Abstract:The Mullaghmore Sandstone Formation of north-west Ireland is a distinctive clastic unit of late Arundian age in an otherwise carbonate-dominant Mississippian succession. The distinctive base is erosive in the more proximal sections but is gradational in the successions deposited further offshore from the pre-Mullaghmore shoreline. The source area lay to the north-west and is interpreted to be dominated by felsic igneous and/or high grade metamorphic rocks due to the presence of large, first cycle feldspars that are common in all of the sandstones. The formation was deposited in the coastal zone with both fluvial and marginal marine deposits present in almost all sections. The fluvial channel deposits are most common in north-western sections and commonly show evidence for tidal currents in the coastal zone. Most of the coastal sediments are dominated by wave-generated structures. The formation is interpreted as the deposits of a deltaic coastal plain that was lobate in plan view. The top of the formation is interpreted as a regional transgressive surface. While there is local autocyclic repetition of facies, no higher-order sequences are detectable on a regional scale. The driving mechanisms for this regional lowstand are most likely regional tectonics rather than glacioeustasy, as the event is not readily correlated over any significant distance.
{"title":"The Mullaghmore Sandstone Formation of north-west Ireland: a regional Mississippian lowstand deposit","authors":"J. R. Graham","doi":"10.3318/IJES.2017.35.19","DOIUrl":"https://doi.org/10.3318/IJES.2017.35.19","url":null,"abstract":"Abstract:The Mullaghmore Sandstone Formation of north-west Ireland is a distinctive clastic unit of late Arundian age in an otherwise carbonate-dominant Mississippian succession. The distinctive base is erosive in the more proximal sections but is gradational in the successions deposited further offshore from the pre-Mullaghmore shoreline. The source area lay to the north-west and is interpreted to be dominated by felsic igneous and/or high grade metamorphic rocks due to the presence of large, first cycle feldspars that are common in all of the sandstones. The formation was deposited in the coastal zone with both fluvial and marginal marine deposits present in almost all sections. The fluvial channel deposits are most common in north-western sections and commonly show evidence for tidal currents in the coastal zone. Most of the coastal sediments are dominated by wave-generated structures. The formation is interpreted as the deposits of a deltaic coastal plain that was lobate in plan view. The top of the formation is interpreted as a regional transgressive surface. While there is local autocyclic repetition of facies, no higher-order sequences are detectable on a regional scale. The driving mechanisms for this regional lowstand are most likely regional tectonics rather than glacioeustasy, as the event is not readily correlated over any significant distance.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"35 1","pages":"19 - 34"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3318/IJES.2017.35.19","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46033628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-01DOI: 10.3318/IJES.2005.23.1.123
I. Sanders
{"title":"Abstracts of the 48th Irish Geological Research Meeting, Trinity College Dublin, February 2005","authors":"I. Sanders","doi":"10.3318/IJES.2005.23.1.123","DOIUrl":"https://doi.org/10.3318/IJES.2005.23.1.123","url":null,"abstract":"","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"23 1","pages":"125 - 145"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46156422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:AbstractNew geological mapping, along with sedimentological and microfaunal analysis, has enabled correlation among three disparate outcrops of early Carboniferous rocks on the north side of Donegal Bay. This area represents the northernmost exposures of the Carboniferous in north-west Ireland and is inferred to have lain close to the Viséan shoreline. A regionally traceable marine flooding event at the base of the Bundoran Shale approximately coincides with the base of the Arundian Stage. Below this, marginal-marine successions can all be assigned to the Lower Viséan based on microfaunas. These successions display a lower, non-marine clastic sequence that passes gradationally upward into a shallow-marine carbonate-dominant sequence. This sequence is succeeded by a regressive event that is regionally correlateable despite lateral variation in facies.
