J. Gregory Shellnutt, Tung-Yi Lee, Yoshiyuki Iizuka, Hao-Yang Lee, Kenshi Suga, Chi Thi Pham
The Silhouette alkaline volcano-plutonic complex is the largest exposed Early Paleogene (62−64 Ma) igneous complex of the Seychelles microcontinent. The rocks of this study were collected from Baie Cipailles, Pte. Vareur, and Pte. Ramasse Tout and include syenite (SiO 2 = 60−63 wt%), microgranite (SiO 2 = 70−74 wt%), tuffaceous trachyte (SiO 2 = 64−65 wt%), and a basaltic xenolith (SiO 2 = 44 wt%; MgO = 6.4 wt%; Mg# = 47.6). The silicic rocks of this study are ferroan, metaluminous to weakly peralkaline, and classify as A1-type granitoids. The whole rock Sr-Nd ( 87 Sr/ 86 Sr i = 0.703894−0.706534; ε Nd ( t ) = +0.5−+1.8) isotopes of the silicic rocks are similar to the basalt xenolith ( 87 Sr/ 86 Sr i = 0.703576; ε Nd ( t ) = +1.9). There is limited to no geochemical evidence for crustal contamination in any of the rocks. The syenitic rocks were likely derived by fractional crystallization of an alkaline basaltic parental magma in the upper crust and under reducing conditions (ΔFMQ = -1). The Sr-Nd isotopes and zircon Hf (ε Hf ( t ) = +3.3−+9.1) isotopes of the silicic rocks are indicative of a moderately depleted source. We found distinct textural, mineralogical, and compositional differences between the syenitic rocks suggesting that the Silhouette complex is composed of at least two syenitic magma pulses.
Silhouette 碱性火山-岩浆岩群是塞舌尔微大陆最大的出露早古新世（62-64 Ma）火成岩群。本研究的岩石采集自 Baie Cipailles、Pte.Vareur 和 Pte.岩石包括正长岩（SiO 2 = 60-63 wt%）、微花岗岩（SiO 2 = 70-74 wt%）、凝灰岩质砂岩（SiO 2 = 64-65 wt%）和玄武质异长岩（SiO 2 = 44 wt%；MgO = 6.4 wt%；Mg# = 47.6）。本研究的硅质岩为铁质、金属铝质至弱碱性，属于A1型花岗岩。硅质岩的全岩 Sr-Nd ( 87 Sr/ 86 Sr i = 0.703894-0.706534; ε Nd ( t ) = +0.5-+1.8) 同位素与玄武岩异质岩 ( 87 Sr/ 86 Sr i = 0.703576; ε Nd ( t ) = +1.9) 相似。在这些岩石中，地壳污染的地球化学证据非常有限，甚至没有。正长岩很可能是由上地壳的碱性玄武质母岩浆在还原条件下（ΔFMQ = -1）分块结晶而成。硅质岩的Sr-Nd同位素和锆石Hf（ε Hf ( t ) = +3.3-+9.1）同位素表明其来源为中度贫化岩。我们发现，不同的闪长岩在质地、矿物学和成分上存在明显差异，这表明Silhouette复合体至少由两个闪长岩岩浆脉冲组成。
{"title":"Two syenitic phases in the Early Paleogene Silhouette Island volcano-plutonic complex, Seychelles","authors":"J. Gregory Shellnutt, Tung-Yi Lee, Yoshiyuki Iizuka, Hao-Yang Lee, Kenshi Suga, Chi Thi Pham","doi":"10.1144/jgs2024-017","DOIUrl":"https://doi.org/10.1144/jgs2024-017","url":null,"abstract":"\u0000 The Silhouette alkaline volcano-plutonic complex is the largest exposed Early Paleogene (62−64 Ma) igneous complex of the Seychelles microcontinent. The rocks of this study were collected from Baie Cipailles, Pte. Vareur, and Pte. Ramasse Tout and include syenite (SiO\u0000 2\u0000 = 60−63 wt%), microgranite (SiO\u0000 2\u0000 = 70−74 wt%), tuffaceous trachyte (SiO\u0000 2\u0000 = 64−65 wt%), and a basaltic xenolith (SiO\u0000 2\u0000 = 44 wt%; MgO = 6.4 wt%; Mg# = 47.6). The silicic rocks of this study are ferroan, metaluminous to weakly peralkaline, and classify as A1-type granitoids. The whole rock Sr-Nd (\u0000 87\u0000 Sr/\u0000 86\u0000 Sr\u0000 i\u0000 = 0.703894−0.706534; ε\u0000 Nd\u0000 (\u0000 t\u0000 ) = +0.5−+1.8) isotopes of the silicic rocks are similar to the basalt xenolith (\u0000 87\u0000 Sr/\u0000 86\u0000 Sr\u0000 i\u0000 = 0.703576; ε\u0000 Nd\u0000 (\u0000 t\u0000 ) = +1.9). There is limited to no geochemical evidence for crustal contamination in any of the rocks. The syenitic rocks were likely derived by fractional crystallization of an alkaline basaltic parental magma in the upper crust and under reducing conditions (ΔFMQ = -1). The Sr-Nd isotopes and zircon Hf (ε\u0000 Hf\u0000 (\u0000 t\u0000 ) = +3.3−+9.1) isotopes of the silicic rocks are indicative of a moderately depleted source. We found distinct textural, mineralogical, and compositional differences between the syenitic rocks suggesting that the Silhouette complex is composed of at least two syenitic magma pulses.\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141927091","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}
Alexandre Hamon, Damien Huyghe, Caroline Mehl, Alexandre Pichat, S. Révillon, J. Callot
