scholarly journals Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern Pacific

2020 ◽  
Author(s):  
Florian Schmid ◽  
Heidrun Kopp ◽  
Michael Schnabel ◽  
Anke Dannowski ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Gravity Data ◽  
Seafloor Spreading ◽  
P Wave ◽  
Spreading Center ◽  
Plate Boundaries ◽  
Volcanic Arc ◽  
Lau Basin ◽  
Refraction Seismic ◽  
Wave Tomography ◽  
Back Arc

<p>The northeastern Lau Basin is one of the fastest opening and magmatically most active back-arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is fairly well understood, the structure and evolution of the back-arc crust are not. We present refraction seismic, multichannel seismic and gravity data from a 300 km long east-west oriented transect crossing the Niuafo’ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17°20’S. Our P wave tomography model shows strong lateral variations in the thickness and velocity-depth distribution of the crust. The thinnest crust is present in the Fonualei Rift and Spreading Center, suggesting active seafloor spreading there. In the much thicker crust of the volcanic arc we identify a region of anomalously low velocities, indicative of partial melts. Surprisingly, the melt reservoir is located at ~17 km distance to the volcanic front, supporting the hypothesis that melts are deviated from the volcanic arc towards the FRSC in sub-crustal domains. We identify two distinct regions in the back-arc crust, representing different opening phases of the northeastern Lau Basin. During initial extension, likely dominated by rifting, crust of generally lower upper-crustal velocities formed. During an advanced opening phase, likely dominated by seafloor spreading, crust of higher upper-crustal velocities formed and is now up to 11 km thick. This thickening is the result of magmatic underplating, which is supported by elevated upper mantle temperatures in this region.</p>

Lithospheric architecture of the Ligurian Basin from seismic travel time tomography

2021 ◽  
Author(s):  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Ingo Grevemeyer ◽  
Grazia Caielli ◽  
Roberto de Franco ◽  
...  
Keyword(s):  
Seismic Data ◽  
Velocity Model ◽  
P Wave ◽  
Central Basin ◽  
Uppermost Mantle ◽  
Mantle Boundary ◽  
Oceanic Spreading ◽  
Refraction Seismic ◽  
Back Arc ◽  
Ligurian Basin

<p>The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning little is known about the style of back-arc rifting. Today, seismicity indicates the closure of this back-arc basin. In the basin, earthquake clusters occur in the lower crust and uppermost mantle and are related to re-activated, inverted, normal faults created during rifting.</p><p>To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile comprises 35 OBS and three land stations at Corsica to give a complete image of the continental thinning including the necking zone.</p><p>The majority of the refraction seismic data show mantle phases with offsets up to 70 km. The arrivals of seismic phases were picked and used to generate a 2-D P-wave velocity model. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The P-wave velocities in the crust reach 6.6 km/s at the base. The uppermost mantle shows velocities >7.8 km/s. The crust-mantle boundary becomes shallower from ~18 km to ~12 km depth within 30 km from Corsica towards the basin centre. The velocity model does not reveal an axial valley as expected for oceanic spreading. Further, it is difficult to interpret the seismic data whether the continental lithosphere was thinned until the mantle was exposed to the seafloor. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly did not initiate oceanic spreading before the opening of the Ligurian Basin stopped. The distribution of earthquakes and their fault plane solutions, projected along our seismic velocity model, is in-line with the counter-clockwise opening of the Ligurian Basin.</p>

Dynamics of the extension in the Fonualei Rift in the northern Lau Basin at 16 °S

2021 ◽  
Author(s):  
Anna Jegen ◽  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Udo Barckhausen ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Lower Crust ◽  
Pacific Plate ◽  
P Wave ◽  
Upper Crust ◽  
Lau Basin ◽  
Australian Plate ◽  
The Pacific ◽  
Refraction Seismic ◽  
Roll Back