{"title":"The Carboniferous geology of northern Donegal Bay","authors":"J. R. Graham, Charlotte Ní Bhroin, G. Sevastopulo","doi":"10.3318/IJES.2014.32.29","DOIUrl":"https://doi.org/10.3318/IJES.2014.32.29","url":null,"abstract":"Abstract:AbstractNew geological mapping, along with sedimentological and microfaunal analysis, has enabled correlation among three disparate outcrops of early Carboniferous rocks on the north side of Donegal Bay. This area represents the northernmost exposures of the Carboniferous in north-west Ireland and is inferred to have lain close to the Viséan shoreline. A regionally traceable marine flooding event at the base of the Bundoran Shale approximately coincides with the base of the Arundian Stage. Below this, marginal-marine successions can all be assigned to the Lower Viséan based on microfaunas. These successions display a lower, non-marine clastic sequence that passes gradationally upward into a shallow-marine carbonate-dominant sequence. This sequence is succeeded by a regressive event that is regionally correlateable despite lateral variation in facies.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"32 1","pages":"29 - 54"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3318/IJES.2014.32.29","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47529427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"REPLY TO WALSH","authors":"G. L. Davies","doi":"10.3318/IJES.2012.30.61","DOIUrl":"https://doi.org/10.3318/IJES.2012.30.61","url":null,"abstract":"","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"30 1","pages":"61 - 61"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48913684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:Two closely-spaced drill-cores through the marginal zone of the Waulsortian Complex in north Co. Galway have been studied petrographically to help identify factors that limited spread of the banks and led to their demise. The Waulsortian limestones found there have textural and structural characters and skeletal-grain content of Waulsortian Phase C, indicating a relatively shallow-water environment but below the depths colonised by calcareous chlorophyte algae. Bank depositional structures of both flat-lying and clinoform type are present. Four associated limestone facies are distinguished: off-bank, precursor (beneath and around the banks), cap (directly overlying banks) and cover facies. Spatial relationships between these are used to construct a depositional model. Five developmental stages are recognised through the sequence and used to correlate the two sections. The distribution of biostratigraphically significant foraminifera supports the sedimentological correlation. Throughout the sequence there was unusual physical disturbance of the sediments by water movement. There is evidence of progressively increasing damage to the polymud-forming processes. Formation of cryptofibrous cements and micritisation were affected at a late stage. Interference in development of precursor muds, probably more vulnerable than the banks, could have ‘killed’ the Complex by halting bank-initiation. The timing of these changes correlates with a sea-level fall identified elsewhere in Ireland and abroad.
{"title":"Anatomy of the marginal zone of the Waulsortian Carbonate bank (mudmound) complex, North Co. Galway","authors":"A. Lees","doi":"10.3318/IJES.2018.36.81","DOIUrl":"https://doi.org/10.3318/IJES.2018.36.81","url":null,"abstract":"Abstract:Two closely-spaced drill-cores through the marginal zone of the Waulsortian Complex in north Co. Galway have been studied petrographically to help identify factors that limited spread of the banks and led to their demise. The Waulsortian limestones found there have textural and structural characters and skeletal-grain content of Waulsortian Phase C, indicating a relatively shallow-water environment but below the depths colonised by calcareous chlorophyte algae. Bank depositional structures of both flat-lying and clinoform type are present. Four associated limestone facies are distinguished: off-bank, precursor (beneath and around the banks), cap (directly overlying banks) and cover facies. Spatial relationships between these are used to construct a depositional model. Five developmental stages are recognised through the sequence and used to correlate the two sections. The distribution of biostratigraphically significant foraminifera supports the sedimentological correlation. Throughout the sequence there was unusual physical disturbance of the sediments by water movement. There is evidence of progressively increasing damage to the polymud-forming processes. Formation of cryptofibrous cements and micritisation were affected at a late stage. Interference in development of precursor muds, probably more vulnerable than the banks, could have ‘killed’ the Complex by halting bank-initiation. The timing of these changes correlates with a sea-level fall identified elsewhere in Ireland and abroad.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"36 1","pages":"106 - 81"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43274164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:AbstractThe Holocene in Ireland was a time of rapidly rising sea level that continued up to about 5000 years ago. This transgression lead to the flooding of mid-Holocene forested landscapes along the western seaboard of the country. Carbon 14 dating of in situ tree stumps set in peat from these forests shows a span of dates from approximately 7400 to 5200 years cal. BP from counties Mayo, Galway and Clare. Peat deposits of up to 2m thickness formed during this time. These dates firstly show that these forests were long-lived features of the Irish landscape. Secondly their presence suggests that at this time sea level was probably lower than that suggested in glacial rebound models for the area. Thirdly the general absence in these peats of evidence of marine incursion confirms that the Holocene highstand did not occur along the central part of the western Irish seaboard, unlike in areas along the north and east coasts of the country.