Deciphering past salt tectonics events is often difficult in orogenic domains. The southwestern Alpine foreland in France presents a long Mesozoic extensive salt tectonics history, inverted during the Cenozoic Alpine orogeny. Syn-orogenic Cenozoic salt-related deformations are rather difficult to identify because of the contemporaneous shortening experienced by the foreland. This study is based on sedimentologic and geochemical approaches (Sr concentration and 87 Sr/ 86 Sr ratio) of the Oligocene non-marine succession of St Geniez (Digne region, France. Oligocene salt influences are highlighted by (1) high strontium concentrations (>1000 ppm) in most of the series, (2) the occurrence of Halophyticgastropods and (3) the deposit of two gypsum beds. 87 Sr/ 86 Sr ratio measured in the limestones and the gypsum beds confirm a Triassic origin for the strontium, originating from the diapir of Sorine, located to the south-west for the first part of the series, and from the Authon Thrust, located to the north, for the upper part. Geochemical values also suggest the occurrence of two Triassic evaporite levels, one already known and attributed to the Carnian-Norian (Late Triassic) and one attributed to the Olenekian-Anisian (Ealy-Middle Triassic). These results support that combined use of field geology and geochemistry can provide information on erased past salt-tectonics.
在造山带中，解读过去的盐构造事件往往十分困难。法国西南部阿尔卑斯山前陆具有漫长的中生代大面积盐构造历史，在新生代阿尔卑斯造山运动期间发生了逆转。由于前陆同时经历了缩短，因此很难确定新生代与盐有关的同步变形。本研究基于沉积学和地球化学方法（锶浓度和 87 Sr/ 86 Sr 比率）对法国迪涅地区圣热尼耶斯的渐新世非海相演替进行研究。新近纪盐的影响突出表现在：(1) 大部分系列的锶浓度较高（>1000 ppm）；(2) 出现了卤代腹足类动物；(3) 有两个石膏床沉积。在石灰岩和石膏层中测量到的 87 Sr/86 Sr 比率证实了锶的三叠纪起源，在该系列的前半部分，锶来源于西南部的索里内斜坡，而在上半部分，锶来源于北部的奥特洪隆起。地球化学值还表明存在两个三叠纪蒸发岩层，一个是已知的卡尼安-诺里安（晚三叠世），另一个是奥伦基-安尼西亚（埃利-中三叠世）。这些结果证明，综合利用野外地质学和地球化学可以提供有关过去被抹去的盐构造的信息。
{"title":"Coupling of X-ray fluorescence and Strontium isotopes to track brine influences in continental deposits: study of the Oligocene sediments in the Digne area (SE basin, France)","authors":"Alexandre Hamon, Damien Huyghe, Caroline Mehl, Alexandre Pichat, S. Révillon, J. Callot","doi":"10.1144/jgs2024-042","DOIUrl":"https://doi.org/10.1144/jgs2024-042","url":null,"abstract":"\u0000 Deciphering past salt tectonics events is often difficult in orogenic domains. The southwestern Alpine foreland in France presents a long Mesozoic extensive salt tectonics history, inverted during the Cenozoic Alpine orogeny. Syn-orogenic Cenozoic salt-related deformations are rather difficult to identify because of the contemporaneous shortening experienced by the foreland. This study is based on sedimentologic and geochemical approaches (Sr concentration and\u0000 87\u0000 Sr/\u0000 86\u0000 Sr ratio) of the Oligocene non-marine succession of St Geniez (Digne region, France. Oligocene salt influences are highlighted by (1) high strontium concentrations (>1000 ppm) in most of the series, (2) the occurrence of Halophyticgastropods and (3) the deposit of two gypsum beds.\u0000 87\u0000 Sr/\u0000 86\u0000 Sr ratio measured in the limestones and the gypsum beds confirm a Triassic origin for the strontium, originating from the diapir of Sorine, located to the south-west for the first part of the series, and from the Authon Thrust, located to the north, for the upper part. Geochemical values also suggest the occurrence of two Triassic evaporite levels, one already known and attributed to the Carnian-Norian (Late Triassic) and one attributed to the Olenekian-Anisian (Ealy-Middle Triassic). These results support that combined use of field geology and geochemistry can provide information on erased past salt-tectonics.\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141926937","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}
Jun Wang, Liangdong Luo, Yujie Yuan, Chen Chu, Hao He
