Mesozoic rift basins of the Eastern North American Margin (ENAM) span from Florida in the United States to the Grand Banks of Canada and formed during progressive extension prior to continental breakup and the opening of the north-central Atlantic. The syn-rift strata from all the individual basins, lumped along the entire margin into the Newark Supergroup, are dominated by fluvial conglomerate and sandstone, lacustrine siltstone, mudstone, and abundant alluvial conglomerate and sandstone lithofacies. Deposition of these syn-rift sedimentary rocks was accommodated in a series of half grabens and subsidiary full grabens situated within the Permo-Carboniferous Appalachian orogen. The Mesozoic ENAM is commonly depicted as a magma-rich continental rift margin, with magmatism (Central Atlantic magmatic province [CAMP]) driving continental breakup. However, the southern portion of the ENAM shows evidence of magmatic breakup (e.g., seaward-dipping reflectors), and rifting and crustal thinning appeared to start ~30 m.y. prior to CAMP emplacement in the Jurassic. This study provides extensive new detrital zircon and apatite U-Pb provenance data to determine the provenance and reconstruct the paleodrainages of the Newark Basin during progressive rifting and magmatic breakup and the implications for the overall rift configuration and asymmetry during progressive rifting along the ENAM rift margin. Detailed new detrital zircon (N = 21; n = 3093) and apatite (N = 4; n = 559) U-Pb results from sandstone outcrop and core samples from the Newark Basin indicate a distinct provenance shift, with relatively older Carnian syn-rift strata predominately sourced from the hanging wall of the basin bounding fault in the east while relatively younger Norian strata were regionally sourced from both the hanging wall and footwall. The syn-rift strata at the Triassic-Jurassic boundary were sourced from the hanging wall before a transition to local footwall terranes. These results suggest two major provenance changes during progressive rifting—the first occurring during Carnian crustal necking and rift flank uplift as predicted by recent numerical models and the second occurring at the onset of the Jurassic due to regional and local thermal uplift during CAMP magmatism as seen along other magma-rich margins, such as the North Atlantic and the southern portion of the South Atlantic margin.
{"title":"Detrital zircon and apatite U-Pb provenance and drainage evolution of the Newark Basin during progressive rifting and continental breakup along the Eastern North American Margin, USA","authors":"Zachary Foster-baril, D. Stockli","doi":"10.1130/ges02610.1","DOIUrl":"https://doi.org/10.1130/ges02610.1","url":null,"abstract":"Mesozoic rift basins of the Eastern North American Margin (ENAM) span from Florida in the United States to the Grand Banks of Canada and formed during progressive extension prior to continental breakup and the opening of the north-central Atlantic. The syn-rift strata from all the individual basins, lumped along the entire margin into the Newark Supergroup, are dominated by fluvial conglomerate and sandstone, lacustrine siltstone, mudstone, and abundant alluvial conglomerate and sandstone lithofacies. Deposition of these syn-rift sedimentary rocks was accommodated in a series of half grabens and subsidiary full grabens situated within the Permo-Carboniferous Appalachian orogen. The Mesozoic ENAM is commonly depicted as a magma-rich continental rift margin, with magmatism (Central Atlantic magmatic province [CAMP]) driving continental breakup. However, the southern portion of the ENAM shows evidence of magmatic breakup (e.g., seaward-dipping reflectors), and rifting and crustal thinning appeared to start ~30 m.y. prior to CAMP emplacement in the Jurassic. This study provides extensive new detrital zircon and apatite U-Pb provenance data to determine the provenance and reconstruct the paleodrainages of the Newark Basin during progressive rifting and magmatic breakup and the implications for the overall rift configuration and asymmetry during progressive rifting along the ENAM rift margin. Detailed new detrital zircon (N = 21; n = 3093) and apatite (N = 4; n = 559) U-Pb results from sandstone outcrop and core samples from the Newark Basin indicate a distinct provenance shift, with relatively older Carnian syn-rift strata predominately sourced from the hanging wall of the basin bounding fault in the east while relatively younger Norian strata were regionally sourced from both the hanging wall and footwall. The syn-rift strata at the Triassic-Jurassic boundary were sourced from the hanging wall before a transition to local footwall terranes. These results suggest two major provenance changes during progressive rifting—the first occurring during Carnian crustal necking and rift flank uplift as predicted by recent numerical models and the second occurring at the onset of the Jurassic due to regional and local thermal uplift during CAMP magmatism as seen along other magma-rich margins, such as the North Atlantic and the southern portion of the South Atlantic margin.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45271995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
cdem is a macOS document-based application for two-dimensional discrete element modeling of tectonic structures and their associated deformation. Documents encapsulate simulations that can be run and explored simultaneously. A document contains three main views: (1) Set-up view, to define the assembly size, element properties, anisotropy, boundary conditions (type of faulting), overburden stress, erosion, and syn-tectonic sedimentation; (2) Summary view, which displays the details of the model after initialization; and (3) Results view, which displays the geometry of the model while it is running or after the run and allows exploring the model’s evolution in terms of geometry, displacement, strain, or stress. We illustrate the use of the program for assembly calibration and the modeling of contractional and extensional structures without and with syn-tectonic sedimentation. In all these cases, cdem produces realistic incremental and finite deformation. cdem is less powerful than its precursor cdem2D, but it can import and visualize cdem2D results, making the combined use of these two programs a robust suite for mechanically modeling tectonic structures.
