The Mid-Atlantic Ridge Near 45 °N. XXI. Magnetic Results from Basalt Drill Cores from the Median Valley

1973 ◽  
Vol 10 (5) ◽  
pp. 679-696 ◽  
Author(s):  
James Ade-Hall ◽  
Fabrizio Aumento ◽  
Patrick J. C. Ryall ◽  
Robert E. Gerstein ◽  
John Brooke ◽  
...  
Keyword(s):  
North Atlantic ◽  
Side Effect ◽  
Fission Track ◽  
Pillow Basalt ◽  
General Lack ◽  
Normal Polarity ◽  
Mid Atlantic Ridge ◽  
Fission Track Ages ◽  
Drill Cores

Natural remanence inclinations and paleointensities have been obtained from six drill cores of oceanic tholeiite pillow basalt taken from within a 4 km by 3 km area of the median valley of the Mid-Atlantic Ridge near 45 °N. Only two of the remanence inclinations agree with the predicted value for the area of +64°. Two others are of normal polarity but at +37 °and +47 °are significantly shallower than the predicted inclination. The remaining two cores have reverse inclinations of −14 °and −47°. Bottom photographs suggest that at least the +37 °and −47 °drill cores were obtained from in situ material.The paleointensities are uniformly high, ranging from 0.63 Oe to 1.17 Oe.The combined remanence inclination and paleointensity results are consistent with the presence on the floor of the median valley of basalts erupted during the Laschamps event, a conclusion in line with the fission-track ages for the basalts.It is suggested that the general lack of agreement between measured and predicted remanence inclinations, a feature that may be widespread in North Atlantic submarine basalts, is a side effect of the tectonic process responsible for the transport of new crust from the floor of the Median Valley to the adjacent crestal mountains.

Fission-Track Ages of Tuff Layers Related to the Pliocene-Pleistocene Boundary on the Boso Peninsula, Japan

1990 ◽  
Vol 33 (1) ◽  
pp. 86-93 ◽  
Author(s):  
Masao Kasuya
Keyword(s):  
Fission Track ◽  
Middle Part ◽  
Late Cenozoic ◽  
Boso Peninsula ◽  
Normal Polarity ◽  
Fission Track Ages ◽  
Age Constraints

AbstractFission-track ages of zircon crystals from four tuff layers in the late Cenozoic sediment sequence of the Boso Peninsula,.Japan, are 1.6 ± 0.2 myr (the Kurotaki Formation), 5.5 ± 0.6 and 5.2 ± 0.5 myr (the uppermost part of the Amatsu Formation), and 11.5 ± 0.8 myr (the middle part of the Amatsu Formation). These ages provide numerical age constraints on magneto-biostratigraphy. The normal polarity interval in the lower part of the Kiwada Formation corresponds to the Olduvai polarity subzone. The boundary between the Pliocene and Pleistocene lies slightly above the Olduvai polarity subzone.

scholarly journals Global zoogeography of fragile macrozooplankton in the upper 100–1000 m inferred from the underwater video profiler

2008 ◽  
Vol 65 (3) ◽  
pp. 433-442 ◽  
Author(s):  
Lars Stemmann ◽  
Marsh Youngbluth ◽  
Kevin Robert ◽  
Aino Hosia ◽  
Marc Picheral ◽  
...  
Keyword(s):  
North Atlantic ◽  
Imaging Systems ◽  
Advective Transport ◽  
Tropical Pacific Ocean ◽  
Underwater Video ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Biogeochemical Provinces ◽  
The Vertical Distribution

