Timescales of magmatic differentiation from alkali basalt to trachyte within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia

Stelten, Mark E.; Downs, Drew T.; Dietterich, H. R.; Mahood, Gail A.; Calvert, Andrew T.; Sisson, T. W.; Zahran, Hani; Shawali, Jamal

doi:10.1007/s00410-018-1495-9

Cited by 12 publications

(23 citation statements)

References 36 publications

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“…It remains possible that kilometer‐scale pockets of melt exist in the crust. The more evolved trachytes (4–6, Figure a) are the most likely to reside in the crust, with estimates of differentiation timescales from 10–25 ka (Stelten et al, ). Given the average volume of past trachyte eruptions, and the amount of basaltic melt required to generate them, a melt volume of 2 km 3 is sufficient to generate an average trachyte eruption.…”

Section: Source Of Lower‐crustal Conductivity and Anisotropymentioning

confidence: 96%

“…Given ongoing extension and volcanism, the lower crust beneath the western Arabian Shield may be thermally primed and maintain a degree of long‐lived partial melt. Erupted lavas record repeated differentiation sequences from alkali basalt to trachyte lasting from 10–25 kyr (Stelten et al, ), suggesting magma storage at midcrustal levels over similar durations. To investigate melt as a potential conducting phase, we calculate the minimum melt fraction required to produce the minimum lower‐crustal conductance and then compare this to independent seismic constraints.…”

Section: Source Of Lower‐crustal Conductivity and Anisotropymentioning

confidence: 99%

“…Volumetrically, HR is dominated by weakly alkali basalts and hawaiites, with <10% of more evolved magmas encompassing mugearite, benmoreite, and trachyte (Figure ). Isotopic similarity across the alkali basalt to trachyte suite suggests the latter magmas are evolved from the former by crystallization differentiation or (and) partial remelting with only minor crustal assimilation (Stelten et al, ). Isotopic and trace element characteristics of the least evolved magmas suggest a mantle source close but not identical in composition to that of the Red Sea Rift magmas, but with residual garnet, consistent with melting of garnet peridotite at depths in excess of 75 km (Salters et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Crustal Magmatism and Anisotropy Beneath the Arabian Shield—A Cautionary Tale

et al. 2019

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Volcanism in Saudi Arabia includes a historic eruption close to the holy city of Al Madinah. As part of a volcanic hazard assessment of this area, magnetotelluric (MT) data were collected to investigate the structural setting, the distribution of melt within the crust, and the mantle source of volcanism. Interpretation of a new 3-D resistivity model includes a shallow graben beneath thin lava fields (Harrats), a melt-free upper crust, and decompression melting in the asthenosphere below thin lithosphere. Within the lower crust the model images elongate conductivity anomalies, one of which was attributed in a previous MT study to melt. The regional MT data, combined with perspective from geology and geophysical modeling, suggest the lower crust is anisotropic with no interconnected melt zones. These divergent interpretations have distinct hazard implications and highlight the importance of large survey aperture and anisotropic modeling to MT studies of volcanic regions. Lower-crustal anisotropy extends beyond the Harrat, with the most conductive direction oriented N10°E and a factor of 3-5, determined from 2-D anisotropic inversion, between the most and least conductive directions. The enhanced conductivity is likely due to interconnected grain boundary graphite, while the anisotropy direction reflects either frozen-in fabric from Neoproterozoic stabilization of the Arabian Shield or modern ductile deformation driven by channelized asthenospheric flow coupled through a thin rigid mantle lid. Asthenospheric melt is interpreted to transect the crust primarily through diking, with limited melt storage and short residence times in the crust.Plain Language Summary Volcanism within the lava fields, or Harrats, of Saudi Arabia includes historic eruptions, such as an eruption in 1256 CE near the holy city of Al Madinah. As part of a volcanic hazard assessment of northern Harrat Rahat, geophysical studies produced a three-dimensional model of electrical resistivity of the crust and upper mantle. In contrast to a more local study, the model shows no evidence of magma in the crust. This is consistent with other evidence in the region that suggests magma does not stay in the crust for long times but ascends rapidly from the upper mantle to the surface. This finding provides a snapshot in the lifecycle of this volcanic field and is important to understanding the hazards it poses. Our model also finds deep electrical anisotropy, probably due to a preferred direction or "fabric" in the lower crust. This fabric may be ancient, frozen in millions of years ago when the crust formed. Alternately, it may be caused by ongoing flow in the ductile lower crust in response to deeper mantle flow.

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Section: Source Of Lower‐crustal Conductivity and Anisotropymentioning

confidence: 96%

Section: Source Of Lower‐crustal Conductivity and Anisotropymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Crustal Magmatism and Anisotropy Beneath the Arabian Shield—A Cautionary Tale

et al. 2019

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“…A method that has proved useful for providing ages on young flows in arid environments that lack extensive vegetation cover and erosion is the 36 Cl cosmogenic surface-exposure dating (e.g., Vazquez and Woolford, 2015;Downs et al, 2018;Downs et al, 2019;Stelten et al, 2018;Stelten et al, 2020;Bromley et al, 2019). We utilized the 36 Cl cosmogenic method (see Supplementary Material for details on sample collection and analysis) for the Brushy Butte flow field to determine its emplacement age, and we couple this with 40 Ar/ 39 Ar ages of surrounding older tholeiitic basalts to better understand the eruptive history of volcanism prior to eruption of the Brushy Butte flow field.…”

