saudi arabia harrat: Topics by Science.gov

May 31, 2021

  • Mantle Earthquakes in Thinned Proterozoic Lithosphere: Harrat Lunayyir, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Blanchette, A. R.; Klemperer, S. L.; Mooney, W. D.; Zahran, H. M.

    2017-12-01

    Harrat Lunayyir is an active volcanic field located in the western Arabian Shield 100 km outside of the Red Sea rift margin. We use common conversion point (CCP) stacking of P-wave receiver functions (PRFs) to show that the Moho is at 38 km depth, close to the 40 km crustal thickness measured in the center of the craton, whereas the lithosphere-asthenosphere boundary (LAB) is at 60 km, far shallower than the 150 km furthest in the craton. We locate 67 high-frequency earthquakes with mL ≤ 2.5 at depths of 40-50 km below the surface, located clearly within the mantle lid. The occurrence of earthquakes within the lithospheric mantle requires a geothermal temperature profile that is below equilibrium. The lithosphere cannot have thinned to its present thickness earlier than 15 Ma, either during an extended period of rifting possibly beginning 24 Ma or, more likely, as part of the second stage of rifting following collision between Arabia and Eurasia.

  • Mapping Intraplate Volcanic Fields: A Case Study from Harrat Rahat, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Downs, D. T.; Stelten, M. E.; Champion, D. E.; Dietterich, H. R.

    2017-12-01

    Continental intraplate mafic volcanoes are typically small-volume (200 volcanic fields proposed to be active worldwide during the Holocene. Their small individual eruption volumes make any hazards low, however their high prevalence offsets this by raising the risk to populations and infrastructure. The western Arabian Plate hosts at least 15 continental, intra-plate volcanic fields that stretch >3,000 km south to north from Yemen to Turkey. In total, these volcanic fields comprise one of the largest alkali basalt volcanic provinces on Earth, covering an area of 180,000 km2. With a total volume of 20,000 km3, Harrat Rahat in western Saudi Arabia is one of the largest of these volcanic fields. Our study focused on mapping the northern third of the Harrat Rahat volcanic field using a multidisciplinary approach. We have discriminated >200 individual eruptive units, mainly basaltic lava flows throughout Harrat Rahat that are distinguished through a combination of field observations, petrography, geochemistry, paleomagnetism, and 40Ar/39Ar radiometric and 36Cl cosmogenic surface-exposure dating. We have compiled these results into a high-resolution geologic map, which provides new information about the timing, compositions, and eruptive processes of Quaternary volcanism in Harrat Rahat. For example, prior mapping and geochronology undertaken during the 1980s suggested that the majority of mafic and silicic volcanics erupted during the Miocene and Pliocene, whereas several of the youngest-appearing lava flows were interpreted to be Neolithic ( 7,000 to 4,500 years BP) to post-Neolithic. New mapping and age-constrained stratigraphic relations indicate that all exposed volcanic units within the northern third of Harrat Rahat erupted during the Pleistocene, with the exception of a single Holocene eruption in 1256 AD. This new multidisciplinary mapping is critical for understanding

  • Paleocene pycnodont fishes from Jabal Umm Himar, Harrat Hadan area, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Madden, Gary T.

    1983-01-01

    Three species of Pycnodus, a genus of extinct holostean fishes, have been identified from the Paleocene of Jabal Umm Himar, Harrat Hadan area, south-central Saudi Arabia, an area that was contiguous with Africa during the Early Tertiary. One of the species is larger than any species identified from the Early Tertiary of Africa. Its lower teeth are from 60 to 100 percent wider and 50 percent longer than those in P. mokattamensis, hitherto the largest species known from Africa. The second species, the most poorly represented of the three, is in dental size roughly 40 percent as large as the first species or about the same size as P. variabilis of Africa. The third species is small and, although the position of its teeth cannot be determined, this species clearly is distinct from the two other pycnodonts from Jabal Umm Himar.

  • Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

    USGS Publications Warehouse

    Duncan, Robert A.; Kent, Adam J R; Thornber, Carl; Schliedler, Tyler D; Al-Amri, Abdullah M

    2016-01-01

    Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K–Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar–39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1–7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60–80 km).

  • Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Duncan, Robert A.; Kent, Adam J. R.; Thornber, Carl R.; Schlieder, Tyler D.; Al-Amri, Abdullah M.

    2016-03-01

    Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K-Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar-39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1-7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60-80 km).

  • Spectral analysis of the 1976 aeromagnetic survey of Harrat Rahat, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Blank, H. Richard; Sadek, Hamdy S.

    1983-01-01

    Harrat Rahat, an extensive plateau of Cenozoic mafic lava on the Precambrian shield of western Saudi Arabia, has been studied for its water resource and geothermal potential. In support of these investigations, the thickness of the lava sequence at more than 300 points was estimated by spectral analysis of low-level aeromagnetic profiles utilizing the integral Fourier transform of field intensity along overlapping profile segments. The optimum length of segment for analysis was determined to be about 40 km or 600 field samples. Contributions from two discrete magnetic source ensembles could be resolved on almost all spectra computed. The depths to these ensembles correspond closely to the flight height (300 m), and, presumably, to the mean depth to basement near the center of each profile segment. The latter association was confirmed in all three cases where spectral estimates could be directly compared with basement depths measured in drill holes. The maximum thickness estimated for the lava section is 380 m and the mean about 150 m. Data from an isopach map prepared from these results suggest that thickness variations are strongly influenced by pre-harrat, north-northwest-trending topography probably consequent on Cenozoic faulting. The thickest zones show a rough correlation with three axially-disposed volcanic shields.

  • Imaging of magma intrusions beneath Harrat Al-Madinah in Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Abdelwahed, Mohamed F.; El-Masry, Nabil; Moufti, Mohamed Rashad; Kenedi, Catherine Lewis; Zhao, Dapeng; Zahran, Hani; Shawali, Jamal

    2016-04-01

    High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.

  • Geologic map of Harrat Hutaymah, with petrologic classification and distribution of ultramafic inclusions, Saudi Arabia

    USGS Publications Warehouse

    Thornber, Carl R.

    1990-01-01

    This map shows detailed geology of the Quaternary and Tertiary volcanic deposits that comprise Harrat Hutaymah and an updated and generalized compilation of the underlying Proterozoic and Paleozoic basement rocks. Quaternary alluvial cover and details of basement geology (that is, faults, dikes, and other features) are not shown. Volcanic unit descriptions and contact relations are based upon field investigation by the author and on compilation and revision of mapping Kellogg (1984; northern half of area) and Pallister (1984; southern half of area). A single K-Ar date of 1.80 ± 0.05 Ma for an alkali olivine basalt flow transected by the Al Hutaymah tuff ring (Pallister, 1984) provides the basis for an estimated late Tertiary to Quaternary age range for all harrat volcanic units other than unit Qtr (tuff reworked during Quaternary age time). Contact relations and unit descriptions for the basement rocks were compiled from Pallister (1984), Kellogg (1984 and 1985), DuBray (1984), Johnson and Williams (1984), Vaslet and others (1987), Cole and Hedge (1986), and Richter and others (1984). All rock unit names in this report are informal and capitalization follows Saudi Arabian stratigraphic nomenclature (Fitch, 1980). Geographic information was compiled from Pallister (1984), Kellogg (1984), and Fuller (in Johnson and Williams, 1984) and from field investigation by the author in 1986. The pie diagrams on the map show the distribution and petrology of ultramafic xenoliths of Harrat Hutaymah. The pie diagrams are explained by a detailed classification of ultramafic xenoliths that is introduced in this report.

  • Shear-wave velocities beneath the Harrat Rahat volcanic field, Saudi Arabia, using ambient seismic noise analysis

    NASA Astrophysics Data System (ADS)

    Civilini, F.; Mooney, W.; Savage, M. K.; Townend, J.; Zahran, H. M.

