Evidence for early fluid channelization, Pikwitonei granulite domain, Manitoba, Canada

1992 ◽  
Vol 29 (8) ◽  
pp. 1701-1716 ◽  
Author(s):  
Julie K. Vry ◽  
Philip E. Brown
Keyword(s):  
Carbon Isotope ◽  
Fluid Inclusions ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Garnet Growth ◽  
High Grade ◽  
Low Oxygen ◽  
The North ◽  
Rock Types ◽  
Lake Region

The results of field mapping and carbon isotope and phase equilibria studies suggest that two different, locally controlled fluid regimes existed during at least the early phases of high-grade metamorphism in the north Cauchon Lake region, Pikwitonei granulite domain, Manitoba, Canada. During the prograde stages of high-grade "anticlockwise" regional metamorphism, rocks already metamorphosed to at least sillimanite grade were thermally metamorphosed at temperatures near 900 °C by the intrusion of a charnockitic magma. It is likely that this magma released an oxidizing, CO2-bearing, probably CO2-rich fluid phase while the region was still at relatively shallow depths. Fluid migration was channelized along the intrusive contact, and local fluid buffering characterized many of the country rocks. The light carbon isotope values of graphites (gr) and CO2 in cordierites (crd) in pelitic lithologies (δ13Cgr = −41.8 to −30.4; δ13Ccrd = −31.8 to −34.9), and the low oxygen fugacities in many samples rule out infiltration of these units by large amounts of an externally derived CO2-rich fluid phase. Texturally early CO2-rich fluid inclusions occur in the cores of garnets in a variety of rock types along the intrusive contact. These fluid inclusions were probably trapped during early garnet growth at high temperatures and relatively low pressures, and appear to have undergone limited or no subsequent reequilibration. They do not appear to provide direct information about the highest regional metamorphic temperature and pressure conditions to have affected the region (750 °C and 7 kbar (1 kbar = 100 MPa)) but may instead retain evidence of the prograde metamorphic path. These studies demonstrate the importance of local controls on the sources, compositions, timing, and transport of metamorphic fluids in the north Cauchon Lake region.

scholarly journals Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 361 ◽  
Author(s):  
Renyu Zeng ◽  
Jianqing Lai ◽  
Xiancheng Mao ◽  
Bin Li ◽  
Jiandong Zhang ◽  
...  
Keyword(s):  
North China Craton ◽  
Tectonic Evolution ◽  
North China ◽  
Regional Metamorphism ◽  
Hf Isotope ◽  
Crustal Growth ◽  
Quartz Syenite ◽  
Isotope Data ◽  
The North ◽  
Rock Types

The Alxa block is located in the southwestern margin of the North China Craton. The Paleoproterozoic tectonic evolution, crustal growth and tectonic affinity of the block remain unknown or controversial. The Longshoushan (LS) area is one of the few areas that outcrop Paleoproterozoic to crystalline basement rocks in the Alxa Block. In this study, we preset whole-rock geochemistry, zircon U–Pb geochronology and Lu–Hf isotope data from metagabbro, metadiorite, quartz syenite, granitic leucosome and pegmatoid leucosome in the LS area. These rocks all are enriched in LREE and LILE, and depleted in HREE and HFSE. Eight new LA-ICP-MS zircon U–Pb ages yielded three magmatic ages of 2044 Ma, 2029 Ma and 1940 Ma, and three metamorphic ages of 1891 Ma, 1848 Ma and 1812 Ma. Lu–Hf analyses reveal that the magmatic zircons and anatectic/metamorphic zircons from all the rock types are characterized by positive εHf(t) (−0.16 to 10.89) and variable εHf(t) (−11.21 to 6.24), respectively. Based on the previous studies and our new data, we conclude that the LS area experienced three magmatic events (2.5–2.45 Ga, ~2.1–2.0 Ga and ~1.95–1.91 Ga) and three regional metamorphism/anataxis events (~1.93–1.89 Ga, ~1.86–1.84 Ga and ~1.81 Ga) in Paleoproterozoic. The age–Hf isotope data establishes two main crustal growth events at ~2.9–2.5 Ga and ~2.2–2.0 Ga in the LS area. These data indicate that the LS area experienced intraplate extensional setting in the middle Paleoproterozoic, and continental subduction, collision and exhumation in the late Paleoproterozoic. Combining the geochronological framework and tectonic evolution, we suggest that the Alxa Block is part of the Khondalite Belt.