<p>The Lau Basin is a young back-arc basin steadily forming at the Indo-Australian-Pacific plate boundary, where the Pacific plate is subducting underneath the Australian plate along the Tonga-Kermadec island arc. Roughly 25 Ma ago, roll-back of the Kermadec-Tonga subduction zone commenced, which lead to break up of the overriding plate and thus the formation of the western Lau Ridge and the eastern Tonga Ridge separated by the emerging Lau Basin.</p><p>As an analogue to the asymmetric roll back of the Pacific plate, the divergence rates decline southwards hence dictating an asymmetric, V-shaped basin opening. Further, the decentralisation of the extensional motion over 11 distinct spreading centres and zones of active rifting has led to the formation of a composite crust formed of a microplate mosaic. A simplified three plate model of the Lau Basin comprises the Tonga plate, the Australian plate and the Niuafo'ou microplate. The northeastern boundary of the Niuafo'ou microplate is given by two overlapping spreading centres (OLSC), the southern tip of the eastern axis of the Mangatolu Triple Junction (MTJ-S) and the northern tip of the Fonualei Rift spreading centre (FRSC) on the eastern side. Slow to ultraslow divergence rates were identified along the FRSC (8-32 mm/a) and slow divergence at the MTJ (27-32 mm/a), both decreasing southwards. However, the manner of divergence has not yet been identified. Additional regional geophysical data are necessary to overcome this gap of knowledge.</p><p>Research vessel RV Sonne (cruise SO267) set out to conduct seismic refraction and wide-angle reflection data along a 185 km long transect crossing the Lau Basin at ~16 °S from the Tonga arc in the east, the overlapping spreading centres, FRSC1 and MTJ-S2, and extending as far as a volcanic ridge in the west. The refraction seismic profile consisted of 30 ocean bottom seismometers. Additionally, 2D MCS reflection seismic data as well as magnetic and gravimetric data were acquired.</p><p>The results of our P-wave traveltime tomography show a crust that varies between 4.5-6 km in thickness. Underneath the OLSC the upper crust is 2-2.5 km thick and the lower crust 2-2.5 km thick. The velocity gradients of the upper and lower crust differ significantly from tomographic models of magmatically dominated oceanic ridges. Compared to such magmatically dominated ridges, our final P-wave velocity model displays a decreased velocity gradient in the upper crust and an increased velocity gradient in the lower crust more comparable to tectonically dominated rifts with a sparse magmatic budget.</p><p>The dominance of crustal stretching in the regional rifting process leads to a tectonical stretching, thus thinning of the crust under the OLSC and therefore increasing the lower crust’s velocity gradient. Due to the limited magmatic budget of the area, neither the magnetic anomaly nor the gravity data indicate a magmatically dominated spreading centre. We conclude that extension in the Lau Basin at the OLSC at 16 °S is dominated by extensional processes with little magmatism, which is supported by the distribution of seismic events concentrated at the northern tip of the FRSC.</p>

scholarly journals Submarine back-arc lava with arc signature: Fonualei Spreading Center, northeast Lau Basin, Tonga

2008 ◽  
Vol 113 (B8) ◽  
Author(s):  
Nicole S. Keller ◽  
Richard J. Arculus ◽  
Jörg Hermann ◽  
Simon Richards
Keyword(s):  
Spreading Center ◽  
Lau Basin ◽  
Back Arc

Reflection and refraction seismic studies in the Great Salt Lake Desert, Utah

Geophysics ◽  
1988 ◽  
Vol 53 (4) ◽  
pp. 431-433 ◽  
Author(s):  
R. M. René ◽  
J. L. Fitter ◽  
D. J. Murray ◽  
J. K. Walters
Keyword(s):  
Salt Lake ◽  
Gravity Data ◽  
Great Salt Lake ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
Gravity Modeling ◽  
Reflection Profile ◽  
Single Fold ◽  
Refraction Seismic ◽  
Basin Floor

Seismic refraction and CDP reflection profiles were acquired across mud flats of the Great Salt Lake Desert, Utah, during the summer of 1983. a combination of weight drops, horizontal hammers, buried explosives, and explosives detonated in air (Poulter method) was used. A 6.4 km refraction and single‐fold reflection profile indicates the presence of a shallow depression (Donner Reed basin) eastb of Donner Reed pass in the Silver Island Mountains. A basin floor ramp of Paleozoic rocks dipping approximately 30 degrees east into the Crater Island graben is interpreted beneath a 4.6 km 12-fold CDP reflection profile obtained by the Poulter method. This ramp extends beneath at least 0.8 km of condolidated Neogene sediments and 0.8 km of younger (largely unconsolidated) sediments. Weight‐drop and horizontal‐hammer profiles for the critical refraction along the Silurian Laketown dolomite yield P-wave and S-wave velocity estimates of 5270 ± 100 and [Formula: see text], respectively. The mud flats, with their laterally uniform finegrained sediments and shallow water table, provided excellent coupling of seismic energy. Air shots of 4.1 to 5.4 kg explosives without a source array gave good penetration to a depth of about 1.6 km. Partial migration before stack facilitated estimation of moveout velocities in the case of layers onlapping against a basin floor ramp, even though the maximum dips were only about 30 degrees. Gravity modeling and seismic ray tracing through intervals of constant velocity bounded by polynomial interfaces aided synergetic interpretation of the reflection, refraction, and gravity data.

scholarly journals The tectonic and volcanic evolution of the Mangatolu Triple Junction