Abstract Stemmann, L., Youngbluth, M., Robert, K., Hosia, A., Picheral, M., Paterson, H., Ibanez, F., Guidi, L., Lombard, F., and Gorsky, G. 2008. Global zoogeography of fragile macrozooplankton in the upper 100–1000 m inferred from the underwater video profiler. – ICES Journal of Marine Science, 65: 433–442. Mesopelagic gelatinous zooplankton fauna are insufficiently known because of inappropriate and infrequent sampling, but may have important trophic roles. In situ imaging systems and undersea vehicles have been used to investigate their diversity, distribution, and abundance. The use of different platforms, however, restricts the comparison of data from different regions. Starting in 2001, the underwater video profiler (UVP) was deployed during 12 cruises in six oceanic regimes (Mediterranean Sea, North Atlantic shelves, Mid-Atlantic Ridge, tropical Pacific Ocean, eastern Indian Ocean, and Subantarctic Ocean) to determine the vertical distribution of organisms in the upper 1000 m. Nine oceanic regions were identified based on the hydrological properties of the water column. They correspond to nine of the biogeochemical provinces defined by Longhurst. In all, 21 morphotypes were recognized: sarcodines (eight groups), ctenophores (two groups), siphonophores, medusae (five groups), crustaceans (one group), chaetognaths, appendicularians, salps, and fish. The similarity in the community assemblages of zooplankton in the 100–1000 m layer was significantly greater within regions than between regions, in most cases. The regions with comparable composition were located in the North Atlantic with adjacent water masses, suggesting that the assemblages were either mixed by advective transport or that environmental conditions were similar in mesopelagic layers. The data suggest that the spatial structuring of mesopelagic macrozooplankton occurs on large scales (e.g. basin scales) but not necessarily on smaller scales (e.g. oceanic front).

scholarly journals Thermo-tectonic studies of Mesozoic basement rocks, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Ruohong Jiao
Keyword(s):  
New Zealand ◽  
Fission Track ◽  
Late Oligocene ◽  
Apatite Fission Track ◽  
Exhumation Rate ◽  
The North ◽  
Basement Rocks ◽  
Thermal Histories ◽  
Fission Track Ages

<p>The basement rocks of North Island, New Zealand, comprise metasedimentary terranes that were accreted onto the eastern Gondwana margin during Mesozoic subduction. Since the Oligocene, these terranes have been sitting at the leading edge of the Australian Plate, as the hanging wall of the Hikurangi subduction margin, overriding the subducting Pacific Plate. This thesis examines the thermo-tectonic histories of the basement rocks in North Island, using fission-track and (U-Th-Sm)/He thermochronology.  In eastern North Island, thermochronological data from the basement rocks record the exhumation histories since the latest Jurassic, related to two subduction cycles. Zircon fission-track analysis yields detrital or slightly reset ages (264–102 Ma); apatite fission-track ages range from 122 to 7.9 Ma and (U-Th-Sm)/He from 33.3 to 6.0 Ma.  In central North Island, modelled thermal histories suggest that the basement rocks were exhumed to shallow levels (<2 km) of the crust in the Early Cretaceous (~150–135 Ma). This was followed by a period of reheating until ~100 Ma, which is interpreted to be the result of burial by sedimentation above the accretionary wedge. From 100 Ma, models indicate thermo-tectonic quiescence until the Late Oligocene.  During the late Cenozoic, exhumation of the basement rocks accelerated at ~27 Ma in the western margin of the axial ranges (Kaimanawa Mountains). This acceleration in exhumation rate is interpreted to reflect the initiation of the subduction of the Pacific Plate beneath central North Island. Since the Late Oligocene, basement exhumation in the axial ranges migrated towards the trough. Modelled thermal histories indicate significant eastwards reverse faulting on the margin-parallel Ngamatea Fault between ~27 and 20 Ma and on the Wellington-Mohaka Fault between ~20 and 10 Ma.  In contrast to the activity in the axial ranges, in western North Island, the exhumational response of the basement rocks to the Cenozoic subduction was less significant and not revealed from the present thermochronological data.  Since the Late Miocene, the exhumation rate in the axial ranges has varied significantly along-strike, lower in the centre and higher to the north and south. During the last 10 Myr, the total magnitude of exhumation has been ~4 km in the Wellington region in the south, >1 km in the Raukumara Range in the north and negligible (less than a few hundred metres) in the central axial ranges in the Hawke’s Bay region. Although the accumulation of underplated material at the basal upper plate may have contributed to the localised rock uplift and exhumation (e.g. in the Raukumara Range), margin-normal shortening of the upper plate in the forearc of the Hikurangi Margin has most likely dominated the unroofing process of the axial ranges.  In northwestern North Island, the Northland Allochthon, an assemblage of Cretaceous–Oligocene sedimentary rocks, was emplaced during the Late Oligocene–earliest Miocene, onto in situ Mesozoic and early Cenozoic rocks. Detrital zircon and apatite fission-track ages reveal that the basal Northland Allochthon sequences and the underlying Miocene autochthonous sedimentary rocks were predominantly derived from the local Jurassic terrane (Waipapa Supergrop) and perhaps the Late Cretaceous volcanics. In addition, the Early Miocene autochthon contains significant sedimentary influx from the Late Oligocene volcanics related to the subduction initiation in northern New Zealand.  Zircon and apatite fission-track data from the in situ Mesozoic basement were inverted using thermo-kinematic models coupled with an inversion algorithm. The results suggest that during the Late Oligocene, ~4–6 km thick nappes were emplaced onto the in situ rocks in the northernmost Northland region. Prior to basement unroofing in the Early Miocene, the nappes thinned towards the south. Following allochthon emplacement, eastern Northland was uplifted and unroofed rapidly over a period of ~1–6 Myr, leading to ~0.4–1.5 km erosion of the allochthon. Since the mid-Miocene, due to the decline in tectonic activity in this region, the Northland Allochthon and the underlying rocks have been eroded slowly.  This thesis has documented variable exhumation and burial processes that occurred in the upper plates of both the Mesozoic Gondwana and late Cenozoic Hikurangi subduction margins. The results provide the foundation for future studies to investigate the kinematics and mechanism of the crustal exhumation and deformation of the North Island basement in further detail.</p>