    2017-12-01

    We present seismic shear-velocities for Harrat Rahat, a Cenozoic bimodal alkaline volcanic field in west-central Saudi Arabia, using seismic tomography from natural ambient noise. This project is part of an overall effort by the Saudi Geological Survey and the United States Geological Survey to describe the subsurface structure and assess hazards within the Saudi Arabian shield. Volcanism at Harrat Rahat began approximately 10 Ma, with at least three pulses around 10, 5, and 2 Ma, and at least several pulses in the Quaternary from 1.9 Ma to the present. This area is instrumented by 14 broadband Nanometrics Trillium T120 instruments across an array aperture of approximately 130 kilometers. We used a year of recorded natural ambient noise to determine group and phase velocity surface wave dispersion maps with a 0.1 decimal degree resolution for radial-radial, transverse-transverse, and vertical-vertical components of the empirical Green’s function. A grid-search method was used to carry out 1D shear-velocity inversions at each latitude-longitude point and the results were interpolated to produce pseudo-3D shear velocity models. The dispersion maps resolved a zone of slow surface wave velocity south-east of the city of Medina spatially correlated with the 1256 CE eruption. A crustal layer interface at approximately 20 km depth was determined by the inversions for all components, matching the results of prior seismic-refraction studies. Cross-sections of the 3D shear velocity models were compared to gravity measurements obtained in the south-east edge of the field. We found that measurements of low gravity qualitatively correlate with low values of shear-velocity below 20 km along the cross-section profile. We apply these methods to obtain preliminary tomography results on the entire Arabian Shield.

  • Earthquake swarm in the non-volcanic area north of Harrat Lunayyir, western Saudi Arabia: observations and imaging

    NASA Astrophysics Data System (ADS)

    Youssof, M.; Mai, P. M.; Parisi, L.; Tang, Z.; Zahran, H. M.; El-Hadidy, S. Y.; Al-Raddadi, W.; Sami, M.; El-Hadidy, M. S. Y.

    2017-12-01

    We report on an unusual earthquake swarm in a non-volcanic area of western Saudi Arabia. Since March 2017, hundreds of earthquakes were recorded, reaching magnitude Ml 3.7, which occurred within a very narrowly defined rock volume. The seismicity is shallow, mostly between 4 to 8 km depths, with some events reaching as deep as 16 km. One set of events aligns into a well-defined horizontal tube of 2 km height, 1 km width, and 4-5 km E-W extent. Other event clusters exist, but are less well-defined. The focal mechanism solutions of the largest earthquakes indicate normal faulting, which agree with the regional stress field. The earthquake swarm occurs 75 km NW of Harrat Lunayyir. However, the area of interest doesn’t seem to be associated with the well-known volcanic area of Harrat Lunayyir, which experienced a magmatic dike intrusion in 2009 with intense seismic activity (including a surface rupturing Mw 5.7 earthquake). Furthermore, the study area is characterized by a complex shear system, which host gold mineralization. Therefore, the exact origin of the swarm sequence is enigmatic as it’s the first of its kind in this region. By using continuous seismological data recorded by the Saudi Geological Survey (SGS) that operates three permanent seismic stations and a temporary network of 11 broadband sensors, we analyze the seismic patterns in space and time. For the verified detected events, we assemble the body wave arrival times that are inverted for the velocity structures along with events hypocenters to investigate possible causes of this swarm sequence, that is, whether the activity is of tectonic- or hydro-thermal origin.

  • Spatial and Temporal Analysis of Eruption Locations, Compositions, and Styles in Northern Harrat Rahat, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Dietterich, H. R.; Stelten, M. E.; Downs, D. T.; Champion, D. E.

    2017-12-01

    Harrat Rahat is a predominantly mafic, 20,000 km2 volcanic field in western Saudi Arabia with an elongate volcanic axis extending 310 km north-south. Prior mapping suggests that the youngest eruptions were concentrated in northernmost Harrat Rahat, where our new geologic mapping and geochronology reveal >300 eruptive vents with ages ranging from 1.2 Ma to a historic eruption in 1256 CE. Eruption compositions and styles vary spatially and temporally within the volcanic field, where extensive alkali basaltic lavas dominate, but more evolved compositions erupted episodically as clusters of trachytic domes and small-volume pyroclastic flows. Analysis of vent locations, compositions, and eruption styles shows the evolution of the volcanic field and allows assessment of the spatio-temporal probabilities of vent opening and eruption styles. We link individual vents and fissures to eruptions and their deposits using field relations, petrography, geochemistry, paleomagnetism, and 40Ar/39Ar and 36Cl geochronology. Eruption volumes and deposit extents are derived from geologic mapping and topographic analysis. Spatial density analysis with kernel density estimation captures vent densities of up to 0.2 %/km2 along the north-south running volcanic axis, decaying quickly away to the east but reaching a second, lower high along a secondary axis to the west. Temporal trends show slight younging of mafic eruption ages to the north in the past 300 ka, as well as clustered eruptions of trachytes over the past 150 ka. Vent locations, timing, and composition are integrated through spatial probability weighted by eruption age for each compositional range to produce spatio-temporal models of vent opening probability. These show that the next mafic eruption is most probable within the north end of the main (eastern) volcanic axis, whereas more evolved compositions are most likely to erupt within the trachytic centers further to the south. These vent opening probabilities, combined with

