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Zhu M.,Zhejiang University | Zhu M.,Research Center for the Structures in Oil and Gas Bearing Basin | Chen H.,Zhejiang University | Chen H.,Research Center for the Structures in Oil and Gas Bearing Basin | And 4 more authors.
Tectonophysics | Year: 2017

The formation of the Sanjiang and Qinling orogens caused by closure of Paleo-Tethys Ocean along the western and northern margins of the Yangtze block during the early Mesozoic created a unique basin-mountain system. Petrology, geochemistry, geochronology, sedimentary facies and paleocurrent data are integrated in order to investigate the changing provenance of Middle-Late Triassic successions from the southwestern Sichuan region, SW China. The detrital compositions from the Middle Triassic successions indicate low mature sediments of mafic and intermediate rocks origin, which derivation mainly from recycled orogenic and secondarily from the Emeishan Large Igneous Province (ELIP). The detrital zircon U-Pb age distribution pattern of the Middle Triassic sandstone samples exhibits four major age Groups at ~ 257 Ma, 650–500 Ma, 880–710 Ma, and 1000–900 Ma. Combined with the geochemical characteristics, an interior Yangtze block source including the Khamdian uplift and ELIP is suggested. The Late Triassic sedimentary rocks yield seven U-Pb age Groups at 245–210 Ma, 290–260 Ma, 460–410 Ma, 650 Ma, 880–710 Ma, 1900–1600 Ma, and 2600–2400 Ma, which are consistent with the data reported from the Sichuan basin, Songpan Ganzi basin and the southern Yidun terrane, and are partly similar to those of the south Qinling orogen, Jiangnan Xuefeng thrust belt. In contrast to the Middle Triassic successions, the sandstone composition modals and whole-rock geochemistry of the Late Triassic samples denote mature deposits and of intermediate and acid rocks origin. Therefore, during the Late Triassic, the southwestern Sichuan basin received materials from the Songpan Ganzi folded belt and Yidun arc complex dominantly, and from the Qinling orogen and Jiangnan Xuefeng thrust belt subsidiarily. The Sanjiang orogen and the Songpan Ganzi folded belt should have controlled the formation of the southwestern Sichuan basin, while the development of the Qinling orogen and the western Jiangnan-Xuefeng orogen may also influenced the formation of the southwestern Sichuan basin. The southwestern Sichuan region evolved from the passive continental margin basin in the Middle Triassic into a foreland basin in the Norian age of the Late Triassic. © 2017 Elsevier B.V.

Dong Y.,Kunming University of Science and Technology | Dong Y.,Zhejiang University | Dong Y.,Research Center for the Structures in Oil and Gas Bearing Basin | Xiao A.,Zhejiang University | And 4 more authors.
Journal of Earth Science | Year: 2014

Field observations of the crossing relationships of fractures have been used to explain the sequence of fractures. Based on field observations from Fuyang-Lin’an anticline, located near Hangzhou, Zhejiang Province, this paper proposes that the formation of synfolding fractures was influenced dominantly by one fracture set, which developed prior to folding and the orientation was nearly parallel to the bedding. The length of the prefolding fractures is longer than the synfolding fractures. These prefolding fractures cut thicker strata into small pieces and form a dense network of fractures in thicker strata. Most synfolding fractures, which are oblique to the bedding, are truncated by prefolding fractures in thicker strata. The synfolding fractures, which result from local stress, are inferred to form during folding. Here, the mechanism of truncation was analyzed using finite-element models. The approach was based on the idea that natural fractures can be interpreted or inferred from stress distribution. The presence or absence of prefolding fractures is shown to strongly control the distribution of stress, and this control has an important implication for interpreting the fracture truncation mechanism from geomechanical models. © China University of Geosciences and Springer-Verlag Berlin Heidelberg 2014.

Dong Y.-P.,Kunming University of Science and Technology | Dong Y.-P.,Zhejiang University | Dong Y.-P.,Research Center for the Structures in Oil and Gas Bearing Basin | Xiao A.-C.,Zhejiang University | And 7 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013

To explore the relationship between the formation of fractures and the deformation of strata, fractures data from outcrops in the Upper Jurassic strata of Lin'an are integrated with geometry modeling in this study. It is found that two main type fractures are secondary structures to the fold, which are referred to as fold accommodation fractures in this paper, and named as D and D' fractures respectively. An angle ranging 44°-80° exists between fractures and stratum layers, with D' fracture directing the motion of local layer and D fracture directing the motion of adjacent layer. The fractures formed primarily because of an increase in bed curvature within fold cores. The relationship between fracture density and layer thickness is established on the basis of geometrical analysis of the fold and we find that fractures density is proportional to the layer thickness.

LIN X.,Zhejiang University | LIN X.,Research Center for the Structures in Oil and Gas Bearing Basin | CHEN H.,Zhejiang University | CHEN H.,Research Center for the Structures in Oil and Gas Bearing Basin | And 8 more authors.
Mining Science and Technology | Year: 2010

Fault related folds and fractures, which always improve reservoirs and trap capacity, especially in the oil and gas fields in western China, are of extreme importance for oil and gas exploration. Based on four assumptions and fault related fold theory, we propose four conceptual models for fracturing in fault related folds, i.e., a simple-step parallel fault bend anticline, a simple-step parallel fault propagation anticline, a multiple-bend fault-bend fold and a break-forward imbricate. Fracture conditions depend on structural evolution and specific site conditions. A case study of the Kulongshan Anticline in the Jiuquan Basin shows that our conceptual models match reality data very well. © 2010 China University of Mining and Technology.

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