Boron and lithium in high-grade rocks and minerals from the Wawa–Kapuskasing region, Ontario

1988 ◽  
Vol 25 (9) ◽  
pp. 1485-1502 ◽  
Author(s):  
D. M. Shaw ◽  
M. G. Truscott ◽  
E. A. Gray ◽  
T. A. Middleton
Keyword(s):  
Fluid Transport ◽  
Fluid Phase ◽  
Distribution Patterns ◽  
Low Grade ◽  
Crustal Material ◽  
High Grade ◽  
Crustal Rocks ◽  
Mineral Equilibria ◽  
Rock Types ◽  
Lower Crustal

There is no preferential partitioning of boron among the principal rock-forming minerals in high-grade rocks of the Kapuskasing Structural Zone (KSZ) and the Wawa Domal Gneiss region (WDG). Lithium is strongly concentrated in biotite and other ferromagnesian minerals but does not show consistent partitioning between these and the sialic minerals.The distribution of B and Li within a rock may be studied using an alpha-track image, which shows that the inconsistencies in partitioning may be largely attributed to disturbance of mineral equilibria by postmetamorphic low-grade alteration that deposited B and Li.Boron has similar concentrations in all the rock types studied, although it is an incompatible element that elsewhere accumulates in pegmatites. Lithium concentrations are low in the anorthositic rocks but are otherwise very variable. In some but not all rocks higher than usual B and Li can be attributed to introduction during alteration.Boron occurs at low concentrations (2–3 ppm) throughout both the KSZ and the WDG areas and has an abundance similar to that in other granulite terranes. It is significantly lower than in average upper crustal rocks (9–15 ppm), and this is attributed to loss by fluid transport during formation of lower crustal material. Lithium occurs at similar concentrations in upper crustal rocks (20–22 ppm) as in the WDG area (27 ppm) but is lower in the KSZ (13 ppm), suggesting again a loss by fluid transport in the deep crust. Both estimates of loss are minima because of the evidence of reintroduction of the elements during later alteration.Although there is field and petrological evidence of anatectic melting in the KSZ–WDG region the distribution patterns of B and Li show no evidence of this: this is not unexpected for elements that readily partition into a fluid phase.

scholarly journals The Almacık mafic-ultramafic complex: exhumed Sakarya subcrustal mantle adjacent to the İstanbul Zone, NW Turkey

2012 ◽  
Vol 150 (2) ◽  
pp. 254-282 ◽  
Author(s):  
ERDİN BOZKURT ◽  
JOHN A. WINCHESTER ◽  
MUHARREM SATıR ◽  
QUENTIN G. CROWLEY ◽  
CHRISTIAN J. OTTLEY
Keyword(s):  
Active Continental Margin ◽  
Late Result ◽  
Ultramafic Rocks ◽  
High Grade ◽  
Calc Alkaline ◽  
The North ◽  
Rock Types ◽  
Mafic Complex ◽  
Nw Turkey ◽  
Northwestern Turkey

