Jillian D. Mallis, George Zemlicka, Sanja Knezevic Antonijevic, T. Lapen, G. Costin, Tania Campbell
Though the Gulf of Mexico has been studied for more than a century, the lithology, age, and origin of the basement crustal terranes remain poorly understood. New U-Pb zircon ages of a volcanic sample in the DeSoto Canyon 535 #1 Raptor well were obtained by in situ laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and resulted in a crystallization age of 509 ± 23 Ma, indicating the crustal terrane beneath the northeastern Gulf of Mexico is likely of peri-Gondwanan affinity. This basement may be associated with the felsic volcanism related to Neoproterozoic to Cambrian subduction along the supercontinent’s western margin. This subduction-related volcanism likely represents the last pulses of magmatic activity before the west coast of Gondwana transitioned into a passive margin ca. 500 Ma. The data presented here for the DeSoto Canyon 535 #1 Raptor trachyte represent the oldest radiometrically dated evidence of volcanism in the present-day deep-water Gulf of Mexico.
{"title":"U-Pb geochronology and petrography of Neoproterozoic to early Cambrian volcanic rocks in basement crustal terranes beneath the deep-water Gulf of Mexico","authors":"Jillian D. Mallis, George Zemlicka, Sanja Knezevic Antonijevic, T. Lapen, G. Costin, Tania Campbell","doi":"10.1130/ges02687.1","DOIUrl":"https://doi.org/10.1130/ges02687.1","url":null,"abstract":"Though the Gulf of Mexico has been studied for more than a century, the lithology, age, and origin of the basement crustal terranes remain poorly understood. New U-Pb zircon ages of a volcanic sample in the DeSoto Canyon 535 #1 Raptor well were obtained by in situ laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and resulted in a crystallization age of 509 ± 23 Ma, indicating the crustal terrane beneath the northeastern Gulf of Mexico is likely of peri-Gondwanan affinity. This basement may be associated with the felsic volcanism related to Neoproterozoic to Cambrian subduction along the supercontinent’s western margin. This subduction-related volcanism likely represents the last pulses of magmatic activity before the west coast of Gondwana transitioned into a passive margin ca. 500 Ma. The data presented here for the DeSoto Canyon 535 #1 Raptor trachyte represent the oldest radiometrically dated evidence of volcanism in the present-day deep-water Gulf of Mexico.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"30 43","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138946918","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}
Our newly acquired and recently published map, geochronologic, and com- positional data for early intermediate-composition central volcanoes in the northeastern San Juan Mountains provide insights about the broad magmatic precursors to the large continental-arc ignimbrite flare-up in the mid-Cenozoic Southern Rocky Mountain volcanic field (SRMVF). Initial volcanism migrated from central Colorado to northern New Mexico ca. 40–29 Ma, as part of a more regional trend of southward-progressing mid-Cenozoic magmatism in the U.S. segment of the North American Cordillera. Within the San Juan locus, which represents the largest preserved erosional remnant of the SRMVF and site of most intense eruptive activity, new 40Ar/39Ar and U-Pb zircon ages show that eruptions at many individual edifices began nearly concurrently, at ca. 35 Ma, with peak activity at 34–32 Ma. Broadly similar precursor effusive volcanism characterizes other major loci of continental-arc ignimbrite magmatism along the western American cordilleras, but none of these sites records early volcanism as voluminous, spatially widespread, well exposed, or compositionally diverse as the San Juan locus in Colorado. Early San Juan volcanism was larger in volume than the later ignimbrites, constituting about two thirds the total erupted. Early lava and breccias are as much as 700–900 m thick where exposed along eroded flanks of the San Juan Mountains; drill holes have penetrated sections as thick as 2600 m. The early volcanoes were dominantly andesitic, with lesser dacite and minor rhyolite. Such volcanism is widely interpreted as initiated by basaltic magma from the mantle, but mid-Cenozoic basalt is almost nonexistent at the San Juan locus—an absence inferred to be due to extensive lower-crustal assimilation and fractionation. The early volcanic rocks are calc-alkaline and typical of high-K continental-arc volcanism; they become modestly more alkalic and enriched in trace elements such as light rare earth elements, Zr, Nb, and Th from the San Juan locus northeastward into central Colorado. Such variations may reflect synmagmatic crustal thickening and deeper levels of primary magma generation concurrent with assembly of upper-crustal magma bodies that could support large ignimbrite eruptions. Substantial uncertainties remain for growth histories of the early volcanoes, however, because of unexposed lower parts of edifices, eroded upper parts, and limited availability of mineral phases that could be dated reliably. Although the early volcanoes are widely distributed within the SRMVF, many are clustered at sites of subsequent ignimbrite calderas. The precursor edifices are inferred to record incubation stages in construction of overall translithospheric batholithic-scale magmatic systems. Prolonged processes of incremental magma generation, accumulation, fractionation, and solidification intermittently generated sufficient liquid to erupt large ignimbrites. Maturation of focused eruptions and in