  • Magma Differentiation and Storage Inferred from Crystal Textures at Harrat Rahat Volcanic Field, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Witter, M. R.; Mahood, G. A.; Stelten, M. E.; Downs, D. T.; Zahran, H. M.

    2015-12-01

    We present results of a petrographic study of Harrat Rahat volcanic field in western Saudi Arabia as part of a collaborative project between the U.S.G.S. and the Saudi Geological Survey. Lavas range in composition from alkali basalt to trachyphonolite. Basalts have Harrat Rahat can form by fractionation of alkali basalts at crustal depths greater than ~25 km. The observed phenocryst assemblage in the trachyphonolites, however, forms at shallow depths, ~2-4 km, according to MELTS modeling. Coupled with CSD data, this suggests that deep extraction events yield crystal-poor trachyphonolite magmas that rise to the upper crust where they undergo crystallization. Extensive shallow crystallization of trachyphonolites may have triggered eruptions by causing vapor saturation, which lowers magma density via vesiculation and

  • Initial results from the Volcanic Risk in Saudi Arabia project: Microearthquakes in the northern Harrat Rahat monogenetic volcanic field, Madinah, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Kenedi, C. L.; Alvarez, M. G.; Abdelwahed, M. F.; Aboud, E.; Lindsay, J. M.; Mokhtar, T. A.; Moufti, M. R.

    2012-12-01

    An 8-station borehole seismic research array is recording microearthquake data in northern Harrat Rahat. This recently active monogenetic volcanic field lies southeast of the Islamic holy city of Madinah, Kingdom of Saudi Arabia. The VORiSA seismographs are operated in collaboration between King Abdulaziz University in Jeddah and the Institute of Earth Science and Engineering, University of Auckland, in New Zealand. The goal of the VORiSA project is to evaluate the seismic and volcanic hazard around Madinah. To this end, we will evaluate the local earthquake activity including the extent to which local earthquakes are tectonic or volcanic. We also will use seismicity to understand the subsurface structure. The analytical goals of the seismic research array are the following: (1) Calculate a new seismic velocity model, (2) Map subsurface structures using seismic tomography, and (3) Explore for fracture zones using shear wave splitting analysis. As compared to seismographs installed on the surface, borehole seismometers detect smaller and more numerous microearthquake signals. The sensitivity and location of the borehole sensors in the VORiSA array are designed to detect these weak signals. The array has a total aperture of 17 km with station spacing at 5 – 10 km. The seismometers are housed in IESE model S21g-2.0, two Hz, 3-component borehole sondes. Sensor depths range from 107 – 121 m. The data acquisition system at each stand-alone station consists of a Reftek 130-01, 6-channel, 24 bit data logger which records at 250 samples per second. The power source is a deep cycle battery with solar recharge. Local temperatures reach extremes of 0° to 50°C, so the battery and recorder are contained in a specially designed underground vault. The vault also provides security in the remote and sparsely populated volcanic field. Recording began on 31 March 2012. An average of one earthquake every three days suggests that currently this is not a highly seismic area. However

  • Pathways of volatile migration in the crust beneath Harrat Lunayyir (Saudi Arabia) during the unrest in 2009 revealed by attenuation tomography

    NASA Astrophysics Data System (ADS)

