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Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes
Jógvan Hansen,
Jon Davidson,
Dougal Jerram,
Christopher Ottley,
Mike Widdowson
Issue:
Volume 8, Issue 5, October 2019
Pages:
235-267
Received:
14 August 2019
Accepted:
23 September 2019
Published:
9 October 2019
Abstract: The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO2 sill category (TiO2 = 0.7-0.9), a relatively high-TiO2 sill category (TiO2 = 1.95-2.6) and an intermediate-TiO2 sill that displays major element compositions lying between the other two categories. Mantle normalised plots for the high-TiO2 and low-TiO2 sills display relatively uniform flat LREE trends and slightly steeper HREE slopes for high-TiO2 relative to low-TiO2 sills. The intermediate-TiO2 Morskranes Sill is LREE depleted. Mantle normalised trace elements of low-TiO2 sill samples define positive Eu and Sr anomalies, whereas high-TiO2 sill samples display negative anomalies for these same lements. Different Nb and Ta anomalies (positive versus negative) in many high-TiO2 versus low-TiO2 sill samples suggest various metasomatism of their sources prior to partial melting. The intermediate-TiO2 sill displays noticeably lower 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios relative to both the high-TiO2 and the low-TiO2 sill samples. Pb isotope compositions displayed by local contaminated basaltic lavas imply that some of these assimilated distinct crustal material from E Greenland or basement from NW Britain, while others probably assimilated only distinct E Greenland type of crustal material. A third crustal source of E Greenland or Rockall-type basement could be required in order to explain some of the range in lead isotopes displayed by the intermediate-TiO2 Morskranes Sill. Geochemical modelling suggest that Faroese high-TiO2 sills, could have formed by ~4 to 7.5% batch melting of moderately fertile lherzolites, while 16 to 21% batch melting fertile mantle sources could explain geochemical compositions of Faroese low-TiO2 sills. The intermediate-TiO2 sill samples could have formed by a range of 6 to 7% batch melting of a depleted mantle source, probably with a composition comparable to sources that gave rise to local low-TiO2 and intermediate-TiO2 host-rocks. Most Faroese sill samples probably developed outside the garnet stabilitry field and probably formed by batch melting of mantle materials comparable in composition to those reported for the sub-continental lithospheric mantle (SCLM) previously at depths of ≤ 85 km. Relative enrichments in LREE (and LILE in general), and their varying Nb and Ta anomalies point to sources affected by metasomatism.
Abstract: The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO2 sill category (TiO2 = 0.7-0.9), a relatively high-TiO2 sill category...
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Present-Day Two-Dimension Maturity History Modelling of Source Rocks from the Central Region of the Andaman Sea Back Arc Depression
Jonathan Atuquaye Quaye,
Sihuang Xu,
Yanick Brice Lemdjou
Issue:
Volume 8, Issue 5, October 2019
Pages:
268-276
Received:
1 September 2019
Accepted:
5 October 2019
Published:
17 October 2019
Abstract: Basin modelling is an essential research tool that aids geologists improve the description and analysis of subsurface activity. The central region of the Andaman Sea back arc basin is a potential oil and gas prospect. Herein, two-dimension present-day maturity models are constructed from four seismic sections of the study area using Basin Mod™ software (Platte River Associates, Inc. of USA). Designated study areas are the South to North Moattama Basin, western Moattama to the Mergui Shelf, Western to Eastern Moattama basin centres through Eastern Moattama basin centre to the Eastern section of Mergui basin and Eastern Andaman Sea Basin to Western Mergui Basin. The two-dimension (2D) maturity models are generated from known data burial and geothermal data. Vitrinite Reflectance (Ro%) which is the main variable in determining source rock (s) maturity showed that the source units were within the oil (0.5% ≤ Ro ≤ 1%) and gas (1.3% ≤ Ro ≤ 4.5%) and had commenced generation of some quantities of hydrocarbons. Data analyzed revealed that most portions of the Oligocene and Lower Miocene shales source units in all study areas buried below 2000 m are matured to generate oil and / or gas. The outcome of modelling also indicated that source units from the Moattama Basin center and the Mergui Basin were mostly matured to produce some form of hydrocarbons, principally gas or dry gas. However, no oil expulsion into limestone reservoirs was observed; only gas or dry gas.
Abstract: Basin modelling is an essential research tool that aids geologists improve the description and analysis of subsurface activity. The central region of the Andaman Sea back arc basin is a potential oil and gas prospect. Herein, two-dimension present-day maturity models are constructed from four seismic sections of the study area using Basin Mod™ soft...