{"title":"Precursors to a continental-arc ignimbrite flare-up: Early central volcanoes of the San Juan Mountains, Colorado, USA","authors":"P. Lipman, M. Zimmerer, A.K. Gilmer","doi":"10.1130/ges02691.1","DOIUrl":"https://doi.org/10.1130/ges02691.1","url":null,"abstract":"Our newly acquired and recently published map, geochronologic, and com- positional data for early intermediate-composition central volcanoes in the northeastern San Juan Mountains provide insights about the broad magmatic precursors to the large continental-arc ignimbrite flare-up in the mid-Cenozoic Southern Rocky Mountain volcanic field (SRMVF). Initial volcanism migrated from central Colorado to northern New Mexico ca. 40–29 Ma, as part of a more regional trend of southward-progressing mid-Cenozoic magmatism in the U.S. segment of the North American Cordillera. Within the San Juan locus, which represents the largest preserved erosional remnant of the SRMVF and site of most intense eruptive activity, new 40Ar/39Ar and U-Pb zircon ages show that eruptions at many individual edifices began nearly concurrently, at ca. 35 Ma, with peak activity at 34–32 Ma. Broadly similar precursor effusive volcanism characterizes other major loci of continental-arc ignimbrite magmatism along the western American cordilleras, but none of these sites records early volcanism as voluminous, spatially widespread, well exposed, or compositionally diverse as the San Juan locus in Colorado.\u0000 Early San Juan volcanism was larger in volume than the later ignimbrites, constituting about two thirds the total erupted. Early lava and breccias are as much as 700–900 m thick where exposed along eroded flanks of the San Juan Mountains; drill holes have penetrated sections as thick as 2600 m. The early volcanoes were dominantly andesitic, with lesser dacite and minor rhyolite. Such volcanism is widely interpreted as initiated by basaltic magma from the mantle, but mid-Cenozoic basalt is almost nonexistent at the San Juan locus—an absence inferred to be due to extensive lower-crustal assimilation and fractionation. The early volcanic rocks are calc-alkaline and typical of high-K continental-arc volcanism; they become modestly more alkalic and enriched in trace elements such as light rare earth elements, Zr, Nb, and Th from the San Juan locus northeastward into central Colorado. Such variations may reflect synmagmatic crustal thickening and deeper levels of primary magma generation concurrent with assembly of upper-crustal magma bodies that could support large ignimbrite eruptions. Substantial uncertainties remain for growth histories of the early volcanoes, however, because of unexposed lower parts of edifices, eroded upper parts, and limited availability of mineral phases that could be dated reliably.\u0000 Although the early volcanoes are widely distributed within the SRMVF, many are clustered at sites of subsequent ignimbrite calderas. The precursor edifices are inferred to record incubation stages in construction of overall translithospheric batholithic-scale magmatic systems. Prolonged processes of incremental magma generation, accumulation, fractionation, and solidification intermittently generated sufficient liquid to erupt large ignimbrites. Maturation of focused eruptions and in","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"101 10","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138954196","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}
Ruixue Wang, Qingfei Wang, C. Kirkland, Erick Ramanaidou, Jun Deng
In the eastern North China Craton, the Zibo bauxitic clay deposits are situated between Permian sandstones. These deposits exhibit distinct characteristics in two horizons. The lower horizon consists of disordered kaolinite with anhedral–subhedral, rounded morphologies that indicate a detrital origin. The upper horizon, however, contains ordered kaolinite. Detrital zircon grains in the lower horizon indicate a unimodal age spectrum with a mean age of ca. 290 Ma and εHf(t) values ranging from −20.8 to −6.0. These findings suggest a continental volcanic arc source on the northern margin of the North China Craton. In contrast, detrital zircon grains in the upper section exhibit a multi-modal detrital age spectrum with significant age peaks at 2500 Ma, 1850 Ma, and 310 Ma that originates from the local basement. The zircon dating establishes a maximum depositional age of ca. 280 ± 3 Ma, which indicates denudation of the source area in the northern North China Craton during the Artinskian stage. The relative abundance of detrital kaolinite indicates a warm and humid climate during the late Artinskian (ca. 283 Ma) to Early Kungurian (ca. 280 Ma), while cold and dry conditions prevailed during the mid–late Kungurian (ca. 277 Ma). The northern North China Craton, which supplied source material to the lower section of Zibo bauxitic clay, experienced rapid uplift and exhumation and underwent intense weathering under high humidity and warm temperatures during the late Artinskian to Early Kungurian. However, the source area shifted from the north to a more central region as the climate transitioned to cold and dry conditions in the mid–late Kungurian. Considering that detrital clay formation is indicative of specific climatic conditions, the Permian bauxitic clay deposits in Zibo provide a valuable record of environmental changes during the late Paleozoic ice age (LPIA; ca. 360–260 Ma).
