Microseismicity and lava flows hint at magmato‐tectonic processes near the southern tip of the Fonualei Rift and Spreading Center in the Lau Basin

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&#8217;ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17&#176;20&#8217;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.

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Hydrothermal trace metal release and microbial metabolism in the northeastern Lau Basin of the South Pacific Ocean

Biogeosciences ◽

10.5194/bg-18-5397-2021 ◽

2021 ◽

Vol 18 (19) ◽

pp. 5397-5422

Author(s):

Natalie R. Cohen ◽

Abigail E. Noble ◽

Dawn M. Moran ◽

Matthew R. McIlvin ◽

Tyler J. Goepfert ◽

...

Keyword(s):

Trace Metals ◽

Pacific Ocean ◽

Hydrothermal Vents ◽

Spreading Center ◽

Marine Microorganisms ◽

Dissolved Metals ◽

Lau Basin ◽

Southwest Pacific ◽

South Pacific Ocean ◽

Close Proximity

Abstract. Bioactive trace metals are critical micronutrients for marine microorganisms due to their role in mediating biological redox reactions, and complex biogeochemical processes control their distributions. Hydrothermal vents may represent an important source of metals to microorganisms, especially those inhabiting low-iron waters, such as in the southwest Pacific Ocean. Previous measurements of primordial 3He indicate a significant hydrothermal source originating in the northeastern (NE) Lau Basin, with the plume advecting into the southwest Pacific Ocean at 1500–2000 m depth (Lupton et al., 2004). Studies investigating the long-range transport of trace metals associated with such dispersing plumes are rare, and the biogeochemical impacts on local microbial physiology have not yet been described. Here we quantified dissolved metals and assessed microbial metaproteomes across a transect spanning the tropical and equatorial Pacific with a focus on the hydrothermally active NE Lau Basin and report elevated iron and manganese concentrations across 441 km of the southwest Pacific. The most intense signal was detected near the Mangatolo Triple Junction (MTJ) and Northeast Lau Spreading Center (NELSC), in close proximity to the previously reported 3He signature. Protein content in distal-plume-influenced seawater, which was high in metals, was overall similar to background locations, though key prokaryotic proteins involved in metal and organic uptake, protein degradation, and chemoautotrophy were abundant compared to deep waters outside of the distal plume. Our results demonstrate that trace metals derived from the NE Lau Basin are transported over appreciable distances into the southwest Pacific Ocean and that bioactive chemical resources released from submarine vent systems are utilized by surrounding deep-sea microbes, influencing both their physiology and their contributions to ocean biogeochemical cycling.

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The tectonic and volcanic evolution of the Mangatolu Triple Junction

10.5194/egusphere-egu2020-19897 ◽

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

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&#8217;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.

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Hafnium isotope constraints on the nature of the mantle beneath the Southern Lau basin (SW Pacific)

Scientific Reports ◽

10.1038/s41598-020-74565-0 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Quanshu Yan ◽

Susanne Straub ◽

Paterno Castillo ◽

Haitao Zhang ◽

Liyan Tian ◽

...

Keyword(s):

Isotope Composition ◽

Isotopic Signature ◽

Spreading Center ◽

Nd Isotope ◽

Lau Basin ◽

Average Value ◽

Isotope Data ◽

Sw Pacific ◽

The Pacific ◽

Ocean Ridge

Abstract New Hf isotope data provide new insights into the nature of the mantle beneath the southern Lau basin, adding new constraints on the displacement process of the Pacific mid-ocean ridge basalt (MORB)-type mantle by the Indian MORB-type mantle. The Hf isotopic ratios (176Hf/177Hf) of submarine lavas from the eastern Lau spreading center (ELSC) range from 0.283194 (εHf = 14.92) to 0.283212 (εHf = 15.54), with an average value of 0.283199 (εHf = 15.11) whereas those from the Valu Fa ridge (VFR) vary from 0.283221 (εHf = 15.88) to 0.283200 (εHf = 15.14), with an average of 0.283214 (15.61), indicating that ELSC lavas have a slightly more radiogenic Hf isotopic composition than VFR lavas. In contrast to the results from previous studies, the new Hf analyses combined with previous Nd isotope data clearly show that both VFR and ELSC have the distinct Hf–Nd isotope composition of the so-called DUPAL isotopic anomaly in the Indian MORB-type mantle. The DUPAL isotopic signature at VFR demonstrates for the first time that the inflow of the Indian MORB-type mantle has reached the southern tip of tectonic propagation in the southern Lau basin.

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

Chemical Geology ◽

10.1016/0009-2541(91)90002-9 ◽

1991 ◽

Vol 91 (3) ◽

pp. 227-256 ◽

Cited By ~ 84

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

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

10.5194/egusphere-egu21-1557 ◽

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

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&#8217;ou and Tongan microplates. The Fonualei Rift and Spreading Center (FRSC) is the eastern plate boundary that separates the Niuafo&#8217;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.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&#8217;ou microplate. P5 and P6 (both oriented W-E) cover the area south of the FRSC.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.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.

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Crustal Structure of the Niuafo'ou Microplate and Fonualei Rift and Spreading Center in the Northeastern Lau Basin, Southwestern Pacific

Journal of Geophysical Research Solid Earth ◽

10.1029/2019jb019184 ◽

2020 ◽

Vol 125 (6) ◽

Author(s):

F. Schmid ◽

H. Kopp ◽

M. Schnabel ◽

A. Dannowski ◽

I. Heyde ◽

...

Keyword(s):

Crustal Structure ◽

Spreading Center ◽

Lau Basin

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