{"title":"英国北部阿卡迪亚变形时代与泥盆纪花岗岩:述评","authors":"\tSociety\t\t\tN. Woodcock, N. Soper, A. Miles","doi":"10.1144/PYGS2018-009","DOIUrl":null,"url":null,"abstract":"Field evidence shows that emplacement of Devonian granites in northern England overlaps in space and time with the end of the supposed Acadian deformation in their country rocks. The age of this Acadian event in England and Wales is in need of review because of revised Rb-Sr and K-Ar decay constants and recently acquired radiometric ages on the granites. Published K-Ar and Ar-Ar cleavage ages recalculated to the new decay constants range from 404 to 394 Ma (Emsian, Early Devonian). Emplacement of the Skiddaw and Weardale granites at 398.8 ± 0.4 and 399.3 ± 0.7 Ma respectively is indicated by U-Pb zircon ages, and is compatible with the field evidence. However, emplacement of the Shap Granite at a Re-Os molybdenite age of 405.2 ± 1.8 Ma and at the youngest U-Pb zircon age of 403 ± 8 Ma matches the field evidence less well. The apparent paradox in these ages is resolved if the K-Ar ages record only the end of millions of years of cleavage formation. An earlier cluster of K-Ar and Ar-Ar cleavage ages at 426–420 Ma (Ludlow to Přidoli, late Silurian) dates a pre-Acadian resetting event soon after Iapetus closure, an event of uncertain significance. Ion microprobe U-Pb zircon ages for the Shap Granite have a mean of 415.6 ± 1.4 Ma but a range of 428–403 Ma, compatible with a long magmatic history. Thermal considerations suggest that this history was not at the upper crustal emplacement site but in a mid-crustal mush zone, now preserved at about 10 km depth as a component of the Lake District and North Pennine batholiths.","PeriodicalId":49665,"journal":{"name":"Proceedings of the Yorkshire Geological Society","volume":null,"pages":null},"PeriodicalIF":0.5000,"publicationDate":"2018-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"15","resultStr":"{\"title\":\"Age of the Acadian deformation and Devonian granites in northern England: a review\",\"authors\":\"\\tSociety\\t\\t\\tN. Woodcock, N. Soper, A. Miles\",\"doi\":\"10.1144/PYGS2018-009\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Field evidence shows that emplacement of Devonian granites in northern England overlaps in space and time with the end of the supposed Acadian deformation in their country rocks. The age of this Acadian event in England and Wales is in need of review because of revised Rb-Sr and K-Ar decay constants and recently acquired radiometric ages on the granites. Published K-Ar and Ar-Ar cleavage ages recalculated to the new decay constants range from 404 to 394 Ma (Emsian, Early Devonian). Emplacement of the Skiddaw and Weardale granites at 398.8 ± 0.4 and 399.3 ± 0.7 Ma respectively is indicated by U-Pb zircon ages, and is compatible with the field evidence. However, emplacement of the Shap Granite at a Re-Os molybdenite age of 405.2 ± 1.8 Ma and at the youngest U-Pb zircon age of 403 ± 8 Ma matches the field evidence less well. The apparent paradox in these ages is resolved if the K-Ar ages record only the end of millions of years of cleavage formation. An earlier cluster of K-Ar and Ar-Ar cleavage ages at 426–420 Ma (Ludlow to Přidoli, late Silurian) dates a pre-Acadian resetting event soon after Iapetus closure, an event of uncertain significance. Ion microprobe U-Pb zircon ages for the Shap Granite have a mean of 415.6 ± 1.4 Ma but a range of 428–403 Ma, compatible with a long magmatic history. Thermal considerations suggest that this history was not at the upper crustal emplacement site but in a mid-crustal mush zone, now preserved at about 10 km depth as a component of the Lake District and North Pennine batholiths.