scholarly journals Magmatism of the Weddell Sea rift system in Antarctica: Implications for the age and mechanism of rifting and early stage Gondwana breakup

2020 ◽  
Vol 79 ◽  
pp. 185-196 ◽  
Author(s):  
Teal R. Riley ◽  
Tom A. Jordan ◽  
Philip T. Leat ◽  
Mike L. Curtis ◽  
Ian L. Millar
Keyword(s):  
Early Stage ◽  
Weddell Sea ◽  
Rift System

scholarly journals Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

1992 ◽  
Vol 154 ◽  
pp. 49-59
Author(s):  
T Winther
Keyword(s):  
Open Systems ◽  
Early Stage ◽  
Rift System ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Low Degree ◽  
Alkaline Magmas ◽  
Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

Chapter 5.4b Marie Byrd Land and Ellsworth Land: petrology

2021 ◽  
pp. M55-2019-50 ◽  
Author(s):  
K. S. Panter ◽  
T. I. Wilch ◽  
J. L. Smellie ◽  
P. R. Kyle ◽  
W. C. McIntosh
Keyword(s):  
Trace Elements ◽  
Fractional Crystallization ◽  
High Pressures ◽  
Early Stage ◽  
Thermal Anomaly ◽  
Rift System ◽  
The West ◽  
Full Spectrum ◽  
West Antarctic Ice Sheet ◽  
West Antarctic

AbstractIn Marie Byrd Land and Ellsworth Land 19 large polygenetic volcanoes and numerous smaller centres are exposed above the West Antarctic Ice Sheet along the northern flank of the West Antarctic Rift System. The Cenozoic (36.7 Ma to active) volcanism of the Marie Byrd Land Volcanic Group (MBLVG) encompasses the full spectrum of alkaline series compositions ranging from basalt to intermediate (e.g. mugearite, benmoreite) to phonolite, peralkaline trachyte, rhyolite and rare pantellerite. Differentiation from basalt is described by progressive fractional crystallization; however, to produce silica-oversaturated compositions two mechanisms are proposed: (1) polybaric fractionation with early-stage removal of amphibole at high pressures; and (2) assimilation–fractional crystallization to explain elevated87Sr/86Sriratios. Most basalts are silica-undersaturated and enriched in incompatible trace elements (e.g. La/YbN>10), indicating small degrees of partial melting of a garnet-bearing mantle. Mildly silica-undersaturated and rare silica-saturated basalts, including tholeiites, are less enriched (La/YbN<10), a result of higher degrees of melting. Trace elements and isotopes (Sr, Nd, Pb) reveal a regional gradient explained by mixing between two mantle components, subduction-modified lithosphere and HIMU-like plume (206Pb/204Pb >20) materials. Geophysical studies indicate a deep thermal anomaly beneath central Marie Byrd Land, suggesting a plume influence on volcanism and tectonism.

A lacustrine record of the early stage of the Miocene Climatic Optimum in Central Europe from the Most Basin, Ohře (Eger) Graben, Czech Republic

2014 ◽  
Vol 151 (6) ◽  
pp. 1013-1033 ◽  
Author(s):  
TOMÁŠ MATYS GRYGAR ◽  
KAREL MACH ◽  
PETR SCHNABL ◽  
PETR PRUNER ◽  
JIŘÍ LAURIN ◽  
...  
Keyword(s):  
Current Knowledge ◽  
Early Stage ◽  
Sedimentary Environment ◽  
Magnetic Polarity ◽  
Early Miocene ◽  
Rift System ◽  
Age Model ◽  
Climatic Optimum ◽  
The Stability ◽  
Lake Deposits

AbstractThis study reports on a ~ 150 m thick macrofossil-barren sequence of siliciclastic sediments from a Burdigalian age (Early Miocene) freshwater lake. The lake was located within an incipient rift system of the Most Basin in the Ohře (Eger) Graben, which was part of the European Cenozoic Rift System, and had an original area of ≈ 1000 km2. Sediments from the HK591 core that cover the entire thickness of the lake deposits and some of the adjacent stratigraphic units were analysed by X-ray fluorescence spectroscopy (a proxy for element composition) and magnetic polarity measurement. The element proxies were subjected to frequency analysis, which provided estimated sedimentation rates, and allowed for sediment dating by magnetostratigraphy and orbital tuning of the age model. Based on the resulting age model and the known biostratigraphy, the lake was present between 17.4 and 16.6 Ma, which includes the onset of the Miocene Climatic Optimum in the latest Early Miocene. The identification of orbital forcing (precession, obliquity and short eccentricity cycles) confirms the stability of the sedimentary environment of the perennial lake in an underfilled basin. The dating allowed the sediment record to be interpreted in the context of the current knowledge of the European climate during that period. The stability of the sedimentary environment confirms that precipitation was relatively stable over the period recorded by the sediments.

scholarly journals Jurassic high heat production granites associated with the Weddell Sea rift system, Antarctica

2018 ◽  
Vol 722 ◽  
pp. 249-264 ◽  
Author(s):  
Philip T. Leat ◽  
Tom A. Jordan ◽  
Michael J. Flowerdew ◽  
Teal R. Riley ◽  
Fausto Ferraccioli ◽  
...  
Keyword(s):  
Heat Production ◽  
High Heat ◽  
Weddell Sea ◽  
Rift System