scholarly journals Thermo-tectonic studies of Mesozoic basement rocks, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Ruohong Jiao
Keyword(s):  
New Zealand ◽  
Fission Track ◽  
Late Oligocene ◽  
Apatite Fission Track ◽  
Exhumation Rate ◽  
The North ◽  
Basement Rocks ◽  
Thermal Histories ◽  
Fission Track Ages

<p>The basement rocks of North Island, New Zealand, comprise metasedimentary terranes that were accreted onto the eastern Gondwana margin during Mesozoic subduction. Since the Oligocene, these terranes have been sitting at the leading edge of the Australian Plate, as the hanging wall of the Hikurangi subduction margin, overriding the subducting Pacific Plate. This thesis examines the thermo-tectonic histories of the basement rocks in North Island, using fission-track and (U-Th-Sm)/He thermochronology.  In eastern North Island, thermochronological data from the basement rocks record the exhumation histories since the latest Jurassic, related to two subduction cycles. Zircon fission-track analysis yields detrital or slightly reset ages (264–102 Ma); apatite fission-track ages range from 122 to 7.9 Ma and (U-Th-Sm)/He from 33.3 to 6.0 Ma.  In central North Island, modelled thermal histories suggest that the basement rocks were exhumed to shallow levels (<2 km) of the crust in the Early Cretaceous (~150–135 Ma). This was followed by a period of reheating until ~100 Ma, which is interpreted to be the result of burial by sedimentation above the accretionary wedge. From 100 Ma, models indicate thermo-tectonic quiescence until the Late Oligocene.  During the late Cenozoic, exhumation of the basement rocks accelerated at ~27 Ma in the western margin of the axial ranges (Kaimanawa Mountains). This acceleration in exhumation rate is interpreted to reflect the initiation of the subduction of the Pacific Plate beneath central North Island. Since the Late Oligocene, basement exhumation in the axial ranges migrated towards the trough. Modelled thermal histories indicate significant eastwards reverse faulting on the margin-parallel Ngamatea Fault between ~27 and 20 Ma and on the Wellington-Mohaka Fault between ~20 and 10 Ma.  In contrast to the activity in the axial ranges, in western North Island, the exhumational response of the basement rocks to the Cenozoic subduction was less significant and not revealed from the present thermochronological data.  Since the Late Miocene, the exhumation rate in the axial ranges has varied significantly along-strike, lower in the centre and higher to the north and south. During the last 10 Myr, the total magnitude of exhumation has been ~4 km in the Wellington region in the south, >1 km in the Raukumara Range in the north and negligible (less than a few hundred metres) in the central axial ranges in the Hawke’s Bay region. Although the accumulation of underplated material at the basal upper plate may have contributed to the localised rock uplift and exhumation (e.g. in the Raukumara Range), margin-normal shortening of the upper plate in the forearc of the Hikurangi Margin has most likely dominated the unroofing process of the axial ranges.  In northwestern North Island, the Northland Allochthon, an assemblage of Cretaceous–Oligocene sedimentary rocks, was emplaced during the Late Oligocene–earliest Miocene, onto in situ Mesozoic and early Cenozoic rocks. Detrital zircon and apatite fission-track ages reveal that the basal Northland Allochthon sequences and the underlying Miocene autochthonous sedimentary rocks were predominantly derived from the local Jurassic terrane (Waipapa Supergrop) and perhaps the Late Cretaceous volcanics. In addition, the Early Miocene autochthon contains significant sedimentary influx from the Late Oligocene volcanics related to the subduction initiation in northern New Zealand.  