{"title":"Provenance shifts in bauxitic clay from Zibo, North China Craton, links tectonics and climate to environmental perturbation","authors":"Ruixue Wang, Qingfei Wang, C. Kirkland, Erick Ramanaidou, Jun Deng","doi":"10.1130/ges02656.1","DOIUrl":"https://doi.org/10.1130/ges02656.1","url":null,"abstract":"In the eastern North China Craton, the Zibo bauxitic clay deposits are situated between Permian sandstones. These deposits exhibit distinct characteristics in two horizons. The lower horizon consists of disordered kaolinite with anhedral–subhedral, rounded morphologies that indicate a detrital origin. The upper horizon, however, contains ordered kaolinite. Detrital zircon grains in the lower horizon indicate a unimodal age spectrum with a mean age of ca. 290 Ma and εHf(t) values ranging from −20.8 to −6.0. These findings suggest a continental volcanic arc source on the northern margin of the North China Craton. In contrast, detrital zircon grains in the upper section exhibit a multi-modal detrital age spectrum with significant age peaks at 2500 Ma, 1850 Ma, and 310 Ma that originates from the local basement. The zircon dating establishes a maximum depositional age of ca. 280 ± 3 Ma, which indicates denudation of the source area in the northern North China Craton during the Artinskian stage. The relative abundance of detrital kaolinite indicates a warm and humid climate during the late Artinskian (ca. 283 Ma) to Early Kungurian (ca. 280 Ma), while cold and dry conditions prevailed during the mid–late Kungurian (ca. 277 Ma). The northern North China Craton, which supplied source material to the lower section of Zibo bauxitic clay, experienced rapid uplift and exhumation and underwent intense weathering under high humidity and warm temperatures during the late Artinskian to Early Kungurian. However, the source area shifted from the north to a more central region as the climate transitioned to cold and dry conditions in the mid–late Kungurian. Considering that detrital clay formation is indicative of specific climatic conditions, the Permian bauxitic clay deposits in Zibo provide a valuable record of environmental changes during the late Paleozoic ice age (LPIA; ca. 360–260 Ma).","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"19 3","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139005428","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. Michalak, S. Cashman, V. Langenheim, T. Team, D. Christensen
Development and evaluation of models for tectonic evolution in the Cascadia forearc require understanding of along-strike heterogeneity of strain distribution, uplift, and upper-plate characteristics. Here, we investigated the Neogene geologic record of the Klamath Mountains province in southernmost Cascadia and obtained apatite (U-Th)/He (AHe) thermochronology of Mesozoic plutons, Neogene graben sediment thickness, detrital zircon records from Neogene grabens, gravity and magnetic data, and kinematic analysis of faults. We documented three aspects of Neogene tectonics: early Miocene and younger rock exhumation, development of topographic relief sufficient to isolate Neogene graben-filling sediments from sources outside of the Klamath Mountains, and initiation of mid-Miocene or younger right-lateral and reverse faulting. Key findings are: (1) 10 new apatite AHe mean cooling ages from the Canyon Creek and Granite Peak plutons in the Trinity Alps range from 24.7 ± 2.1 Ma to 15.7 ± 2.1 Ma. Inverse thermal modeling of these data and published apatite fission- track ages indicate the most rapid rock cooling between ca. 25 and 15 Ma. One new AHe mean cooling age (26.7 ± 3.2 Ma) from the Ironside Mountain batholith 40 km west of the Trinity Alps, combined with previously published AHe ages, suggests geographically widespread latest Oligocene to Miocene cooling in the southern Klamath Mountains province. (2) AHe ages of 39.4 ± 5.1 Ma on the downthrown side and 22.7 ± 3.0 Ma on the upthrown side of the Browns Meadow fault suggest early Miocene to younger fault activity. (3) U-Pb detrital zircon ages (n = 862) and Lu-Hf isotope geochemistry from Miocene Weaverville Formation sediments in the Weaverville, Lowden Ranch, Hayfork, and Hyampom grabens south and southwest of the Trinity Alps can be traced to entirely Klamath Mountains sources; they suggest the south-central Klamath Mountains had, by the middle Miocene, sufficient relief to isolate these grabens from more distal sediment sources. (4) Two Miocene detrital zircon U-Pb ages of 10.6 ± 0.4 Ma and 16.7 ± 0.2 Ma from the Lowden Ranch graben show that the maximum depositional age of the upper Weaverville Formation here is younger than previously recognized. (5) A prominent steep-sided negative gravity anomaly associated with the Hayfork graben shows that both the north and south margins are fault-controlled, and inversion of gravity data suggests basin fill is between 1 km and 1.9 km thick. Abrupt elevation changes of basin fill-to-bedrock contacts reported in well logs record E-side-up and right-lateral faulting at the eastern end of the Hayfork graben. A NE-striking gravity gradient separates the main graben on the west from a narrower, thinner basin to the east, supporting this interpretation. (6) Offset of both the base of the Weaverville Formation and the cataclasite-capped La Grange fault surface by a fault on the southwest margin of the Weaverville basin documents 200 m of reverse and 1500 m of ri
{"title":"Neogene faulting, basin development, and relief generation in the southern Klamath Mountains (USA)","authors":"M. Michalak, S. Cashman, V. Langenheim, T. Team, D. Christensen","doi":"10.1130/ges02612.1","DOIUrl":"https://doi.org/10.1130/ges02612.1","url":null,"abstract":"Development and evaluation of models for tectonic evolution in the Cascadia forearc require understanding of along-strike heterogeneity of strain distribution, uplift, and upper-plate characteristics. Here, we investigated the Neogene geologic record of the Klamath Mountains province in southernmost Cascadia and obtained apatite (U-Th)/He (AHe) thermochronology of Mesozoic plutons, Neogene graben sediment thickness, detrital zircon records from Neogene grabens, gravity and magnetic data, and kinematic analysis of faults. We documented three aspects of Neogene tectonics: early Miocene and younger rock exhumation, development of topographic relief sufficient to isolate Neogene graben-filling sediments from sources outside of the Klamath Mountains, and initiation of mid-Miocene or younger right-lateral and reverse faulting. Key findings are: (1) 10 new apatite AHe mean cooling ages from the Canyon Creek and Granite Peak plutons in the Trinity Alps range from 24.7 ± 2.1 Ma to 15.7 ± 2.1 Ma. Inverse thermal