scholarly journals Geochemical composition and origin of mafic rocks of the Jurassic accretionarycomplex in the North Kitakami Belt, the Kuji area, Iwate Prefecture, Northeast Japan

2021 ◽  
Vol 72 (3) ◽  
pp. 173-190
Author(s):  
Satoshi NAKAE
Keyword(s):  
Geochemical Composition ◽  
Mafic Rocks ◽  
The North ◽  
Iwate Prefecture

Contrasting spatial distributions of surface sediment compositions from the Emperor Seamount Chain, North Pacific

2020 ◽  
Author(s):  
Jie Chen ◽  
Jianjun Zou ◽  
Xuefa Shi ◽  
Lester Lembke-Jene ◽  
Dirk Nürnberg ◽  
...  
Keyword(s):  
Negative Correlation ◽  
North Pacific ◽  
Surface Sediments ◽  
Marine Ecosystem ◽  
Spatial Distributions ◽  
Geochemical Composition ◽  
The North ◽  
Clayey Silt ◽  
Seamount Chain ◽  
Emperor Seamount Chain

<p>The Emperor Seamount chain is located in the North Pacific Ocean and beneath the Northern Westerly wind belt. It extends from the subtropical to subarctic North Pacific oceans between 30°N-50°N. Modern observations have shown this region has complex physical oceanic processes, including the Kuroshio Extension, the Oyashio Current, the polar front and the subarctic front. A large amount of dust from the central Asian continent is delivered to this area, which affects the regional marine ecosystem and the global carbon cycle. Due to the lack of sediments from the Emperor Seamount chain, few studies have examined the composition of surface sediments in this ocean realm. On the basis of 50 samples collected during the SO264 Expedition in 2018 using multicorers, we investigate the spatial distributions of sediment grainsize, total organic carbon, CaCO<sub>3</sub> and major and minor elements in surface sediments of this ocean realm. Our data show that the detritus sediments mainly consist of siltly sand and clayey silt with more coarse fractions between ~45°N and 48°N, which has strong negative correlations with water depth. The content of CaCO<sub>3</sub> varies between 0.04% and 83.67% with higher values at the south of 48°N. The TOC content ranges between 0.07% and 1.36% with lower values (<0.3%) occurring at the north of ~45°N. The concentration of ∑REEs ranges from 31 ppm to 136 ppm with lower values between ~45° N and 48°N. There is significant positive Eu anomaly at all stations, indicating widespread occurrence of volcanic detritus. A significant negative correlation between sediment grainsize and ∑REEs and some lithophile elements, such as Al<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, K<sub>2</sub>O, Th, REEs, etc., indicates a strong effect of sediment grainsize on sediment geochemical composition. A strong negative correlation between Al and CaCO<sub>3</sub> suggests contrasting sources, such as terrigenous vs biogenic sources, respectively. Our data confirms the contributions of terrigenous, volcanic and biogenic materials to the bulk sediment with contrasting spatial distribution along the Emperor Seamount Chain.</p><p>Note: This study was supported by the National Natural Science Foundation of China (Grant No.41876065, U1606401) and National Program on Global Change and Air-Sea Interaction(GASI-GEOGE-04). </p>

The ophiolites of the Tibetan Geotraverses, Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986)

1988 ◽  
Vol 327 (1594) ◽  
pp. 215-238 ◽  
Keyword(s):  
Subduction Zone ◽  
Oceanic Lithosphere ◽  
Island Arc ◽  
Passive Margin ◽  
Jinsha River ◽  
Geochemical Composition ◽  
The North ◽  
Kunlun Mountains ◽  
Slow Spreading ◽  
Back Arc

Ophiolite belts are found in Tibet along the Zangbo, Banggong and Jinsha River Sutures and in the Anyemaqen mountains, the eastern extension of the Kunlun mountains. Where studied, the Zangbo Suture ophiolites are characterized by: apparently thin crustal sequences (3-3.5 k m ); an abundance of sills and dykes throughout the crustal and uppermost mantle sequences; common intraoceanic melanges and unconformities; and an N-MORB petrological and geochemical composition. The ophiolites probably formed within the main neo-Tethyan ocean and the unusual features may be due to proximity to ridge-transform intersections, rather than to genesis at very slow -spreading ridges as the current consensus suggests. The Banggong Suture ophiolites have a supra-subduction zone petrological and geochemical composition — although at least one locality in the Ado Massif shows MORB characteristics. However, it is also apparent that the dykes and lavas show a regional chemical zonation, from boninites and primitive island arc tholeiites in the south of the ophiolite belt, through normal island arc tholeiites in the central belt to island arc tholeiites transitional to N-MORB in the north. The ophiolites could represent fragments of a fore-arc, island arc, back-arc complex developed above a Jurassic, northward-dipping subduction zone and emplaced in several stages during convergence of the Lhasa and Qiangtang terranes. The ophiolites of the Jinsha River Suture have a N-MORB composition where analysed, but more information is needed for a proper characterization. The Anyemaqen ophiolites, where studied, have a within-plate tholeiite composition and may have originated at a passive margin: it is not, however, certain whether true oceanic lithosphere, as opposed to strongly attenuated continental lithosphere, existed in this region.