{"title":"cdem: A macOS program for discrete element modeling of tectonic structures","authors":"N. Cardozo, S. Hardy","doi":"10.1130/ges02647.1","DOIUrl":"https://doi.org/10.1130/ges02647.1","url":null,"abstract":"cdem is a macOS document-based application for two-dimensional discrete element modeling of tectonic structures and their associated deformation. Documents encapsulate simulations that can be run and explored simultaneously. A document contains three main views: (1) Set-up view, to define the assembly size, element properties, anisotropy, boundary conditions (type of faulting), overburden stress, erosion, and syn-tectonic sedimentation; (2) Summary view, which displays the details of the model after initialization; and (3) Results view, which displays the geometry of the model while it is running or after the run and allows exploring the model’s evolution in terms of geometry, displacement, strain, or stress. We illustrate the use of the program for assembly calibration and the modeling of contractional and extensional structures without and with syn-tectonic sedimentation. In all these cases, cdem produces realistic incremental and finite deformation. cdem is less powerful than its precursor cdem2D, but it can import and visualize cdem2D results, making the combined use of these two programs a robust suite for mechanically modeling tectonic structures.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47238452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the paleogeographic reconstructions of the Rodinia supercontinent, the circum-global 1.1–0.9 Ga collisional belt is speculated to skirt the SE coast of India, incorporating the Rodinian-age Eastern Ghats Province. But the Eastern Ghats Province may not have welded with the Indian landmass until 550–500 Ma. Instead, the ~1500-km-long, E-striking Central Indian Tectonic Zone provides an alternate option for linking the 1.1–0.9 Ga circum-global collisional belt through India. The highly tectonized Central Indian Tectonic Zone formed due to the early Neoproterozoic collision of the North India and the South India blocks. Based on a summary of the recent findings in the different crustal domains within the Central Indian Tectonic Zone, we demonstrate that the 1.03–0.93 Ga collision involved thrusting that resulted in the emplacement of low-grade metamorphosed allochthonous units above the high-grade basement rocks; the development of crustal-scale, steeply dipping, orogen-parallel transpressional shear zones; syn-collisional felsic magmatism; and the degeneration of orogenesis by extensional exhumation. The features are analogous to those reported in the broadly coeval Grenville and Sveconorwegian orogens. We suggest that the 1.1–0.9 Ga circum-global collisional belt in Rodinia swings westward from the Australo-Antarctic landmass and passes centrally through the Greater India landmass, which for the most part welded at 1.0–0.9 Ga. It follows that the paleogeographic positions of India obtained from paleomagnetic data older than 1.1–0.9 Ga are likely to correspond to the positions of the North and South India blocks, respectively, and not to the Greater India landmass in its entirety.