AbstractThe Almacık Mountains in northwestern Turkey expose an upper-amphibolite-facies complex consisting of alternating ultramafic (harzburgitic and websteritic) and mafic (metagabbroic) rock types. In the eastern part of this complex are island arc meta-tholeiites and transitional to calc-alkaline metabasites that are chemically quite similar to those of the Permo-Triassic Çele mafic complex north of Bolu, and this suggests an equivalence. However, much of the section exposes structurally deeper and chemically different mafic and ultramafic rocks, which have no equivalent in the Çele mafic complex, and isotopic dating has suggested that these rocks also formed during the Permian period and underwent Triassic and Jurassic metamorphism. Furthermore, sparse inherited ages, unlike those from İstanbul Zone granitoids, suggest a link with North African-derived Armorican-type basement (and hence the Sakarya Zone), rather than Amazonia-derived Avalonian basement. Alternating mafic and ultramafic rocks suggest structural repetition, supported by the exposure of discrete high-strain zones or poorly exposed shattered rock west of each outcrop of ultramafic rocks. The high grade of metamorphism, and the absence of either extrusive lavas or sheeted dyke rocks, suggests that the Almacık complex was not an ophiolite, but formed instead as subcontinental lower crust and subjacent mantle. Dominantly calc-alkaline geochemistry suggests that it formed the basement to an active continental margin bounding the north side of the Sakarya Continent, with S-dipping subduction of Palaeotethys. The Almacık complex was uplifted as a late result of compression against the southern margin of the İstanbul Zone in the Jurassic period. Lack of coeval high-grade metamorphism in the İstanbul Zone indicates that the latter was overthrust southwards over the Sakarya margin, and that there was therefore a change of subduction polarity in the Triassic period. The evidence further casts doubt on the existence of a Mesozoic Intra-Pontide Ocean in northwestern Turkey and suggests that the latest Permian magmatism, with subsequent Triassic and Jurassic metamorphism, was instead related to the closure of the Palaeotethyan Ocean.

scholarly journals Linking metamorphism, magma generation, and synorogenic sedimentation to crustal thickening during Southern Appalachian mountain building, USA

Lithosphere ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 722-749
Author(s):  
H.H. Stowell ◽  
J.J. Schwartz ◽  
S.B. Ingram ◽  
J. Madden ◽  
C. Jernigan ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Foreland Basin ◽  
Progressive Increase ◽  
Crustal Thickening ◽  
Garnet Growth ◽  
Metamorphic Rocks ◽  
Blue Ridge ◽  
Magma Generation ◽  
The North ◽  
North American Craton

Abstract The nature of metamorphism, magma compositions, the spatial distribution of plutons, and foreland sediments reflect, in part, the character and thickness of continental crust. We utilized metamorphic pressure-temperature-time (P-T-t) paths, garnet Sm-Nd ages, zircon U-Pb ages, and pluton compositions to estimate paleocrustal thickness and temporal changes in crustal magma sources in the Blue Ridge of the southernmost Appalachians. Garnet Sm-Nd ages for amphibolite-facies metamorphic rocks range from 331 ± 4 to 320 ± 3 Ma. Low- and high-Sr/Y plutons that intruded these metamorphic rocks have zircon U-Pb ages of 390 ± 1 to 365 ± 1 Ma and 349 ± 2 to 335 ± 1 Ma, respectively. Therefore, garnet growth began during regional metamorphism synchronous with or shortly after intrusion of the youngest high-Sr/Y trondhjemite plutons. Phase diagram sections and thermobarometry indicate that garnet growth initiated at ∼5.8 kbar and 540 °C and grew during temperature increases of 60–100 °C and pressure increases of 2–3 kbar. The older, low-Sr/Y magmas are inferred to have been sourced in the crust at depths <∼30 km, insufficient for garnet to be stable. However, the younger, high-Sr/Y magmas are inferred to have been sourced at >30 km depths where garnet was stable. Hafnium isotopic compositions for all the plutons, but one, exhibit a range from negative initial εHf(i) to weakly positive initial εHf(i), indicating incomplete mixing of dominantly crustal sources. Our data require minimum crustal thicknesses of ∼33 km at 331 Ma; however, Alleghanian crustal thicknesses must have locally reached 39 km, based on crustal reconstruction adding the Alleghanian thrust sheet beneath the eastern Blue Ridge. We infer the presence of hot, tectonically thickened crust during intrusion of the early Alleghanian high-Sr/Y plutons and conclude that garnet growth and plutonism reflect a progressive increase in crustal thickness and depth of magma generation. The crustal thickening was synchronous with deposition of Mississippian to early Pennsylvanian sediments in the foreland basin of the Appalachian orogen between 350 and 320 Ma. This crustal thickening may have preceded emplacement of the Alleghanian thrust sheets onto the North American craton.

