Subduction of the Izanagi-Pacific Ridge–transform intersection at the northeastern end of the Eurasian plate

Geology ◽  
2021 ◽  
Author(s):  
Toru Yamasaki ◽  
Gen Shimoda ◽  
Kenichiro Tani ◽  
Jinichiro Maeda ◽  
Futoshi Nanayama
Keyword(s):  
Partial Melting ◽  
Spreading Center ◽  
Transform Fault ◽  
Eurasian Plate ◽  
Isotopic Data ◽  
Ridge Axis ◽  
Plate Motions ◽  
Ridge Subduction ◽  
Ca 50 ◽  
Slab Tearing

Recent reconstructions of global plate motions suggest that the Izanagi-Pacific Ridge was subducted along the eastern margin of Eurasia at ca. 50 Ma. In the Hidaka magmatic zone (HMZ), which was located at the northeastern end of the Eurasian plate, three magmatic pulses occurred (46–45, 40–36, and 19–18 Ma). We report whole-rock geochemical and Sr-Nd-Pb isotopic data for 36 Ma high-Sr/Y (adakitic) rocks from the HMZ and show that these rocks formed by partial melting of oceanic crust and were emplaced as near-trench intrusions during ridge subduction. We reevaluate the nature of plutonic rocks in the HMZ and show that both the 46–45 and 40–36 Ma granitoids have essentially identical geochemical features. The distribution of plutons and magmatic cessation between 45 and 40 Ma are best explained by subduction of a ridge-transform intersection with a large offset of the ridge axis. The boundary between the Eocene granitoids corresponds to the position of a paleo–transform fault, and adakitic magmatism was caused by partial melting triggered by slab tearing at an overlapping spreading center. The paleoridge-transform configuration coincides with the locations of later large faults and a peridotite body.

Thermal regime around the Chile Triple Junction based on JAMSTEC MR18-06 cruise 'EPIC'

2020 ◽  
Author(s):  
Masataka Kinoshita ◽  
Ryo Anma ◽  
Yuka Yokoyama ◽  
Kosuke Ohta ◽  
Yusuke Yokoyama ◽  
...  
Keyword(s):  
Heat Flow ◽  
Sedimentation Rate ◽  
Thermal Regime ◽  
Triple Junction ◽  
Accretionary Prism ◽  
Age Dating ◽  
Spreading Center ◽  
Ridge Axis ◽  
Ridge Subduction ◽  
Chile Triple Junction

<p><span>The Chile triple junction (CTJ) is a unique place where a spreading center of mid-ocean ridge is subducting near the Taitao peninsula. Around CTJ, presence of high heat flow on the continental slope and near-trench young granitic rocks on the Taitao peninsula suggests the thermal and petrological impact of subducting ridge on the continental side. The tectonic history of the southeast Pacific since early Cenozoic to the present suggests that ridge subduction continuously occurred along the Chile trench, which migrated northward.</span></p><p><span>In January 2019, the MR18-06 cruise Leg 2 was conducted at CTJ, as a part of 'EPIC' expedition by using R.V Mirai of JAMSTEC. During the leg, we completed 4 SCS lines, 6 piston coring with heat flow measurements, 2 dredges, and underway geophysics observations, as well as deployment of 13 OBSs. Coring/heatflow sites were located across the ridge axis, HP5 on the seaward plateau of axial graben, HP1/HP2/HP6 on the axis, and HP3/HP7 on the forearc slope near the trench axis. The primary object of heat flow measurement at CTJ is to better constrain the thermal regime around CTJ by adding new data right above CTJ. The key question is whether CTJ is thermally dominated by ridge activity (magmatic, tectonic, and/or hydrothermal) or by subduction initiation (tectonic thickening, accretion, and/or erosion). The ultimate goal is to model the temperature at the plate interface from the heat flow and other data, and to infer how the thermal regime at CTJ contributes the seismogenic behavior at the M~9 megathrust zone. </span></p><p><span>Onboard and post-cruise measurements include; bulk density, porosity, Vp, resistivity, CT imags, iTracks element scan, age dating, etc. Core saples seaward of ridge axis (HP5) has few turbidites with higher density (~2 g/cc) and low sedimentation rate (SR; 0.2 m/ky), whereas cores on the axis the density are turbidite dominant with lower (1.6~1.8 g/cc) and very high SR (1~3 m/ky). The accretionary prism (landward of trench) cores have the density of 1.6~1.7 g/cc and SR=0.5~1 m/ky. They suggest that the turbidite covers only the axial graben. </span></p><p><span>Heat flow in the axial graben range 140-210 mW/m^2, which is lower than on the seaward plateau (370 mW/m^2). This apparent controversy may be due to lower magmatic activity and/or high sedimentation rate on the axis. The lower spreading rate (2.6 cm/yr one side) and the rapid convergent rate at the trench (7.2 cm/yr) may suppress sufficient magma supply or hydrothermal circulation. Heat flow on the accretionary prism (230 mW/m^2) is higher than borehole or BSR-derived heat flow (~<100 mW/m^2). It is suggestive of fluid upwelling along the decollement as proposed in the previous study. Some numerical thermal models will be presented to show the effect of ridge subduction. </span></p>