The Lufeng Basin (LFB) in central Yunnan is located on the southwestern margin of the Yangtze Block in the eastern segment of the Tethys tectonic domain, where the Paleo-Tethys and the Paleo-Pacific tectonic domains converge. Jurassic red beds in this basin record the closure of the Paleo-Tethys Ocean and key information of the tectonic transition driven by the spreading of the Paleo-Pacific plate. We present sedimentary provenance analysis on these Jurassic red beds based on heavy mineral assemblages and detrital zircon geochronology. The results indicate that the strata in this basin were deposited after 214 Ma, and the Early Jurassic Lufeng Formation (Lufeng Fm.) mainly sourced from the west of the LFB with minor contributions from the western Yunnan. In contrast, the sedimentary provenance of the Middle Jurassic Chuanjie Formation (Chuanjie Fm.) and Laoluocun Formation (Laoluocun Fm.) shifted to the proximal ancient basement surrounding the basin and the east of the LFB. The regional unconformity between the Early and the Middle Jurassic may have resulted from the subduction of the Paleo-Pacific plate, jointly influenced by two tectonic domains. The sedimentary provenance shift in the Middle Jurassic may be related to the local uplift of the southwestern Yangtze Block caused by the subduction of the Paleo-Pacific plate. The tectonic regime transition associated with this highest peak of local uplift occurred at ∼170 Ma.
滇中禄丰盆地位于特提斯构造域东段长江地块西南缘，是古特提斯构造域和古太平洋构造域的交汇处。该盆地的侏罗纪红床记录了古特提斯洋的闭合过程，以及古太平洋板块扩张所驱动的构造转换的关键信息。我们根据重矿物组合和锆英石地质年代学，对这些侏罗纪红床进行了沉积成因分析。结果表明，该盆地的地层沉积于 214 Ma 之后，早侏罗世禄丰地层主要来源于禄丰盆地西部，少量来源于云南西部。相比之下，中侏罗世川街地层和老罗村地层的沉积产地则转向盆地周围的近古基底和低褶皱盆地东部。早侏罗世与中侏罗世之间的区域不整合可能是古太平洋板块俯冲的结果，受到两个构造域的共同影响。中侏罗世的沉积产状转变可能与古太平洋板块俯冲造成的西南扬子地块局部隆起有关。与这一局部隆升最高峰相关的构造体系转换发生在170Ma∼170Ma。
{"title":"Jurassic tectonic regime transition of the southwestern Yangtze Block, SW China: evidence from sedimentary provenance analysis","authors":"Jun Wang, Liangdong Luo, Yujie Yuan, Chen Chu, Hao He","doi":"10.1144/jgs2023-190","DOIUrl":"https://doi.org/10.1144/jgs2023-190","url":null,"abstract":"The Lufeng Basin (LFB) in central Yunnan is located on the southwestern margin of the Yangtze Block in the eastern segment of the Tethys tectonic domain, where the Paleo-Tethys and the Paleo-Pacific tectonic domains converge. Jurassic red beds in this basin record the closure of the Paleo-Tethys Ocean and key information of the tectonic transition driven by the spreading of the Paleo-Pacific plate. We present sedimentary provenance analysis on these Jurassic red beds based on heavy mineral assemblages and detrital zircon geochronology. The results indicate that the strata in this basin were deposited after 214 Ma, and the Early Jurassic Lufeng Formation (Lufeng Fm.) mainly sourced from the west of the LFB with minor contributions from the western Yunnan. In contrast, the sedimentary provenance of the Middle Jurassic Chuanjie Formation (Chuanjie Fm.) and Laoluocun Formation (Laoluocun Fm.) shifted to the proximal ancient basement surrounding the basin and the east of the LFB. The regional unconformity between the Early and the Middle Jurassic may have resulted from the subduction of the Paleo-Pacific plate, jointly influenced by two tectonic domains. The sedimentary provenance shift in the Middle Jurassic may be related to the local uplift of the southwestern Yangtze Block caused by the subduction of the Paleo-Pacific plate. The tectonic regime transition associated with this highest peak of local uplift occurred at ∼170 Ma.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141678815","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}
Ning Huo, S. Ao, W. Xiao, Q. Guo, Q. Mao, Dongfang Song