\",\"PeriodicalId\":49665,\"journal\":{\"name\":\"Proceedings of the Yorkshire Geological Society\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.5000,\"publicationDate\":\"2018-12-19\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"15\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Proceedings of the Yorkshire Geological Society\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://doi.org/10.1144/PYGS2018-009\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"GEOLOGY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Proceedings of the Yorkshire Geological Society","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1144/PYGS2018-009","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"GEOLOGY","Score":null,"Total":0}
引用次数: 15
摘要
现场证据表明,英格兰北部泥盆纪花岗岩的就位在空间和时间上与他们的乡村岩石中假定的阿卡迪亚变形的结束重叠。由于修订的Rb-Sr和K-Ar衰变常数以及最近获得的花岗岩辐射年龄,需要对英格兰和威尔士阿卡迪亚事件的年龄进行审查。已公布的K-Ar和Ar-Ar解理年龄重新计算到新的衰变常数范围为404 ~ 394 Ma (Emsian,早泥盆世)。Skiddaw和Weardale花岗岩的侵位位置分别为398.8±0.4和399.3±0.7 Ma, U-Pb锆石年龄表明其侵位位置与野外证据一致。然而,Shap花岗岩的Re-Os辉钼矿年龄为405.2±1.8 Ma,最年轻的U-Pb锆石年龄为403±8 Ma,与现场证据不太吻合。如果K-Ar年龄只记录了数百万年解理形成的结束,那么这些年龄的明显矛盾就解决了。早期的K-Ar和Ar-Ar裂解年龄在426-420 Ma (Ludlow至Přidoli,志留纪晚期),表明Iapetus关闭后不久发生了前阿卡代重置事件,这是一个意义不确定的事件。Shap花岗岩的离子探针U-Pb锆石年龄平均值为415.6±1.4 Ma,但范围为428 ~ 403 Ma,与较长的岩浆历史相适应。热因素表明,这段历史不是在上地壳位址,而是在地壳中部的泥状带,现在作为湖区和北彭宁岩基的组成部分保存在大约10公里深的地方。
Age of the Acadian deformation and Devonian granites in northern England: a review
Field evidence shows that emplacement of Devonian granites in northern England overlaps in space and time with the end of the supposed Acadian deformation in their country rocks. The age of this Acadian event in England and Wales is in need of review because of revised Rb-Sr and K-Ar decay constants and recently acquired radiometric ages on the granites. Published K-Ar and Ar-Ar cleavage ages recalculated to the new decay constants range from 404 to 394 Ma (Emsian, Early Devonian). Emplacement of the Skiddaw and Weardale granites at 398.8 ± 0.4 and 399.3 ± 0.7 Ma respectively is indicated by U-Pb zircon ages, and is compatible with the field evidence. However, emplacement of the Shap Granite at a Re-Os molybdenite age of 405.2 ± 1.8 Ma and at the youngest U-Pb zircon age of 403 ± 8 Ma matches the field evidence less well. The apparent paradox in these ages is resolved if the K-Ar ages record only the end of millions of years of cleavage formation. An earlier cluster of K-Ar and Ar-Ar cleavage ages at 426–420 Ma (Ludlow to Přidoli, late Silurian) dates a pre-Acadian resetting event soon after Iapetus closure, an event of uncertain significance. Ion microprobe U-Pb zircon ages for the Shap Granite have a mean of 415.6 ± 1.4 Ma but a range of 428–403 Ma, compatible with a long magmatic history. Thermal considerations suggest that this history was not at the upper crustal emplacement site but in a mid-crustal mush zone, now preserved at about 10 km depth as a component of the Lake District and North Pennine batholiths.
期刊介绍:
The Proceedings of the Yorkshire Geological Society (PYGS) has been published without a break since 1839. It is one of the leading journals of British geology. Each year two parts are issued containing original research papers on all aspects of geology. Traditionally the Proceedings has given particular attention to the geology of northern England and its neighbouring areas. The submission of papers on related topics but of a more general interest is encouraged. All papers are subjected to the full scrutiny of two independent referees.