{"title":"The Central Indian Tectonic Zone: A Rodinia supercontinent-forming collisional zone and analogy with the Grenville and Sveconorwegian orogens","authors":"A. Bhattacharya, A. Banerjee, N. Sequeira","doi":"10.1130/ges02597.1","DOIUrl":"https://doi.org/10.1130/ges02597.1","url":null,"abstract":"In the paleogeographic reconstructions of the Rodinia supercontinent, the circum-global 1.1–0.9 Ga collisional belt is speculated to skirt the SE coast of India, incorporating the Rodinian-age Eastern Ghats Province. But the Eastern Ghats Province may not have welded with the Indian landmass until 550–500 Ma. Instead, the ~1500-km-long, E-striking Central Indian Tectonic Zone provides an alternate option for linking the 1.1–0.9 Ga circum-global collisional belt through India. The highly tectonized Central Indian Tectonic Zone formed due to the early Neoproterozoic collision of the North India and the South India blocks. Based on a summary of the recent findings in the different crustal domains within the Central Indian Tectonic Zone, we demonstrate that the 1.03–0.93 Ga collision involved thrusting that resulted in the emplacement of low-grade metamorphosed allochthonous units above the high-grade basement rocks; the development of crustal-scale, steeply dipping, orogen-parallel transpressional shear zones; syn-collisional felsic magmatism; and the degeneration of orogenesis by extensional exhumation. The features are analogous to those reported in the broadly coeval Grenville and Sveconorwegian orogens. We suggest that the 1.1–0.9 Ga circum-global collisional belt in Rodinia swings westward from the Australo-Antarctic landmass and passes centrally through the Greater India landmass, which for the most part welded at 1.0–0.9 Ga. It follows that the paleogeographic positions of India obtained from paleomagnetic data older than 1.1–0.9 Ga are likely to correspond to the positions of the North and South India blocks, respectively, and not to the Greater India landmass in its entirety.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42535128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Eastern California shear zone (USA) is a broad zone of transtensional deformation related to the relative motion between the Pacific and North American plates. Due to its active deformation and seismicity, the zone receives great attention, with specific focus on slip rates of major active faults. To contribute to a better understanding of the long-term strain accumulation in this zone, this study quantifies the long-term E–W-directed extensional strain rate based on the analysis of N–S-trending normal fault scarps in the 765-k.y.-old Bishop tuff (Volcanic Tableland). The average extensional strain rate determined over the past 765 k.y. is 0.29 ± 0.10 mm/yr per 10 km (29 ± 10 nanostrain/yr) and similar to the current rate of elastic strain accumulation rate in the Volcanic Tableland (0.30 ± 0.13 mm/yr per 10 km; 30 ± 13 nanostrain/yr) determined by Global Positioning System (GPS) data. The present-day E–W strain rate across the entire Eastern California shear zone at the latitude of the Volcanic Tableland is 0.36 ± 0.05 mm/yr per 10 km (36 ± 5 nanostrain/yr). This suggests that the local rate of E–W extension has not changed significantly since the mid-Pleistocene. Furthermore, if the Volcanic Tableland is representative of the greater region, as the GPS data suggest, this would also indicate a constant extension rate across the Eastern California shear zone at the latitude of ~37.5°N over the 765 k.y. time period. These results suggest that late Pleistocene and Holocene extension rates of major faults in this zone can be interpreted in light of a presumably unchanged far-field stress system since at least the mid-Pleistocene.
{"title":"Rate of E–W extension in the Volcanic Tableland, California (USA): A comparison of strain rates on two different timescales","authors":"Eric Salomon","doi":"10.1130/ges02633.1","DOIUrl":"https://doi.org/10.1130/ges02633.1","url":null,"abstract":"The Eastern California shear zone (USA) is a broad zone of transtensional deformation related to the relative motion between the Pacific and North American plates. Due to its active deformation and seismicity, the zone receives great attention, with specific focus on slip rates of major active faults. To contribute to a better understanding of the long-term strain accumulation in this zone, this study quantifies the long-term E–W-directed extensional strain rate based on the analysis of N–S-trending normal fault scarps in the 765-k.y.-old Bishop tuff (Volcanic Tableland). The average extensional strain rate determined over the past 765 k.y. is 0.29 ± 0.10 mm/yr per 10 km (29 ± 10 nanostrain/yr) and similar to the current rate of elastic strain accumulation rate in the Volcanic Tableland (0.30 ± 0.13 mm/yr per 10 km; 30 ± 13 nanostrain/yr) determined by Global Positioning System (GPS) data. The present-day E–W strain rate across the entire Eastern California shear zone at the latitude of the Volcanic Tableland is 0.36 ± 0.05 mm/yr per 10 km (36 ± 5 nanostrain/yr). This suggests that the local rate of E–W extension has not changed significantly since the mid-Pleistocene. Furthermore, if the Volcanic Tableland is representative of the greater region, as the GPS data suggest, this would also indicate a constant extension rate across the Eastern California shear zone at the latitude of ~37.5°N over the 765 k.y. time period. These results suggest that late Pleistocene and Holocene extension rates of major faults in this zone can be interpreted in light of a presumably unchanged far-field stress system since at least the mid-Pleistocene.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47993597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A suite of subduction-related early Triassic igneous rocks crops out in the Pingxiang area of the Dian-Qiong suture (DQS) in southwest China; this suite represents an important geological record of subduction and closure of the Paleo-Tethys Ocean. In this study, we report geochronological, geochemical, and Nd-Hf isotope data for newly discovered rhyolites and biotite granites in the Pingxiang area. We use these data to constrain their emplacement ages, origins, and geodynamic implications. Zircon U-Pb dating indicates that the rhyolites and biotite granites were emplaced at 251–250 Ma and 249 Ma (early Triassic), respectively. The rhyolites and biotite granites have elevated FeOT/(FeOT + MgO) (0.78–0.89) and 10,000 × Ga/Al (2.83–4.11) ratios, with geochemical affinities to A2-type granites. These rocks are enriched in some large-ion lithophile elements (e.g., Rb, Th, and Ba) and depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), indicating their formation in a subduction-related arc. The rhyolites and biotite granites have negative whole-rock εNd(t) (−11.5 to −9.7) and zircon εHf(t) (−14.5 to −6.2) values, suggesting that these magmas were derived from an ancient crust-dominated source. Geochemical and Nd isotope data reveal that the peraluminous A2-type rhyolites and biotite granites were derived by partial melting of felsic crustal rocks under low-pressure and high-temperature conditions. By integrating all the available data with the regional tectonic evolution of the southwestern Youjiang Basin and adjacent regions, we attribute the generation of the peraluminous A2-type rhyolites and biotite granites to the extensional setting that existed during oceanic subduction, which was induced by roll-back of the Paleo-Tethys oceanic lithosphere at 251–249 Ma. This study indicates that subduction-related magmatism related to Paleo-Tethys oceanic lithosphere was still active in the early Triassic.