    Sychev, Ilya; Koulakov, Ivan; El Khrepy, Sami; Al-Arifi, Nassir

    2017-01-01

    Harrat Lunayyir is a relatively young basaltic field in Saudi Arabia located at the western margin of the Arabian Peninsula. In April-June 2009, strong seismic activity and ground deformations at this site marked the activation of the magma system beneath Harrat Lunayyir. In this study, we present new three-dimensional models of the attenuation of P and S waves during the unrest in 2009 based on the analysis of t*. We measured 1658 and 3170 values of t* for P and S waves, respectively, for the same earthquakes that were previously used for travel time tomography. The resulting anomalies of the P and S wave attenuation look very similar. In the center of the study area, we observe a prominent high-attenuation pattern, which coincides with the most active seismicity at shallow depths and maximum ground deformations. This high-attenuation zone may represent a zone of accumulation and ascending of gases, which originated at depths of 5-7 km due to the decompression of ascending liquid volatiles. Based on these findings and previous tomography studies, we propose that the unrest at Harrat Lunayyir in 2009 was triggered by a sudden injection of unstable liquid volatiles from deeper magma sources. At some depths, they were transformed to gases, which caused the volume to increase, and this led to seismic activation in the areas of phase transformations. The overpressurized gases ultimately found the weakest point in the rigid basaltic cover at the junction of several tectonic faults and escaped to the surface.

  • Pathways of volatile migration in the crust beneath Harrat Lunayyir (Saudi Arabia) during the unrest in 2009 revealed by attenuation tomography

    NASA Astrophysics Data System (ADS)

    El Khrepy, Sami; Koulakov, Ivan; Al-Arifi, Nassir; Sychev, Ilya

    2017-04-01

    Harrat Lunayyir is a relatively young basaltic field in Saudi Arabia located at the western margin of the Arabian Peninsula. In April-June 2009, strong seismic activity and ground deformations at this site marked the activation of the magma system beneath Harrat Lunayyir. In this study, we present new three-dimensional models of the attenuation of P and S waves during the unrest in 2009 based on the analysis of t*. We measured 1658 and 3170 values of t* for P and S waves, respectively, for the same earthquakes that were previously used for travel time tomography. The resulting anomalies of the P and S wave attenuation look very similar. In the center of the study area, we observe a prominent high-attenuation pattern, which coincides with the most active seismicity at shallow depths and maximum ground deformations. This high-attenuation zone may represent a zone of accumulation and ascending of gases, which originated at depths of 5-7 km due to the decompression of ascending liquid volatiles. Based on these findings and previous tomography studies, we propose that the unrest at Harrat Lunayyir in 2009 was triggered by a sudden injection of unstable liquid volatiles from deeper magma sources. At some depths, they were transformed to gases, which caused the volume to increase, and this led to seismic activation in the areas of phase transformations. The overpressurized gases ultimately found the weakest point in the rigid basaltic cover at the junction of several tectonic faults and escaped to the surface.

  • Late Holocene lava flow morphotypes of the northern Harrat Rahat, Kingdom of Saudi Arabia: implications for the description of continental lava fields

    NASA Astrophysics Data System (ADS)

    Murcia, H. F.; Nemeth, K.; Moufti, R.; Lindsay, J. M.; El-Masry, N.; Cronin, S. J.; Qaddah, A.; Smith, I. E.

    2013-12-01

    Lava morphotype refers to the surface morphology of a lava flow after solidification. In Saudi Arabia, young and well-preserved mafic lava fields (Harrats) display a wide range of these morphotypes. This study examines those exhibited by four of the post-4500 yrs. BP lava fields in the northern Harrat Rahat (Harrat Rahat lava fields include one or more lobes that may extend over 20 km from the source, with thicknesses varying between 1-2 m up to 12 m. Each lava flow episode covered areas between ~32 and ~61 km2, with individual volumes estimated between ~0.085 and ~0.29 km3. The whole-rock chemical compositions of these lavas lie between 44.3 to 48.4% SiO2, 9.01-4.28% MgO and 3.13-6.19% NaO+K2O. Seven different morphotypes with several lava structures are documented: Shelly, Slabby, Rubbly-pahoehoe, Platy, Cauliflower, Rubbly-a’a, and Blocky. These may be related to the shear strain and/or apparent viscosity of the lava flows formed from typical pahoehoe (pure or Hawaiian-pahoehoe, or sheet-pahoehoe). The well-preserved lava fields in Harrat Rahat allow the development of a more expanded classification scheme than has been traditionally applied. In addition to the whole-rock composition, these morphotypes may be indicators of other properties such as vesicularity, crystallization, effusion mechanism, as well as significant along-flow variations in topography and lava thickness and temperature that modify the rheology. The linearity of transitions between morphotypes observed in the lava fields suggest that real time forecasting of the evolution of lava flows might be possible.

