Deformational history and regional tectonic significance of the Redwood Creek schist, northwestern California

A large block of Upper Paleozoic limestone at Blind Creek near Keremeos, B.C. was emplaced by dry gravity sliding, probably associated with uplift related to nearby Eocene volcanism. The block is a nearly flat tabular unit, exposed over an area of 650 m by 1300 m, and is separated from underlying chaotic breccias derived from adjacent Paleozoic rocks and from Eocene volcanic flow rocks by a sole fault. The block comprises two lithologically and tectonically distinct units, a lower imbricated unit consisting of several slices repeating the same sequence of strata, separated from an upper unit of massive limestone by a low-angle fault. Within the imbricated unit, early faults emanate from lenticular masses of breccia along the sole, become increasingly steeper upward, and are truncated above by the upper low angle fault. Associated minor folds and fractures have a clockwise sense of rotation. Later fractures and associated minor folds have the opposite dip and sense of rotation. These two subsets comprise a conjugate set whose inferred compressive stress direction coincides with the present overall dip direction of the entire mass.The northwesterly adjacent autochthonous Olalla limestone, or a similar body now buried by younger units, is a likely source for the Blind Creek allochthon.Absence of any structures within the limestone indicative of ductile deformation contrasts markedly with those of the highly deformed rocks of the Old Tom and Shoemaker Formations, the Kobau Group, and the nearby gneisses of the western Shuswap Complex.

Download Full-text

Petrochemistry and regional tectonic significance of metabasites in basement windows of the central Scandinavian Caledonides

Geologiska Foereningan i Stockholm Foerhandlingar ◽

10.1080/11035898009454503 ◽

1980 ◽

Vol 102 (4) ◽

pp. 499-514 ◽

Cited By ~ 7

Author(s):

Leif Johansson

Keyword(s):

Scandinavian Caledonides ◽

Tectonic Significance ◽

Regional Tectonic

Download Full-text

Petrogenesis of the Cretaceous Intraplate Mafic Intrusions in the Eastern Tianshan Orogen, NW China

Frontiers in Earth Science ◽

10.3389/feart.2021.665610 ◽

2021 ◽

Vol 9 ◽

Author(s):

Weifeng Zhang ◽

Xin Deng ◽

Bing Tu ◽

Lianhong Peng ◽

Xinbiao Jin

Keyword(s):

Stability Field ◽

Magma Evolution ◽

Nd Isotope ◽

Eastern Tianshan ◽

Nw China ◽

Late Mesozoic ◽

Mafic Intrusions ◽

Tectonic Significance ◽

Regional Tectonic ◽

Garnet Stability Field

In this study, we conducted zircon U-Pb dating, and whole-rock geochemical and Sr-Nd isotope analyses on the Late Mesozoic dolerite dykes in the Bailingshan Fe deposit (Eastern Tianshan Orogen, NW China) to unravel their petrogenesis and regional tectonic significance. Zircon U-Pb dating on the dolerite yielded an Early Cretaceous age of 129.7 ± 1.4 Ma. The dolerite is calc-alkaline sodic (Na2O/K2O = 4.71 to 6.80), and enriched in LILEs (Rb, K, Sr, and Pb) but depleted in HFSEs (Nb, Ta, and Ti). The intermediate Nb/U (16.7 to 18.5) and Ce/Pb (6.33 to 6.90) values, and the presence of xenocrystic zircons in these dolerite dykes suggest crustal assimilation during the magma evolution. Petrological modeling suggests fractionation of olivine, pyroxene, garnet, and spinel. All the dolerite samples have low initial 87Sr/86Sr (0.7041 to 0.7043) and positive εNd(t) (+ 4.6 to + 5.1) values, indicative of a depleted asthenospheric mantle source. Partial melting modeling suggests that the melting has occurred in the spinel-garnet stability field. Integrating the data from ore deposit geology, geochronology, geochemistry and Sr-Nd isotopes, we proposed that the Late Cretaceous Eastern Tianshan mafic magmatism was developed in an intraplate extension setting.

Download Full-text

Fractal and Multifractal Characteristics of Lineaments in the Qianhe Graben and Its Tectonic Significance Using Remote Sensing Images

Remote Sensing ◽

10.3390/rs13040587 ◽

2021 ◽

Vol 13 (4) ◽

pp. 587

Author(s):

Zhiheng Liu ◽

Ling Han ◽

Chengyan Du ◽

Hongye Cao ◽

Jianhua Guo ◽

...

Keyword(s):

Fractal Dimension ◽

Tectonic Activity ◽

Mountainous Area ◽

Tensor Voting ◽

Self Similarity ◽

Plate Movement ◽

Tectonic Significance ◽

Regional Tectonic ◽

Fractal Spectrum ◽

Tracing Algorithm

The distribution and characteristics of geological lineaments in areas with active faulting are vital for providing a basis for regional tectonic identification and analyzing the tectonic significance. Here, we extracted the lineaments in the Qianhe Graben, an active mountainous area on the southwest margin of Ordos Block, China, by using the tensor voting algorithm after comparing them with the segment tracing algorithm (STA) and LINE algorithm in PCI Geomatica Software. The main results show that (1) the lineaments in this area are mostly induced by the active fault events with the main trending of NW–SE, (2) the box dimensions of all lineaments, NW–SE trending lineaments, and NE–SW trending lineaments are 1.60, 1.48, and 1.44 (R2 > 0.9), respectively, indicating that the faults exhibit statistical self-similarity, and (3) the lineaments have multifractal characteristics according to the mass index τ(q), generalized fractal dimension D(q), fractal width (Δα = 2.25), fractal spectrum shape (f(α) is a unimodal left-hook curve), and spectrum width (Δf = 1.21). These results are related to the tectonic activity in this area, where a higher tectonic activity leads to more lineaments being produced and a higher fractal dimension. All of these results suggest that such insights can be beneficial for providing potential targets in reconstructing the tectonic structure of the area and trends of plate movement.

Download Full-text