Evolution of migrating transform faults in anisotropic oceanic crust: examples from Iceland

2019 ◽  
Vol 56 (12) ◽  
pp. 1297-1308 ◽  
Author(s):  
Jeffrey A. Karson ◽  
Bryndís Brandsdóttir ◽  
Páll Einarsson ◽  
Kristján Sæmundsson ◽  
James A. Farrell ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Fault Zones ◽  
Plate Boundaries ◽  
Transform Fault ◽  
Eurasian Plate ◽  
Transform Faults ◽  
The North ◽  
Rift Propagation ◽  
Oriented Parallel ◽  
Ocean Ridge

Major transform fault zones link extensional segments of the North American – Eurasian plate boundary as it transects the Iceland Hotspot. Changes in plate boundary geometry, involving ridge jumps, rift propagation, and related transform fault zone migration, have occurred as the boundary has moved relative to the hotspot. Reconfiguration of transform fault zones occurred at about 6 Ma in northern Iceland and began about 3 Ma in southern Iceland. These systems show a range of different types of transform fault zones, ranging from diffuse, oblique rift zones to narrower, well-defined, transform faults oriented parallel to current plate motions. Crustal deformation structures correlate with the inferred duration and magnitude of strike-slip displacements. Collectively, the different expressions of transform zones may represent different stages of development in an evolutionary sequence that may be relevant for understanding the tectonic history of plate boundaries in Iceland as well as the structure of transform fault zones on more typical parts of the mid-ocean ridge system.

The Eastern Romanche ridge-transform intersection (Equatorial Atlantic): slow spreading under extreme low mantle temperatures. Preliminary results of the SMARTIES cruise.

2020 ◽  
Author(s):  
Marcia Maia ◽  
Daniele Brunelli ◽  
Keyword(s):  
Thick Layer ◽  
Tectonic Activity ◽  
Normal Faults ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Ridge Axis ◽  
Nodal Basin ◽  
Spreading Axis ◽  
Geophysical Surveys ◽  
Damaged Zone

<p>A strong edge effect is predicted at the intersections between long-offset transforms and mid ocean ridge segments. The Equatorial Atlantic hosts several megatransforms, where the connections of potentially low mantle temperatures due to the large lithospheric age contrast with melt production are poorly understood. The SMARTIES cruise focused on the Romanche transform that offsets the Mid Atlantic Ridge (MAR) laterally by 900 km with an age offset of 55 Ma. The eastern Ridge-Transform Intersection (RTI) markedly shows the effects of the lateral cooling of the ridge segment. To better understand the thermal regime at these complex domains, we acquired surface geophysical data and bathymetry of the area, and geological observations and sampling during 25 HOV Nautile dives. The integrated study of rock characteristics and of geophysical surveys allows tackling the connections between magmatism and tectonics. A network of 19 OBS was also deployed to study the seismic activity during the cruise in collaboration with the ILAB project.</p><p>There is a striking change in deformation patterns along the ridge axis moving away from the transform southwards. The bathymetry is extremely complex, with several structural directions, partly resulting from transtension. A low melt supply is focused at the ridge axis resulting in a long oblique axial domain, that forms a relay zone between the roughly north-south ridge axis in the south and the area close to the transform fault, while the transform fault domain is highly complex. Trends oblique to both the main spreading axis direction and the transform fault direction are widespread. A clear Principal Transform Displacement Zone (PTDZ) can be followed as a long, near continuous alignment, on the seafloor of the wide Romanche valley. However, the valley morphology suggests a migration of the PTDZ and intense deformation within the transform domain. The RTI is complex and the position of the spreading axis clearly evolved with time, through at least two and possibly three eastward ridge jumps.</p><p>Six Nautile dives explored the northern wall of the Romanche, the damaged zone of the transform fault, and the exceptionally deep nodal basin. The north wall exposes a very thick basalt unit covered with a thick layer of sediments. Eight dives explored the southern flank of the Romanche identifying fragments of old Oceanic Core Complexes (OCCs) formed by highly deformed peridotites, and a large OCC located at the RTI that exposes mylonitized peridotites and is dissected by several normal faults. The magmatic zones of the axial domain (nine dives) are formed by volcanic ridges affected by important tectonic activity. The dives show pillow and tube volcanic flows with intersecting faults. An oblique elongated faulted and sedimented ridge (2 dives) parallel to the oblique relay zone was shown to be of peridotitic nature Recent faults have been observed, as well as traces of high-T hydrothermal activity consistent with black-smoker type venting, recently overprinted by low temperature diffuse venting related to active faulting.</p>

