Cretaceous; the series of strong seismic events that can be deduced from them must be considered as a response to the destruction of the North China Craton.     

GEOMORPHOLOGY OF THE GYARING CO FAULT ZONAL DRAINAGE SYSTEM AND ITS STRUCTURAL IMPLICATIONS

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau. The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau. The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone. The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co. From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin. Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics. In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement. In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images (Landsat and GeoEye) and field work. We acquired basic geomorphic parameters of 153 sub-basin (such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve. Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault. Southern drainage basins' relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity. Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east. By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins. Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift. The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.     

FIRST REPORT OF BERO ZECO ACTIVE FAULT IN GÊRZÊ, NORTHERN TIBET

In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ₁)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ₁, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms.     

Control of differential tectonic evolution on petroleum occurrence in Bohai Bay Basin

The Bohai Bay Basin(BBB)is the most petroliferous Cenozoic basin in the east of China.It consists of seven depressions.Each depression has been subjected to different stress states and then has experienced varying faulting processes since the Neogene,especially during the Neotectonism(from the Pliocene to the present).On the basis of the investigation of fault patterns,fault densities and fault activity rates(FARs)for each depression,this paper demonstrates the discrepancy of faulting development and evolution across the BBB.The dynamic mechanism for the differences in faulting is also discussed by the analysis of the regional stress state.The Bozhong Depression is just situated in the transtensional zone induced by the two active strike-slip faults,namely Yingkou-Weifang and Beijing-Penglai.In this depression,the major faults which cut through the Paleogene or the Cenozoic have had higher than 10 m/Ma FARs since the Neogene,and the highest FARs have reached or exceeded 25 m/Ma during the Neotectonism.As a result,most of the petroleum has migrated along these major faults and accumulated within the Neogene.In contrast,in the other depressions of the BBB away from the Bozhong Depression,the FARs of the major faults were decreased to lower than 10 m/Ma since the Neogene,and tended to be zero during the Neotectonism.Therefore,the major faults could not serve as vertical conduits for petroleum migration,and the petroleum was entrapped in the Paleogene.Consequently,the faulting since the Neogene,especially during the Neotectonism,controlled the petroleum richness in vertical strata.     

双山—李家庄断裂地表破裂特征与最新活动性研究

利用地质地貌调查、探槽、工程探测以及年代测试等方法,对双山—李家庄断裂的地表破裂形态、最新活动性以及古地震事件展开研究。结果表明:(1)双山—李家庄断裂的最新活动时代为晚更新世,在(17.0±0.85) ka～(21.4±1.7) ka B.P.之间,总体以左旋走滑正断为主,局部逆断。依据第四纪活动特征和破裂形式,从南往北可分为两段,即南段(双山—大马山)和北段(大马山—五里)。其中南段又可分为3个小段:双山—丹河水库小段表现为左阶斜列状展布的两条断层,以左行走滑兼正断活动为主;丹河水库—营子小段表现为两条相交的断裂,东支在剖面上则表现为正断活动,第四纪以来不活动;西支在剖面上以逆冲破裂为主,最新活动时代为晚更新世;营子—大马山小段隐伏于第四系之下,具有正断走滑破裂特征。北段总体表现为多条近平行的断裂构造系,破裂形式以逆断为主。(2)双山—李家庄断裂晚第四纪以来可能发生过两次古地震事件,分别发生在(17.0±0.85) ka～(21.4±1.7) ka B.P.和(77.0±3.8) ka～(84.0±4.2) ka B.P.。(3) 1829年青州、临朐6级地震的发生与上五井断裂和双...     

Analogue models of the effect of long-term basement fault movement on volcanic edifices