Zircon and apatite fission-track data from the in situ Mesozoic basement were inverted using thermo-kinematic models coupled with an inversion algorithm. The results suggest that during the Late Oligocene, ~4–6 km thick nappes were emplaced onto the in situ rocks in the northernmost Northland region. Prior to basement unroofing in the Early Miocene, the nappes thinned towards the south. Following allochthon emplacement, eastern Northland was uplifted and unroofed rapidly over a period of ~1–6 Myr, leading to ~0.4–1.5 km erosion of the allochthon. Since the mid-Miocene, due to the decline in tectonic activity in this region, the Northland Allochthon and the underlying rocks have been eroded slowly.  This thesis has documented variable exhumation and burial processes that occurred in the upper plates of both the Mesozoic Gondwana and late Cenozoic Hikurangi subduction margins. The results provide the foundation for future studies to investigate the kinematics and mechanism of the crustal exhumation and deformation of the North Island basement in further detail.</p>

scholarly journals P–Tevolution and timing of a late Palaeozoic fore-arc system and its heterogeneous Mesozoic overprint in north-central Chile (latitudes 31–32°S)

2011 ◽  
Vol 149 (2) ◽  
pp. 177-207 ◽  
Author(s):  
ARNE P. WILLNER ◽  
HANS-JOACHIM MASSONNE ◽  
UWE RING ◽  
MASAFUMI SUDO ◽  
STUART N. THOMSON
Keyword(s):  
Fission Track ◽  
White Mica ◽  
North Central ◽  
Subduction Channel ◽  
Central Chile ◽  
Late Palaeozoic ◽  
Zircon Fission Track ◽  
Slip Event ◽  
Fission Track Ages

AbstractIn the late Palaeozoic fore-arc system of north-central Chile at latitudes 31–32°S (from the west to the east) three lithotectonic units are telescoped within a short distance by a Mesozoic strike-slip event (derived peakP–Tconditions in brackets): (1) the basally accreted Choapa Metamorphic Complex (CMC; 350–430°C, 6–9 kbar), (2) the frontally accreted Arrayán Formation (AF; 280–320°C, 4–6 kbar) and (3) the retrowedge basin of the Huentelauquén Formation (HF; 280–320°C, 3–4 kbar). In the CMC, Ar–Ar spot ages locally date white-mica formation at peakP–Tconditions and during early exhumation at 279–242 Ma. In a local garnet mica-schist intercalation (570–585°C, 11–13 kbar) Ar–Ar spot ages refer to the ascent from the subduction channel at 307–274 Ma. Portions of the CMC were isobarically heated to 510–580°C at 6.6–8.5 kbar. The age of peakP–Tconditions in the AF can only vaguely be approximated at ≥ 310 Ma by relict fission-track ages consistent with the observation that frontal accretion occurred prior to basal accretion. Zircon fission-track dating indicates cooling below ~ 280°C at ~ 248 Ma in the CMC and the AF, when a regional unconformity also formed. Ar–Ar white-mica spot ages in parts of the CMC and within the entire AF and HF point to heterogeneous resetting during Mesozoic extensional and shortening events at ~ 245–240 Ma, ~ 210–200 Ma, ~ 174–159 Ma and ~ 142–127 Ma. The zircon fission-track ages are locally reset at 109–96 Ma. All resetting of Ar–Ar white-mica ages is proposed to have occurred byin situdissolution/precipitation at low temperature in the presence of locally penetrating hydrous fluids. Hence syn- and postaccretionary events in the fore-arc system can still be distinguished and dated in spite of its complex heterogeneous postaccretional overprint.

