Crustal and lithospheric complexity beneath the North Tanzanian Divergence from seismological and geochemical analyses.

2020 ◽  
Author(s):  
Stéphanie Gautier ◽  
Adeline Clutier ◽  
Fleurice Parat ◽  
Christel Tiberi
Keyword(s):  
Surface Deformation ◽  
Receiver Function ◽  
Geochemical Data ◽  
Joint Analysis ◽  
Lithospheric Structure ◽  
Magma Plumbing System ◽  
Local Tomography ◽  
The North ◽  
Magmatic Processes ◽  
Combined Images

<p>We present a joint analysis of seismological images and petrophysical data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. In this part of the East African Rift, the current surface deformation is related to complex interaction between tectonic (active fault, pre-rift lithospheric structure) and magmatic processes within the mantle and the crust. We present here the compilation of seismological results such as receiver function, local tomography, regional tomography on datasets collected during CRAFTI-CoLiBrEA and HaTARi projects, in a region with clearly opposite seismological and magmatic behaviours: near Natron the seismicity is well located within the upper crust and linked to present day magmatism (Lengai edifice), whereas Manyara area is characterized by a deep seismicity and no evidence of present magmatic activity at the surface. First, these different approaches deliver Vp, Vs and deduced Vp/Vs images with both different resolution and different depth investigation. The combined images of crustal and lithospheric structure provide the appropriate scale to point out the interactions between melt, gas, faults, and inherited fabrics in specific areas. We then compare those geophysical observations with magma composition, magma storage (depth of reservoir, magma volume) and ascent as well as partial melts content at depth obtained from petrophysical and geochemical analysis of lava samples. We will analyze if this combination of seismological approaches constrained with petrological and geochemical data produce accurate images of the entire current magma plumbing system.  Finally, we will discuss the results in terms of magmatic processes and how they interact with the rifting in a cratonic lithosphere.</p>

Striking differences in lithospheric structure between the north- and south-western Alps: insights from receiver functions along the Cifalps profiles and a new Vs model

2021 ◽  
Author(s):  
Anne Paul ◽  
Ahmed Nouibat ◽  
Liang Zhao ◽  
Stefano Solarino ◽  
Stéphane Schwartz ◽  
...  
Keyword(s):  
Receiver Function ◽  
Negative Polarity ◽  
Western Alps ◽  
Lithospheric Structure ◽  
Seismic Stations ◽  
Continental Subduction ◽  
The North ◽  
Ligurian Alps ◽  
The Alps ◽  
Converted Waves

<p>The CIFALPS receiver-function (RF) profile in the southwestern Alps provided the first seismological evidence of continental subduction in the Alps, with the detection of waves converted on the European Moho at 75-80 km depth beneath the western edge of the Po basin (Zhao et al., 2015). To complement the CIFALPS profile and enhance our knowledge of the lithospheric structure of the Western Alps, we installed CIFALPS2, a temporary network of 55 broadband seismic stations that operated for ~14 months (2018-2019) across the North-Western Alps (Zhao et al., 2018). The CIFALPS2 line runs from the Eastern Massif Central to the Ligurian coast, across the Mont-Blanc and Gran Paradiso massifs and the Ligurian Alps. Seismic stations were installed along a quasi-linear profile with a spacing of 7-10 km.</p><p>We will show 2 receiver-function CCP (common-conversion point) depth-migrated sections along the CIFALPS2 profile, the first one across the Alps, and the second one across the Ligurian Alps and the Po basin. The time-to-depth migration of RF data is based on the new 3-D Vs model of the Greater Alpine region derived by Nouibat et al. (2021) using transdimensional ambient noise tomography on a large dataset including the AlpArray seismic network. Depth sections across the Vs model are also useful for interpreting the RF CCP sections as they have striking similarities.</p><p>The images of the lithospheric structure of the NW Alps along CIFALPS2 are surprisingly different from those of the SW Alps along CIFALPS. The deepest P-to-S converted phases on the European Moho are detected at 60-65 km depth beneath the Ivrea-Verbano zone, that is 15 km less than on CIFALPS. The negative polarity converted phase interpreted as the base of the Ivrea body mantle flake on the CIFALPS section is still visible on CIFALPS2, but with a lower amplitude. The RF section confirms the existence of a jump of the European Moho of ~10 km amplitude in less than 10 km distance, which is located within a few km from the western boundary of the Mont Blanc external crystalline massif. All these observations are confirmed by the Vs model that also displays a less deep continental subduction than on CIFALPS, weaker S-wave velocities in the Ivrea body wedge, and the jump of the European Moho.</p><p>The Moho beneath the Ligurian Alps is detected at 25-30 km depth both on the RF and on the Vs depth sections. Moving northwards, this Ligurian Moho is separated from the Adriatic Moho by a puzzling S-dipping set of P-to-S converted waves with negative polarity. The crust of the Ligurian Alps is characterized by a set of north-dipping negative-polarity converted waves at 10 to 20 km depth beneath the Valosio massif, which is a small internal crystalline massif of (U)HP metamorphic rocks located north of Voltri. The similarity of this set of negative-polarity conversions to the one observed beneath the Dora Maira massif on the CIFALPS profile suggests that it may be a relic of the Alpine structure overprinted by the opening of the Ligurian sea.</p>