{"title":"Dates from drowned mid-Holocene landscapes on the central western Irish seaboard","authors":"D. Williams, Eamon Doyle","doi":"10.3318/IJES.2014.32.23","DOIUrl":"https://doi.org/10.3318/IJES.2014.32.23","url":null,"abstract":"Abstract:AbstractThe Holocene in Ireland was a time of rapidly rising sea level that continued up to about 5000 years ago. This transgression lead to the flooding of mid-Holocene forested landscapes along the western seaboard of the country. Carbon 14 dating of in situ tree stumps set in peat from these forests shows a span of dates from approximately 7400 to 5200 years cal. BP from counties Mayo, Galway and Clare. Peat deposits of up to 2m thickness formed during this time. These dates firstly show that these forests were long-lived features of the Irish landscape. Secondly their presence suggests that at this time sea level was probably lower than that suggested in glacial rebound models for the area. Thirdly the general absence in these peats of evidence of marine incursion confirms that the Holocene highstand did not occur along the central part of the western Irish seaboard, unlike in areas along the north and east coasts of the country.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"32 1","pages":"23 - 27"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3318/IJES.2014.32.23","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45494462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-01DOI: 10.3318/IJES.2006.24.1.51
Mags Duncan
Abstract:Microscopic teeth of the chondrichthyan genera Denaea and Protacrodus together with a number of unclassified microscopic teeth attributed to 'Chondrichthyan Pavement Dentition' are described from the Mississippian (Tournaisian) rocks of Ireland. These have not been described before from Ireland. The microscopic teeth were extracted from crinoidal limestones or calcareous mudstones whose palaeoenvironments are interpreted as ranging from relatively deep offshore, through moderately shallow high-energy carbonate shelf to nearshore shallow water. The richest fauna has been recovered from the high-energy carbonate shelf facies with the 'cladodont' type only appearing within this facies, together with more numerous crushing dentition type teeth. The symmoriid and protacrodontid teeth are described to genus level, while the remaining crushing teeth are left in open nomenclature.
{"title":"Various Chondrichthyan Microfossil Faunas from the Lower Mississippian (Carboniferous) of Ireland","authors":"Mags Duncan","doi":"10.3318/IJES.2006.24.1.51","DOIUrl":"https://doi.org/10.3318/IJES.2006.24.1.51","url":null,"abstract":"Abstract:Microscopic teeth of the chondrichthyan genera Denaea and Protacrodus together with a number of unclassified microscopic teeth attributed to 'Chondrichthyan Pavement Dentition' are described from the Mississippian (Tournaisian) rocks of Ireland. These have not been described before from Ireland. The microscopic teeth were extracted from crinoidal limestones or calcareous mudstones whose palaeoenvironments are interpreted as ranging from relatively deep offshore, through moderately shallow high-energy carbonate shelf to nearshore shallow water. The richest fauna has been recovered from the high-energy carbonate shelf facies with the 'cladodont' type only appearing within this facies, together with more numerous crushing dentition type teeth. The symmoriid and protacrodontid teeth are described to genus level, while the remaining crushing teeth are left in open nomenclature.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"24 1","pages":"51 - 69"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47946338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:This paper documents the first record of carbonate-filled neptunean dykes within the Ox Mountains Granodiorite. A post-Carboniferous age for the formation of the dykes is rejected and a Viséan age favoured. Differential uplift and tilting of segments of the Ox Mountains inlier could have contributed to a complex sub-Viséan unconformity and Viséan deposition.