scholarly journals North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Martin Edwards ◽  
Pierre Hélaouët ◽  
Eric Goberville ◽  
Alistair Lindley ◽  
Geraint A. Tarling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Range Shift ◽  
The Core ◽  
Krill Abundance ◽  
The North ◽  
Living Space ◽  
Warming Climate ◽  
Two Temperatures ◽  
The North Atlantic

AbstractIn the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show, however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a ‘habitat squeeze’, with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that, as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the ‘Atlantification’ of the sub-Arctic.

Downstream Changes of Alpine Zircon Fission-Track Ages in the Rhone and Rhine Rivers

2004 ◽  
Vol 74 (1) ◽  
pp. 82-94 ◽  
Author(s):  
M. Bernet ◽  
M. T. Brandon ◽  
J. I. Garver ◽  
B. Molitor
Keyword(s):  
Fission Track ◽  
Zircon Fission Track ◽  
Fission Track Ages

Uplift of the lesser Himalayas, Northern Pakistan, as inferred from fission-track ages of sphene, epidote, and zircon

1981 ◽  
Vol 5 (1-2) ◽  
pp. 252
Author(s):  
P.K. Zeitler ◽  
R.A.K. Tahirkheli ◽  
C.W. Naeser ◽  
N.M. Johnson ◽  
J.B. Lyons
Keyword(s):  
Fission Track ◽  
Northern Pakistan ◽  
Lesser Himalayas ◽  
Fission Track Ages

scholarly journals Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 285-302 ◽  
Author(s):  
F. L. Schenker ◽  
M. G. Fellin ◽  
J.-P. Burg
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Fission Track ◽  
Regional Scale ◽  
Normal Faults ◽  
Recent Sediment ◽  
Northern Greece ◽  
Rapid Cooling ◽  
Fission Track Ages ◽  
Pelagonian Zone

Abstract. The Pelagonian zone, situated between the External Hellenides/Cyclades to the west and the Axios/Vardar/Almopias zone (AVAZ) and the Rhodope to the east, was involved in late Early Cretaceous and in Late Cretaceous–Eocene orogenic events whose duration and extent are still controversial. This paper constrains their late thermal imprints. New and previously published zircon (ZFT) and apatite (AFT) fission-track ages show cooling below 240 °C of the metamorphic western AVAZ imbricates between 102 and 93–90 Ma, of northern Pelagonia between 86 and 68 Ma, of the eastern AVAZ at 80 Ma and of the western Rhodope at 72 Ma. At the regional scale, this heterogeneous cooling is coeval with subsidence of Late Cretaceous marine basin(s) that unconformably covered the Early Cretaceous (130–110 Ma) thrust system from 100 Ma. Thrusting resumed at 70 Ma in the AVAZ and migrated across Pelagonia to reach the External Hellenides at 40–38 Ma. Renewed thrusting in Pelagonia is attested at 68 Ma by abrupt and rapid cooling below 240 °C and erosion of the gneissic rocks. ZFT and AFT in western and eastern Pelagonia, respectively, testify at ~40 Ma to the latest thermal imprint related to thrusting. Central-eastern Pelagonia cooled rapidly and uniformly from 240 to 80 °C between 24 and 16 Ma in the footwall of a major extensional fault. Extension started even earlier, at ~33 Ma in the western AVAZ. Post-7 Ma rapid cooling is inferred from inverse modeling of AFT lengths. It occurred while E–W normal faults were cutting Pliocene-to-recent sediment.

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