scholarly journals Geochemistry of basalt from the North Gorda segment of the Gorda Ridge: Evolution toward ultraslow spreading ridge lavas due to decreasing magma supply

2008 ◽  
Vol 9 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
A. S. Davis ◽  
D. A. Clague ◽  
B. L. Cousens ◽  
R. Keaten ◽  
J. B. Paduan
Keyword(s):  
Spreading Ridge ◽  
The North ◽  
Magma Supply ◽  
Gorda Ridge ◽  
Ultraslow Spreading Ridge

First mid-ocean ridge-type ophiolite from the Meso-Tethys suture zone in the north-central Tibetan plateau

2020 ◽  
Vol 132 (9-10) ◽  
pp. 2202-2220 ◽  
Author(s):  
Yue Tang ◽  
Qing-Guo Zhai ◽  
Sun-Lin Chung ◽  
Pei-Yuan Hu ◽  
Jun Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Ocean Basin ◽  
Suture Zone ◽  
The Tibetan Plateau ◽  
Spreading Ridge ◽  
North Central ◽  
The North ◽  
Central Tibetan Plateau ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Abstract The Meso-Tethys was a late Paleozoic to Mesozoic ocean basin between the Cimmerian continent and Gondwana. Part of its relicts is exposed in the Bangong–Nujiang suture zone, in the north-central Tibetan Plateau, that played a key role in the evolution of the Tibetan plateau before the India-Asia collision. A Penrose-type ophiolitic sequence was newly discovered in the Ren Co area in the middle of the Bangong–Nujiang suture zone, which comprises serpentinized peridotites, layered and isotropic gabbros, sheeted dikes, pillow and massive basalts, and red cherts. Zircon U-Pb dating of gabbros and plagiogranites yielded 206Pb/238U ages of 169–147 Ma, constraining the timing of formation of the Ren Co ophiolite. The mafic rocks (i.e., basalt, diabase, and gabbro) in the ophiolite have uniform geochemical compositions, coupled with normal mid-ocean ridge basalt-type trace element patterns. Moreover, the samples have positive whole-rock εNd(t) [+9.2 to +8.3], zircon εHf(t) [+17 to +13], and mantle-like δ18O (5.8–4.3‰) values. These features suggest that the Ren Co ophiolite is typical of mid-ocean ridge-type ophiolite that is identified for the first time in the Bangong–Nujiang suture zone. We argue that the Ren Co ophiolite is the relic of a fast-spreading ridge that occurred in the main oceanic basin of the Bangong–Nujiang segment of Meso-Tethys. Here the Meso-Tethyan orogeny involves a continuous history of oceanic subduction, accretion, and continental assembly from the Early Jurassic to Early Cretaceous.

Petrology of a transform fault zone and adjacent ridge segments

1971 ◽  
Vol 268 (1192) ◽  
pp. 423-441 ◽  
Keyword(s):  
Oceanic Crust ◽  
Fault Zone ◽  
Fracture Zone ◽  
Volcanic Eruptions ◽  
Spreading Ridge ◽  
Transform Fault ◽  
Transform Faults ◽  
Near Surface ◽  
The North ◽  
Transform Fault Zone

The Verna Fracture Zone in the North Atlantic (9 to 11° N), which has been identified as a transform fault zone, contains exposures of serpentinized peridotites, while its adjacent ridge segments are floored mainly by typical abyssal ocean ridge basalts. This petrologic contrast correlates with the greater frequency of volcanic eruptions along the actively spreading ridge segments compared to the transform fault zone. Where rifting components occur across transform faults, exposures of the deeper zone of oceanic crust may result. The bathymetry of the Verna Fracture Zone suggests that some uplift parallel to the fracture zone as well as rifting led to exposures of deeper rocks. The basalts from the adjacent ridge axes contain ‘xenocrysts’ of plagioclase and olivine and more rarely of chromite. These appear to have a cognate origin, perhaps related to cooling and convection in near surface magma chambers. The basalts from the ridge axes, offset and on opposite sides of the transform fault, have similar features and compositions. The plagioclase peridotites have mineralogical features which indicate equilibration in the plagioclase pyrolite facies, suggesting maximum equilibration depths of around 30 km for a temperature of around 1200 °C. The chemical characteristics of the Vema F.Z. peridotites suggest that they may be undifferentiated mantle, emplaced as a subsolidus hot plastic intrusion or as a crystal mush. The abundance of peridotites and serpentinized peridotites is believed to reflect their abundance in seismic layer three of the oceanic crust.

Physical modeling of the formation of the microcontinent Jan Mayen

2020 ◽  
Author(s):  
Grigory Agranov ◽  
Eugene Dubinin ◽  
Andrey Grokholsky ◽  
Anna Makushkina
Keyword(s):  
Physical Simulation ◽  
Hot Spot ◽  
Magnetic Anomalies ◽  
Local Heat ◽  
Spreading Ridge ◽  
Spreading Axis ◽  
The North ◽  
The World ◽  
Initial Geometry ◽  
Northern Branch