modeling of these data and published apatite fission- track ages indicate the most rapid rock cooling between ca. 25 and 15 Ma. One new AHe mean cooling age (26.7 ± 3.2 Ma) from the Ironside Mountain batholith 40 km west of the Trinity Alps, combined with previously published AHe ages, suggests geographically widespread latest Oligocene to Miocene cooling in the southern Klamath Mountains province. (2) AHe ages of 39.4 ± 5.1 Ma on the downthrown side and 22.7 ± 3.0 Ma on the upthrown side of the Browns Meadow fault suggest early Miocene to younger fault activity. (3) U-Pb detrital zircon ages (n = 862) and Lu-Hf isotope geochemistry from Miocene Weaverville Formation sediments in the Weaverville, Lowden Ranch, Hayfork, and Hyampom grabens south and southwest of the Trinity Alps can be traced to entirely Klamath Mountains sources; they suggest the south-central Klamath Mountains had, by the middle Miocene, sufficient relief to isolate these grabens from more distal sediment sources. (4) Two Miocene detrital zircon U-Pb ages of 10.6 ± 0.4 Ma and 16.7 ± 0.2 Ma from the Lowden Ranch graben show that the maximum depositional age of the upper Weaverville Formation here is younger than previously recognized. (5) A prominent steep-sided negative gravity anomaly associated with the Hayfork graben shows that both the north and south margins are fault-controlled, and inversion of gravity data suggests basin fill is between 1 km and 1.9 km thick. Abrupt elevation changes of basin fill-to-bedrock contacts reported in well logs record E-side-up and right-lateral faulting at the eastern end of the Hayfork graben. A NE-striking gravity gradient separates the main graben on the west from a narrower, thinner basin to the east, supporting this interpretation. (6) Offset of both the base of the Weaverville Formation and the cataclasite-capped La Grange fault surface by a fault on the southwest margin of the Weaverville basin documents 200 m of reverse and 1500 m of ri","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"174 S398","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139006195","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}
Rose I. Gallo, M. Ort, Kayla Iacovino, Aurora Silleni, Victoria C. Smith, Guido Giordano, R. Isaia, Joseph Boro
The 39.8-ka Campanian Ignimbrite was emplaced during a large caldera-forming eruption of Campi Flegrei near Naples, Italy. The ignimbrite is found up to 80 km from the caldera, and co-ignimbrite ash-fall deposits occur 3200 km away. The proximal and distal stratigraphy of the Campanian Ignimbrite has not been definitively correlated due to the dissimilar appearance of the proximal and distal deposits, a lack of medial exposures, and the inconsistency and heterogeneity of the proximal stratigraphy. Here, we document the major-element glass-shard chemistry, matrix componentry, and lithic componentry of the proximal and distal stratigraphic sequences of the ignimbrite to attempt to correlate the units. The results of these disparate observations taken together suggest that the established stratigraphic units cannot be directly and uniquely correlated between the proximal and distal regions and that neither the proximal nor distal stratigraphy provides a record of the entire eruptive sequence. However, the characteristics studied can be used to demarcate eruptive phases that are connected to some of the defined units in the proximal and distal stratigraphy.
{"title":"Reconciling complex stratigraphic frameworks reveals temporally and geographically variable depositional patterns of the Campanian Ignimbrite","authors":"Rose I. Gallo, M. Ort, Kayla Iacovino, Aurora Silleni, Victoria C. Smith, Guido Giordano, R. Isaia, Joseph Boro","doi":"10.1130/ges02651.1","DOIUrl":"https://doi.org/10.1130/ges02651.1","url":null,"abstract":"The 39.8-ka Campanian Ignimbrite was emplaced during a large caldera-forming eruption of Campi Flegrei near Naples, Italy. The ignimbrite is found up to 80 km from the caldera, and co-ignimbrite ash-fall deposits occur 3200 km away. The proximal and distal stratigraphy of the Campanian Ignimbrite has not been definitively correlated due to the dissimilar appearance of the proximal and distal deposits, a lack of medial exposures, and the inconsistency and heterogeneity of the proximal stratigraphy. Here, we document the major-element glass-shard chemistry, matrix componentry, and lithic componentry of the proximal and distal stratigraphic sequences of the ignimbrite to attempt to correlate the units. The results of these disparate observations taken together suggest that the established stratigraphic units cannot be directly and uniquely correlated between the proximal and distal regions and that neither the proximal nor distal stratigraphy provides a record of the entire eruptive sequence. However, the characteristics studied can be used to demarcate eruptive phases that are connected to some of the defined units in the proximal and distal stratigraphy.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"2 3","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139005633","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}
Jared W. Kluesner, Samuel Y. Johnson, Stuart P. Nishenko, Elisa Medri, Alexander R. Simms, H. Gary Greene, Harrison J. Gray, Shannon A. Mahan, Jason S. Padgett, Emma T. Krolczyk, Daniel S. Brothers, James E. Conrad
The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri slope. The Cross-Hosgri slope is comprised of two distinct stratigraphic units. The lower unit (unit 1) overlies the post–Last Glacial Maximum transgressive erosion surface and is interpreted as a Younger Dryas (ca. 12.85–11.65 ka) shoreface deposit based on radiocarbon and optically stimulated luminescence (OSL) ages, Bayesian age modeling, seismic facies, sediment texture, sediment infauna, and heavy mineral component. The shoreface was abandoned and partly eroded during rapid sea-level rise from ca. 11.5 to 7 ka. Unit 2 consists of fine sand and silt deposited in a midshelf environment when the rate of sea-level rise slowed between ca. 7 ka and the present. Although unit 2 provides a thin, relatively uniform cover over the lower slope break of the older shoreface, this feature still represents a valuable piercing point, providing a Hosgri fault slip rate of 2.6 ± 0.8 mm/yr. Full-waveform processing of chirp data resulted in significantly higher resolution in coarser-grained strata, which are typically difficult to interpret with more traditional envelope processing. Our novel combination of offshore radiocarbon and OSL dating is the first application to offshore paleoseismic studies, and our results indicate the utility of this approach for future marine neotectonic investigations.