The Central Asian Orogenic Belt involves amalgamation of numerous magmatic arcs, accretionary complexes, and continental fragments during long-lived subduction and accretion. However, the nature of key microcontinental terranes, as well as their continuity, remains unclear. This study conducted outcrop observation, heavy mineral assemblage, whole-rock geochemistry, detrital zircon U-Pb dating and Lu-Hf isotope analysis on sandstones in the Beishan orogenic belt. The findings from field observations, petrographic analysis and weathering indices that the tectonic setting of the sandstone is a fore-arc sedimentary basin. The MDAs of sandstones are 503.8 ± 6.9 Ma and 431.9 ± 6.0 Ma. The provenance of the sandstone is complex, which probably originating from the Shuangyingshan and the Hanshan blocks. By comparing the detrital zircons U-Pb ages with adjacent terranes such as Central Tianshan, Duhuang and Tarim, it was observed that the Shuangyingshan block shares similary provenance with the Dunhaung terrane, while the Mazongshan-Hanshan shows affinity to the Central Tianshan Terrane. This study highlights the complex nature of sediment provenance in the Beishan orogenic belt, influenced by tectonic processes involving thrusting, accretionary complexes, and the presence of multiple terranes.
{"title":"Accretion of micro-continents and arcs in the southern Central Asian Orogenic Belt: Insights from provenance analyses of early Paleozoic sedimentary records in Beishan","authors":"Ning Huo, S. Ao, W. Xiao, Q. Guo, Q. Mao, Dongfang Song","doi":"10.1144/jgs2023-223","DOIUrl":"https://doi.org/10.1144/jgs2023-223","url":null,"abstract":"The Central Asian Orogenic Belt involves amalgamation of numerous magmatic arcs, accretionary complexes, and continental fragments during long-lived subduction and accretion. However, the nature of key microcontinental terranes, as well as their continuity, remains unclear. This study conducted outcrop observation, heavy mineral assemblage, whole-rock geochemistry, detrital zircon U-Pb dating and Lu-Hf isotope analysis on sandstones in the Beishan orogenic belt. The findings from field observations, petrographic analysis and weathering indices that the tectonic setting of the sandstone is a fore-arc sedimentary basin. The MDAs of sandstones are 503.8 ± 6.9 Ma and 431.9 ± 6.0 Ma. The provenance of the sandstone is complex, which probably originating from the Shuangyingshan and the Hanshan blocks. By comparing the detrital zircons U-Pb ages with adjacent terranes such as Central Tianshan, Duhuang and Tarim, it was observed that the Shuangyingshan block shares similary provenance with the Dunhaung terrane, while the Mazongshan-Hanshan shows affinity to the Central Tianshan Terrane. This study highlights the complex nature of sediment provenance in the Beishan orogenic belt, influenced by tectonic processes involving thrusting, accretionary complexes, and the presence of multiple terranes.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141679282","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}
Alejandra Sánchez-Roda, Paul B. Wignall, Yijun Xiong, S. Poulton
The cause of the Late Ordovician mass extinction (LOME) is widely debated, with glaciation, volcanism and oceanic redox fluctuations being proposed as possible drivers. Here, we apply a multi-proxy approach to deep water Iapetus Ocean samples from Dob's Linn, Scotland, to determine oceanic redox conditions and changes in chemical weathering intensity. We document major redox fluctuations between anoxic ferruginous and oxic conditions during the first, end-Katian extinction pulse, while the end-Hirnantian extinction phase witnessed more persistent anoxia. These two episodes were separated by oxic conditions and a major, short-lived decline in chemical weathering during the Hirnantian glaciation, suggesting that while global cooling may have placed stress on certain biota, it was unlikely the cause of the extinction crisis. Late Hirnantian anoxia persisted into the Silurian, with widespread euxinia resulting in global drawdown of redox-sensitive trace metals. Recent studies have identified a mid-Katian biotic crisis and recovery prior to the LOME, although the precise stratigraphic position is not yet defined. The mid-Katian record at Dob's Linn shows a major redox change, with dysoxic to anoxic-ferruginous deep ocean waters giving way to well-oxygenated conditions at this time. However, links between the mid-Katian biotic crisis and these redox changes remain unclear.