<p>The split between the North American and Eurasian plates began in the Late Pleistocene - Early Eocene (58-60 million years). As the stretching took place, overlapping rift cracks formed. With further evolution, the crack that came from the north fully formed, while the south at that time died out, forming the axis of paleospreading (early Ypresian Age, 49.7 Ma). A hot spot was already functioning near Greenland at that time. In the Priabonian Age (33.1 million years), the hot spot ended under the axis of paleospreading. As a result, the spreading axis jumped (Peron-Pinvidic et al., 2012) creating the Jan Mine main microcontinent and the Kolbeinsain spreading ridge. In addition, the northern branch of the spreading ridge died out and the Aegir paleospreading ridge formed. These raises a number of questions arise:</p><p>-What is the mechanism for the separation of the Jan Mine continental block?</p><p>-Why did the spreading axis jumped and the Aegir Ridge wither away?</p><p>-What is the effect of the Icelandic hot spot on microblock formation?</p><p>-Are there similar structures in the world formed through a similar mechanism?</p><p>To answer these questions, a physical simulation was performed. Some of these issues were considered in (Muller et al., 2001, Gaina et al., 2003, Mjelde et al., 2008, Mjelde, Faleide, 2009).</p><p>Modelling was based on the initial geometry of rift cracks, known oldest magnetic anomalies and existing reconstructions. It showed two possibilities for the formation of the Jan Mayen microcontinent.</p><p>The first model is associated with parallel or oblique strike of rift cracks, the oncoming movement of which leads to their overlap, isolation of the microcontinental block, which experienced deformation and rotation.</p><p>The second model is associated with the presence of a local heat source (hot spot), the influence of which led to a jump of one branch of the rift towards the hot spot, and to the generation of a significant amount of magmatic material, which could significantly change the initial continental structure of the microblock. The second method, which combines the influence of the overlap zone and the hot spot, showed the best correlation with natural structures.</p>

Modes of seafloor generation at a melt-poor ultraslow-spreading ridge

Geology ◽  
2006 ◽  
Vol 34 (7) ◽  
pp. 605 ◽  
Author(s):  
Mathilde Cannat ◽  
Daniel Sauter ◽  
Véronique Mendel ◽  
Etienne Ruellan ◽  
Kyoko Okino ◽  
...  
Keyword(s):  
Spreading Ridge ◽  
Ultraslow Spreading Ridge

Geochronometry of the Bridge River Camp, southwestern British Columbia

1991 ◽  
Vol 28 (2) ◽  
pp. 195-208 ◽  
Author(s):  
C. H. B. Leitch ◽  
P. van der Heyden ◽  
C. I. Godwin ◽  
R. L. Armstrong ◽  
J. E. Harakal
Keyword(s):  
Volcanic Rocks ◽  
Older Age ◽  
Spreading Ridge ◽  
Early Permian ◽  
The North ◽  
Epithermal Mineralization ◽  
Minimum Age ◽  
Mineralizing Activity ◽  
Intrusive Suite ◽  
Ocean Ridge

Mineralization at the Bralorne mesothermal gold vein deposit is closely related to a suite of early Late Cretaceous to early Tertiary dykes. Premineral albitite dykes (91.4 ± 1.4 Ma by U–Pb on zircons) and postmineral lamprophyre dykes (43.5 ± 1.5 Ma by K–Ar on biotite) set definite age limits on the mineralizing event. A late intra- to post-mineral green hornblende dyke set (85.7 ± 3.0 Ma by K–Ar on hornblende) that forms a transitional series to the albitites may further restrict the age. Thus, mineralization occurred long after emplacement of the host Bralorne intrusions, dated as Early Permian (minimum age of approximately 270 ± 5 Ma by U–Pb on zircons, 284 ± 20 Ma by K–Ar on hornblende, and 40Ar/39Ar plateau at 276 ± 31 Ma). Lithologically similar intrusions 20 km to the north near Gold Bridge are also Early Permian (287 ± 20 Ma by K–Ar on hornblende and 320 ± 80 Ma by a Rb–Sr whole-rock isochron). Geochronology, radiogenic and stable isotopes, and fluid-inclusion studies suggest that there were several pulses of mineralizing activity adjacent to and east of the Coast Plutonic Complex (CPC). Decreasing temperatures and younger age of mineralization with increasing distance from the CPC imply that plutons of the CPC were the main heat source responsible for mineralization. The main pulses were about 90 Ma for mesothermal Au–Ag–As ± W,Mo mineralization at Bralorne near the CPC, ranging outwards to 65 Ma for Ag–Au–Sb–As ± Hg mineralization at the Minto and Congress deposits, to 45 Ma for Ag–Au epithermal mineralization at Blackdome, 100 km east of the CPC.The Bralorne intrusions may have been emplaced below the sea floor in a spreading-ridge oceanic environment, as suggested by the petrology of the intrusive suite, which includes serpentinized ultramafite, hornblende diorite, and soda granite (trondhjemite), typical of an ophiolite association. The chemistry of volcanic rocks mapped as Cadwallader Group, which host these intrusive bodies, is transitional from mid-ocean-ridge basalts to island-arc tholeiite, suggesting a back-arc-basin setting. Gradational contact relations between the hornblende diorite and the volcanic rocks suggest that the diorite intruded its own volcanic products. Intrusive contacts of the diorite with adjacent elongate ultramafic bodies imply that the ultramafic rocks are of Permian or older age and had been structurally emplaced into crustal levels by the time of diorite intrusion. In the Bralorne fault block the Bralorne intrusions appear to cut the adjacent Cadwallader and Bridge River groups, implying an Early Permian or older age for at least parts of these groups. Thus, rocks mapped as Cadwallader Group in the Bralorne area could be distinct from and older than lithologic equivalents exposed elsewhere, although they are similar in terms of their petrology and major- and trace-element chemistry.

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