{"title":"High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault","authors":"Jared W. Kluesner, Samuel Y. Johnson, Stuart P. Nishenko, Elisa Medri, Alexander R. Simms, H. Gary Greene, Harrison J. Gray, Shannon A. Mahan, Jason S. Padgett, Emma T. Krolczyk, Daniel S. Brothers, James E. Conrad","doi":"10.1130/ges02657.1","DOIUrl":"https://doi.org/10.1130/ges02657.1","url":null,"abstract":"The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri slope. The Cross-Hosgri slope is comprised of two distinct stratigraphic units. The lower unit (unit 1) overlies the post–Last Glacial Maximum transgressive erosion surface and is interpreted as a Younger Dryas (ca. 12.85–11.65 ka) shoreface deposit based on radiocarbon and optically stimulated luminescence (OSL) ages, Bayesian age modeling, seismic facies, sediment texture, sediment infauna, and heavy mineral component. The shoreface was abandoned and partly eroded during rapid sea-level rise from ca. 11.5 to 7 ka. Unit 2 consists of fine sand and silt deposited in a midshelf environment when the rate of sea-level rise slowed between ca. 7 ka and the present. Although unit 2 provides a thin, relatively uniform cover over the lower slope break of the older shoreface, this feature still represents a valuable piercing point, providing a Hosgri fault slip rate of 2.6 ± 0.8 mm/yr. Full-waveform processing of chirp data resulted in significantly higher resolution in coarser-grained strata, which are typically difficult to interpret with more traditional envelope processing. Our novel combination of offshore radiocarbon and OSL dating is the first application to offshore paleoseismic studies, and our results indicate the utility of this approach for future marine neotectonic investigations.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"30 37","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135818593","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 Cretaceous intrusive units of the Sahwave and Nightingale ranges in northwestern Nevada, USA, located between the Sierra Nevada and Idaho batholiths, represent a critical segment of Cretaceous arc magmatism. U-Pb zircon age dating shows that the older, 104 Ma Power Line intrusive complex is dominantly granodioritic in composition, while the younger 94–88 Ma Sahwave Range intrusive suite (the Juniper Pass, Bob Springs, and Sahwave plutons) is similar in composition (tonalite to granodiorite) and age to the plutons of the Tuolumne intrusive suite of the east-central Sierra Nevada batholith. We present new field measurements, microstructural observations, and anisotropy of magnetic susceptibility analyses of the Power Line intrusive complex and Sahwave Range intrusive suite. The Power Line intrusive complex is characterized by a vertical, N–S-striking, solid-state foliation and down-dip lineation. Evidence of dextral shearing is observed on subhorizontal planes that are perpendicular to the lineation, which is consistent with pure shear-dominated transpression. This fabric is similar in style and timing to both the western Idaho shear zone of the Idaho batholith and mid-Cretaceous shear zones of the central Sierra Nevada. The plutons of the Sahwave Range intrusive suite are not affected by the pure shear-dominated transpressional fabric observed in the Power Line intrusive complex, which indicates that this deformation ceased by ca. 94 Ma. Rather, the Juniper Pass pluton contains an E–W-striking magmatic foliation fabric that rotates to a steep NW–SE-striking, solid-state foliation in the younger Sahwave pluton. These fabrics are strikingly similar to fabrics in the Tuolumne intrusive suite, Sierra Nevada, California, USA. Recent work in the western Idaho shear zone also indicates that late-stage deformation occurred there until ca. 85 Ma. Therefore, the intrusions of northwestern Nevada provide a tectonic link between the Sierra Nevada and Idaho batholiths, which suggests that two distinct phases of mid-Cretaceous, transpressional deformation occurred in at least three magmatic arc segments of the western U.S. margin.
