U–Pb Dating of the Sill-Like (Plated) Bodies of the Early Kinematic Series of Gabbrodiorite–Granodiorites in the Svecofennian Fold-and-Thrust Assemblage of the Ladoga Region
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Thrust fault
New 40Ar/39Ar ages representing a number of basaltic sills and a key lava flow from the Faroe Islands are presented in this contribution and utilised in order to assess the igneous history of parts of this region. In turn, the acquired ages are contrasted against other Faroese rocks of known ages as well as against other comparable igneous regions in the North Atlantic area. Altogether, the novel ages obtained in this work enable us to put new constraints on the timing of late stage magmatic activity and hence lithospheric extension within this part of the North Atlantic Igneous Province, which the Faroe Islands form part of. Even though the main stages of igneous activity within the North Atlantic Igneous Province generally took place within a time span of ~61 Ma to ~55 Ma, examples of more recent magmatism have been documented for W Greenland, E Greenland, the Norwegian – Greenland Sea, igneous centres at the eastern fringes of the Rockall Plateau and in the Rockall trough, thus testifying that lithospheric extension off rift axes continued for some noticeable time following onset of regional seafloor spreading. In this research we present new ages as young as ~50.5 Ma for some of the smallest Faroese sills and demonstrate that the larger and oldest sills of the Faroe Islands, grouped into the Streymoy/Kvívík sills and the Eysturoy/Sundini sills respectively (~55.5 Ma), likely formed just subsequent to the formation of the uppermost parts of the Enni Formation, which represent the latest stages of local surface magmatism at ~55.8 Ma. Gradually decreasing volumes of Faroese sills coupled with sequentially younger ages point to systematic decrease of local igneous activity with increasing distances to active regional rifting zones in the Early Paleogene Period, as the young Faroese lava plateau gradually drifted away from the then active regional rift axis. Similar scenarios in other parts of the North Atlantic Igneous Province support our inferences that it was commonplace within this large igneous province to experience relatively small-scale lithospheric extension and magmatism at some distances from zones/axes of active seafloor-spreading. Age variations between igneous products of the Faroe Islands versus those of the central E Greenland point to a somewhat diachronous evolution pattern within this part of the North Atlantic Igneous Province subsequent to ~57.5 Ma. Accordingly, our study does not preclude the existence of a contemporaneous Icelandic microcontinent between Faroe Islands and central E Greenland.
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Large igneous province
Seafloor Spreading
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Luzong Mesozoic volcanic basin is located in the Lower Yangtze River fault-depression zone, where is the north margin of the Yangtze block. The volcanic and intrusive plutons occur widely in Luzong basin, including four formations of volcanic rocks, such as, Longmenyuan Formation, Zhuanqiao Formation, Shuangmiao Formation and Fushan Formation and 34 intrusive plutons. Based on detailed field geological work and our former geochronology research on five plutons such as Bajiatan pluton, Chengshan pluton, Huashan pluton, Huangmeijian pluton and Zongyang pluton, we further carried out systematic geology and geochronology study of intrusive plutons in the Luzong Basin. LA-ICP-MS zircon U-Pb dating for 15 plutons has been carried out, which yield the ages of Huangtun pluton (134.4 ± 2.2 Ma), Yueshan pluton (132.7 ± 1.5 Ma), Bamaoshan pluton (132.7 ± 1.9 Ma), Jianshan pluton (132.0 ± 1.3 Ma), Xiewani pluton (131.6 ± 1.1 Ma), Longqiao pluton (131.1 ± 1.5 Ma), Jiaochong pluton (129.6 ± 1.3 Ma), Tudishan pluton (127.4 ± 2. 8 Ma), Fenghuangshan pluton (128.4 ±0.9 Ma), Luolin pluton (126.3 ± 2.O Ma), Longwangjian pluton (126.5 ± 1.5 Ma), Xiaolin pluton (126.2 ± 1.8 Ma), Dagangyao pluton (125.9 ± 1.3 Ma), Batan pluton (125.1 ± 1.1 Ma), Maowangmiao pluton (123.9 ± 1.9 Ma), respectively. The epoch of plutons in the Luzong basin is 134-123Ma. According to the epoch and geological characteristics, the intrusive rocks in the Luzong basin can be divided into two stages. The early stage monzonite-diorite plutons outcrop in the north part of the Luzong basin with epoch of 134-130Ma, are controlled by NNE orient structures and volcano-structure and have close relationship with Longmenyuan and Zhuanqiao cycle volcanic activity. The late stage intrusive plutons have two types. One type is syenite and outcrops in