{"title":"Early Triassic roll-back of subducted Paleo-Tethys oceanic lithosphere: Insights from A2-type silicic igneous rocks in the Pingxiang area, southwest China","authors":"Wenlong Huang, Xijun Liu, Lei Liu, Zhenglin Li, Xinyu Liu, Hao Wu","doi":"10.1130/ges02617.1","DOIUrl":"https://doi.org/10.1130/ges02617.1","url":null,"abstract":"A suite of subduction-related early Triassic igneous rocks crops out in the Pingxiang area of the Dian-Qiong suture (DQS) in southwest China; this suite represents an important geological record of subduction and closure of the Paleo-Tethys Ocean. In this study, we report geochronological, geochemical, and Nd-Hf isotope data for newly discovered rhyolites and biotite granites in the Pingxiang area. We use these data to constrain their emplacement ages, origins, and geodynamic implications. Zircon U-Pb dating indicates that the rhyolites and biotite granites were emplaced at 251–250 Ma and 249 Ma (early Triassic), respectively. The rhyolites and biotite granites have elevated FeOT/(FeOT + MgO) (0.78–0.89) and 10,000 × Ga/Al (2.83–4.11) ratios, with geochemical affinities to A2-type granites. These rocks are enriched in some large-ion lithophile elements (e.g., Rb, Th, and Ba) and depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), indicating their formation in a subduction-related arc. The rhyolites and biotite granites have negative whole-rock εNd(t) (−11.5 to −9.7) and zircon εHf(t) (−14.5 to −6.2) values, suggesting that these magmas were derived from an ancient crust-dominated source. Geochemical and Nd isotope data reveal that the peraluminous A2-type rhyolites and biotite granites were derived by partial melting of felsic crustal rocks under low-pressure and high-temperature conditions. By integrating all the available data with the regional tectonic evolution of the southwestern Youjiang Basin and adjacent regions, we attribute the generation of the peraluminous A2-type rhyolites and biotite granites to the extensional setting that existed during oceanic subduction, which was induced by roll-back of the Paleo-Tethys oceanic lithosphere at 251–249 Ma. This study indicates that subduction-related magmatism related to Paleo-Tethys oceanic lithosphere was still active in the early Triassic.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49214686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Grocott, K. Thrane, K. McCaffrey, Phoebe R. Sleath, A. Dziggel
The “Rinkian belt” of West Greenland is a metamorphic terrain of Paleoproterozoic age comprising: (1) the north Rinkian fold-thrust belt (FTB)—a pro- or fore-arc domain, highly deformed and metamorphosed with widespread anatexis; (2) the Prøven Igneous Complex—a magmatic arc characterized by hypersthene granitic rocks (“charnockites”); (3) the south Rinkian FTB—an inverted back-arc basin; and 4) a continental margin or foreland. Recognition of this tectonic architecture demonstrates that the “Rinkian” is a bona fide orogenic belt—the Rinkian orogen—and not simply the imbricated lower plate of the Nagssugtoqidian orogen. Arc plutons of the Prøven Igneous Complex were emplaced into the Karrat Group at ca. 1.90–1.85 Ga, dividing a back arc basin into pro- and retro-arc domains. In the former—the north Rinkian FTB—WSW-directed thrusting (deformation events D1-D2) and high-grade metamorphism were taking place by ca. 1.875 Ga and were continuous through ca. 1.850 Ga with a peak temperature at ca. 1.830 Ma accompanied by anatexis in the Karrat Group and lower units of the Prøven Igneous Complex. In the retro-arc domain—the south Rinkian FTB—thrusting to the E (D1) began at ca. 1.870 Ma followed by thrusting to the W (D2) at ca. 1.830–1.820 Ga with displacement focused into a major high-temperature ductile shear zone which carried the Prøven Igneous Complex in the hanging wall of an Andean-type, crustal-scale, “pop-up” structure. High-temperature deformation continued during D3 when the pro-arc, arc, and retro-arc domains were shortened by bivergent detachment folding and thrusting at ca. 1.820–1.810 Ga.
