Lithofacies characteristics and their controlling effects on reservoirs in buried hills of metamorphic rocks: A case study of late Paleozoic units in the Aryskum depression, South Turgay Basin, Kazakhstan

Structural defects in the form of relict joints are frequently found in residual soils derived from the decomposition of igneous and metamorphic rocks. Previous studies indicate that the shear strength along relict joints is generally less than that of the intact material and therefore such joints form planes of weakness in the jointed soil. Slope designs in jointed soils, based on the strength of the intact material without considering the presence of adversely oriented relict joints, may be unsafe. The distribution of mass strength of jointed soils in the field is bimodal, with the intact strength as an upper limit and the joint strength as a lower limit; it varies with direction and with the geometry of the potential slip surface. In order to describe this behaviour, a probabilistic method to estimate the mass strength is presented and its practical application is illustrated by a case study.

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Supplemental Material: Crustal material recycling induced by subduction erosion and subduction-channel exhumation: A case study of central Tibet (western China) based on P-T-t paths of the eclogite-bearing Baqing metamorphic complex

10.1130/gsab.s.13190657 ◽

2020 ◽

Author(s):

Xin Jin ◽

Yu-Xiu Zhang ◽

Kai-Jun Zhang ◽

et al.

Keyword(s):

Western China ◽

Metamorphic Rocks ◽

Crustal Material ◽

Metamorphic Complex ◽

Subduction Channel ◽

Material Recycling ◽

Subduction Erosion ◽

Mineral Compositions ◽

Central Tibet

Compositional mapping images of one garnet, Triassic paleo-geographic facies of Qiangtang, summarized published Paleozoic and Proterozoic ages in Tibetan Plateau and Himalaya, mineral compositions, and chronology data of the Baqing metamorphic rocks.

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The Duration and Geodynamics of Formation of the Angara–Vitim Batholith: Results of U–Pb Isotope (LA-ICP-MS) Dating of Magmatic and Detrital Zircons

Russian Geology and Geophysics ◽

10.2113/rgg20204223 ◽

2021 ◽

Vol 62 (12) ◽

pp. 1331-1349

Author(s):

V.B. Khubanov ◽

A.A. Tsygankov ◽

G.N. Burmakina

Keyword(s):

Drainage Basin ◽

Detrital Zircons ◽

Late Paleozoic ◽

Metamorphic Rocks ◽

Zircon Geochronology ◽

Geochronological Data ◽

Pb Isotope ◽

Alluvial Deposits ◽

Detrital Zircon Geochronology ◽

Icp Ms

Abstract —We present results of U–Pb (LA-ICP-MS) dating of detrital zircons from the alluvial deposits of the Angarakan River (North Muya Ridge, northern Baikal region), whose drainage basin is composed mainly of granitoids of the Barguzin Complex, typomorphic for the late Paleozoic Angara–Vitim batholith (AVB). Three age clusters with peaks at 728, 423, and 314 Ma have been identified in the studied population of detrital zircons. It is shown that small outliers of igneous and metamorphic rocks, probably similar to the large AVB roof pendants mapped beyond the drainage basin, are the source of Neoproterozoic and early Paleozoic zircons. The late Paleozoic cluster comprises two close peaks at 314 and 28 Ma, which totally “overlap” with the time of the AVB formation and mark a granitoid source of the zircons. The results of detrital-zircon geochronology, together with the data on bedrocks, point to the prolonged (~40 Myr) formation of the AVB, but the intensity of magmatism during this period calls for additional study. Based on the analysis of published geological, geochemical, and geochronological data, we assume that the AVB resulted from the plume–lithosphere interaction that began in the compression setting and gave way to extension 305–300 Ma (the Carboniferous–Permian boundary), which caused replacement of “crustal” granitoids by granitoids formed from a mixed mantle–crustal source.

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