  • InSAR Observations of the 2009 Harrat Lunayyir (western Saudi Arabia) Dyke Intrusion and Post-Diking Deformation

    NASA Astrophysics Data System (ADS)

    Jónsson, Sigurjón; Lu, Zhong; Lundgren, Paul

    2010-05-01

    Interferometric Satellite Radar (InSAR) observations of one of the volcanic provinces in western Saudi Arabia, Harrat Lunayyir (also known as Harrat Al-Shaqah), provide rich information about the geometry and evolution of a dyke intrusion and surface faulting that occurred in the region in April-July 2009. The first sign of activity was the start of a seismic swarm on 24 April that steadily intensified until six magnitude 4.6-5.7 earthquakes struck on 17-20 May. More than 30000 people were evacuated from the area following the activity in mid-May and stayed in the neighboring cities of Yanbu and Medina for several weeks. During the intensive activity in mid-May we sent a request for emergency satellite radar data acquisitions to the European Space Agency and later activated an International Charter to guarantee satellite data collection of the area. We have analyzed a number of Envisat, ALOS, and TerraSAR-X interferograms of the area and the results are outstanding, owing to the stable and vegetation-free surface conditions. Interferograms spanning the main seismic activity in mid-May exhibit strong deformation that extends across a large 40 km × 40 km area, with broad uplift and over a meter of WSW-ENE extension. In addition, the data show clear signs of surface faulting and graben-like subsidence in the middle of the deformed area with the graben subsidence exceeding 50 cm. Modeling of deformation strongly suggests that a near-vertical dyke intruded with a WNW-ESE orientation, parallel to the Red Sea, and that the intruded volume is ~0.13 km3. The dyke intrusion appears to have triggered faulting on graben-bounding and inward-dipping normal faults. The shallowest part of the dyke seems to have reached within only 2 km of the surface, right below where the graben is the narrowest and under an area with a number of cinder cones from previous volcanic events. While the day-to-day temporal evolution of the deformation cannot be derived from the InSAR data, the

  • Mapping b-value for 2009 Harrat Lunayyir earthquake swarm, western Saudi Arabia and Coulomb stress for its mainshock

    NASA Astrophysics Data System (ADS)

    Abdelfattah, Ali K.; Mogren, Saad; Mukhopadhyay, Manoj

    2017-01-01

    The Harrat Lunayyir (HL) earthquake swarm of 2009 originated in the HL volcanic field and attracted global attention mainly due to three factors: (i) its relatively short life span that ushered a large frequency of the swarm population (30,000 events in Saudi Arabia (LIP-SA) where it correlates to the Great Dikes locally. Our aim in this study is to describe the spatial distribution of the hypocenters, b-value character, and Coulomb stress failure (CSF) in an attempt to analyze the underlying geodynamic process that caused the swarm. We utilize the relocated hypocenters monitored by local networks to examine the b-value characteristics for the swarm. This is best represented in a cross section showing two domains of higher b-value anomalies: two patches occurring at shallow depth and at the deeper crust to the SE from the mainshock originated at the shallower depth northwestward. Consistently positive ΔCFF pattern with a large percentage of aftershocks imply how the mainshock rupture controlled the aftershocks activity. This implies that the failure along the NNW fault trend is due to the prevailing ambient stress field imparted to the swarm. We model this by CSF associated with the mainshock for three time dependent situations: (a) foreshock and aftershock epicenters, (b) foreshock hypocenters, and (c) aftershock hypocenters. In actuality, multiple factors might have controlled the aftershock activity as we speculate that positive Coulomb stress was associated in an area where the higher b-value prevails. The CSF produced by the mainshock illustrates how the stress dissipated along the NNW normal fault zone that interrupts the Great Dykes along the Red Sea coast. These results further suggest that the crustal

  • Li-Be-B Systematics of mantle Xenoliths from Harrat Uwayrid (Saudi Arabia)

    NASA Astrophysics Data System (ADS)

    Kaliwoda, M.; Altherr, R.