美国内华达州西北部的Sahwave和Nightingale山脉的白垩纪侵入单元位于内华达山脉和爱达荷岩基之间，是白垩纪弧岩浆活动的关键段。U-Pb锆石年龄测年表明，较老的104 Ma Power Line侵入杂岩以花岗闪长岩为主，而较年轻的94-88 Ma Sahwave Range侵入组(Juniper Pass、Bob Springs和Sahwave岩体)在成分(闪长岩与花岗闪长岩)和年龄上与内华达山脉中东部的Tuolumne侵入组的岩体相似。本文介绍了电力线侵入杂岩和萨波范围侵入岩套新的野外测量、微观结构观测和磁化率各向异性分析。电力线侵入杂岩具有纵向、南北向、固态片理和下倾线理的特征。在垂直于线理的亚水平面上观察到右向剪切作用的证据，这与纯剪切作用为主的逆压作用相一致。这种构造在风格和时间上与爱达荷州基底的爱达荷州西部剪切带和内华达山脉中部的白垩纪中期剪切带相似。萨波山脉侵入岩组的岩体不受电力线侵入杂岩中观察到的纯剪切为主的跨扭构造的影响，这表明这种变形在约94 Ma时停止了。更确切地说，Juniper Pass岩体包含一个东西向的岩浆叶理构造，在较年轻的Sahwave岩体中，它旋转成一个陡峭的nw - se向的固态叶理构造。这些织物与美国加利福尼亚州内华达山脉的Tuolumne侵入套件中的织物惊人地相似。最近在爱达荷州西部剪切带的工作也表明，直到约85 Ma，那里发生了晚期变形。因此，内华达西北部的侵入提供了内华达山脉和爱达荷州岩基之间的构造联系，这表明在美国西部边缘的至少三个岩浆弧段发生了中白垩纪的两个不同阶段的挤压变形。
{"title":"Two phases of Cretaceous dextral shearing recorded in the plutonic rocks of NW Nevada (USA): A tectonic link between intra‑arc shearing in the Sierra Nevada and Idaho batholiths","authors":"Sarah F. Trevino, Basil Tikoff","doi":"10.1130/ges02682.1","DOIUrl":"https://doi.org/10.1130/ges02682.1","url":null,"abstract":"The Cretaceous intrusive units of the Sahwave and Nightingale ranges in northwestern Nevada, USA, located between the Sierra Nevada and Idaho batholiths, represent a critical segment of Cretaceous arc magmatism. U-Pb zircon age dating shows that the older, 104 Ma Power Line intrusive complex is dominantly granodioritic in composition, while the younger 94–88 Ma Sahwave Range intrusive suite (the Juniper Pass, Bob Springs, and Sahwave plutons) is similar in composition (tonalite to granodiorite) and age to the plutons of the Tuolumne intrusive suite of the east-central Sierra Nevada batholith. We present new field measurements, microstructural observations, and anisotropy of magnetic susceptibility analyses of the Power Line intrusive complex and Sahwave Range intrusive suite. The Power Line intrusive complex is characterized by a vertical, N–S-striking, solid-state foliation and down-dip lineation. Evidence of dextral shearing is observed on subhorizontal planes that are perpendicular to the lineation, which is consistent with pure shear-dominated transpression. This fabric is similar in style and timing to both the western Idaho shear zone of the Idaho batholith and mid-Cretaceous shear zones of the central Sierra Nevada. The plutons of the Sahwave Range intrusive suite are not affected by the pure shear-dominated transpressional fabric observed in the Power Line intrusive complex, which indicates that this deformation ceased by ca. 94 Ma. Rather, the Juniper Pass pluton contains an E–W-striking magmatic foliation fabric that rotates to a steep NW–SE-striking, solid-state foliation in the younger Sahwave pluton. These fabrics are strikingly similar to fabrics in the Tuolumne intrusive suite, Sierra Nevada, California, USA. Recent work in the western Idaho shear zone also indicates that late-stage deformation occurred there until ca. 85 Ma. Therefore, the intrusions of northwestern Nevada provide a tectonic link between the Sierra Nevada and Idaho batholiths, which suggests that two distinct phases of mid-Cretaceous, transpressional deformation occurred in at least three magmatic arc segments of the western U.S. margin.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"136 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135222301","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}
Naomi A. Becker, Freya R. George, George L. Guice, James L. Crowley, Wendy R. Nelson, Joseph F. Browning-Hanson, Supratik Roy, Daniel R. Viete
The Dadeville Complex of Alabama and Georgia (southeastern United States) represents the largest suite of exposed mafic-ultramafic rocks in the southern Appalachians. Due to poor preservation, chemical alteration, and tectonic reworking, a specific tectonic origin for the Dadeville Complex has been difficult to deduce. We obtained new whole-rock and mineral geochemistry coupled with zircon U-Pb geochronology to investigate the magmatic and metamorphic processes recorded by the Dadeville Complex, as well as the timing of these processes. Our data reveal an up-stratigraphic evolution in the geochemistry of the volcanic rocks, from forearc basalts to boninites. Our new U-Pb zircon crystallization data—obtained from three amphibolite samples—place the timing of forearc/protoarc volcanism no later than ca. 467 Ma. New thermobarometry suggests that the Dadeville Complex rocks subsequently experienced deep, high-grade metamorphism, at pressure-temperature conditions of >7 kbar and >760 °C. The data presented here support a model for formation of the Dadeville Complex in the forearc region of a subduction zone during subduction initiation and protoarc development, followed by deep burial/underthrusting of the complex during orogenesis.
