Dinosaur tracks in intrusive igneous rock
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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 intrusionKeywords:
Sill
Large igneous province
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.
Sill
Large igneous province
Seafloor Spreading
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Reliable geochronological results gathered so far (n = 76) have considerably constrained the timing of the emplacement of the Karoo large igneous province (LIP). Yet strikingly missing from this dating effort is the huge southern sill complex cropping out in the >0.6 × 10 6 km 2 Main Karoo sedimentary basin. We present 16 new 40 Ar/ 39 Ar analyses carried out on fresh plagioclase and biotite separates from 15 sill samples collected along a N–S trend in the eastern part of the basin. The results show a large range of plateau and miniplateau ages (176.2 ± 1.3 to 183.8 ± 2.4 Ma), with most dates suggesting a ∼3 Ma (181–184 Ma) duration for the main sill events. The available age database allows correlation of the Karoo LIP emplacement with the Pliensbachian‐Toarcian second‐order biotic extinction, the global warming, and the Toarcian anoxic event (provided that adequate calibration between the 40 K and 238 U decay constant is made). The mass extinction and the isotopic excursions recorded at the base of the Toarcian appear to be synchronous with both the increase of magma emission of the Karoo LIP and the emplacement of the sills. The CO 2 and SO 2 derived from both volcanic emissions as well as carbon‐rich sedimentary layers intruded by sills might be the main culprits of the Pliensbachian‐Toarcian climate perturbations. We propose that the relatively low eruption rate of the Karoo LIP is one of the main reasons explaining why its impact on the biosphere is relatively low contrary to, e.g., the CAMP (Triassic‐Jurassic) and Siberia (Permo‐Triassic) LIPs.
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Large igneous province
Flood basalt
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Large igneous provinces are exceptional intraplate igneous events throughout Earth's history. Their significance and potential global impact are related to the total volume of magma intruded and released during these geologically brief events (peak eruptions are often within 1–5 m.y. in duration) where millions to tens of millions of cubic kilometers of magma are produced. In some cases, at least 1% of Earth's surface has been directly covered in volcanic rock, being equivalent to the size of small continents with comparable crustal thicknesses. Large igneous provinces thus represent important, albeit episodic, periods of new crust addition. However, most magmatism is basaltic, so that contributions to crustal growth will not always be picked up in zircon geochronology studies, which better trace major episodes of extension-related silicic magmatism and the silicic large igneous provinces. Much headway has been made in our understanding of these anomalous igneous events over the past 25 yr, driving many new ideas and models. (1) The global spatial and temporal distribution of large igneous provinces has a long-term average of one event approximately every 20 m.y., but there is a clear clustering of events at times of supercontinent breakup, and they are thus an integral part of the Wilson cycle and are becoming an increasingly important tool in reconnecting dispersed continental fragments. (2) Their compositional diversity in part reflects their crustal setting, such as ocean basins and continental interiors and margins, where, in the latter setting, large igneous province magmatism can be dominated by silicic products. (3) Mineral and energy resources, with major platinum group elements (PGEs) and precious metal resources, are hosted in these provinces, as well as magmatism impacting on the hydrocarbon potential of volcanic basins and rifted margins through enhancing source-rock maturation, providing fluid migration pathways, and initiating trap formation. (4) Biospheric, hydrospheric, and atmospheric impacts of large igneous provinces are now widely regarded as key trigger mechanisms for mass extinctions, although the exact kill mechanism(s) are still being resolved. (5) Their role in mantle geodynamics and thermal evolution of Earth as large igneous provinces potentially record the transport of material from the lower mantle or core-mantle boundary to the Earth's surface and are a fundamental component in whole mantle convection models. (6) Recognition of large igneous provinces on the inner planets, with their planetary antiquity and lack of plate tectonics and erosional processes, means that the very earliest record of large igneous province events during planetary evolution may be better preserved there than on Earth.
Large igneous province
Silicic
Flood basalt
Supercontinent
Felsic
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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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Mass extinction events are short-lived and characterized by catastrophic biosphere collapse and subsequent reorganization. Their abrupt nature necessitates a similarly short-lived trigger, and large igneous province magmatism is often implicated. However, large igneous provinces are long-lived compared to mass extinctions. Therefore, if large igneous provinces are an effective trigger, a subinterval of magmatism must be responsible for driving deleterious environmental effects. The onset of Earth's most severe extinction, the end-Permian, coincided with an abrupt change in the emplacement style of the contemporaneous Siberian Traps large igneous province, from dominantly flood lavas to sill intrusions. Here we identify the initial emplacement pulse of laterally extensive sills as the critical deadly interval. Heat from these sills exposed untapped volatile-fertile sediments to contact metamorphism, likely liberating the massive greenhouse gas volumes needed to drive extinction. These observations suggest that large igneous provinces characterized by sill complexes are more likely to trigger catastrophic global environmental change than their flood basalt- and/or dike-dominated counterparts.Although the mass end-Permian extinction is linked to large igneous provinces, its trigger remains unclear. Here, the authors propose that the abrupt change from flood lavas to sills resulted in the heating of sediments and led to the release of large-scale greenhouse gases to drive the end-Permian extinction.
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Flood basalt
Large igneous province
Permian–Triassic extinction event
Extinction (optical mineralogy)
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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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Sill
Large igneous province
Silicic
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Flood basalt
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