    2003-04-01

    The Harrat Uwayrid is a Late Miocene to Quaternary volcanic field located in the northwestern part of the Arabian plate and related to the opening of the Red Sea. Numerous cinder cones contain abundant mantle xenoliths. Based on mineralogy and textures, these xenoliths can be subdivided into 3 different groups. Group IA1 are “anhydrous” spinel lherzolites and harzburgites consisting of olivine (ol), orthopyroxene (opx), clinopyroxene (cpx) and spinel (spl). Group IA2 xenoliths represent group IA1 materials that were moderately metasomatized. In addition to cpx, opx, ol and spl these xenoliths contain subordinate amounts of Cr-pargasite (par). Group IB xenoliths were strongly metasomatized by fluids and fluid-rich melts resulting in newly formed Ba-phlogopite (phl), Ba-bearing pargasite, Ba-feldspar (celsian) and Ba-rich phonolitic glasses. Li-Be-B systematics of the different xenoliths were studied by secondary ion mass spectrometry (SIMS). The results show that the partitioning of Li, Be and B among the various minerals is virtually independent of pressure and temperature. The absolute abundances, however, depend on the degree of initial depletion and later metasomatic overprint. Group IA1 spinel lherzolites are characterized by Li(cpx) = 0.65-1.19 µg/g, Li(opx) = 1.29-1.63 µg/g and Li(ol) = 2.15-2.43 µg/g, while group IB xenoliths show much higher abundances of Li: Li(cpx) = 1.89-2.16 µg/g, Li(opx) = 1.88-2.83 µg/g, Li(ol) = 3.06-4.12 µg/g. Similar differences are observed for the abundances of B (IA1: B(cpx) = 0.46-0.83 µg/g, B(opx) = 0.047-0.189 µg/g, B(ol) = 0.16-1.15 µg/g; IB: B(cpx) = 0.16-1.15 µg/g, B(opx)= 1.01-1.47 µg/g, B(ol) = 0.44-0.55 µg/g). In marked contrast to Li and B, the abundances of Be were not changed during metasomatism. Group IA1 xenoliths are characterized by Be(cpx) = 0.09-0.13 µg/g, Be(opx) = 0.023-0.027 µg/g and Be(ol) = 0.002 µg/g and group IB xenoliths show Be(cpx) = 0.05-0.09 µg/g, Be(opx) = 0.03-0.08 µg/g and Be

  • Late Holocene lava flow morphotypes of northern Harrat Rahat, Kingdom of Saudi Arabia: Implications for the description of continental lava fields

    NASA Astrophysics Data System (ADS)

    Murcia, H.; Németh, K.; Moufti, M. R.; Lindsay, J. M.; El-Masry, N.; Cronin, S. J.; Qaddah, A.; Smith, I. E. M.

    2014-04-01

    A “lava morphotype” refers to the recognizable and distinctive characteristics of the surface morphology of a lava flow after solidification, used in a similar way to a sedimentary facies. This classification method is explored on an example volcanic field in the Kingdom of Saudi Arabia, where copious lava outpourings may represent an important transition between monogenetic and flood basalt fields. Here, young and well-preserved mafic lava fields display a wide range of surface morphologies. We focussed on four post-4500 yrs. BP lava flow fields in northern Harrat Rahat (Harrat Rahat lava flow fields studied extend up to 23 km from the source, and vary between 1-2 m and 12 m in thickness. Areas of the lava flow fields are between ˜32 and ˜61 km2, with individual flow field volumes estimated between ˜0.085 and ˜0.29 km3. They exhibit Shelly-, Slabby-, and Rubbly-pahoehoe, Platy-, Cauliflower-, and Rubbly-a’a, and Blocky morphotypes. Morphotypes reflect the intrinsic parameters of: composition, temperature, crystallinity and volatile-content/vesicularity; along with external influences, such as: emission mechanism, effusion rate, topography and slope control of flow velocity. One morphotype can transition to another in individual flow-units or lobes and they may dominate zones. Not all morphotypes were found in a single lava flow field. Pahoehoe morphotypes are related to the simple mechanical disaggregation of the crust, whereas a’a morphotypes are related to the transitional emergence and subsequent transitional disappearance of clinker. Blocky morphotypes result from fracturing and auto-brecciation. A’a morphotypes (i.e. platy-, cauliflower-, rubbly-a’a) dominate the lava flow

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