Geochemistry and origin of Archean granites from the Black Hills, South Dakota

1990 ◽  
Vol 27 (1) ◽  
pp. 57-71 ◽  
Author(s):  
D. C. Gosselin ◽  
J. J. Papike ◽  
C. K. Shearer ◽  
Z. E. Peterman ◽  
J. C. Laul
Keyword(s):  
Rare Earth ◽  
South Dakota ◽  
Partial Melting ◽  
Residence Time ◽  
Earth Element ◽  
Black Hills ◽  
Isotopic Data ◽  
Tectonic Environment ◽  
Sedimentary Source ◽  
Wyoming Province

The Little Elk Granite (2549 Ma) and granite at Bear Mountain (BMG) (~2.5 Ga) of the Black Hills formed as a result of a collisional event along the eastern margin of the Wyoming Province during the late Archean. Geochemical modelling and Nd isotopic data indicate that the Little Elk Granite was generated by the partial melting of a slightly enriched (εNd = −1.07 to −3.69) granodioritic source that had a crustal residence time of at least 190 Ma. The medium-grained to pegmatitic, peraluminous, leucocratic BMG was produced by melting a long-lived (>600 Ma), compositionally variable, enriched (εNd = −7.6 to −12.3) crustal source. This produced a volatile-rich, rare-earth-element-poor magma that experienced crystal–melt–volatile fractionation, which resulted in a lithologically complex granite.The production of volatile-rich granites, such as the BMG and the younger Harney Peak Granite (1715 Ma), is a function of the depositional and post-depositional tectonic environment of the sedimentary source rock. These environments control protolith composition and the occurrence of dehydration and melting reactions that are necessary for the generation of these volatile-rich leucocratic granites. These types of granites are commonly related to former continental–continental accretionary boundaries, and therefore their occurrence may be used as signatures of ancient continental suture zones.

The Mid-Atlantic Ridge Near 45°N. XXIII. Analysis of Bathymetric and Magnetic Data

1975 ◽  
Vol 12 (3) ◽  
pp. 337-346 ◽  
Author(s):  
P. J. Bhattacharyya ◽  
R. D. Hyndman ◽  
M. J. Keen
Keyword(s):  
Cross Correlation ◽  
General Trend ◽  
Magnetic Data ◽  
Spreading Center ◽  
Transform Fault ◽  
Contour Maps ◽  
Regional Trends ◽  
Mid Atlantic Ridge ◽  
Lateral Displacements ◽  
East West

Bathymetric and magnetic data obtained from the Mid-Atlantic Ridge near 45°N have been analyzed numerically to determine trends, offsets and local structure. The estimates of regional trends in the data reveal that the average structural trend in this area is 17°E of north, made up of nearly north–south segments periodically offset by small right lateral displacements. The east–west offsets, not always visually manifest in contour maps of the data have been located by a cross-correlation scheme. Frequent small offsets may be the way a ridge crest accommodates to a spreading direction not perpendicular to the general trend of the crest. There is evidence for an old, now dead spreading center to the west of the median valley. This old center with an orientation of about 15°W, terminating in a right lateral transform fault has been abandoned in favor of frequent small offsets which provide smaller resistance to spreading.

scholarly journals Supplemental Material: Subduction of the Izanagi-Pacific Ridge–transform intersection at the northeastern end of the Eurasian plate

2021 ◽  
Author(s):  
Toru Yamasaki ◽  
et al.
Keyword(s):  
Data Sources ◽  
Geochemical Data ◽  
Calculation Methods ◽  
Eurasian Plate ◽  
Isotopic Data ◽  
Mode Of Occurrence