Long-term fault movement under volcanoes can control the edifice structure and can generate collapse events. To study faulting effects, we explore a wide range of fault geometries and motions, from normal, through vertical to reverse and dip-slip to strike-slip, using simple analogue models. We explore the effect of cumulative sub-volcanic fault motions and find that there is a strong influence on the structural evolution and potential instability of volcanoes. The variety of fault types and geometries are tested with realistically scaled displacements, demonstrating a general tendency to produce regions of instability parallel to fault strike, whatever the fault motion. Where there is oblique-slip faulting, the instability is always on the downthrown side and usually in the volcano flank sector facing the strike-slip sense of motion. Different positions of the fault beneath the volcano change the location, type and magnitude of the instability produced. For example, the further the fault is from the central axis, the larger the destabilised sector. Also, with greater fault offset from the central axis larger unstable volumes are generated. Such failures are normal to fault strike. Using simple geometric dimensionless numbers, such as the fault dip, degree of oblique motion (angle of obliquity), and the fault position, we graphically display the geometry of structures produced. The models are applied to volcanoes with known underlying faults, and we demonstrate the importance of these faults in determining volcanic structures and slope instability. Using the knowledge of fault patterns gained from these experiments, geological mapping on volcanoes can locate fault influence and unstable zones, and hence monitoring of unstable flanks could be carried out to determine the actual response to faulting in specific cases.     

Fault slip and modern tectonic stress field in and around Kunming basin

Kunming basin is a Cenozoic faulted basin under the control of mainly SN-trending active faults. In and around the basin, there are a total of eight major active faults. Seismo-geological survey and fault slip observation show that the SN- and NE-trending active faults are mostly sinistral strike-slip faults, while the NW-trending faults are mostly dextral strike-slip faults. Using stress tensor inversion method with 706 active fault striation data at 22 measurement sites, we determined tectonic stress field of the study area. The result shows that modern tectonic stress field in and around Kunming basin is characterized by NNW-SSE compression, ENE-WSW extension, and strike-slip stress regimes. The maximum principal compressional stress (σ1) is oriented 335o~2o, with an average dip angle of 21°; the minimum (σ3) is oriented 44o~93o, with an average dip angle of 14°, and the intermediate (σ2) has a high, or nearly vertical, dip angle. The inversion result from fault slip data is consistent with the result from focal mechanism solutions.     

山东胶东半岛地区断裂最新活动性研究

山东胶东半岛地区发育有北北东-北东向和北西西向两组断裂,前者分属蓬莱-栖霞断裂系和即墨-牟平断裂带,为半岛的主体断裂构造;后者分布在半岛北缘及其北侧海域,由多条断裂组成。实地调查表明,断层在第四纪期间是活动的,控制着附近山地和盆地的构造演化与地貌发育,最新活动主要发生在第四纪早期,垂直活动幅度可达百米以上;第四纪晚期,断裂活动性迅速减弱,甚至停止,但依然发现北北东-北东向断裂的多个局部段落还在活动,明显地错断了晚更新世地层,垂直断距最大为10m左右。     

Basement structural architecture and hydrocarbon conduit potential of polygonal faults in the Cooper‐Eromanga Basin,Australia

A thorough and complete understanding of the structural geology and evolution of the Cooper‐Eromanga Basin has been hampered by low‐resolution seismic data that becomes particularly difficult to interpret below the thick Permian coal measures. As a result, researchers are tentative to interpret the basement fault architecture within the basin, which is largely undefined. To provide a better understanding of the basement fault geometry, all available two‐dimensional seismic lines together with 12 three‐dimensional seismic surveys were structurally interpreted with assistance from seismic attribute analysis. The Upper Cretaceous Cadna‐owie Formation and top Permian reflectors were analysed using a common seismic attribute technique (incoherency) that was used to infer the presence of faults that may have otherwise been overlooked. Detailed basement fault maps for each seismic survey were constructed and used in conjunction with two‐dimensional seismic data interpretation to produce a regional basement fault map. Large north‐northeast–south‐southwest‐striking sinistral strike–slip faults were identified within the Patchawarra Trough appearing to splay from the main northeast–southwest‐striking ridge. These sinistral north‐northeast–south‐southwest‐striking faults, together with field‐scale southeast–northwest‐striking dextral strike–slip faults, are optimally oriented to have potentially developed as a conjugated fault set under a south‐southeast–north‐northwest‐oriented strike–slip stress regime. Geomechanical modelling for a regionally extensive system of Cretaceous polygonal faults was performed to calculate the Leakage Factor and Dilation Tendency of individual faults. Faults that extend into Lower Cretaceous oil‐rich reservoirs with strikes of between 060°N and 140°N and a high to near‐vertical dip angle were identified to most likely be acting as conduits for the tertiary migration of hydrocarbons from known Lower Cretaceous hydrocarbon reservoirs into shallow Cretaceous sediments. This research provides valuable information on the regional basement fault architecture and a more detailed exploration target for the Cooper‐Eromanga Basin, which were previously not available in literature.     