{"title":"A Note on Carbonate-Filled Neptunean Dykes in the Ox Mountains Granodiorite, NW Ireland","authors":"W. Taylor","doi":"10.3318/IJES.2007.25.81","DOIUrl":"https://doi.org/10.3318/IJES.2007.25.81","url":null,"abstract":"Abstract:This paper documents the first record of carbonate-filled neptunean dykes within the Ox Mountains Granodiorite. A post-Carboniferous age for the formation of the dykes is rejected and a Viséan age favoured. Differential uplift and tilting of segments of the Ox Mountains inlier could have contributed to a complex sub-Viséan unconformity and Viséan deposition.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"25 1","pages":"81 - 84"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41842082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:‘Cotterite’ is a varietal name for an extremely rare form of quartz that displays a distinctive pearly metallic, but not vitreous, lustre. Originally discovered in a horizontal vein of calcite, quartz and ferruginous mud that crosscut Carboniferous limestone in a quarry at Rockforest (near Mallow, County Cork, Ireland) by ‘Miss Cotter’ in 1875/76, this quartz variety has been the subject of only two scientific papers, the second of which was by Professor Robert Harkness (then of Queen's College Cork) who named the variety in 1878. Genealogical research reveals that the mineral's dedicatee was Grace Elizabeth Cotter (1830–79), first-born daughter of Reverend George Edward Cotter (third son of the second Baronet Cotter of Rockforest) and Grace La Touche. Both father and daughter were involved in distributing specimens to Irish and British institutions. Currently, some 34 cotterites from Rockforest are extant. There are also two quartz's labelled as cotterite from Nova Scotia (Canada) and two from Devon (England). New observations reveal that cotterite's lustre results from light reflections off partial delamination structures and microfracture crazing patterns within the many late-stage lamellar-style quartz growth layers that comprise cotterite quartz's pyramidal faces.
{"title":"Cotterite: Historical review; extant specimens; etymology of ‘Cotterite’ and the genealogy of ‘Miss Cotter’; new observations on the Cotterite texture","authors":"P. Roycroft","doi":"10.3318/ijes.2016.34.45","DOIUrl":"https://doi.org/10.3318/ijes.2016.34.45","url":null,"abstract":"Abstract:‘Cotterite’ is a varietal name for an extremely rare form of quartz that displays a distinctive pearly metallic, but not vitreous, lustre. Originally discovered in a horizontal vein of calcite, quartz and ferruginous mud that crosscut Carboniferous limestone in a quarry at Rockforest (near Mallow, County Cork, Ireland) by ‘Miss Cotter’ in 1875/76, this quartz variety has been the subject of only two scientific papers, the second of which was by Professor Robert Harkness (then of Queen's College Cork) who named the variety in 1878. Genealogical research reveals that the mineral's dedicatee was Grace Elizabeth Cotter (1830–79), first-born daughter of Reverend George Edward Cotter (third son of the second Baronet Cotter of Rockforest) and Grace La Touche. Both father and daughter were involved in distributing specimens to Irish and British institutions. Currently, some 34 cotterites from Rockforest are extant. There are also two quartz's labelled as cotterite from Nova Scotia (Canada) and two from Devon (England). New observations reveal that cotterite's lustre results from light reflections off partial delamination structures and microfracture crazing patterns within the many late-stage lamellar-style quartz growth layers that comprise cotterite quartz's pyramidal faces.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"34 1","pages":"45 - 78"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41888377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract:The northern part of the ~470 Ma syntectonic D2 basic and ultrabasic Roundstone intrusion into the Connemara Dalradian metasediments has been mapped in detail for the first time and consists of metagabbros containing a 180m peridotite xenolith and later injections of Quartz diorite gneiss which silicified and agmatised some of the metagabbros. With the already studied southern (Errisbeg) part, plus over 300 chemical analyses of rocks and over 400 probe analyses of minerals, this enables a synthesis of the geology of the whole intrusion. A tholeiitic magma crystallised olivine Fo83-76, orthopyroxene En84-59, diopside to salite and plagioclase from An96-42, and late stage cumulus magnetite. The exceptionally high An% is indicative of high pH2O with copious water (derived from dewatering of a subduction zone?) as is the abundant hornblende that replaced most of the magmatic minerals, the magma being comparable with that of the Lesser Antilles Island arc. The intrusion was formed by numerous already fractionated magma pulses intruded in upward sequence, closely (~467 Ma) followed by pulses of Quartz diorite to granite gneisses with magmatic hornblende, not by closed system fractionation of a single magma injection. The peridotites were mostly carried in as already solidified xenoliths by pulses of gabbro magma. Only the larger bodies in the Errisbeg part of the intrusion were intruded as magma.Igneous fractionation as measured by molecular MgO/(MgO+FeO+Fe2O3+MnO), Cr and Ni contents plus normative An/(An+Ab), because of heavy saussuritisation of the plagioclase, shows the intrusion is inverted from early metaperidotites and metagabbros from around the 300m Errisbeg summit downwards through the sideways injected meta-SE Gabbros to the later northern metagabbros, which last are virtually all <30m in altitude, to the underlying most fractionated metagabbros and fine-grained metagabbros, called Epidiorites. Parts of the last two together with a little included gneiss were converted into a mylonitic amphibolite, the Ballyconneely Amphibolite, immediately above the 447 ± 4 Ma (Tanner et al. 1989) D5 Mannin Thrust and form part of the Delaney Dome, west of the intrusion. The thrust underlies the whole of the Roundstone intrusion and Connemara but would have been deformed by D6 (~440 Ma) and D7 (~426 Ma). The N-S axial planar folding (most unusual in Connemara) which completed the formation of the Delaney Dome and also formed the Errisbeg antiform in the centre of the intrusion is shown to be D6 for the first time. The inversion of the metagabbros, west of the Delaney Dome, and over the Dome and to the east in the Roundstone intrusion and still further east in Gowla demonstrates that the Errismore-Roundstone-Gowla body and practically all of the 80 x >20km Grampian metagabbro-gneiss complex from Slyne Head to Galway is inverted except the Cashel-Lough Wheelaun-Loughaunanny intrusion and its envelope.