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An Alternative Structural Model for the Development of the Cape Fold Belt Syntaxis and Groundwater Potential
Blignault Hendrik Johan,
Theron Johannes Nicolaas
Issue:
Volume 8, Issue 5, October 2019
Pages:
277-284
Received:
11 September 2019
Accepted:
7 October 2019
Published:
25 October 2019
Abstract: The syntaxis separates the eastern and western branches of the Cape Fold Belt, South Africa. A satisfactory and holistic solution remains unresolved. This investigation is to develop an alternative hypothesis for the development of the syntaxis. Because macroscopic fold structures are considered most relevant in resolving a tectonic solution on subcontinental scale, the fold hinge traces of macroscopic structures were comprehensively compiled from published geological maps. The fold patterns of the eastern and western fold belt branches are separated across the hypothetical Ceres lineament without any identified interaction. The en echelon fold pattern of the western branch is interpreted as the result of northern movement of a lower crustal block. The eastern branch is dominated by north-verging over folding and thrusting in the east and westwards towards the Ceres lineament the folds are predominantly upright. It is suggested that differential basal slip causes the fold belt to terminate against the lineament with a sinistral rotation that is also accommodated by the sinistral Villiersdorp ductile shear zone. It appears that basal slip retardation increases from east to west. The two fold belt branches were developed in adjacent crustal blocks that reacted differently to northward tectonic transport driven by subduction and accretion further south along southern Gondwana. The hypothesis is testifiable. The structural investigation revealed the hitherto unknown existence of special structural situations with wellfield potential for groundwater that remains to be tested by drilling.
Abstract: The syntaxis separates the eastern and western branches of the Cape Fold Belt, South Africa. A satisfactory and holistic solution remains unresolved. This investigation is to develop an alternative hypothesis for the development of the syntaxis. Because macroscopic fold structures are considered most relevant in resolving a tectonic solution on sub...
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1D Inversion of Large Loop Transient Electromagnetic Data Acquired Using Offset Loop Configuration Over Multi-layer Earth Models
Satya Prakash Maurya,
Nagendra Pratap Singh,
Ashish Kumar Tiwari
Issue:
Volume 8, Issue 5, October 2019
Pages:
285-293
Received:
14 September 2019
Accepted:
15 October 2019
Published:
25 October 2019
Abstract: The present research describes a 1D inversion scheme for interpretation of large loop TEM data acquired using offset loop configuration due to a large loop source, over the layered earth models. The inversion is based on a non-linear least square method that generates a smooth layered earth model by minimizing the residual misfit function in an iterative process. It produces an inverted model from the data using the criteria of minimization of misfit function and/or convergence of residual in two successive iterations. The forward problem is formulated in frequency domain, and then it is transformed into the time domain using Fourier cosine and sine transform. The accuracy and robustness of algorithm is tested by inverting the large loop TEM data acquired using offset loop configurations over the homogeneous, two layer, three layer and four layer earth models, with or without the addition of random noises. Inverted results are in good accordance with the theoretical models and validate that different parameters are recovered with high accuracy. The program works satisfactorily with noisy data and produces inverted results with acceptable accuracy for synthetic data up to 5% random noises.
Abstract: The present research describes a 1D inversion scheme for interpretation of large loop TEM data acquired using offset loop configuration due to a large loop source, over the layered earth models. The inversion is based on a non-linear least square method that generates a smooth layered earth model by minimizing the residual misfit function in an ite...
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Spatial Prediction of Soil Organic Matter Using Geostatistics and Topographic Unit Zoning Integrated in GIS: A Case Study
Zhou Ziyan,
Fu Peihong,
Han Zongwei,
Huang Wei
Issue:
Volume 8, Issue 5, October 2019
Pages:
294-302
Received:
30 May 2019
Accepted:
22 October 2019
Published:
28 October 2019
Abstract: The spatial distribution of soil organic matter (SOM) has a close connection with topography. To understand the effects of topographic synergy effects in traditional geostatistic methods, the influence of topography is considered in SOM geostatistic studies by combining geographic unit zoning and spatial prediction. We explored the changes in the SOM distribution between that obtained using spatial interpolation integrated with 13 different classical topographic units and determined using global interpolation with 6485 random soil samples obtained from Zhongxiang City, Hubei Province, China. The steps are as follows. At first, the terrain factors were calculated from the digital elevation data (DEM) and the topographic units were precisely divided into 13 different classical types more subtly by integrating the terrain factors. The regions were divided, which was based on terrain classification rules formed by the distribution of terrain factors in different landforms. Secondly, soil samples were collected in different topographic types, and the distribution of SOM for each sample set in different topographic units was generated by ordinary Kriging. Then, the corresponding results of interpolation for each sample set were segmented based on topographic unit region, and combining the result in each region, the spatial distribution of SOM based on topographic unit was obtained. Finally, verification and comparison with the accuracy of each SOM distributions were performed, which were obtained by using topography based geostatistics and traditional global geostatistics, respectively. Our results indicated that more accurate SOM spatial distributions can be obtained using the proposed method, especially in regions with gentle topography, such as ridge, shoulder, summit, toe slope (north/northeast side), and low-lying terrain units.
Abstract: The spatial distribution of soil organic matter (SOM) has a close connection with topography. To understand the effects of topographic synergy effects in traditional geostatistic methods, the influence of topography is considered in SOM geostatistic studies by combining geographic unit zoning and spatial prediction. We explored the changes in the S...
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