کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10144988 | 1646331 | 2018 | 58 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Paleomagnetism, magnetic anisotropy and U-Pb baddeleyite geochronology of the early Neoproterozoic Blekinge-Dalarna dolerite dykes, Sweden
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
![عکس صفحه اول مقاله: Paleomagnetism, magnetic anisotropy and U-Pb baddeleyite geochronology of the early Neoproterozoic Blekinge-Dalarna dolerite dykes, Sweden Paleomagnetism, magnetic anisotropy and U-Pb baddeleyite geochronology of the early Neoproterozoic Blekinge-Dalarna dolerite dykes, Sweden](/preview/png/10144988.png)
چکیده انگلیسی
Paleogeographic proximity of Baltica and Laurentia in the supercontinent Rodinia has been widely accepted. However, robust paleomagnetic poles are still scarce, hampering quantitative tests of proposed relative positions of the two cratons. A recent paleomagnetic study of the early Neoproterozoic Blekinge-Dalarna dolerite (BDD) dykes in Sweden provided a 946-935â¯Ma key pole for Baltica, but earlier studies on other BDD dykes discerned large variances in paleomagnetic directions that appeared to indicate more complicated motion of Baltica, or alternatively, unusual geodynamo behavior in early Neoproterozoic time. We present combined paleomagnetic, rock magnetic, magnetic fabric and geochronological studies on BDD dykes in the Dalarna region, southern Sweden. Positive baked-contact and paleosecular variation tests support the reliability of the 951-935â¯Ma key pole (Platâ¯=â¯â2.6°N, Plonâ¯=â¯239.6°E, A95â¯=â¯5.8°, Nâ¯=â¯12 dykes); and the ancient magnetic field was likely a stable geocentric axial dipole at that time, based on a positive reversal test. Detailed analysis of the 947â¯Ma Nornäs dyke, one of the dykes previously showing anomalous directions, suggests a partial viscous remagnetization. Therefore, the observed large variances in nearly coeval BDD dykes are suspected to result from present-day overprints that were not adequately removed in earlier studies. In addition, we obtained a 971â¯Ma virtual geomagnetic pole (Platâ¯=â¯â27.0°N, Plonâ¯=â¯230.4°E, A95â¯=â¯14.9°, Nâ¯=â¯4 dykes) for Baltica. Comparing similar-aged poles from Laurentia, we suggest that Baltica and Laurentia drifted together from high to low latitude between 970-960â¯Ma and 950-935â¯Ma, and returned back to high latitude by 920-870â¯Ma. In this scenario, the apparent polar wander paths of Baltica and Laurentia may be more complicated than the previously proposed, solitary Sveconorwegian and Grenville loops. The new U-Pb baddeleyite ages do not support BDD dykes as a giant circumferential swarm generated by a mantle plume, and the prolonged timespan of dyke intrusion is likely associated with the plate boundary forces as causing gravitational extension at the waning stage of the Sveconorwegian orogeny.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Precambrian Research - Volume 317, October 2018, Pages 14-32
Journal: Precambrian Research - Volume 317, October 2018, Pages 14-32
نویسندگان
Zheng Gong, David A.D. Evans, Sten-Ã
ke Elming, Ulf Söderlund, Johanna M. Salminen,