{"title":"Andean-type, bivergent crustal shortening in the Rinkian orogen: New constraints on the tectonic evolution of Laurentia–West Greenland in the Paleoproterozoic","authors":"J. Grocott, K. Thrane, K. McCaffrey, Phoebe R. Sleath, A. Dziggel","doi":"10.1130/ges02614.1","DOIUrl":"https://doi.org/10.1130/ges02614.1","url":null,"abstract":"The “Rinkian belt” of West Greenland is a metamorphic terrain of Paleoproterozoic age comprising: (1) the north Rinkian fold-thrust belt (FTB)—a pro- or fore-arc domain, highly deformed and metamorphosed with widespread anatexis; (2) the Prøven Igneous Complex—a magmatic arc characterized by hypersthene granitic rocks (“charnockites”); (3) the south Rinkian FTB—an inverted back-arc basin; and 4) a continental margin or foreland. Recognition of this tectonic architecture demonstrates that the “Rinkian” is a bona fide orogenic belt—the Rinkian orogen—and not simply the imbricated lower plate of the Nagssugtoqidian orogen. Arc plutons of the Prøven Igneous Complex were emplaced into the Karrat Group at ca. 1.90–1.85 Ga, dividing a back arc basin into pro- and retro-arc domains. In the former—the north Rinkian FTB—WSW-directed thrusting (deformation events D1-D2) and high-grade metamorphism were taking place by ca. 1.875 Ga and were continuous through ca. 1.850 Ga with a peak temperature at ca. 1.830 Ma accompanied by anatexis in the Karrat Group and lower units of the Prøven Igneous Complex. In the retro-arc domain—the south Rinkian FTB—thrusting to the E (D1) began at ca. 1.870 Ma followed by thrusting to the W (D2) at ca. 1.830–1.820 Ga with displacement focused into a major high-temperature ductile shear zone which carried the Prøven Igneous Complex in the hanging wall of an Andean-type, crustal-scale, “pop-up” structure. High-temperature deformation continued during D3 when the pro-arc, arc, and retro-arc domains were shortened by bivergent detachment folding and thrusting at ca. 1.820–1.810 Ga.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42181975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Bello, M. Perna, Ada Consalvo, F. Brozzetti, P. Galli, D. Cirillo, Carlo Andrenacci, A. C. Tangari, Andrea Carducci, M. Menichetti, G. Lavecchia, F. Stoppa, G. Rosatelli
The systematic study of faults that have released strong earthquakes in the past is a challenge for seismic hazard assessment. In carbonate landscapes, the use of rare earth element (REE) concentrations on slickensides may aid the reconstruction of fault slip history. We applied this methodology to the Caggiano normal fault (Southern Apennines, Italy), cropping out southeast of the Irpinia 1980 CE earthquake fault (Mw 6.9), which was responsible for both the 1561 CE and partly the 1857 CE Basilicata earthquakes (Mw 6.7 and 7.1). We integrated the REE analysis approach with a high-resolution topographic analysis along 98 serial topographic profiles to measure vertical separations attributable to faulting since the Last Glacial Maximum (LGM). The asymmetric scarp height profiles suggest fault-lateral propagation and along-strike variations in the fault evolution. Our results indicate the occurrence of 7 to 11 earthquakes with variable slip between ~40 cm and ~70 cm within post-LGM times. We estimated the magnitudes of the respective earthquakes, between 5.5 and 7.0, and most commonly between 6.3 and 6.5. The results suggest a recurrence time between 1.6 k.y. and 2.3 k.y. and a slip rate ranging between 0.6 mm/yr and 0.9 mm/yr. This approach may be useful for application to carbonate fault planes in similar tectonic contexts worldwide.