Methods, data sources and calculation methods for Figure 2, Figure S1 (mode of occurrence and photomicrographs), and Tables S1–S5 (whole-rock geochemical data, Sr-Nd-Pb isotopic data, zircon U-Pb dating results, references for compiled data, and parameters for melting-mixing calculations).<br>

scholarly journals Basalt from the Extinct Spreading Center in the West Philippine Basin: New Geochemical Results and Their Petrologic and Tectonic Implications

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1277
Author(s):  
Zhengxin Yin ◽  
Weiping Wang ◽  
Liang Chen ◽  
Zhengyuan Li ◽  
Qiang Liu ◽  
...  
Keyword(s):  
Mantle Source ◽  
Spreading Center ◽  
Isotopic Data ◽  
The West ◽  
Mafic Rocks ◽  
West Philippine Basin ◽  
Mantle Reservoir ◽  
Back Arc ◽  
Parental Melts ◽  
Ocean Ridge

We present geological, bulk-rock geochemical and Sr–Nd–Hf isotopic data for mafic rocks from the West Philippine Basin (WPB). These mafic rocks comprise pillow basalts characterized by a vesicular structure. The mid-ocean ridge basalt (MORB)-normalized trace element patterns of basalts from the study area display depletions in Nb. In addition, the chondrite-normalized lanthanide patterns of basalts from the WPB are characterized by significant depletions in the light lanthanides and nearly flat Eu to Lu segments. The investigated rocks have initial 87Sr/86Sr ratios (87Sr/86Sr(i)) of 0.703339–0.703455 and high εNd(t) values (8.0 to 8.7). Furthermore, basalts from the WPB have 176Hf/177Hf ratios that range from 0.28318 to 0.28321 and high εHf(t) from 15.2 to 16.3. Semi-quantitative modeling demonstrates that the parental melts of basalts from the study area were derived by ~20% adiabatic decompression melting of a rising spinel-bearing peridotite source. The Sr–Nd–Hf isotopic compositions of basalts from the WPB indicate that their parental magmas were derived from an upper mantle reservoir possessing the so-called Indian-type isotopic anomaly. Interpretation of the isotopic data suggests that the inferred mantle source was most likely influenced by minor inputs of a sediment melt derived from a downgoing lithospheric slab. Collectively, the petrographic and geochemical characteristics of basalts from the study area are analogous to those of mafic rocks with a back-arc basin (BAB)-like affinity. As such, the petrogenesis of basalts from the WPB can be linked to upwelling of an Indian-type mantle source due to lithospheric slab subduction that was followed by back-arc spreading.

Bay of Islands and Little Port complexes, revisited: age, geochemical and isotopic evidence confirm suprasubduction-zone origin

1991 ◽  
Vol 28 (10) ◽  
pp. 1635-1652 ◽  
Author(s):  
G. A. Jenner ◽  
G. R. Dunning ◽  
J. Malpas ◽  
M. Brown ◽  
T. Brace
Keyword(s):  
Transform Fault ◽  
Isotopic Data ◽  
Isotopic Study ◽  
Zircon Age ◽  
Suprasubduction Zone ◽  
Mid Ocean Ridge ◽  
Appalachian Orogen ◽  
Ocean Ridge ◽  
Source Materials ◽  
Oceanic Domain

The Bay of Islands Complex of the Humber Arm allochthon, west Newfoundland, contains the best-exposed ophiolite in the Appalachian Orogen. Associated structural slices, the Little Port and Skinner Cove complexes, also contain rocks formed in an oceanic domain, although their relationship to the Bay of Islands Complex remains controversial.To constrain the origin of the complexes and obtain a better understanding of the geology of the Humber Arm allochthon, we have undertaken an integrated geochronological, geochemical, and isotopic study. A U/Pb zircon age of [Formula: see text] Ma for the Little Port Complex and a zircon and baddeleyite age of 484 ± 5 Ma for the Bay of Islands Complex have been obtained. Geochemical and isotopic data on trondhjemitic rocks from the two complexes indicate that petrogenetic models for these rocks must account for fundamental differences in source materials and mineralogy during differentiation. The Little Port Complex trondhjemites are characterized by initial εNd of −1 to +1, whereas those in the Bay of Islands have εNd of +6.5. Geochemical signatures in mafic and felsic volcanics of the complexes are diverse, and show a complete gradation between arc and non-arc.The Bay of Islands and Little Port complexes are not related by any form of a major mid-ocean-ridge – transform-fault model. An alternative model to explain the relationships between the two complexes interprets the Little Port as arc-related and the Bay of Islands as a suprasubduction-zone ophiolite.

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