Meso- and Neoarchean Banded Iron Formations and Genesis of High-Grade Magnetite Ores in the Anshan-Benxi Area, North China Craton

2017 ◽  
Vol 112 (7) ◽  
pp. 1629-1651 ◽  
Author(s):  
Yanpei Dai ◽  
Yudi Zhu ◽  
Lianchang Zhang ◽  
Mingtian Zhu
Keyword(s):  
North China Craton ◽  
North China ◽  
Regional Metamorphism ◽  
High Grade ◽  
Banded Iron Formations ◽  
Nd Isotope ◽  
The North ◽  
Metamorphic Fluids ◽  
Iron Deposits ◽  
Iron Formations

Abstract The Anshan-Benxi area in the North China craton has numerous occurrences of Algoma-type banded iron formations (BIFs) with subordinate high-grade magnetite ores. These ores provide insight into iron metallogenesis and early evolution of the North China craton. In this paper, we present Sm-Nd-Fe-O isotope, mineralogical, and structural data for four BIF-type iron deposits to place constraints on their depositional ages and formation mechanism. Previous SIMS and LA-ICP-MS zircon U-Pb dating results indicated a Mesoarchean age (ca. 3.10 Ga) for the Dagushan BIF and a Neoarchean age (ca. 2.55 Ga) for other regional BIFs (Dai et al., 2012, 2013, 2014). This is confirmed by Sm-Nd isochron ages of these BIFs, high-grade magnetite ores, and host metavolcanics, which yield two regression lines and match apparent ages of 3149 ± 85 Ma (MSWD = 1.2) for Dagushan, and 2671 ± 120 Ma (MSWD = 3.0) for the other three deposits. Our new chronological data thus suggest Meso- and Neoarchean BIF deposition and potentially significant BIF-type iron deposits at depth. The regional high-grade magnetite ores are all hosted in the BIFs that occur in the same orientation and have transitional boundaries between them. They also show similar Sm-Nd isotope compositions and magnetite rare earth elements + yttrium (REY) profiles, indicating that the Anshan-Benxi BIFs were most likely the source beds. The high-grade magnetite ores contain abundant pyrite and actinolite, with systematically lower δ56Fe values (0.67–0.40‰) when compared to the BIFs (1.88–0.64‰), suggesting a hydrothermal origin. In the field, some high-grade orebodies with schistose textures are adjacent to undeformed granitic plutons. This geologic relationship implies that the high-grade magnetite ores were formed earlier and probably did not result from magmatic hydrothermal fluids. Therefore we suggest that the Anshan-Benxi high-grade magnetite ores were most likely produced by infiltration of metamorphic fluids into primary BIFs, based on the following: (1) magnetite δ18O values within the high-grade magnetite ores (+2.5 to −0.6‰) are significantly lower than those in the BIFs (9.2–2.6‰); (2) magnetite (avg 0.39 ppm) and pyrite (avg 0.098 ppm) in the high-grade magnetite ores have much lower REY abundances than magnetite in the BIFs (avg 14.6 ppm); (3) skeletal quartz in the high-grade magnetite ores shows systematically higher FeOtolal contents (1.36–0.56 wt %) than those in laminated chert bands (0.06–0.00 wt %); and (4) hydrothermal zircons within the Nanfen BIF yield a U-Pb age of 2480 Ma, which is comparable to ca. 2.48 Ga regional metamorphism (Zhu et al., 2015). Furthermore, microstructural textures indicate a maximum regional deformation temperature of up to 500°C, which is lower than the plastic flow temperature (>600°C) of magnetite. Finite strain measurements and electron backscatter diffraction analyses suggest a general flattening deformation and similar crystallographic preferred orientation for all magnetite crystals. These structural features reveal that magnetite in the high-grade magnetite ores never experienced a separate tectonic event. Our microscopic studies also show that microfractures at the interfaces of BIF bands contain fragmented quartz crystals and are filled with abundant metamorphic minerals (e.g., actinolite and chlorite). Considering that the Anshan-Benxi high-grade magnetite ores are commonly adjacent to weak structural planes (e.g., faults), we propose that macro- and microscopic fractures probably provided channels for metamorphic fluids. Recent zircon U-Pb geochronology has indicated widespread BIF formation at ca. 2.55 Ga in the North China craton, corresponding to a pronounced peak in BIF deposition of other Precambrian cratons. It is thus implied that a global geologic event triggered the extensive occurrence of BIFs. We correlate the Neoarchean tectonic evolution of the North China craton with the 2.7 to 2.5 Ga Kenorland supercontinent. Significantly, planar distribution signatures of the North China craton BIFs indicate ca. 2.5 Ga cratonization through the amalgamation of at least seven microblocks that were welded by several Neoarchean greenstone belts. Hf-Nd isotope studies have highlighted the Archean episodic crustal evolution of the North China craton, and the Meso- and Neoarchean BIF deposition could have benefitted from these geologic processes. The Anshan-Benxi high-grade magnetite ores that formed at ca. 2.48 Ga were closely related to important metamorphic events during the North China cratonization process.