{"title":"Subduction initiation recorded in the Dadeville Complex of Alabama and Georgia, southeastern United States","authors":"Naomi A. Becker, Freya R. George, George L. Guice, James L. Crowley, Wendy R. Nelson, Joseph F. Browning-Hanson, Supratik Roy, Daniel R. Viete","doi":"10.1130/ges02643.1","DOIUrl":"https://doi.org/10.1130/ges02643.1","url":null,"abstract":"The Dadeville Complex of Alabama and Georgia (southeastern United States) represents the largest suite of exposed mafic-ultramafic rocks in the southern Appalachians. Due to poor preservation, chemical alteration, and tectonic reworking, a specific tectonic origin for the Dadeville Complex has been difficult to deduce. We obtained new whole-rock and mineral geochemistry coupled with zircon U-Pb geochronology to investigate the magmatic and metamorphic processes recorded by the Dadeville Complex, as well as the timing of these processes. Our data reveal an up-stratigraphic evolution in the geochemistry of the volcanic rocks, from forearc basalts to boninites. Our new U-Pb zircon crystallization data—obtained from three amphibolite samples—place the timing of forearc/protoarc volcanism no later than ca. 467 Ma. New thermobarometry suggests that the Dadeville Complex rocks subsequently experienced deep, high-grade metamorphism, at pressure-temperature conditions of >7 kbar and >760 °C. The data presented here support a model for formation of the Dadeville Complex in the forearc region of a subduction zone during subduction initiation and protoarc development, followed by deep burial/underthrusting of the complex during orogenesis.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"75 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136234987","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 Sevier and Laramide belts of the U.S. Cordillera are differentiated based on thin- and thick-skinned structural domains, commonly inferred to have formed under different plate-boundary conditions. However, spatial and temporal overlap in the Idaho-Montana fold-thrust belt suggests that thin- and thick-skinned thrust systems are kinematically linked. We present the first balanced and sequentially restorable cross section that integrates the Sevier and Laramide belts. Encompassing most of the width of the Cordilleran retroarc, our kinematic model accounts for at least 244 km of horizontal shortening, linking thin- and thick-skinned thrust systems. We hypothesize that thin strata overlying the Lemhi arch basement high determined the geometry and relative timing of the later thrusting. Early shortening (pre–ca. 90 Ma) was thin skinned, with the décollement of the Medicine Lodge–McKenzie thrust system following Devonian shales on top of the Lemhi arch unconformity. Displacement on upper thin- and lower thick-skinned thrusts overlapped between ca. 90 and 70 Ma as a mid-crustal décollement was activated, efficiently transmitting strain through the Lemhi arch to the Blacktail-Snowcrest uplift in the foreland. A regional-scale duplex (Patterson culmination) linked the lower and upper décollements, internally thickening and increasing the basal slope of the orogenic wedge. Thick-skinned thrusts of the Dillon cutoff (Hawley Creek, Cabin, and Johnson thrusts) eventually thickened the wedge and exhumed the abandoned upper décollement. Following this, the thick-skinned wedge advanced in-sequence from ca. 70 to 55 Ma. This kinematic model establishes continuity between thin- and thick-skinned thrust systems by a mid-crustal décollement. In this model, the stratigraphic thicknesses of sedimentary cover rocks limit the availability of décollement horizons, determining the style of mountain building and triggering a slow transition from thin- to thick-skinned thrusting.
{"title":"A kinematic model linking the Sevier and Laramide belts in the Idaho-Montana fold-thrust belt, U.S. Cordillera","authors":"Stuart D. Parker, David M. Pearson","doi":"10.1130/ges02649.1","DOIUrl":"https://doi.org/10.1130/ges02649.1","url":null,"abstract":"The Sevier and Laramide belts of the U.S. Cordillera are differentiated based on thin- and thick-skinned structural domains, commonly inferred to have formed under different plate-boundary conditions. However, spatial and temporal overlap in the Idaho-Montana fold-thrust belt suggests that thin- and thick-skinned thrust systems are kinematically linked. We present the first balanced and sequentially restorable cross section that integrates the Sevier and Laramide belts. Encompassing most of the width of the Cordilleran retroarc, our kinematic model accounts for at least 244 km of horizontal shortening, linking thin- and thick-skinned thrust systems. We hypothesize that thin strata overlying the Lemhi arch basement high determined the geometry and relative timing of the later thrusting. Early shortening (pre–ca. 90 Ma) was thin skinned, with the décollement of the Medicine Lodge–McKenzie thrust system following Devonian shales on top of the Lemhi arch unconformity. Displacement on upper thin- and lower thick-skinned thrusts overlapped between ca. 90 and 70 Ma as a mid-crustal décollement was activated, efficiently transmitting strain through the Lemhi arch to the Blacktail-Snowcrest uplift in the foreland. A regional-scale duplex (Patterson culmination) linked the lower and upper décollements, internally thickening and increasing the basal slope of the orogenic wedge. Thick-skinned thrusts of the Dillon cutoff (Hawley Creek, Cabin, and Johnson thrusts) eventually thickened the wedge and exhumed the abandoned upper décollement. Following this, the thick-skinned wedge advanced in-sequence from ca. 70 to 55 Ma. This kinematic model establishes continuity between thin- and thick-skinned thrust systems by a mid-crustal décollement. In this model, the stratigraphic thicknesses of sedimentary cover rocks limit the availability of décollement horizons, determining the style of mountain building and triggering a slow transition from thin- to thick-skinned thrusting.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"74 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136317565","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}