Chronology of the Red Wine alkaline province, central Labrador

1977 ◽  
Vol 14 (8) ◽  
pp. 1940-1946 ◽  
Author(s):  
Alan B. Blaxland ◽  
Laurence W. Curtis
Keyword(s):  
Red Wine ◽  
Early Stage ◽  
Regional Metamorphism ◽  
Strong Support ◽  
New Age ◽  
Igneous Rocks ◽  
Rift System ◽  
Alkaline Rocks ◽  
Plutonic Rocks ◽  
Basaltic Lavas

An 11-point Rb–Sr whole-rock isochron for the regionally metamorphosed Red Wine alkaline province gives an age of intrusion of 1345 ± 75 Ma (errors quoted at 2σ) and an initial 87Sr/86Sr ratio of (1.7021 ± 0.0103. Two 5-point mineral isochrons give ages of ~1000 Ma that represent metamorphic 'resetting' of the alkaline rocks. The whole-rock intrusion age compares closely with the early stage of magmatism in the Gardar Province of south Greenland where un-metamorphosed agpaitic igneous rocks, similar to those of the Red Wine Province, occur. In both provinces, alkaline plutonic rocks are associated, both spatially and chronologically, with thick sequences of continental sediments and basaltic lavas, and the new age data lend strong support to the supposition that the Gardar and Red Wine rocks are parts of the same pre-drift magmatic province and inferred rift system. The Gardar Province has, however, escaped the effects of the Grenville regional metamorphism which severely affected the Red Wine rocks.

Overview of West Antarctic tectonic evolution from ~500 Ma to the present

2021 ◽  
Author(s):  
Tom Jordan ◽  
Teal Riley ◽  
Christine Siddoway
Keyword(s):  
Tectonic Evolution ◽  
Weddell Sea ◽  
East Antarctica ◽  
Rift System ◽  
West Antarctica ◽  
The West ◽  
Magmatic Arc ◽  
West Antarctic ◽  
The Pacific ◽  
Tectonically Active

&lt;p&gt;West Antarctica developed as the tectonically active margin separating East Antarctica and the Pacific Ocean for almost half a billion years. Its dynamic history of magmatism, continental growth and fragmentation are recorded in sparse outcrops, and revealed by regional geophysical patterns. Compared with East Antarctica, West Antarctica is younger, more tectonically active and has a lower average elevation. We identify three broad physiographic provinces within West Antarctica and present their overlapping and interconnected tectonic and geological history as a framework for future study: 1/ The Weddell Sea region, which lay furthest from the subducting margin, but was most impacted by the Jurassic initiation of Gondwana break-up. 2/ Marie Byrd Land and the West Antarctic rift system which developed as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin. 3/ The Antarctic Peninsula and Thurston Island which preserve an almost complete magmatic arc system. We conclude by briefly discussing the evolution of the West Antarctic system as a whole, and the key questions which need to be addressed in future. One such question is whether West Antarctica is best conceived as an accreted collection of rigid microcontinental blocks (as commonly depicted) or as a plastically deforming and constantly growing melange of continental fragments and juvenile magmatic regions. This distinction is fundamental to understanding the tectonic evolution of young continental lithosphere. Defining the underlying geological template of West Antarctica and constraining its linkages to the dynamics of the overlying ice sheet, which is vulnerable to change due to human activity, is of critical importance.&lt;/p&gt;

scholarly journals Extension and inversion of salt-bearing rift systems

Solid Earth ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 1187-1204
Author(s):  
Tim P. Dooley ◽  
Michael R. Hudec
Keyword(s):  
Early Stage ◽  
Structural Evolution ◽  
Physical Models ◽  
Salt Diapir ◽  
Rift System ◽  
Brittle Deformation ◽  
High Atlas ◽  
Fault Systems ◽  
Transfer Zones ◽  
And Inversion

Abstract. We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent inversion. An early stage of extension generated structural topography consisting of a series of en-échelon graben. Our salt analog filled these graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems, whereas deformation in suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults, forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was enhanced along and up the major relay or transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest, and salt had risen diapirically on the horst blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New pop-up structures also formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to natural examples such as those in the Moroccan High Atlas.

scholarly journals Extension and Inversion of Salt-Bearing Rift Systems

2020 ◽  
Author(s):  
Tim P. Dooley ◽  
Michael R. Hudec
Keyword(s):  
Early Stage ◽  
Structural Evolution ◽  
Physical Models ◽  
Salt Diapir ◽  
Rift System ◽  
Brittle Deformation ◽  
High Atlas ◽  
Fault Systems ◽  
Transfer Zones ◽  
And Inversion

Abstract. We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent inversion. An early stage of extension generated structural topography consisting of a series of en-échelon graben. Our salt analog filled these graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems whereas deformation in suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults, forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was enhanced along and up the major relay/transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest and salt had risen diapirically on the horst blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New popup structures also formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to natural examples such as those in the Moroccan High Atlas.

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