对过去曾发生过强烈地震的断层进行系统研究是地震危险性评估的挑战。在碳酸盐岩景观中，利用切片边缘的稀土元素（REE）浓度可能有助于重建断层滑动历史。我们将该方法应用于1980年Irpinia CE地震断层（Mw 6.9）东南部的Caggiano正断层（意大利亚平宁山脉南部），这是1561 CE和1857 CE Basilicata地震（Mw 6.7和7.1）的部分原因。不对称陡崖高度剖面表明，断层在演化过程中发生了横向传播和沿走向变化。我们的结果表明，在LGM后的时间内，发生了7至11次滑动在~40厘米至~70厘米之间的地震。我们估计了各自地震的震级，在5.5到7.0之间，最常见的是在6.3到6.5之间。结果表明，复发时间在1.6千年至2.3千年之间，滑动率在0.6毫米/年至0.9毫米/年之间。该方法可用于世界范围内类似构造背景下的碳酸盐断层面。
{"title":"Coupling rare earth element analyses and high-resolution topography along fault scarps to investigate past earthquakes: A case study from the Southern Apennines (Italy)","authors":"S. Bello, M. Perna, Ada Consalvo, F. Brozzetti, P. Galli, D. Cirillo, Carlo Andrenacci, A. C. Tangari, Andrea Carducci, M. Menichetti, G. Lavecchia, F. Stoppa, G. Rosatelli","doi":"10.1130/ges02627.1","DOIUrl":"https://doi.org/10.1130/ges02627.1","url":null,"abstract":"The systematic study of faults that have released strong earthquakes in the past is a challenge for seismic hazard assessment. In carbonate landscapes, the use of rare earth element (REE) concentrations on slickensides may aid the reconstruction of fault slip history. We applied this methodology to the Caggiano normal fault (Southern Apennines, Italy), cropping out southeast of the Irpinia 1980 CE earthquake fault (Mw 6.9), which was responsible for both the 1561 CE and partly the 1857 CE Basilicata earthquakes (Mw 6.7 and 7.1). We integrated the REE analysis approach with a high-resolution topographic analysis along 98 serial topographic profiles to measure vertical separations attributable to faulting since the Last Glacial Maximum (LGM). The asymmetric scarp height profiles suggest fault-lateral propagation and along-strike variations in the fault evolution. Our results indicate the occurrence of 7 to 11 earthquakes with variable slip between ~40 cm and ~70 cm within post-LGM times. We estimated the magnitudes of the respective earthquakes, between 5.5 and 7.0, and most commonly between 6.3 and 6.5. The results suggest a recurrence time between 1.6 k.y. and 2.3 k.y. and a slip rate ranging between 0.6 mm/yr and 0.9 mm/yr. This approach may be useful for application to carbonate fault planes in similar tectonic contexts worldwide.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41421543","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The relationships between brittle detachment faulting and ductile shear zones in metamorphic core complexes are often ambiguous. Although it is commonly assumed that these two structures are kinematically linked and genetically related, direct observations of this coupling are rare. Here, we conducted a detailed field investigation to probe the connection between a detachment fault and mylonitic shear zone in the Ruby Mountain–East Humboldt Range metamorphic core complex, northeast Nevada. Field observations, along with new and published geochronology, demonstrate that Oligocene top-to-the-west mylonitic shear zones are crosscut by ca. 17 Ma subvertical basalt dikes, and these dikes are in turn truncated by middle Miocene detachment faults. The detachment faults appear to focus in preexisting weak zones in shaley strata and Mesozoic thrust faults. We interpret that the Oligocene mylonitic shear zones were generated in response to domal upwelling during voluminous plutonism and partial melting, which significantly predated the middle Miocene onset of regional extension and detachment slip. Our model simplifies mechanical issues with low-angle detachment faulting because there was an initial dip to the weak zones exploited by the future detachment-fault zone. This mechanism may be important for many apparent low-angle normal faults in the eastern Great Basin. We suggest that the temporal decoupling of mylonitic shearing and detachment faulting may be significant and underappreciated for many of the metamorphic core complexes in the North American Cordillera. In this case, earlier Eocene–Oligocene buoyant doming may have preconditioned the crust to be reactivated by Miocene extension thus explaining the spatial relationship between structures.