{"title":"Redox changes in the Iapetus Ocean during the Late Ordovician extinction crises","authors":"Alejandra Sánchez-Roda, Paul B. Wignall, Yijun Xiong, S. Poulton","doi":"10.1144/jgs2023-195","DOIUrl":"https://doi.org/10.1144/jgs2023-195","url":null,"abstract":"The cause of the Late Ordovician mass extinction (LOME) is widely debated, with glaciation, volcanism and oceanic redox fluctuations being proposed as possible drivers. Here, we apply a multi-proxy approach to deep water Iapetus Ocean samples from Dob's Linn, Scotland, to determine oceanic redox conditions and changes in chemical weathering intensity. We document major redox fluctuations between anoxic ferruginous and oxic conditions during the first, end-Katian extinction pulse, while the end-Hirnantian extinction phase witnessed more persistent anoxia. These two episodes were separated by oxic conditions and a major, short-lived decline in chemical weathering during the Hirnantian glaciation, suggesting that while global cooling may have placed stress on certain biota, it was unlikely the cause of the extinction crisis. Late Hirnantian anoxia persisted into the Silurian, with widespread euxinia resulting in global drawdown of redox-sensitive trace metals. Recent studies have identified a mid-Katian biotic crisis and recovery prior to the LOME, although the precise stratigraphic position is not yet defined. The mid-Katian record at Dob's Linn shows a major redox change, with dysoxic to anoxic-ferruginous deep ocean waters giving way to well-oxygenated conditions at this time. However, links between the mid-Katian biotic crisis and these redox changes remain unclear.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141677908","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}
We reside within a relatively interior position within the Milky Way galaxy which hinders our ability to understand its structure. Nonetheless, astrophysical observations of other galaxies in unison with spectroscopic measurements have produced a model for the Milky Way as a grand design, barred, spiral arm galaxy, with either two or four arms. Viewing through the plane of the Milky Way is not possible with any current astrophysical technique. However, perhaps terrestrial geology can help where current observations of our stellar environment cannot. During the orbit of our solar system around the galactic centre, Earth will have seen different cosmic surroundings, as a function of the solar system's orbit (240 km/s) that is faster than the spiral arm's density waves (210 km/s). Specifically, if the terrestrial impact record, or proxies for it, in some cryptic way reflect perturbations on the gravity field of the local solar system, then Earth may act as a geological orrery, with some interesting implications. Here we explore various models for the design of the Milky Way and compare these to geological proxies proposed by some as indicators for impact flux, through the deep time record within our planet. Isotope signatures in zircon are statistically coherent with a four-armed spiral model. However, even better correspondence is shown between the terrestrial isotopic record and more complex atomic hydrogen models of the galaxy.
{"title":"A geological telescope through the galaxy?","authors":"C. L. Kirkland, P. Sutton","doi":"10.1144/jgs2023-219","DOIUrl":"https://doi.org/10.1144/jgs2023-219","url":null,"abstract":"We reside within a relatively interior position within the Milky Way galaxy which hinders our ability to understand its structure. Nonetheless, astrophysical observations of other galaxies in unison with spectroscopic measurements have produced a model for the Milky Way as a grand design, barred, spiral arm galaxy, with either two or four arms. Viewing through the plane of the Milky Way is not possible with any current astrophysical technique. However, perhaps terrestrial geology can help where current observations of our stellar environment cannot. During the orbit of our solar system around the galactic centre, Earth will have seen different cosmic surroundings, as a function of the solar system's orbit (240 km/s) that is faster than the spiral arm's density waves (210 km/s). Specifically, if the terrestrial impact record, or proxies for it, in some cryptic way reflect perturbations on the gravity field of the local solar system, then Earth may act as a geological orrery, with some interesting implications. Here we explore various models for the design of the Milky Way and compare these to geological proxies proposed by some as indicators for impact flux, through the deep time record within our planet. Isotope signatures in zircon are statistically coherent with a four-armed spiral model. However, even better correspondence is shown between the terrestrial isotopic record and more complex atomic hydrogen models of the galaxy.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141678843","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}
The ancient city of Sparti (Greece) suffered extensive damage from a M w ∼7.2 earthquake in 464 B.C.E. resulting in ∼ 20,000 fatalities, but questions remain on the short (∼10 4 yrs) and long-term (10 5 – 10 6 yrs) activity of this important structure. This paper presents new structural data and fluvial geomorphologic analysis from the Sparta Fault, and in particular considers the northern fault segment that is less well known. A new topographic profile on the well-developed post-glacial fault scarp from the northern strand indicates a 7.53 m offset over the last ∼15 ka, suggesting a throw rate of ∼0.5 mm/yr. The longitudinal profiles of rivers flowing across the fault allow elucidation of longer-term fault activity. Along the strike of the fault rivers exhibit up to two slope-break knickpoints, which decrease in height from south to north. These knickpoints are interpreted to have formed owing to the initiation of faulting and a subsequent slip-rate acceleration. The post-glacial fault scarp and fluvial geomorphology both indicate that entire fault is active and has an asymmetrical throw profile that results in the highest slip-rate in the south.
