{{Short description|Type of igneous intrusion of subvolcanic rock}} [[File:Cone Sheet Mingary Ardnamurchan 01.jpg|thumb|A cone sheet at Mingary, [[Ardnamurchan]], [[Scotland]]]] [[File:Cone sheet at Mingary - geograph.org.uk - 4378.jpg|thumb|Closer view of a cone sheet at Mingary, Ardnamurchan]] [[File:Presa del Parralillo on Gran Canaria in Canary Islands 2011.jpg|thumb|Tejeda cone sheets on [[Gran Canaria]]. The lower two-thirds of the photo shows the Tejeda cone sheet swarm of Miocene age; the cone sheets [[Strike and dip|dip]] down towards the bottom left. The cone sheets are overlain by Pliocene flat-lying [[lava flow]]s and [[pyroclastic rock]]s.<ref name="CarracedoTroll2016">{{cite book | title=The Geology of the Canary Islands | publisher=Elsevier | last1=Carracedo | first1=J.C. | last2=Troll | first2=V.R. | year=2016 | location=Amsterdam | page=433, figure 6.80 | isbn=978-0-12-809663-5}}</ref>]] A '''cone sheet''' is a type of high-level [[igneous]] [[intrusion]] of [[subvolcanic rock]], found in partly eroded central volcanic complexes. Cone sheets are relatively thin inclined sheets, generally just a few metres thick, with the geometry of a downward-pointing cone. Viewed from above, their [[outcrop]] is typically circular to elliptical. They were originally described from the [[Ardnamurchan]], [[Isle of Mull|Mull]] and other central complexes of the [[British Tertiary Volcanic Province]] (now recognised as part of the [[North Atlantic Igneous Province]]).
==Occurrence== Cone sheets are widely distributed at the lower levels of volcanic complexes.
{| class="wikitable" style="margin:left" |+ Examples of cone sheet complexes !Name!!Location!!Age!!Dominant rock type!!Reference |- |Ardnamurchan |[[Scotland]] |[[Paleogene]] |[[dolerite]] |<ref name="GeldmacherEtAl1998">{{cite journal | title=The petrogenesis of Tertiary cone-sheets in Ardnamurchan, NW Scotland: petrological and geochemical constraints on crustal contamination and partial melting | first=Jörg | last=Geldmacher | first2=Karsten M. | last2=Haase | first3=Colin W. | last3= Devey | first4=C. Dieter | last4=Garbe-Schönberg | journal=Contributions to Mineralogy and Petrology | year=1998 | volume=131 | issue=2–3 | pages=196–209 | doi=10.1007/s004100050388}}</ref><ref>{{Cite journal|last=Geldmacher|first=J.|last2=Troll|first2=V. R.|last3=Emeleus|first3=C. H.|last4=Donaldson|first4=C. H.|date=May 2002|title=Pb-isotope evidence for contrasting crustal contamination of primitive to evolved magmas from Ardnamurchan and Rum: implications for the structure of the underlying crust|url=https://doi.org/10.1144/sjg38010055|journal=Scottish Journal of Geology|volume=38|issue=1|pages=55–61|doi=10.1144/sjg38010055|issn=0036-9276|url-access=subscription}}</ref> |- |Tejeda |[[Gran Canaria]] |[[Miocene]] |[[trachyte]], [[phonolite]] |<ref name="Schirnick_etal_1999">{{Cite journal |last=Schirnick |first=C. |last2=van den Bogaard |first2=P. |last3=Schminke |first3=H.-U. |date=1999 |title=Cone sheet formation and intrusive growth of an oceanic island—The Miocene Tejeda complex on Gran Canaria (Canary Islands) |journal=Geology |volume=27 |issue=3 |pages=207–210 |doi=10.1130/0091-7613(1999)027<0207:CSFAIG>2.3.CO;2}}</ref> |- |Vallehermoso |[[La Gomera]] |Miocene |trachyte, phonolite |<ref name="Vallehermoso2004">{{cite journal | title=The felsic complex of the Vallehermoso Caldera: interior of an ancient volcanic system (La Gomera, Canary Islands) | first1=J.A. | last1=Rodriguez-Losada | first2=J. | last2=Martinez-Frias | journal=Journal of Volcanology and Geothermal Research | year=2004 | volume=137 | issue=4 | pages=261–284 | doi=10.1016/j.jvolgeores.2004.05.021}}</ref> |- |Jabal Arknu |[[Libya]] |[[Tertiary period|Tertiary]] | |<ref name="Tawadros">{{cite book | title=Geology of North Africa | publisher=CRC Press | author=Tawadros, E. Edward | year=2011 | location=Boca Raton | page=79 | isbn=9780415874205}}</ref> |- |Otoge |[[Japan]] |Miocene |[[alkali basalt]], [[trachyandesite]] |<ref name="Geshi2005">{{cite journal | title=Structural development of dike swarms controlled by the change of magma supply rate: the cone sheets and parallel dike swarms of the Miocene Otoge igneous complex, Central Japan | last=Geshi | first=N. | journal=Journal of Volcanology and Geothermal Research | year=2005 | volume=141 | issue=3–4 | pages=267–281 | doi=10.1016/j.jvolgeores.2004.11.002}}</ref> |- |Zarza |[[Mexico]] |[[Cretaceous]] |[[gabbro]] |<ref name="JohnsonEtAl1999">{{cite journal | title=Structure and emplacement history of a multiple-center, cone-sheet–bearing ring complex: The Zarza Intrusive Complex, Baja California, Mexico | last=Johnson | first=S. E. | last2=Paterson | first2=S. R. | last3=Tate | first3=M. C. | journal=Geological Society of America Bulletin | year=1999 | volume=111 | issue=4 | pages=607–619 | doi=10.1130/0016-7606(1999)111<0607:SAEHOA>2.3.CO;2}}</ref> |- |Houshihushan |[[China]] |Cretaceous |[[granite]] [[Porphyry (geology)|porphyry]] |<ref name="XiaEtAl2015">{{cite journal | title=Subterranean origin of accreted lapilli in cone-sheets of the houshihushan sub-volcanic ring complex, Shanhaiguan, China | last=Wen | first=X. | last2=Ma | first2=C. | last3=Mason | first3=R. | last4=Sang | first4=L. | last5=Zhao | first5=J. | journal=Journal of Earth Science | year=2015 | volume=26 |issue = 5| pages=661–668 | doi=10.1007/s12583-015-0581-4}}</ref> |- |Boa Vista |[[Cape Verde]] |Miocene |phonolite |<ref name="AncocheaEtAl2014">{{cite journal | title=A new felsic cone-sheet swarm in the Central Atlantic Islands: The cone-sheet swarm of Boa Vista (Cape Verde) | first=Eumenio | last=Ancochea | first2=María José | last2=Huertas | first3=Francisco | last3=Hernán | first4=José Luis | last4=Brändle | journal=Journal of Volcanology and Geothermal Research | year=2014 | volume=274 | pages=1–15 | doi=10.1016/j.jvolgeores.2014.01.010}}</ref> |- |Ruri Hills |[[Kenya]] |Miocene |[[carbonatite]] |<ref name="King1972">{{cite journal | url=http://jgs.lyellcollection.org/content/128/2/173.short | title=The history of the alkaline volcanoes and intrusive complexes of eastern Uganda and western Kenya | first=B. C. | last=King | first2=M. J. | last2=Le Bas | first3=D. S. | last3=Sutherland | journal=Journal of the Geological Society | year=1972 | volume=128 | issue=2 | pages=173–205 | doi=10.1144/gsjgs.128.2.0173| url-access=subscription }}</ref> |- |Bagstowe |[[Queensland]] |late [[Paleozoic]] |[[rhyolite]] |<ref name="Branch1959">{{cite book | url=https://d28rz98at9flks.cloudfront.net/10535/Rec1959_104.pdf | title=Progress Report on Upper Palaeozoic Intrusions Controlled by Ring Fractures near Kidston, North Queensland | publisher=Bureau of Mineral Resources Geology and Geophysics, Department of National Development, Commonwealth of Australia | author=Branch, C.D. | year=1959}}</ref> |- |Thverartindur |[[Iceland]] |[[Pliocene]] | |<ref name="Klausen2004">{{cite journal | title=Geometry and mode of emplacement of the Thverartindur cone sheet swarm, SE Iceland | author=Klausen, M.B. | journal=Journal of Volcanology and Geothermal Research | year=2004 | volume=138 | issue=3–4 | pages=185–204 | doi=10.1016/j.jvolgeores.2004.05.022}}</ref> |- |Tehilla |[[Sudan]] |[[Cambrian]]–[[Ordovician]] |granite, [[monzonite]] |<ref name="Ahmed1977">{{cite journal | title=Petrology and Evolution of the Tehilla Igneous Complex, Sudan | author=Ahmed, F. | journal=Journal of Geology | year=1977 | volume=85 | issue=3 | pages=331–343 | doi=10.1086/628303}}</ref> |- |}
==Formation== Soon after cone sheets were first described, their formation was explained in terms of intrusion along conical fractures extending from the top of an intrusive body into the overlying rocks, caused by high [[magma]]tic pressure.<ref>{{Cite journal|last=Walter|first=Thomas R.|last2=Troll|first2=Valentin R.|date=2001-06-01|title=Formation of caldera periphery faults: an experimental study|url=https://doi.org/10.1007/s004450100135|journal=Bulletin of Volcanology|language=en|volume=63|issue=2|pages=191|doi=10.1007/s004450100135|issn=1432-0819|url-access=subscription}}</ref><ref name="Magee et al">{{cite journal | url=http://pure-oai.bham.ac.uk/ws/files/10156780/Magee.pdf | title=An alternative emplacement model for the classic Ardnamurchan cone sheet swarm, NW Scotland, involving lateral magma supply via regional dykes |author1=Magee C. |author2=Stevenson C. |author3=O'Driscoll B. |author4=Schofield N. |author5=McDermott K. | journal=Journal of Structural Geology | year=2012 | volume=44 | pages=73–91 | doi=10.1016/j.jsg.2012.08.004| doi-access=free }}</ref>
==References== {{Reflist}}
[[Category:Sheet intrusions]]