the south part of the Luzong basin, whose epoch is 129-123Ma. Those syenite plutons are mainly controlled by NNE orient structures or volcano-structure and share close relationship with Shuangmiao and Fushan cycle volcanic activity. The other type is A-type granites and outcrops in the southeast margin of the basin, whose epoch is 126-123 Ma. Those A-type granites are controlled by regional NNE deep faults and have no relationship with the basin volcano-structures. The iron, copper, gold, lead, zinc and uranium deposits in the study area related to magmatic activities can be classified into three metallogenic seiries. The monzonite-diorite plutons have close relationship with Luohe, Nihe and Longqiao iron deposits, Yueshan lead and zinc deposit and Jingbian and Bamaoshan copper deposits. The syenite plutons have close relationship with Makou and other iron deposits. The A-type granites have close relationship with No. 3440 and other gold uranium deposits. Regionally, there are three periods (145-136Ma, 135-127Ma, 126-123Ma) of magmatic and ore-forming activities in the Middle-Lower Yangtze River Valley metallogenic belt. The intrusive plutons in the Ning-Wu basin were the products of the second and third period magmatic activity and obviously later than the first period high-K calc-alkaline intrusions related to skarn-porphyry Cu-Au mineralizations in the uplift areas in the Middle-Lower Yangtze River Valley metallogenic belt. The intrusive plutons in Luzong volcanic basin were thought to be formed under regional lithospheric extension and thinning environment which has great significance for further research and exploration.
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Abstract Well preserved brontosaur footprints are replicated as impressions at the top of a dacitic igneous sill that intruded the track‐rich Cretaceous Jindong Formation, Kyeongsang basin South Korea. Although an unusual occurrence, the example shows the potential of such intrusions for enhancing preservation of trace fossils in some cases Key words: brontosaur footprintsCretaceousKoreaigneous intrusion
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Large igneous province
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Dike
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In this contribution we present novel radiometric 40Ar/39Ar ages representing a number of basaltic sills/lavas of the Faroe Islands, which themselves form part of the North Atlantic Igneous Province. Measured ages are utilised in an attempt to assess the local igneous history, where the new ages are contrasted against those of other local rocks of known ages as well as against those of comparable/neighbouring North Atlantic igneous regions. The novel ages presented in this contribution allow us to put new constraints on the timing of late stage magmatic activity and associated crustal extension of this part of the North Atlantic area. In this research we present new ages as young as ~50.5 Ma for some of the smallest Faroese sills and demonstrate that the larger and oldest local sills, grouped into the low-TiO2 Streymoy/Kvívík sills and the high-TiO2 Eysturoy/Sundini sills respectively (~55.5 Ma), likely formed immediately subsequent to the formation of the uppermost parts of the Enni Formation, which itself represent the latest stages of local surface magmatism at ~55.8 Ma. Gradually decreasing sill volumes coupled with successively younger ages point to systematic decrease of local igneous activity with increasing distances to active contemporaneous local rifting zones. Comparable scenarios recorded for other parts of the North Atlantic Igneous Province support our inferences regarding the nature of late-stage magmatic activity at some distances from zones of active seafloor-spreading. Comparisons between ages of Faroese igneous products versus those of e. g. central E Greenland point to a somewhat diachronous evolution pattern within this part of the North Atlantic Igneous Province subsequent to ~57.5 Ma. The lithosphere-asthenosphere boundary is commonly thought to be critical for the formation of basaltic magmas. Accordingly, the close spatial and temporal associations between many high-TiO2 and low-TiO2 Faroese rock suites are interpreted in the context of a regional version of this boundary.
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Seafloor Spreading
Large igneous province
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Large igneous province
Silicic
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Flood basalt
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Anticline
Thrust fault
Monocline
Strain partitioning
Echelon formation
Normal fault
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