公元前 464 年，希腊斯巴达（Sparti）古城在 M w ∼ 7.2 级地震中遭受了严重破坏，造成 20,000 人死亡，但人们对这一重要结构的短期（10 4 年）和长期（10 5 - 10 6 年）活动仍存有疑问。本文介绍了斯巴达断层的新结构数据和河流地貌分析，尤其是对鲜为人知的北部断层段进行了分析。北段冰川期后发育良好的断层峭壁上的新地形剖面显示，在过去 ∼15 ka 的时间里，断层峭壁偏移了 7.53 米，这表明断层的抛移速率为 ∼0.5 毫米/年。流经断层的河流的纵向剖面可以阐明更长期的断层活动。沿着断层的走向，河流呈现出多达两个斜坡断裂节理点，高度由南向北递减。据解释，这些节理点的形成是由于断层的启动以及随后的滑动速度加快所致。冰川期后的断层疤痕和河川地貌都表明，整个断层都很活跃，其抛掷剖面不对称，导致南部的滑移率最高。
{"title":"Structural and geomorphological constraints on the activity of the Sparta Fault (Greece)","authors":"Çağatay Çal, S. J. Boulton, Zoë Mildon","doi":"10.1144/jgs2024-066","DOIUrl":"https://doi.org/10.1144/jgs2024-066","url":null,"abstract":"\u0000 The ancient city of Sparti (Greece) suffered extensive damage from a M\u0000 w\u0000 ∼7.2 earthquake in 464 B.C.E. resulting in ∼ 20,000 fatalities, but questions remain on the short (∼10\u0000 4\u0000 yrs) and long-term (10\u0000 5\u0000 – 10\u0000 6\u0000 yrs) activity of this important structure. This paper presents new structural data and fluvial geomorphologic analysis from the Sparta Fault, and in particular considers the northern fault segment that is less well known. A new topographic profile on the well-developed post-glacial fault scarp from the northern strand indicates a 7.53 m offset over the last ∼15 ka, suggesting a throw rate of ∼0.5 mm/yr. The longitudinal profiles of rivers flowing across the fault allow elucidation of longer-term fault activity. Along the strike of the fault rivers exhibit up to two slope-break knickpoints, which decrease in height from south to north. These knickpoints are interpreted to have formed owing to the initiation of faulting and a subsequent slip-rate acceleration. The post-glacial fault scarp and fluvial geomorphology both indicate that entire fault is active and has an asymmetrical throw profile that results in the highest slip-rate in the south.\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141679099","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}
A pebbly gritstone–microconglomerate outcrop at Trainor's Rocks in the Mourne Mountains is one of the youngest (∼430 Ma) coarse clastic units within the Ordovician-Silurian Southern Uplands – Down-Longford Terrane. The ∼400m by 1 km outcrop lies within fine-grained Hawick Group (Wenlock) strata, and is rich in extraformational clasts including granite, rhyolite, andesite, basalt, vein quartz and metamorphic rocks, plus intraformational rip-up clasts of mudstone. Detrital zircons, analysed by SHRIMP, yield predominantly Ordovician U-Pb ages of 450-490 Ma, peaking at ∼470 Ma, coincident with arc-related magmatism in the Midland Valley Terrane. Whole rock geochemical data are consistent with derivation from a calc-alkaline continental arc, with clast provenance matching 473-464 Ma arc volcanic and intrusive rocks from the Tyrone Igneous Complex. A small proportion of analysed zircons have Proterozoic and Neoarchaean ages typical of sediments derived from the Dalradian Supergroup (Grampian Terrane). The youngest zircon analysed, 435 ±8 Ma, may indicate that magmatism continued during closure of Iapetus in the Llandovery. In these samples there is no evidence for Gondwana-derived sediment. The influx of detritus from the volcanic arc–Laurentian hinterland suggests episodic tectonic unroofing in response to syndepositional strike-slip movements.