Geochemistry of pink corundum-bearing feldspathic gneiss, Frenchvale quarry, Cape Breton Island, Canada: metamorphism of albitised, Fe-poor clastic rocks

2019 ◽  
Vol 83 (02) ◽  
pp. 249-260
Author(s):  
J. Victor Owen ◽  
Jacob J. Hanley ◽  
Mitchell J. Kerr ◽  
Matthew Stimson ◽  
Brandon Boucher
Keyword(s):  
Fluid Inclusions ◽  
Quartz Vein ◽  
Isotope Composition ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Dolomitic Marble ◽  
Cape Breton Island ◽  
Clastic Rocks ◽  
Silica Alumina ◽  
O Isotope

AbstractFrenchvale quarry, once mined for dolomitic marble, contains pink corundum-bearing, quartz-free/-poor, feldspathic gneiss that is unusually sodic (~7% wt.% Na2O) and iron-poor (~0.6 wt.% Fe2O3), but has silica, alumina and immobile trace-element contents resembling those of suspended fluvial particulate matter (e.g. in the Congo River). The protolith of the gneiss, interpreted as a fine-grained clastic sediment deposited offshore, evidently was albitised prior to deformation and regional metamorphism. Variably-altered gneiss samples show a narrow range of δ18OVSMOW values (8.1 to 10.7‰) and no systematic differences in bulk O isotope composition as a function of alteration intensity. With the exception of an extensively fuchsitised zone adjacent to a thick (1.2 m), cross-cutting quartz vein that contains H2O–NaCl+CO2+CH4-bearing fluid inclusions, the O isotope data do not support interaction of the gneiss with an externally-derived fluid phase except at low fluid:rock ratio, even where granodiorite occurs in direct contact with the gneiss. Fluid inclusions in the quartz vein have bulk $X_{{\rm H}_2{\rm O}}$, $X_{{\rm C}{\rm O}_{\rm 2}}$ and $X_{{\rm C}{\rm H}_{\rm 4}}$ values (in mol.%) of 99.60, 0.14 and 0.26, respectively, as determined by gas chromatography. Although the protolith of the gneiss was associated with carbonate platformal rocks (now marble), corundum is confined to the feldspathic rocks. These feldspathic rocks lack calc-silicate minerals; they are not skarns. As such, they are distinct from well-known Himalayan sapphire and ruby deposits cited previously as analogues of the Frenchvale corundum occurrence.

The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

2019 ◽  
Vol 60 (10) ◽  
pp. 1991-2024 ◽  
Author(s):  
M G Kopylova ◽  
E Tso ◽  
F Ma ◽  
J Liu ◽  
D G Pearson
Keyword(s):  
North Atlantic ◽  
Thermal State ◽  
Mineral Chemistry ◽  
Mantle Metasomatism ◽  
Labrador Sea ◽  
The North ◽  
Rock Types ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as &lt;1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as &lt;1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

Stages of Late Palaeozoic deformation and intrusive activity in the western part of the North Patagonian Massif (southern Argentina) and their geotectonic implications

