Zhang Peizhen

Increased sedimentation rates and grain sizes 2–4 Myr ago due to the influence of climate change on erosion rates

Around the globe, and in a variety of settings including active and inactive mountain belts, increases in sedimentation rates as well as in grain sizes of sediments were recorded at ∼2–4 Myr ago, implying increased erosion rates. A change in climate represents the only process that is globally synchronous and can potentially account for the widespread increase in erosion and sedimentation, but no single process—like a lowering of sea levels or expanded glaciation—can explain increases in sedimentation in all environments, encompassing continental margins and interiors, and tropical as well as higher latitudes. We suggest that climate affected erosion mainly by the transition from a period of climate stability, in which landscapes had attained equilibrium configurations, to a time of frequent and abrupt changes in temperature, precipitation and vegetation, which prevented fluvial and glacial systems from establishing equilibrium states.

Intracrustal detachment within zones of continental deformation

Geologic mapping of active to recently active geologic structures in Panamint Valley (western United States) and in the Haiyuan region and northern Tibetan plateau (China) suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres. Detachment occurs similarly in predominantly extensional (Panamint Valley) and in predominantly compressional (China) environments. It involves structures with displacements of more than 10 km and displacement rates of more than 3 mm/yr, perhaps more than 10 mm/yr. The steeply dipping strike-slip faults present in all three areas (Hunter Mountain fault, Haiyuan fault, and Altyn Tagh fault zone) terminate in zones of extension or compression, and geometric relations indicate that all structures (including strike-slip faults) are thin-skinned and restricted to the upper crust. In Panamint Valley and in the Haiyuan region deformation within these systems can be reconstructed in three dimensions. Displacement on the strike-slip faults is absorbed by extension or compression occurring at the termination of the faults, so strike-slip displacement is roughly equal to and in the same direction as shortening or extension. We propose that left slip on the Altyn Tagh fault zone in northern Tibet is similarly absorbed by shortening southeast of the fault zone within the Qaidam basin and the Nan Shan.

Bounds on the Holocene slip rate of the Haiyuan fault, North-Central China

Abstract We measured the offsets of six stream valleys, of 30 to 90 m, along the northwest-southeast trending, left-lateral Haiyuan strike-slip fault, in north-central China. Minimum ages of these offsets were determined to estimate lower bounds for the Holocene slip rate. The most reliable bounds are 7.6 ± 1.0 and 6.7 ± 1.0 mm/yr, with three others that are smaller (3.4 ± 0.7, 3.5 ± 0.9, and 4.1 ± 0.4 mm/yr) and one large value (16.4 ± 5.9 mm/yr) that we doubt. Thus, the average Holocene slip rate of the Haiyuan fault is larger than 6 mm/yr and probably exceeds 7 mm/yr. If the average slip rate of 5 to 10 mm/yr for the Quaternary Period is applicable to the Holocene Epoch, the average rate is 8 ± 2 mm/yr.

Late Cenozoic tectonic evolution of the Ningxia-Hui Autonomous Region, China

Part of the transition from active crustal shortening and strike-slip faulting in northwestern China to active extension in northeastern China takes place within the Ningxia Autonomous Region. Four arcuate zones of both strike-slip faults and thrust faults with associated ramp anticlines dominate the structures in southern Ningxia. Deformation in these zones indicates that a component of left-slip displacement is transferred into crustal shortening on north-south-trending folds and thrust faults. The average Quaternary slip rate along the Haiyuan-Liupan Shan fault zone is 5-10 mm/yr, and that along the Tianjin Shan-Mibo Shan fault zone is about 1.5-2.7 mm/yr. The amount of offset and rate of slip along the Yanton Shan and the Niushou Shan-Daluo Shan fault zones are unknown, but the topography of the mountains suggests that the rates of slip along these zones is lower than that of the Haiyuan-Liupan Shan fault zone. Deformation in northern Ningxia is dominated by normal faulting and extension. The Helan Shan rise about 2,000 m above the Yinchuan basin, reportedly filled with a few kilometers of Cenozoic sediments. The average rate of vertical separation in Quaternary time along the East Helan Shan fault is estimated to be at least 0.5-0.8 mm/yr. Opening of the Yinchuan graben is probably partly related to left-lateral slip on the Niushou Shan and Daluo Shan fault zone. The northeastern margin of Tibetan Plateau is probably being elevated by the irregular growth of convergent and left-slip structural zones. The evolution of deformation along the Haiyuan-Liupan Shan structural zone probably foreshadows the future deformation in the ranges north of it. Left slip and shortening within the Ningxia region appears to accommodate less than 20-25 km of east or northeast displacement of crustal fragments of the northern Tibetan Plateau. Large-magnitude lateral transport of crust with respect to the area to the east has not taken place within the part of the Ningxia region covered by this study.