{"title":"Decoupled Oligocene mylonitic shearing and Miocene detachment faulting in the East Humboldt Range metamorphic core complex, northeast Nevada, USA","authors":"A. Zuza, Seth M. Dee","doi":"10.1130/ges02619.1","DOIUrl":"https://doi.org/10.1130/ges02619.1","url":null,"abstract":"The relationships between brittle detachment faulting and ductile shear zones in metamorphic core complexes are often ambiguous. Although it is commonly assumed that these two structures are kinematically linked and genetically related, direct observations of this coupling are rare. Here, we conducted a detailed field investigation to probe the connection between a detachment fault and mylonitic shear zone in the Ruby Mountain–East Humboldt Range metamorphic core complex, northeast Nevada. Field observations, along with new and published geochronology, demonstrate that Oligocene top-to-the-west mylonitic shear zones are crosscut by ca. 17 Ma subvertical basalt dikes, and these dikes are in turn truncated by middle Miocene detachment faults. The detachment faults appear to focus in preexisting weak zones in shaley strata and Mesozoic thrust faults. We interpret that the Oligocene mylonitic shear zones were generated in response to domal upwelling during voluminous plutonism and partial melting, which significantly predated the middle Miocene onset of regional extension and detachment slip. Our model simplifies mechanical issues with low-angle detachment faulting because there was an initial dip to the weak zones exploited by the future detachment-fault zone. This mechanism may be important for many apparent low-angle normal faults in the eastern Great Basin. We suggest that the temporal decoupling of mylonitic shearing and detachment faulting may be significant and underappreciated for many of the metamorphic core complexes in the North American Cordillera. In this case, earlier Eocene–Oligocene buoyant doming may have preconditioned the crust to be reactivated by Miocene extension thus explaining the spatial relationship between structures.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44140566","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A striated surface is present at an erosional unconformity between foliated Paleoproterozoic Michigamme Formation and fluvial conglomerate and sandstone of the Neoproterozoic Jacobsville Formation exposed at L’Anse Bay (Michigan, USA). These striations have been interpreted to be the result of ice flow in either the Proterozoic, the Pleistocene, or the modern. Recently, the glacial origin interpretation for this striated surface has been used to argue that it may be related to ca. 717–635 Ma Cryogenian snowball Earth glaciation. This interpretation would make the surface a rare example of a Neoproterozoic glacial pavement, with major chronostratigraphic implications that in turn impose constraints on the timing of intracratonic erosion related to the formation of the Great Unconformity. In this contribution, we present new observations showing that the surface is a tectonic slickenside caused by largely unconformity-parallel slip along the erosional unconformity. We document structural repetition of the Michigamme-Jacobsville contact with associated small-scale folding. The unconformity-parallel slip transitions into thrust faults that ramp up into the overlying Jacobsville Formation. We interpret that the surface records contractional deformation rather than ancient glaciation, recent ice movement, or recent mass wasting. The faulting likely occurred during the Rigolet phase of the Grenvillian orogeny, which also folded the Jacobsville Formation in the footwall of the Keweenaw fault.
{"title":"Grooving in the midcontinent: A tectonic origin for the mysterious striations of L’Anse Bay, Michigan, USA","authors":"Tadesse B. Alemu, E. Hodgin, N. Swanson‐Hysell","doi":"10.1130/ges02603.1","DOIUrl":"https://doi.org/10.1130/ges02603.1","url":null,"abstract":"A striated surface is present at an erosional unconformity between foliated Paleoproterozoic Michigamme Formation and fluvial conglomerate and sandstone of the Neoproterozoic Jacobsville Formation exposed at L’Anse Bay (Michigan, USA). These striations have been interpreted to be the result of ice flow in either the Proterozoic, the Pleistocene, or the modern. Recently, the glacial origin interpretation for this striated surface has been used to argue that it may be related to ca. 717–635 Ma Cryogenian snowball Earth glaciation. This interpretation would make the surface a rare example of a Neoproterozoic glacial pavement, with major chronostratigraphic implications that in turn impose constraints on the timing of intracratonic erosion related to the formation of the Great Unconformity. In this contribution, we present new observations showing that the surface is a tectonic slickenside caused by largely unconformity-parallel slip along the erosional unconformity. We document structural repetition of the Michigamme-Jacobsville contact with associated small-scale folding. The unconformity-parallel slip transitions into thrust faults that ramp up into the overlying Jacobsville Formation. We interpret that the surface records contractional deformation rather than ancient glaciation, recent ice movement, or recent mass wasting. The faulting likely occurred during the Rigolet phase of the Grenvillian orogeny, which also folded the Jacobsville Formation in the footwall of the Keweenaw fault.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45161894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Unsworth, M. Comeau, D. Díaz, H. Brasse, B. Heit, A. Favetto, C. Pomposiello, H. Barcelona, Gisel Peri, F. Ticona