{"title":"New light on the geology of the Roundstone intrusion, its inversion and that of the Grampian metagabbro-gneiss complex, Connemara, western Ireland","authors":"Katrina Downs-Rose, B. Leake","doi":"10.3318/ijes.2019.37.4","DOIUrl":"https://doi.org/10.3318/ijes.2019.37.4","url":null,"abstract":"Abstract:The northern part of the ~470 Ma syntectonic D2 basic and ultrabasic Roundstone intrusion into the Connemara Dalradian metasediments has been mapped in detail for the first time and consists of metagabbros containing a 180m peridotite xenolith and later injections of Quartz diorite gneiss which silicified and agmatised some of the metagabbros. With the already studied southern (Errisbeg) part, plus over 300 chemical analyses of rocks and over 400 probe analyses of minerals, this enables a synthesis of the geology of the whole intrusion. A tholeiitic magma crystallised olivine Fo83-76, orthopyroxene En84-59, diopside to salite and plagioclase from An96-42, and late stage cumulus magnetite. The exceptionally high An% is indicative of high pH2O with copious water (derived from dewatering of a subduction zone?) as is the abundant hornblende that replaced most of the magmatic minerals, the magma being comparable with that of the Lesser Antilles Island arc. The intrusion was formed by numerous already fractionated magma pulses intruded in upward sequence, closely (~467 Ma) followed by pulses of Quartz diorite to granite gneisses with magmatic hornblende, not by closed system fractionation of a single magma injection. The peridotites were mostly carried in as already solidified xenoliths by pulses of gabbro magma. Only the larger bodies in the Errisbeg part of the intrusion were intruded as magma.Igneous fractionation as measured by molecular MgO/(MgO+FeO+Fe2O3+MnO), Cr and Ni contents plus normative An/(An+Ab), because of heavy saussuritisation of the plagioclase, shows the intrusion is inverted from early metaperidotites and metagabbros from around the 300m Errisbeg summit downwards through the sideways injected meta-SE Gabbros to the later northern metagabbros, which last are virtually all <30m in altitude, to the underlying most fractionated metagabbros and fine-grained metagabbros, called Epidiorites. Parts of the last two together with a little included gneiss were converted into a mylonitic amphibolite, the Ballyconneely Amphibolite, immediately above the 447 ± 4 Ma (Tanner et al. 1989) D5 Mannin Thrust and form part of the Delaney Dome, west of the intrusion. The thrust underlies the whole of the Roundstone intrusion and Connemara but would have been deformed by D6 (~440 Ma) and D7 (~426 Ma). The N-S axial planar folding (most unusual in Connemara) which completed the formation of the Delaney Dome and also formed the Errisbeg antiform in the centre of the intrusion is shown to be D6 for the first time. The inversion of the metagabbros, west of the Delaney Dome, and over the Dome and to the east in the Roundstone intrusion and still further east in Gowla demonstrates that the Errismore-Roundstone-Gowla body and practically all of the 80 x >20km Grampian metagabbro-gneiss complex from Slyne Head to Galway is inverted except the Cashel-Lough Wheelaun-Loughaunanny intrusion and its envelope.","PeriodicalId":35911,"journal":{"name":"Irish Journal of Earth Sciences","volume":"37 1","pages":"33 - 59"},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41809033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：