Geophysical interpretation of the geology of the northeast Gander Terrane, Newfoundland

1988 ◽  
Vol 25 (8) ◽  
pp. 1161-1174 ◽  
Author(s):  
H. G. Miller
Keyword(s):  
Gravity Data ◽  
Geochemical Data ◽  
Ultramafic Rocks ◽  
Thrust Belt ◽  
Mafic Rocks ◽  
Geological Interpretation ◽  
The North ◽  
Geophysical Interpretation ◽  
Lateral Extent ◽  
North And South

New gravity data from the northeastern portion of the Gander Terrane of Newfoundland are analysed in association with existing gravity data. These are combined with the digitized and filtered aeromagnetic and geochemical data to produce an interpretation of the subsurface geology.Interpretation of these data suggests that there are two extensive areas underlain at depth by rocks similar to the Dunnage Terrane mafic and ultramafic rocks that outcrop at the Gander River ultrabasic belt. These regions of ultramafic and mafic rocks extend in two north–south belts throughout the study area, and both may have tongues continuing seaward beneath the Deadman's Bay pluton. The western belt, the Ocean Pond belt, probably consists of a series of granitic plutons underlain by mafic and ultramafic rocks. Geophysical modelling corroborates an earlier geological interpretation that the eastern belt, the Indian Bay Big Pond thrust belt, is a thrust sheet. The lateral extent of the thrust belt is accurately determined by new geophysical data. The presence of these two subsurface units composed of material similar to typical Dunnage Terrane rocks demonstrates that the Gander River ultrabasic belt is neither the most eastward extent of the Dunnage Terrane nor the sole thrust upon which Dunnage Terrane material was transported eastward. The two belts have associated diagnostic geochemical signatures and are bounded on the north and south by linear patterns in both the geophysical and geochemical patterns. The block defined by these geophysical and geochemical patterns is the same as that upon which the classic Gander Terrane was defined. The evidence presented in this paper suggests that this block may be allochthonous, which implies that the nature of the Gander Terrane may need to be reconsidered.

scholarly journals Mapping undercover: integrated geoscientific interpretation and 3D modelling of a Proterozoic basin

2020 ◽  
Author(s):  
Mark Lindsay ◽  
Sandra Occhipinti ◽  
Crystal Laflamme ◽  
Alan Aitken ◽  
Lara Ramos
Keyword(s):  
Three Dimensional ◽  
Mineral Resources ◽  
High Amplitude ◽  
High Density ◽  
Tectonic Activity ◽  
Surprising Result ◽  
Mafic Rocks ◽  
The North ◽  
Geophysical Imaging ◽  
Surface Geology

Abstract. Gravity and three-dimensional modelling combined with geochemical analysis are used to examine the subsurface within, and below the poorly exposed Paleoproterozoic Yerrida Basin in central Western Australia. Understanding the structure of a region is important as key features indicating past geodynamic processes and tectonic activity can be revealed. However, in stable, post-depositional tectonic settings only the younger sedimentary units tend to be widely exposed rendering direct observation of basement and intrusive rocks impossible. Geophysical imaging and modelling can reveal the structure of a region under cover. High amplitude density anomalies around the basin cannot be reconciled with current geological knowledge in the case presented here. The density anomalies infer an abundance of buried and high-density material that is not indicated by the surface geology. A hypothetical causative source for the high-density anomalies is considered to be intrusion and extrusion of volcanic mafic rocks during rifting of the basin. The simplest and plausible stratigraphic attribution of these interpreted mafic rocks is to the Killara Formation within the Mooloogool Group. However, geochemistry reveals that the Killara Formation is not the only host to mafic rocks within the region. Mafic rocks present in the Juderina Formation have largely been ignored in previous descriptions of Yerrida Basin magmatism and results indicate that they may be far more substantial than once thought. Sulphur isotopic data indicates no Archean signature to the mafic rocks, a somewhat surprising result given the basement to the Basin is Archean Yilgarn Craton. It is proposed the mafic rocks were sourced from vents located to the north along the Goodin Fault or under the Bryah sub-basin and Padbury Basins. The conclusion is that the formation of the Yerrida Basin involves a geodynamic history more complex than previously thought. The utility to the approach described here is examined for application to cratonic sag-basin environments. This result highlights the value in geophysics and geochemistry to reveal complexity in the earlier geodynamic evolution of the basin that may be indiscernible from surface geology, but may have high importance for the tectonic development of the region and its mineral resources.

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