Cullen Kortyna, Daniel F. Stockli, Timothy F. Lawton, Jacob A. Covault, Glenn R. Sharman
Late Cretaceous to Eocene Laramide basement–involved shortening fragmented the Sevier and Mexican foreland basins. This resulted in a major drainage reorganization in response to the emerging topography of Laramide basement–cored uplifts and Mexican inverted Border rift basins. This study presents new depth-profile detrital zircon U-Pb data (3679 ages from 28 samples) from Upper Cretaceous–Eocene fluvial strata of the Tornillo basin in west Texas to determine sedimentary provenance and reconstruct sediment dispersal through the U.S.-Mexico border region. Detrital zircon U-Pb data are dominated by Hauterivian–Coniacian (130–87 Ma; ~20%) and Coniacian–Ypresian (87–52 Ma; ~30%) ages that represent Cordilleran and Laramide arc magmatism, respectively. Subordinate age groups are Paleoproterozoic–Mesoproterozoic (1900–1300 Ma; ~12%), Ectasian–Tonian (1300–900 Ma; ~8%), Tonian–Pennsylvanian (900–300 Ma, ~10%); Permian–Triassic (300–200 Ma; ~8%), and Jurassic–Early Cretaceous (200–130 Ma; ~11%). Detrital zircon maximum depositional ages provide new constraints on the chronostratigraphic framework of the Tornillo Group, the stratigraphic nature of the Cretaceous-Paleogene boundary, and the stratigraphic level of the Paleocene–Eocene thermal maximum. Depth-profile core-rim age pairs yielded Paleoproterozoic–Mesoproterozoic and Jurassic cores with Cretaceous–Paleogene rims, which represent zircons derived from Laramide magmatic rocks that intruded Yavapai-Mazatzal basement and Cordilleran-Nazas magmatic rocks. Zircon grains with Ectasian–Tonian cores and Paleozoic rims likely represent Appalachian-derived and/or Coahuila terrane zircons recycled from the inverted Mesozoic Bisbee basin and Chihuahua trough. These results demonstrate that fluvial strata in the Tornillo basin were sourced from Laramide and Cordilleran magmatic rocks, Yavapai-Mazatzal basement, and recycled Mexican Border rift sedimentary rocks in the southwest United States and northern Sonora, and these sediments were delivered via a large (>103-km-long), axial-trunk river. Additional recycled detritus from Mexican Border rift sedimentary rocks in the Chihuahua fold belt was delivered via transverse tributaries. This drainage reconstruction indicates that the Tornillo river flowed along an inversion-flank drainage corridor adjacent to topography formed by the inverted Mexican Border rift. Therefore, inherited Mexican Border rift architecture represented a first-order control on sediment routing to the Tornillo basin.
{"title":"Impact of Mexican Border rift structural inheritance on Laramide rivers of the Tornillo basin, west Texas (USA): Insights from detrital zircon provenance","authors":"Cullen Kortyna, Daniel F. Stockli, Timothy F. Lawton, Jacob A. Covault, Glenn R. Sharman","doi":"10.1130/ges02516.1","DOIUrl":"https://doi.org/10.1130/ges02516.1","url":null,"abstract":"Late Cretaceous to Eocene Laramide basement–involved shortening fragmented the Sevier and Mexican foreland basins. This resulted in a major drainage reorganization in response to the emerging topography of Laramide basement–cored uplifts and Mexican inverted Border rift basins. This study presents new depth-profile detrital zircon U-Pb data (3679 ages from 28 samples) from Upper Cretaceous–Eocene fluvial strata of the Tornillo basin in west Texas to determine sedimentary provenance and reconstruct sediment dispersal through the U.S.-Mexico border region. Detrital zircon U-Pb data are dominated by Hauterivian–Coniacian (130–87 Ma; ~20%) and Coniacian–Ypresian (87–52 Ma; ~30%) ages that represent Cordilleran and Laramide arc magmatism, respectively. Subordinate age groups are Paleoproterozoic–Mesoproterozoic (1900–1300 Ma; ~12%), Ectasian–Tonian (1300–900 Ma; ~8%), Tonian–Pennsylvanian (900–300 Ma, ~10%); Permian–Triassic (300–200 Ma; ~8%), and Jurassic–Early Cretaceous (200–130 Ma; ~11%). Detrital zircon maximum depositional ages provide new constraints on the chronostratigraphic framework of the Tornillo Group, the stratigraphic nature of the Cretaceous-Paleogene boundary, and the stratigraphic level of the Paleocene–Eocene thermal maximum. Depth-profile core-rim age pairs yielded Paleoproterozoic–Mesoproterozoic and Jurassic cores with Cretaceous–Paleogene rims, which represent zircons derived from Laramide magmatic rocks that intruded Yavapai-Mazatzal basement and Cordilleran-Nazas magmatic rocks. Zircon grains with Ectasian–Tonian cores and Paleozoic rims likely represent Appalachian-derived and/or Coahuila terrane zircons recycled from the inverted Mesozoic Bisbee basin and Chihuahua trough. These results demonstrate that fluvial strata in the Tornillo basin were sourced from Laramide and Cordilleran magmatic rocks, Yavapai-Mazatzal basement, and recycled Mexican Border rift sedimentary rocks in the southwest United States and northern Sonora, and these sediments were delivered via a large (>103-km-long), axial-trunk river. Additional recycled detritus from Mexican Border rift sedimentary rocks in the Chihuahua fold belt was delivered via transverse tributaries. This drainage reconstruction indicates that the Tornillo river flowed along an inversion-flank drainage corridor adjacent to topography formed by the inverted Mexican Border rift. Therefore, inherited Mexican Border rift architecture represented a first-order control on sediment routing to the Tornillo basin.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136357779","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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