Paleomagnetism of the Carboniferous Gresford Block,Tamworth Belt,southern New England Orogen: minor counter-clockwise rotation of a primary arc segment     

C. Klootwijk 《Australian Journal of Earth Sciences》2020,67(4):525-573

Abstract

Four oroclinal structures have been identified from structural, magnetic and gravity trends across a Carboniferous continental arc, forearc basin [Tamworth Belt (TB)] and conjugate accretionary complex in the southern New England Orogen (SNEO) of eastern Australia. None of the structures has yet been confirmed conclusively by paleomagnetism as oroclinal. Ignimbrites are common within the forearc basin and have been demonstrated to retain primary magnetisations despite prevalent overprinting. They are well exposed across six major tectono-stratigraphic blocks with partly interlinked stratigraphies, making the forearc basin highly prospective to oroclinal testing by comparing pole path segments for individual blocks across curved structures. Paleomagnetic studies have shown no noticeable rotation across the western/southwestern TB (Rocky Creek, Werrie and Rouchel blocks), but documented herein is a minor counter-clockwise rotation of the Gresford Block of the southern TB. This study details paleomagnetic, rock magnetic and magnetic fabric results for 87 sites (969 samples) across the southern Gresford Block. Predominantly thermal, also alternating field and liquid nitrogen, demagnetisations show a widely present low-temperature overprint, attributed to regional late Oligocene weathering, and high-temperature primary and overprint components residing in both mainly magnetite and mainly hematite carriers. Subtle, but systematic, directional differences between magnetite and hematite subcomponents show the latter as the better cleaned, better-defined, preferred results, detailing nine primary poles of middle and late Carboniferous ages and Permian and Permo-Triassic overprints as observed elsewhere in the western/southwestern TB. The primary poles update a poorly defined mid-Carboniferous section of the SNEO pole path and demonstrate counter-clockwise rotation, quantified at about 15° ± 13° from comparison of mid-Carboniferous Martins Creek Ignimbrite Member poles for the Rouchel and Gresford blocks, that may not necessarily have been completed prior to the Hunter–Bowen phase of the Gondwanide Orogeny. This minor counter-clockwise rotation of the Gresford Block accentuates a primary curvature of the southwestern/southern TB and heralds further, more complex, rotations of the Myall Block of the southeastern TB.  相似文献   

Paleomagnetism and U–Pb geochronology of the Black Range dykes,Pilbara Craton,Western Australia: a Neoarchean crossing of the polar circle     

D. A. D. Evans  A.V. Smirnov  A. P. Gumsley 《Australian Journal of Earth Sciences》2017,64(2):225-237

We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS ²⁰⁷Pb/²⁰⁶Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (>2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (>2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP ²⁰⁷Pb/²⁰⁶Pb baddeleyite weighted mean date from the same swarm, with slight discordance interpreted as being caused by thin metamorphic zircon overgrowths. The updated Black Range suite mean remanence direction (D = 031.5°, I = 78.7°, k = 40, α₉₅ = 8.3°) corresponds to a paleomagnetic pole calculated from the mean of nine virtual geomagnetic poles at 03.8°S, 130.4°E, K = 13 and A₉₅ = 15.0°. The pole's reliability is bolstered by a positive inverse baked-contact test on a younger Round Hummock dyke, a tentatively positive phreatomagmatic conglomerate test, and dissimilarity to all younger paleomagnetic poles from the Pilbara region and contiguous portions of Australia. The Black Range pole is distinct from that of the Mt Roe Basalt (or so-called ‘Package 1’ of the Fortescue Group), which had previously been correlated with the Black Range dykes based on regional stratigraphy and imprecise SHRIMP U–Pb ages. We suggest that the Mt Roe Basalt is penecontemporaneous to the Black Range dykes, but with a slight age difference resolvable by paleomagnetic directions through a time of rapid drift of the Pilbara craton across the Neoarchean polar circle.  相似文献   

Paleomagnetism of Cretaceous Red beds from Eastern Part of South China Block     

Hayao Morinaga  Hiroyuki Kashimura 《中国地质大学学报(英文版)》1999,10(3)

INTRODUCTIONCollisionofIndiawithAsiaappearstohavebroughtaboutlargetectonicdeformationofAsia,especiallyEastAsia(Tapponnieretal.,1986).Post-Cretaceousdeformation(translationand/orrotation)ofSimaoandIndochinablocks,whicharelocatedatthesouthernsideofRedRiverfault(RRF),hasbeenreportedfromCretaceouspaleomagneticin-vestigations(Yangetal.,l995;HuangandOpdyke,l993IYangandBesse,1993).AlsoinSouthChinablock(SCB)locatedatnorthsideoftheRRF,localdeformationofsomeregionsneartheRRFhasbeendocum…  相似文献   

浙江长兴煤山剖面磁性地层学新研究   总被引：5，自引：0，他引：5  

刘育燕  朱艳明  田五红 《地球科学》1999,24(2):151-154

通过对浙江长兴煤山剖面的高分辨率磁性地层学研究,得出了以下结论：（１）浙江长兴煤山剖面可划分为５个正向极性亚带和４个反向极性亚带,其中,长兴阶下部为正向极性,上部为正反相间的混合极性;二叠－三叠系古生物界线处为反向极性;哥里斯介底部为正向极性,（２）浙江长兴煤山剖面所在下扬子陆块二叠－三叠纪之交的古地磁偏角为２８．１°,古纬度为２０．１°Ｎ,这说明自二叠－三叠纪至今,该陆块曾经过自南而北的纬向漂移  相似文献   

The development of a regional geomagnetic daily variation model using neural networks   总被引：1，自引：0，他引：1  

P. R. Sutcliffe 《Annales Geophysicae》1999,18(1):120-128

Global and regional geomagnetic field models give the components of the geomagnetic field as functions of position and epoch; most utilise a polynomial or Fourier series to map the input variables to the geomagnetic field values. The only temporal variation generally catered for in these models is the long term secular variation. However, there is an increasing need amongst certain users for models able to provide shorter term temporal variations, such as the geomagnetic daily variation. In this study, for the first time, artificial neural networks (ANNs) are utilised to develop a geomagnetic daily variation model. The model developed is for the southern African region; however, the method used could be applied to any other region or even globally. Besides local time and latitude, input variables considered in the daily variation model are season, sunspot number, and degree of geomagnetic activity. The ANN modelling of the geomagnetic daily variation is found to give results very similar to those obtained by the synthesis of harmonic coefficients which have been computed by the more traditional harmonic analysis of the daily variation.  相似文献   

Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination     

Takahiro Katagiri  Hajime Naruse  Naoto Ishikawa  Takafumi Hirata 《Island Arc》2020,29(1)

The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (?9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc.  相似文献