Tertiary basin evolution along the northeastern margin of the Tibetan Plateau: Evidence for basin formation during Oligocene transtension

The development of high topography associated with the Indo-Asian collision plays a central role in ongoing debates over the linkages between development of the Tibetan Plateau and climate. In northeastern Tibet, the widespread appearance of coarse terrestrial sediment during the Oligocene is commonly interpreted to herald the development of a foreland basin in response to crustal thickening along the present-day margin of the plateau. However, a lack of direct observations relating sediment accumulation to fault activity leaves this interpretation uncertain. Here, we present new stratigraphic observations along the northern margin of the Longzhong basin that provide insight into the tectonic setting of basin development. A combination of field and subsurface observations, including the geometry of basin-bounding faults, sedimentary provenance, paleoflow direction, isopach and sedimentary facies distribution patterns, constrains basin evolution from the Middle Tertiary through Quaternary time. Our results suggest that NE-SW extension across normal faults controlled development of accommodation space in the northern Longzhong basin during the Oligocene to early Miocene. Continued sediment accumulation from the mid-Miocene through Pliocene occurred in a broad, shallow basin, consistent with thermal subsidence following extension. Basin inversion initiated between 10 Ma and 6 Ma, associated with the development of the modern Haiyuan fault system. Our results imply that the onset of Tertiary sedimentation in the Longzhong basin does not represent a developing foredeep associated with a nascent Tibetan Plateau, but rather reflects transtensional deformation inboard of extensional basins along the East Asian margin.

Illuminating the active Haiyuan fault, China by Airborne Light Detection and Ranging

Accurately measuring landform offset is a core component in active fault studies, the resolution of topographic description of landform thus plays a critical role. Airborne Light Detection and Ranging (LiDAR) is a new and powerful tool for efficient acquisition of topographic data with cm- to mm- resolution. We recently acquired approximately 128 kilometers of airborne LiDAR topographic data along the Haiyuan fault, producing 0.5 meter DEMs of the ground surface. The newly obtained LiDAR data reveal fault traces with unprecedented clarity. Airbone LiDAR data, carrying features such as high density, large areal coverage and true 3D, provide an extraordinary opportunity to advance our understanding of active faults and their earthquake recurrence behavior.

Dextral strike-slip of Sanguankou-Niushoushan fault zone and extension of arc tectonic belt in the northeastern margin of the Tibet Plateau

The kinematic characteristics of the Sanguankou-Niushoushan fault (SGK-NSSF) are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. Using field surveys and various data collection methods, including large-scale geological mapping, measurement of typical topographies, and dating of sedimentary strata, it was determined that the SGK-NSSF exhibits obvious dextral strike-slip characteristics and thus is not a sinistral strike-slip fault, as believed by previous researchers. The results of this study show that the geological boundaries for the Paleozoic, Mesozoic, and Cenozoic eras were all dextrally dislocated by the fault, with the faulted displacements being similar. The maximum strike-slip displacement of the fault, after elimination of topographic effects, was found to be 961±6 m. The Sanguankou fault at the northern section exhibits obvious characteristics of more recent activities, with a series of small gullies having undergone synchronized dextral writhing after traversing the fault. The average horizontal slip rate of the fault since the late Quaternary was determined to be approximately 0.35 mm/a. The pre-existing fold structures formed during the late Pliocene were dislocated by the fault and became ex situ, indicating that dextral strike-slip of the fault could not have occurred prior to the late Pliocene. The maximum displacements and average slip rates were used to estimate the onset time of the dextral strike-slip activities of the fault as being after 2.7 Ma. In this study, the understanding of previous researchers concerning the extension in the northeastern margin of the Tibet Plateau was combined with analyses of the successive relationships between fold deformations and fault activities. This led to the finding that the extension in the northeastern margin of the Tibet Plateau reached the vicinity of the SGK-NSSF during the late Pliocene (∼2.7 Ma), causing regional uplift and fold deformations of the strata there. During the early Quaternary, the northeastern compression of the Tibet Plateau and the counterclockwise rotation of the Ordos block collectively resulted in the dextral strike-slip activities of the SGK-NSSF. This then formed the foremost margin of the arc tectonic belt extension in the northeastern margin of the Tibet Plateau.

Far-field coseismic displacements associated with the great Sumatra earthquakes of December 26,2004 and March 29,2005 constrained by Global Positioning System

Based on continuous GPS observations within China as well as global GPS tracking network, a calculation has been made of far-field coseismic displacements associated with the December, 2004 (Mw = 9.3) and March, 2005 (Mw = 8.7) earthquakes. The far-field coseismic displacements are associated with the 2004 shock range more than 6000–7000 km in both north-south and east-west dimensions, and depict an undulated wave pattern of contraction and extension. The coseismic displacements associated with the 2005 event, however, are distributed near the epicentral region, and the event itself may be an aftershock of the 2004 earthquake.

Continental dynamics and continental earthquakes

Two key research projects in geoscience field in China since the IUGG meeting in Birmingham in 1999, the project of “East Asian Continental Geodynamics” and the project of “Mechanism and Prediction of Strong Continental Earthquakes” are introduced in this paper. Some details of two projects, such as their sub-projects, some initial research results published are also given here. Because of the large magnitude of the November 14, 2001 Kunlun Mountain PassMS=8.1 earthquake, in the third part of this paper, some initial research results are reviewed for the after-shock monitoring and the multi-discipline field survey, the impact and disaster of this earthquake on the construction site of Qinghai-Xizang (Tibet) railway and some other infrastructure.