scholarly journals Earth Surface Deformation in the North China Plain Detected by Joint Analysis of GRACE and GPS Data

Sensors ◽  
2014 ◽  
Vol 14 (10) ◽  
pp. 19861-19876 ◽  
Author(s):  
Renli Liu ◽  
Jiancheng Li ◽  
Hok Fok ◽  
C.K. Shum ◽  
Zhao Li
Keyword(s):  
North China Plain ◽  
North China ◽  
Surface Deformation ◽  
Joint Analysis ◽  
Gps Data ◽  
Earth Surface ◽  
The North ◽  
The North China Plain

scholarly journals Fault source investigation of the 6 December 2016 MwMw 6.5 Pidie Jaya, Indonesia, earthquake based on GPS and its implications of the geological survey result

2020 ◽  
Vol 14 (4) ◽  
pp. 405-412
Author(s):  
Endra Gunawan ◽  
Takuya Nishimura ◽  
Susilo Susilo ◽  
Sri Widiyantoro ◽  
Nanang T. Puspito ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Source Parameters ◽  
Secondary Effects ◽  
Near Surface ◽  
Morphological Attributes ◽  
Ground Shaking ◽  
The North ◽  
Coulomb Failure ◽  
North And South ◽  
Fault Source

AbstractOn 6 December 2016 at 22:03 UTC, a devastating magnitude 6-class strike-slip earthquake occurred along an unidentified and unmapped fault in Pidie Jaya, northern Sumatra. We analysed the possible fault using continuous Global Positioning System (GPS) observation available in the region. In our investigation, we searched for the fault source parameters of the north- and south-dipping left-lateral faults and the west- and east-dipping right-lateral faults. We identified that the fault responsible for the earthquake was located offshore, with a southwest-northeast direction. We also computed the Coulomb failure stress and compared the result with the distribution of the aftershocks. In this study, we demonstrated that the result of the geological field survey conducted soon after the mainshock was attributed to the secondary effects of ground shaking and near-surface deformation, and not surface faulting. The newly identified offshore fault proposed by this study calls for further investigation of the corresponding submarine morphological attributes in this particular region.

scholarly journals Mantle Melting and Magmatic Processes Under La Picada Stratovolcano (CSVZ, Chile)

2019 ◽  
Vol 60 (5) ◽  
pp. 907-944 ◽  
Author(s):  
Jacqueline Vander Auwera ◽  
Olivier Namur ◽  
Adeline Dutrieux ◽  
Camilla Maya Wilkinson ◽  
Morgan Ganerød ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Geochemical Data ◽  
Upper Crust ◽  
Volcanic Zone ◽  
Nazca Plate ◽  
Southern Volcanic Zone ◽  
Magmatic Processes ◽  
Crystal Accumulation ◽  
Primary Magmas ◽  
Differentiation Trend