{"title":"Provenance of the Trainor's Rocks microconglomerate, Northern Ireland: a mid-Silurian (Hawick Group) submarine channel fan deposit in the closing Iapetus Ocean","authors":"N. Moles, Mark R. Cooper, S. Hollis, B. McConnell","doi":"10.1144/jgs2024-025","DOIUrl":"https://doi.org/10.1144/jgs2024-025","url":null,"abstract":"A pebbly gritstone–microconglomerate outcrop at Trainor's Rocks in the Mourne Mountains is one of the youngest (∼430 Ma) coarse clastic units within the Ordovician-Silurian Southern Uplands – Down-Longford Terrane. The ∼400m by 1 km outcrop lies within fine-grained Hawick Group (Wenlock) strata, and is rich in extraformational clasts including granite, rhyolite, andesite, basalt, vein quartz and metamorphic rocks, plus intraformational rip-up clasts of mudstone. Detrital zircons, analysed by SHRIMP, yield predominantly Ordovician U-Pb ages of 450-490 Ma, peaking at ∼470 Ma, coincident with arc-related magmatism in the Midland Valley Terrane. Whole rock geochemical data are consistent with derivation from a calc-alkaline continental arc, with clast provenance matching 473-464 Ma arc volcanic and intrusive rocks from the Tyrone Igneous Complex. A small proportion of analysed zircons have Proterozoic and Neoarchaean ages typical of sediments derived from the Dalradian Supergroup (Grampian Terrane). The youngest zircon analysed, 435 ±8 Ma, may indicate that magmatism continued during closure of Iapetus in the Llandovery. In these samples there is no evidence for Gondwana-derived sediment. The influx of detritus from the volcanic arc–Laurentian hinterland suggests episodic tectonic unroofing in response to syndepositional strike-slip movements.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141678224","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}
Joe Connolly, Mark Anderson, Catherine M. Mottram, Gregory D Price, Randall Parrish, David J. Sanderson
The Bristol Channel Basin is a Mesozoic continental rift basin. The basin is an important analogue for offshore reservoirs. Relative cross-cutting relationships and correlation with adjacent sedimentary basins have previously been used to constrain the timing of basin development. In-situ U-Pb carbonate geochronology has been used to date calcite slickenfibre development in the cores of normal, thrust and strike-slip faults in the East Quantoxhead and Kilve region of Somerset for the first time. Protracted N-S extension from c a. 150–120 Ma formed normal faults. Subsequent N-S shortening from ca. 50–20 Ma was accommodated by (i) mutually cross-cutting strike-slip faults (ii) minor E-W-striking thrust faults and (ii) the reactivation of pre-existing normal faults. Throughout Cenozoic contraction, σ 2 and σ 3 remained similar in magnitude and periodically flipped to become vertical, this was likely controlled by local stress permutations and changes in fluid pressure. The timing of inversion is contemporaneous with dominant Pyrenean and later Alpine orogenic events, as well as the opening of the Mid Atlantic Rift. Early inversion of the Bristol Channel Basin was likely driven by far-field Pyrenean deformation, with later contraction caused by Alpine forces. Ridge push from the Mid Atlantic Rift exacerbated the reactivation of the basin.
布里斯托尔海峡盆地是中生代大陆裂谷盆地。该盆地是近海储层的重要模拟对象。以前曾利用与邻近沉积盆地的相对横切关系和相关性来确定盆地的开发时间。现场 U-Pb 碳酸盐地质年代学首次被用来确定萨默塞特郡东泉托克斯海德和基尔夫地区正断层、推断断层和走向滑动断层岩芯中方解石淤积层的发育时间。 约 150-120 Ma 的 N-S 向延伸形成了正断层。其后约 50-20 Ma 的 N-S 向缩短由 (i) 相互交叉的走向滑动断层 (ii) 轻微的 E-W 向冲击断层和 (ii) 原已存在的正断层重新激活所容纳。在整个新生代收缩过程中，σ 2 和 σ 3 的大小保持相似，并周期性地翻转成垂直状态，这很可能是受当地应力排列和流体压力变化的控制。 反转的时间与主要的比利牛斯造山运动和后来的阿尔卑斯造山运动以及大西洋中部裂谷的开启同时发生。布里斯托尔海峡盆地早期的反转可能是由远场比利牛斯变形所驱动的，而后期的收缩则是由阿尔卑斯力量所造成的。大西洋中部裂谷的海脊推动加剧了盆地的重新激活。