A NEW DISCOVERY OF ACTIVITY OF FUSHAN SECTION OF THE TAN-LU FAULT ZONE IN THE LATE QUATERNARY

The east branch fault of Tan-Lu fault zone extends from Fengshan Town of Sihong County on the north shore of the Huaihe River in Jiangsu Province, into Fushan Town of Mingguang City on the south shore of Huaihe River in Anhui Province. The landform changes from Subei plain on the north of Huaihe River to Zhangbaling uplift area on the south of Huaihe River. The terrain rises gradually with larger relief amplitude. The Fushan section of the Tan-Lu fault zone is located in Ziyang to Fushan area of Mingguang City. The fault is shown in the satellite image as a clear linear image, and the fault extends along the east side of a NNE-trending hillock. In this section the Quaternary strata are unevenly distributed, which causes some difficulties in the study of recent fault activity.In recent years, the author has found that the fault of the Fushan section of the Tan-Lu fault zone on the south of the Huaihe River still has a certain control effect on the landform and the Quaternary strata. Based on satellite imagery and geological data, we select the appropriate location in the Fushan section to excavate the Santang trench Tc1 and Fushannan trench Tc2, and clean up the Fushannan profile Pm, which reveals rich phenomena of recent fault activity. Santang trench reveals three faults, and the faulting phenomenon is obvious. One of the faults shows the characteristic of right-lateral strike-slip normal faulting; Fushannan profile reveals one fault, with the same faulting behavior of right-lateral strike-slip normal fault. Comprehensive stratigraphic sample dating results indicate that the fault dislocated the middle Pleistocene strata, late Quaternary strata and early Holocene strata. All our work shows that the fault of Fushan section has intensive activity since late Pleistocene, and the latest active age can reach early Holocene. The latest earthquake occurred at(10.6±0.8)~(7.6±0.5)ka BP. The faults exposed by trenches and profiles show the characteristics of right-lateral strike-slip normal faulting, which reflects the complexity of the tectonic stress field in the area where the fault locates.     

Analogue models of caldera collapse in strike-slip tectonic regimes

Regional-scale faulting, particularly in strike-slip tectonic regimes, is a relatively poorly constrained factor in the formation of caldera volcanoes. To examine interactions between structures associated with regional-tectonic strike-slip deformation and volcano-tectonic caldera subsidence, we made scaled analogue models. Tabular (sill-like) inclusions of creamed honey in a sand/gypsum mix replicated shallow-level granitic magma chambers in the brittle upper crust. Lateral motion of a base plate sited below half the sand/gypsum pack allowed simulation of regional strike-slip deformation. Our experiments modelled: (1) strike-slip deformation of a homogeneous brittle medium; (2) strike-slip deformation of a brittle medium containing a passive magma reservoir; (3) caldera collapse into sill-like magma reservoirs without regional strike-slip deformation; and (4) caldera collapse into sill-like magma reservoirs after regional strike-slip deformation. Our results show that whilst the magma chamber shape principally influences the development and geometry of volcano-tectonic collapse structures, regional-tectonic strike-slip faults (Riedel shears and Y-shears) may affect a caldera’s structural evolution in two main ways. Firstly, regional strike-slip faults above the magma chamber may form a pre-collapse structural grain that is exploited and reactivated during subsidence. Our experiments show that such faults may preferentially reactivate where tangential to the collapse area and coincident with the chamber margins. In this case, volcano-tectonic extension in the caldera periphery tends to localise on regional-tectonic faults that lie just outside the chamber margins. In addition, volcano-tectonic reverse faults may link with and reactivate pre-collapse regional-tectonic faults that lie just inside the chamber margins. Secondly, where regional-tectonic strike-slip faults define corners in the magma chamber margin, they may halt the propagation of volcano-tectonic reverse faults. The experiments also highlight the potential difficulties in assessing the relative contributions of volcano-tectonic and regional-tectonic subsidence processes to the final caldera structure seen in the field. Disruption of the pre-collapse surface by regional-tectonic faulting was preserved during coherent volcano-tectonic subsidence to produce a caldera floor of differentially-subsided fault blocks. Without definitive evidence for syn-eruptive growth faulting, thickness changes in caldera fill across such regional-tectonic fault blocks in nature could be mistaken as evidence for piecemeal volcano-tectonic collapse.