Abstract Where and how arc magmas are generated and differentiated are still debated and these questions are investigated in the context of part of the Andean arc (Chilean Southern Volcanic Zone) where the continental crust is thin. Results are presented for the La Picada stratovolcano (41°S) that belongs to the Central Southern Volcanic Zone (CSVZ) (38°S–41·5°S, Chile) which results from the subduction of the Nazca plate beneath the western margin of the South American continent. Forty-seven representative samples collected from different units of the volcano define a differentiation trend from basalt to basaltic andesite and dacite (50·9 to 65·6 wt % SiO2). This trend straddles the tholeiitic and calc-alkaline fields and displays a conspicuous compositional Daly Gap between 57·0 and 62·7 wt % SiO2. Interstitial, mostly dacitic, glass pockets extend the trend to 76·0 wt % SiO2. Mineral compositions and geochemical data indicate that differentiation from the basaltic parent magmas to the dacites occurred in the upper crust (∼0·2 GPa) with no sign of an intermediate fractionation stage in the lower crust. However, we have currently no precise constraint on the depth of differentiation from the primary magmas to the basaltic parent magmas. Stalling of the basaltic parent magmas in the upper crust could have been controlled by the occurrence of a major crustal discontinuity, by vapor saturation that induced volatile exsolution resulting in an increase of melt viscosity, or by both processes acting concomitantly. The observed Daly Gap thus results from upper crustal magmatic processes. Samples from both sides of the Daly Gap show contrasting textures: basalts and basaltic andesites, found as lavas, are rich in macrocrysts, whereas dacites, only observed in crosscutting dykes, are very poor in macrocrysts. Moreover, modelling of the fractional crystallization process indicates a total fractionation of 43% to reach the most evolved basaltic andesites. The Daly Gap is thus interpreted as resulting from critical crystallinity that was reached in the basaltic andesites within the main storage region, precluding eruption of more evolved lavas. Some interstitial dacitic melt was extracted from the crystal mush and emplaced as dykes, possibly connected to small dacitic domes, now eroded away. In addition to the overall differentiation trend, the basalts to basaltic andesites display variable MgO, Cr and Ni contents at a given SiO2. Crystal accumulation and high pressure fractionation fail to predict this geochemical variability which is interpreted as resulting from variable extents of fractional crystallization. Geothermobarometry using recalculated primary magmas indicates last equilibration at about 1·3–1·5 GPa and at a temperature higher than the anhydrous peridotite solidus, pointing to a potential role of decompression melting. However, because the basalts are enriched in slab components and H2O compared to N-MORB, wet melting is highly likely.

scholarly journals Three-dimensional deformation time series of glacier motion from multiple-aperture DInSAR observation

2019 ◽  
Vol 93 (12) ◽  
pp. 2651-2660 ◽  
Author(s):  
Sergey Samsonov
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Ground Deformation ◽  
Three Dimensional ◽  
Data Sets ◽  
Ice Flow ◽  
The North ◽  
Glacier Ice ◽  
Deformation Component ◽  
3D Deformation

AbstractThe previously presented Multidimensional Small Baseline Subset (MSBAS-2D) technique computes two-dimensional (2D), east and vertical, ground deformation time series from two or more ascending and descending Differential Interferometric Synthetic Aperture Radar (DInSAR) data sets by assuming that the contribution of the north deformation component is negligible. DInSAR data sets can be acquired with different temporal and spatial resolutions, viewing geometries and wavelengths. The MSBAS-2D technique has previously been used for mapping deformation due to mining, urban development, carbon sequestration, permafrost aggradation and pingo growth, and volcanic activities. In the case of glacier ice flow, the north deformation component is often too large to be negligible. Historically, the surface-parallel flow (SPF) constraint was used to compute the static three-dimensional (3D) velocity field at various glaciers. A novel MSBAS-3D technique has been developed for computing 3D deformation time series where the SPF constraint is utilized. This technique is used for mapping 3D deformation at the Barnes Ice Cap, Baffin Island, Nunavut, Canada, during January–March 2015, and the MSBAS-2D and MSBAS-3D solutions are compared. The MSBAS-3D technique can be used for studying glacier ice flow at other glaciers and other surface deformation processes with large north deformation component, such as landslides. The software implementation of MSBAS-3D technique can be downloaded from http://insar.ca/.

A Kinematic Reconstruction of Jurassic ocean spreading from the ophiolites of California, the western U.S. using structural geology and paleomagnetism.