{"title":"Using U-Pb carbonate dating to constrain the timing of extension and fault reactivation within the Bristol Channel Basin, SW England","authors":"Joe Connolly, Mark Anderson, Catherine M. Mottram, Gregory D Price, Randall Parrish, David J. Sanderson","doi":"10.1144/jgs2024-021","DOIUrl":"https://doi.org/10.1144/jgs2024-021","url":null,"abstract":"\u0000 The Bristol Channel Basin is a Mesozoic continental rift basin. The basin is an important analogue for offshore reservoirs. Relative cross-cutting relationships and correlation with adjacent sedimentary basins have previously been used to constrain the timing of basin development.\u0000 In-situ\u0000 U-Pb carbonate geochronology has been used to date calcite slickenfibre development in the cores of normal, thrust and strike-slip faults in the East Quantoxhead and Kilve region of Somerset for the first time.\u0000 \u0000 \u0000 Protracted N-S extension from c\u0000 a.\u0000 150–120 Ma formed normal faults. Subsequent N-S shortening from\u0000 ca.\u0000 50–20 Ma was accommodated by (i) mutually cross-cutting strike-slip faults (ii) minor E-W-striking thrust faults and (ii) the reactivation of pre-existing normal faults. Throughout Cenozoic contraction,\u0000 \u0000 \u0000 σ\u0000 \u0000 \u0000 2\u0000 and\u0000 \u0000 \u0000 σ\u0000 \u0000 \u0000 3\u0000 remained similar in magnitude and periodically flipped to become vertical, this was likely controlled by local stress permutations and changes in fluid pressure.\u0000 \u0000 The timing of inversion is contemporaneous with dominant Pyrenean and later Alpine orogenic events, as well as the opening of the Mid Atlantic Rift. Early inversion of the Bristol Channel Basin was likely driven by far-field Pyrenean deformation, with later contraction caused by Alpine forces. Ridge push from the Mid Atlantic Rift exacerbated the reactivation of the basin.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141680463","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}
The Stac Fada Member (Stoer Group) is a ∼1.2 Ga melt-rich impact breccia whose source crater and, therefore, proximity remains debated. We present a detailed in situ geochemical dataset for altered impact melt clasts within Stac Fada samples from Bay of Stoer and Second Coast. These altered impact melt clasts are now predominantly composed of clinochlore. Geothermometry of this clinochlore indicates formation temperatures within the ejecta blanket at 188-231°C, in agreement with previous estimates. A positive correlation between platinum group elements Ir, Pt, and Rh — apparently independent of Ni — indicates two geochemical sources for platinum group elements enrichment. We propose that these represent an Mg-Ni rich chondritic impactor and a mafic/ultramafic layered body within the target lithology. Spatial variation in Ni content suggests that geochemical data, in combination with field observations, may be instrumental in assessing the likely location of the impact crater.
Stac Fada 成员（Stoer 组）是一个 ∼1.2 Ga 的富含熔体的撞击角砾岩，其源火山口及其邻近性仍存在争议。我们为来自斯托尔湾和第二海岸的斯塔克法达样本中的蚀变冲击熔体碎屑提供了详细的原位地球化学数据集。这些蚀变的撞击熔块目前主要由闪长岩组成。这种倩彩石的测地温度表明，喷出岩毯中的形成温度为 188-231°C ，与之前的估计一致。铂族元素Ir、Pt和Rh之间的正相关性--显然与Ni无关--表明铂族元素富集有两个地球化学来源。我们认为这两个来源分别是富含镁镍的软玉撞击体和目标岩性中的岩浆/超岩浆层状体。镍含量的空间变化表明，地球化学数据与实地观测相结合，可能有助于评估撞击坑的可能位置。
{"title":"Geochemical evidence for a chondritic impactor in altered impact glass from the Stac Fada Member impactite, NW Scotland","authors":"A. Goodwin, R. J. Garwood, R. Tartèse","doi":"10.1144/jgs2023-213","DOIUrl":"https://doi.org/10.1144/jgs2023-213","url":null,"abstract":"The Stac Fada Member (Stoer Group) is a ∼1.2 Ga melt-rich impact breccia whose source crater and, therefore, proximity remains debated. We present a detailed in situ geochemical dataset for altered impact melt clasts within Stac Fada samples from Bay of Stoer and Second Coast. These altered impact melt clasts are now predominantly composed of clinochlore. Geothermometry of this clinochlore indicates formation temperatures within the ejecta blanket at 188-231°C, in agreement with previous estimates. A positive correlation between platinum group elements Ir, Pt, and Rh — apparently independent of Ni — indicates two geochemical sources for platinum group elements enrichment. We propose that these represent an Mg-Ni rich chondritic impactor and a mafic/ultramafic layered body within the target lithology. Spatial variation in Ni content suggests that geochemical data, in combination with field observations, may be instrumental in assessing the likely location of the impact crater.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681865","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}
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