2020 ◽  
Author(s):  
Rebecca Mensing ◽  
Margaret Stewart ◽  
Mark Hannington ◽  
Alan Baxter ◽  
Dorothee Mertmann
Keyword(s):  
Triple Junction ◽  
Hydrothermal Systems ◽  
Spreading Center ◽  
Valuable Insight ◽  
Triple Junctions ◽  
Lau Basin ◽  
The North ◽  
Spreading Centers ◽  
Spreading Rates ◽  
Back Arc

<p>The Mangatolu Triple Junction (MTJ) is an intraoceanic back-arc spreading center that is host to at least 3 distinct hydrothermal systems. It is located in the NE Lau Basin, which opened due to rollback of the Pacific plate along the Tonga-Kermadec trench. At the MTJ, three spreading centers meet in a ridge-ridge-ridge (RRR)-type triple junction separating the Tonga plate in the east, the Niuafo’ou microplate in the southwest, and an unnamed microplate in the north. The MTJ is directly linked to the formation and evolution of the Northeast Lau microplate mosaic, as plate fragmentation inevitably results in the formation of triple junctions, but it remains unclear whether the spreading centers are the drivers of plate fragmentation or a consequence of stress relocation related to microplate rotation. Detailed investigation of the geology and structural setting of the MTJ therefore provides valuable insight into the development in the northeast Lau Basin. Here we present the first comprehensive 1:200,000 geological map of the MTJ, based on a compilation of marine geophysical data (hydroacoustics, magnetics, and gravity) derived from 7 research cruises that have investigated the region between 2004 and 2018. Analysis of the mapped geological formations at the MTJ shows the importance of relict arc crust originating from the Tofua Arc in the architecture of the triple junction, which includes three stages of back-arc crust development and extensive off-axis volcanism. The spreading centers along each arm of the MTJ exploit pre-existing crustal weaknesses, interpreted to have formed during initial Lau Basin opening. A reconstruction of the basin opening, based on the mapped features and published spreading rates, revealed that initiation of the MTJ commenced approximately 180,000 years ago, consistent with the very recent and ongoing dynamic evolution of the NE Lau Basin and emerging microplate mosaic. Intersecting fabrics indicate sequential evolution of the 3 arms of the triple junction, with extension along the northeast arm dominant in the early history and more recent extension along the southern and western arms. The results of this study contribute to our growing understanding of the tectonic framework of the northeast Lau Basin and the role of triple junctions in microplate formation.</p>

scholarly journals Structure of oceanic crust in back-arc basins modulated by mantle source heterogeneity

Geology ◽  
2020 ◽  
Author(s):  
Ingo Grevemeyer ◽  
Shuichi Kodaira ◽  
Gou Fujie ◽  
Narumi Takahashi
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Seismic Data ◽  
Lower Crust ◽  
Subduction Zones ◽  
P Wave ◽  
Spreading Ridge ◽  
Volcanic Arc ◽  
Depleted Mantle ◽  
Back Arc

Subduction zones may develop submarine spreading centers that occur on the overriding plate behind the volcanic arc. In these back-arc settings, the subducting slab controls the pattern of mantle advection and may entrain hydrous melts from the volcanic arc or slab into the melting region of the spreading ridge. We recorded seismic data across the Western Mariana Ridge (WMR, northwestern Pacific Ocean), a remnant island arc with back-arc basins on either side. Its margins and both basins show distinctly different crustal structure. Crust to the west of the WMR, in the Parece Vela Basin, is 4–5 km thick, and the lower crust indicates seismic P-wave velocities of 6.5–6.8 km/s. To the east of the WMR, in the Mariana Trough Basin, the crust is ~7 km thick, and the lower crust supports seismic velocities of 7.2–7.4 km/s. This structural diversity is corroborated by seismic data from other back-arc basins, arguing that a chemically diverse and heterogeneous mantle, which may differ from a normal mid-ocean-ridge–type mantle source, controls the amount of melting in back-arc basins. Mantle heterogeneity might not be solely controlled by entrainment of hydrous melt, but also by cold or depleted mantle invading the back-arc while a subduction zone reconfigures. Crust formed in back-arc basins may therefore differ in thickness and velocity structure from normal oceanic crust.