2008 ◽  
Vol 146 (1) ◽  
pp. 48-71 ◽  
Author(s):  
W. VON GOSEN
Keyword(s):  
Regional Metamorphism ◽  
The North ◽  
Magmatic Rocks ◽  
Late Palaeozoic ◽  
Intrusive Rocks ◽  
Gondwana Margin ◽  
Intrusive Activity ◽  
Magmatic History ◽  
Crust Deformation ◽  
Deformational Event

AbstractAnalyses of structures in the western part of the North Patagonian Massif (southern Argentina) suggest a polyphase evolution, accompanied by continuous intrusive activity. The first two deformations (D1, D2) and metamorphism affected the upper Palaeozoic, partly possibly older Cushamen Formation clastic succession and different intrusive rocks. A second group of intrusions, emplaced after the second deformational episode (D2), in many places contain angular xenoliths of the foliated country rocks, indicating high intrusive levels with brittle fracturing of the crust. Deformation of these magmatic rocks presumably began during (the final stage of) cooling and continued under solid-state conditions. It probably coincided with the third deformational event (D3) in the country rocks. Based on published U–Pb zircon ages of deformed granitoids, the D2-deformation and younger event along with the regional metamorphism are likely to be Permian in age. An onset of the deformational and magmatic history during Carboniferous times, however, cannot be excluded. The estimated ~W–E to NE–SW compression during the D2-deformation, also affecting the first group of intrusive rocks, can be related to subduction beneath the western Patagonia margin or an advanced stage of collisional tectonics within extra-Andean Patagonia. The younger ~N–S to NE–SW compression might have been an effect of oblique subduction in the west and/or continuing collision-related deformation. As a cause for its deviating orientation, younger block rotations during strike-slip faulting cannot be excluded. The previous D2-event presumably also had an effect on compression at the northern Patagonia margin that was interpreted as result of Patagonia's late Palaeozoic collision with the southwestern Gondwana margin. With the recently proposed Carboniferous subduction and collision south of the North Patagonian Massif, the entire scenario might suggest that Patagonia consists of two different pieces that were amalgamated with southwestern Gondwana during Late Palaeozoic times.

scholarly journals Haemoglobin polymorphisms affect the oxygen-binding properties in Atlantic cod populations

2008 ◽  
Vol 276 (1658) ◽  
pp. 833-841 ◽  
Author(s):  
Øivind Andersen ◽  
Ola Frang Wetten ◽  
Maria Cristina De Rosa ◽  
Carl Andre ◽  
Cristiana Carelli Alinovi ◽  
...  
Keyword(s):  
Evolutionary Biology ◽  
Quaternary Structure ◽  
Atlantic Cod ◽  
Three Dimensional ◽  
Oxygen Affinity ◽  
Oxygen Binding ◽  
Low Oxygen ◽  
Binding Properties ◽  
Important Species ◽  
The North

A major challenge in evolutionary biology is to identify the genes underlying adaptation. The oxygen-transporting haemoglobins directly link external conditions with metabolic needs and therefore represent a unique system for studying environmental effects on molecular evolution. We have discovered two haemoglobin polymorphisms in Atlantic cod populations inhabiting varying temperature and oxygen regimes in the North Atlantic. Three-dimensional modelling of the tetrameric haemoglobin structure demonstrated that the two amino acid replacements Met55β 1 Val and Lys62β 1 Ala are located at crucial positions of the α 1 β 1 subunit interface and haem pocket, respectively. The replacements are proposed to affect the oxygen-binding properties by modifying the haemoglobin quaternary structure and electrostatic feature. Intriguingly, the same molecular mechanism for facilitating oxygen binding is found in avian species adapted to high altitudes, illustrating convergent evolution in water- and air-breathing vertebrates to reduction in environmental oxygen availability. Cod populations inhabiting the cold Arctic waters and the low-oxygen Baltic Sea seem well adapted to these conditions by possessing the high oxygen affinity Val55–Ala62 haplotype, while the temperature-insensitive Met55–Lys62 haplotype predominates in the southern populations. The distinct distributions of the functionally different haemoglobin variants indicate that the present biogeography of this ecologically and economically important species might be seriously affected by global warming.

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