The Central Andes are unique in the global system of subduction zones in that a significant, high-altitude plateau has formed above a subduction zone. In this region, both subduction and the associated magmatism have been shown to vary in both space and time. Geophysical data have been invaluable in determining the subsurface structure of this region. Extensive seismic studies have determined the regional-scale distribution of partial melt in the crust and upper mantle. Magnetotelluric studies have been effective in providing independent constraints on the quantity and composition of partial melt in the crust and upper mantle. Geodetic studies have shown that a small number of volcanic centers exhibit persistent, long-term uplift that may indicate the formation of plutons or future eruptions. This paper describes a detailed study of the Southern Puna using magnetotelluric (MT) data. This region is located at the southern limit of the Central Andes in a region where a recent transition from flat-slab subduction to normal subduction has caused an increase in magmatism, in addition to hypothesized lithospheric delamination. It is also a region where an extensive zone adjacent to the volcanic arc is undergoing surface uplift, located near Volcán Lastarria and Cordon del Azufre (collectively called Lazufre). The main goals of the work are to define the crustal structure and to investigate processes that may cause surface uplift of relatively large regions not associated with active volcanism. As part of the PLUTONS project, MT data were collected on an east-west transect (approximately along 25°S) that extended across the Southern Puna, from Lazufre to north of Cerro Galan. The data were combined with previously collected MT data around Lazufre and inverted to give a 3-D resistivity model of the crust. The low resistivity of the crust resulted in limited sensitivity to mantle structure. A number of major crustal conductors were detected and included (1) a mid-crustal conductor extending eastward from the volcanic arc as far as the Salar de Antofalla; (2) an upper- to mid-crustal conductor located north of Cerro Galan; and (3) a conductor that rises westward from (1) and terminates directly beneath the region of surface uplift at Lazufre. These conductors are broadly coincident with the location of crustal lowshear-wave anomalies. The conductive features were interpreted to be due to zones of partial melt stored in the crust, and petrological data were used to estimate melt fractions. Below Lazufre, it is likely that aqueous fluids contribute to the high conductivity, which is observed within the depth range of the inflation source, giving evidence that the surface uplift may be associated with both magmatic and hydrothermal processes.
{"title":"Crustal structure of the Lazufre volcanic complex and the Southern Puna from 3-D inversion of magnetotelluric data: Implications for surface uplift and evidence for melt storage and hydrothermal fluids","authors":"M. Unsworth, M. Comeau, D. Díaz, H. Brasse, B. Heit, A. Favetto, C. Pomposiello, H. Barcelona, Gisel Peri, F. Ticona","doi":"10.1130/ges02506.1","DOIUrl":"https://doi.org/10.1130/ges02506.1","url":null,"abstract":"The Central Andes are unique in the global system of subduction zones in that a significant, high-altitude plateau has formed above a subduction zone. In this region, both subduction and the associated magmatism have been shown to vary in both space and time. Geophysical data have been invaluable in determining the subsurface structure of this region. Extensive seismic studies have determined the regional-scale distribution of partial melt in the crust and upper mantle. Magnetotelluric studies have been effective in providing independent constraints on the quantity and composition of partial melt in the crust and upper mantle. Geodetic studies have shown that a small number of volcanic centers exhibit persistent, long-term uplift that may indicate the formation of plutons or future eruptions.\u0000 This paper describes a detailed study of the Southern Puna using magnetotelluric (MT) data. This region is located at the southern limit of the Central Andes in a region where a recent transition from flat-slab subduction to normal subduction has caused an increase in magmatism, in addition to hypothesized lithospheric delamination. It is also a region where an extensive zone adjacent to the volcanic arc is undergoing surface uplift, located near Volcán Lastarria and Cordon del Azufre (collectively called Lazufre). The main goals of the work are to define the crustal structure and to investigate processes that may cause surface uplift of relatively large regions not associated with active volcanism.\u0000 As part of the PLUTONS project, MT data were collected on an east-west transect (approximately along 25°S) that extended across the Southern Puna, from Lazufre to north of Cerro Galan. The data were combined with previously collected MT data around Lazufre and inverted to give a 3-D resistivity model of the crust. The low resistivity of the crust resulted in limited sensitivity to mantle structure. A number of major crustal conductors were detected and included (1) a mid-crustal conductor extending eastward from the volcanic arc as far as the Salar de Antofalla; (2) an upper- to mid-crustal conductor located north of Cerro Galan; and (3) a conductor that rises westward from (1) and terminates directly beneath the region of surface uplift at Lazufre. These conductors are broadly coincident with the location of crustal lowshear-wave anomalies. The conductive features were interpreted to be due to zones of partial melt stored in the crust, and petrological data were used to estimate melt fractions. Below Lazufre, it is likely that aqueous fluids contribute to the high conductivity, which is observed within the depth range of the inflation source, giving evidence that the surface uplift may be associated with both magmatic and hydrothermal processes.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44882084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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