Subalkaline andesite from Valu Fa Ridge, a back-arc spreading center in southern Lau Basin: petrogenesis, comparative chemistry, and tectonic implications

1991 ◽  
Vol 91 (3) ◽  
pp. 227-256 ◽  
Author(s):  
T.L. Vallier ◽  
G.A. Jenner ◽  
F.A. Frey ◽  
J.B. Gill ◽  
A.S. Davis ◽  
...  
Keyword(s):  
Spreading Center ◽  
Lau Basin ◽  
Tectonic Implications ◽  
Back Arc

scholarly journals A Decade of Global Navigation Satellite System/Acoustic Measurements of Back-Arc Spreading in the Southwestern Okinawa Trough

2021 ◽  
Vol 9 ◽  
Author(s):  
Horng-Yue Chen ◽  
Ryoya Ikuta ◽  
Ya-Ju Hsu ◽  
Toshiaki Tsujii ◽  
Masataka Ando ◽  
...  
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Okinawa Trough ◽  
Spreading Center ◽  
Integrated Analysis ◽  
Plate Boundaries ◽  
Velocity Change ◽  
Upward Migration ◽  
The Okinawa Trough ◽  
Back Arc

Long-term seafloor geodetic measurements are important for constraining submarine crustal deformation near plate boundaries. Here we present an integrated analysis of a decade of GNSS/acoustic data collected at a site 60 km to the east of northeast Taiwan near the axis of the Okinawa Trough back-arc basin. We obtained a time-series of horizontal and vertical positions based on 18 measurements from 2009 to 2019. These data reveal a southeastward movement at a rate of 43 ± 5 mm/yr since 2012 with respect to the Yangtze Plate. The horizontal motion can be explained by the clockwise rotation of the Yonaguni Block and northern Central Range. In addition, the vertical displacement of the transponder array shows rapid subsidence of 22 ± 9 mm/yr from 2012 to 2019. The fast subsidence rate and negative free-air gravity anomaly in this region indicate that crustal thinning is compensated mainly by surface deformation rather than upward migration of the Moho. Taking into account the offset in 2012 owing to the replacement of the transponder array, the horizontal position time series of our site are best explained by two linear lines with a slope change in July 2013. The timing of the velocity change coincides broadly with a change in the nearby seismicity rate and dike intrusion 150 km away from the site. Our results highlight the potential of seafloor geodesy in assessing temporal changes in deformation near the spreading center of the Okinawa Trough, which cannot be one using data from onland GNSS stations.

Tectonic activity of the northern and southern plate boundaries of the Niuafo’ou microplate, Lau Basin, southwest Pacific Ocean

2021 ◽  
Author(s):  
Anouk Beniest ◽  
Michael Schnabel ◽  
Anke Dannowski ◽  
Florian Schmid ◽  
Anna Jegen ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Tectonic Evolution ◽  
Tectonic Setting ◽  
Tectonic Activity ◽  
Scale Model ◽  
Spreading Center ◽  
Rift System ◽  
Plate Boundaries ◽  
Lau Basin ◽  
Southwest Pacific

<p>The northern Lau Basin in the southwest Pacific Ocean is one of the fastest opening back-arc basins on Earth, resulting in a mosaic of microplates, including the Niuafo’ou and Tongan microplates. The Fonualei Rift and Spreading Center (FRSC) is the eastern plate boundary that separates the Niuafo’ou from the Tongan microplate. The northern part of the FRSC is actively spreading, whereas the southern part is rifting. What is unclear, however, is how extension of the Lau Basin is accommodated north and south of the FRSC.</p><p>We present the results of six Multi-Channel Seismic profiles acquired during the ARCHIMEDES-I expedition and show an analogue lithosphere-scale model example of our proposed tectonic evolution. Profiles P1 (oriented NW-SE) and P2 (oriented W-E) cover the Mangatolu Triple Junction (MTJ) and the northern part of the FRSC. P3 and P4 (both oriented W-E) cover the southern Niuafo’ou microplate. P5 and P6 (both oriented W-E) cover the area south of the FRSC.</p><p>The northern profiles (P1 and P2) reveal a thick package of sediment towards the east, covering a heavily faulted basement over a wide area. Some indication for intrusive material is observed closer to the volcanic arc, but also further towards the western end of P2. Faults cross-cutting the basement but that do not reach the surface are considered inactive today. Faults reach the surface close to the MTJ and the northern tip of the FRSC and are considered active today. This leads to the interpretation that an earlier rift phase accommodated extension in a wide rift tectonic setting, whereas today, the extension is accommodated in a narrow rift or spreading tectonic setting. We will show an analogue model example that demonstrates this wide-to-narrow extensional tectonic evolution.</p><p>The profiles that cover the southern extent of the FRSC (P3, P4, P5 and P6), show that active faulting occurs towards the west, close to the Central Lau Spreading Center. Hidden faults that have deformed the basement, but do not affect the surface today anymore are observed in the abyssal parts of P3, P4, P5 and P6. Active faults that reach the surface are also observed towards the east. Recent volcanism is observed, both in the form of intrusive bodies, i.e. sills, as well as volcanoes that pierce through the stratigraphy. The observations lead to the conclusion that south of the FRSC an earlier (wide) rift system affected a larger area in the current abyssal parts of the profiles, whereas extension is currently accommodated through spreading in the CLSC, west of the southern tip of the FRSC.</p>

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