2021 ◽  
Author(s):  
Cemil Arkula ◽  
Nalan Lom ◽  
John Wakabayashi ◽  
Grant Rea-Downing ◽  
Mark Dekkers ◽  
...  
Keyword(s):  
North America ◽  
Relative Position ◽  
North American ◽  
Fault System ◽  
Paleomagnetic Data ◽  
Geochemical Data ◽  
Ophiolite Belt ◽  
The North ◽  
Western Us ◽  
Jurassic Ophiolites

<p>The western edge of the North America plate contains geological records that formed during the long-lived convergence between plates of the Panthalassa Ocean and North America. The geology of different segments along western North America indicates different polarities (eastward and westward) for subducted slabs and thereby various tectonic histories and settings. The western United States (together with Mexico) plays a key role in this debate, many geologic interpretations assume continuous eastward subduction in contrast to observations within proximal geologic segments and tomographic images of the lower mantle below North America and the eastern Pacific Ocean which suggest a more complex subduction history. In this study, we aim to evaluate the plate tectonic setting in which the Jurassic ophiolites of California formed. Geochemical data from these ophiolites suggest that they formed above a nascent intra-oceanic or continental margin subduction zone. We first developed a kinematic reconstruction of the western US geology back to the Jurassic based on published structural geological data. Importantly, we update the reconstruction of the various branches of the San Andreas fault system to determine the relative position of the ophiolite fragments and adopt a previous restoration of Basin and Range extension which we expand northward towards Washington state. We then reconstruct North American margin deformation associated with Cretaceous to Paleogene shortening and strike-slip faulting. We find no clear candidates in the geological record that may have accommodated major subduction between the Jurassic ophiolite belt and the North American margin and consequently concur with the school of thought that considers that the ophiolite belt, as well as the underlying subduction-accretionary Franciscan Complex, likely formed in the North American fore-arc. We collected paleomagnetic data to reconstruct the spreading direction of the Jurassic Californian ophiolites, by providing new paleomagnetic data from sheeted dykes of the Josephine and Mt. Diablo Ophiolites. These suggest a NE-SW paleo-ridge orientation, oblique to the North American margin which may be explained by partitioning of a dextral component of subduction obliquity relative to North America. We used this spreading direction in combination with published ages of the ophiolites and our restoration of the relative position of these ophiolites prior to post-Jurassic deformation to construct a ridge-transform system at which the Jurassic ophiolites accreted. The results will be used to evaluate which parts of the subduction systems that existed in the eastern Panthalassa Ocean may reside in the western US, and which parts may be better sought in the northern Canadian Segment or/and in the southern Caribbean region.</p>

Sediment Thickness and Moho Depth Beneath Western Indonesian Region From Teleseismic Receiver Function

2021 ◽  
Author(s):  
Syaiful Bahri ◽  
Wiwit Suryanto ◽  
Drajat Ngadmanto
Keyword(s):  
Shear Wave ◽  
Shear Wave Velocity ◽  
Receiver Function ◽  
Velocity Model ◽  
Moho Depth ◽  
Sediment Layer ◽  
The North ◽  
East Kalimantan ◽  
Crust Layer ◽  
Teleseismic Receiver Function

Abstract The Earth's crust layer and sediment in Western Indonesia has been studied using the inversion of teleseismic receiver function from BMKG’s seismic network. Earthquake events were analyzed in this study with a moment magnitude greater than 6.0 with epicentral distances of 30° to 90°. A total of 60 earthquake events were observed and recorded by 91 stations around the study area. Furthermore, an inversion process was carried out using the initial velocity model from the modification of the AK135f velocity model to obtain the shear wave velocity structure below each stations. The velocity model from the azimuthally stacked vertical receiver function showed that the sediment layer had a relatively medium shear wave velocity value with an average of 2.1 km/s, while the crust layer had 4.60 km/s. The sedimentary layer thickness in this region also varies between 2 km to 10 km. A relatively thick sediment layer of about 8 km to 10 km was observed in two locations, in East Kalimantan associated with the Kutai Basin and Northern part of Sumatera in the North Sumatera Basin, a two major oil producer basinal area in Indonesia. The Moho discontinuity was also found at depths that vary between 16 km to 50 km. In addition, the most shallow Moho depth is 16 km below the North Kalimantan and North part of West Java, while the deeper Moho depth of 50 km is located below East Kalimantan, Central Kalimantan, North Sumatera and South Sumatera.

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