Section: Geochronologymentioning

confidence: 99%

A Multidisciplinary Investigation Into the Eruptive Style, Processes, and Duration of a Cascades Back-Arc Tholeiitic Basalt: A Case Study of the Brushy Butte Flow Field, Northern California, United States

et al. 2021

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The Cascades back-arc in northern California is dominated by monogenetic tholeiitic basalts that erupted throughout the Pleistocene. Elucidating their eruptive history and processes is important for understanding potential future eruptions here. We focus on the well-exposed monogenetic volcano that emplaced the Brushy Butte flow field, which constructed a ∼150 m tall edifice, has flow lobes up to >10 km long, and in total covers ∼150 km2 with an eruptive volume of 3.5 km3. We use a multidisciplinary approach of field mapping, petrography, geochemistry, paleomagnetism, geochronology, and lidar imagery to unravel the eruptive history and processes that emplaced this flow field. Tholeiitic basalts in northern California have diverse surface morphology and vegetation cover but similar petrographic appearances, which makes them hard to distinguish in the field. Geochemistry and paleomagnetism offer an independent means of distinguishing tholeiitic basalts. Brushy Butte flow field lavas are similar in major-oxide and trace-element abundances but differ from adjacent tholeiitic basalts. This is also apparent in remanent magnetic directions. Additionally, paleomagnetism indicates that the flow field was emplaced during a geologically brief time interval (10–20 years), which 36Cl cosmogenic dating puts at 35.7 ± 1.7 ka. Lidar imagery shows that these flows erupted from at least 28 vents encompassing multiple scoria cones, spatter cones, and craters. Flows can be grouped into four pulses using stratigraphic position and volume. Pulse 1 is the most voluminous, comprising eight eruptions and ∼2.3 km3. Each subsequent pulse started rapidly but decayed quickly, and each successive pulse erupted less lava (i.e., 2.3 km3 for pulse 1, 0.6 km3 for pulse 2, 0.3 km3 for pulse 3, and 0.2 km3 for pulse 4). Many of these flows host well-established lava channels and levees (with channel breakouts) that lead to lava fans, with some flows hosting lava ponds. Similar flow features from tholeiitic eruptions elsewhere demonstrate that these morphologies generally occur over weeks, months, or longer (e.g., Puʻu ʻŌʻō eruption at K–llauea, Hawaiʻi). This multidisciplinary study shows the range of eruptive styles and durations of a Cascades back-arc eruption and illustrates how potential future tholeiitic eruptive activity in the western United States might progress.

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“…The majority of Madinah lavas, including three historic eruptions in 641, 1256 and 1293 C.E., crop out in the northern region of Harrat Rahat. Given their recent activity and close proximity to Madinah al Munawwarah, the Madinah lavas have been subject to several recent radiometric-dating and geochemical studies (e.g., Stelten et al, 2018;Stelten et al, 2020). In contrast, as far as we are aware the Shawahit and Hammah lavas have not been examined since the late 1980's, and have not been analyzed for trace element concentrations using ICP-MS techniques.…”

Section: Introductionmentioning

confidence: 99%

Evolution of intraplate magmatism atop a mantle plume: geochemical and chronological analysis of Shawahit Basalt, Harrat Rahat, Saudi Arabia

Roberts¹,

Ball²

2022

Preprint

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Harrat Rahat is the largest volcanic eld in Saudi Arabia and has been active from ~10 Ma to the present day. Due to its close proximity to important population centres, Harrat Rahat's recent eruptions, the Medinah lava flows (< 1.7 Ma), have been extensively studied to identify volcanic risk. However, the evolution of Harrat Rahat's most extensive and oldest lava flows, known collectively as the Shawahit Basalt (> 2.5 Ma), is poorly understood. In this study, we collected, dated and geochemically analyzed lava samples from Harrat Rahat, primarily targeting the under-sampled Shawahit unit. We 40Ar/39Ar dated 23 Shawahit samples that erupted between 9.4-2.7 Ma. Over the lifetime of Harrat Rahat, we observe a geochemical transition from predominantly tholeiitic to alkalic eruptions coupled with a counter-intuitive decrease in incompatible element concentrations. We attribute these changes to a decrease in melt productivity and a reduction in contamination by enriched lithospheric melts, respectively. Thermobarometric analysis of Harrat Rahat basalts indicates that these lavas were generated by melting of asthenospheric mantle with a potential temperature of ~1456 +50/-32 oC beneath lithosphere 50-60 km thick. These results indicate that volcanic activity at Harrat Rahat was initiated by the arrival of a mantle plume beneath lithosphere thinned by a combination of Red-Sea rifting and thermal erosion. Furthermore, we believe that this plume, either acting alone or in combination with a number of other plumes, is responsible for the formation of the Arabian swell, as well as much of the Neogene-recent intraplate volcanic activity observed across western Arabia. Our conclusions are consistent with a wide range of geochemical, seismologic, gravimetric, thermochronologic and geomorphologic observations.

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Timescales of magmatic differentiation from alkali basalt to trachyte within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia

Cited by 12 publications

References 36 publications

Crustal Magmatism and Anisotropy Beneath the Arabian Shield—A Cautionary Tale

Crustal Magmatism and Anisotropy Beneath the Arabian Shield—A Cautionary Tale

A Multidisciplinary Investigation Into the Eruptive Style, Processes, and Duration of a Cascades Back-Arc Tholeiitic Basalt: A Case Study of the Brushy Butte Flow Field, Northern California, United States

Evolution of intraplate magmatism atop a mantle plume: geochemical and chronological analysis of Shawahit Basalt, Harrat Rahat, Saudi Arabia

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