Terra Nova
SCOPUS (1989-2023)SCIE-ISI
1365-3121
0954-4879
Anh Quốc
Cơ quản chủ quản: Wiley-Blackwell Publishing Ltd , WILEY
Lĩnh vực:
Geology
Các bài báo tiêu biểu
The snowball Earth hypothesis: testing the limits of global changeThe gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth's orbital obliquity > 60° (making the tropics colder than the poles) for 4.0 billion years following the lunar‐forming impact, or did climate cool globally for some reason to the point at which runaway ice‐albedo feedback created a `snowball' Earth? The high‐obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10‰) negative δ13 C shifts in seawater proxies, the deposition of strange carbonate layers (`cap carbonates') globally during post‐glacial sea‐level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice‐covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post‐glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world‐wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the δ13 C of seawater, as is observed. If cap carbonates are the `smoke' of a snowball Earth, what was the `gun'? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative δ13 C shifts of 10–20‰ precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.
Tập 14 Số 3 - Trang 129-155 - 2002
The Variscan collage and orogeny (480–290 Ma) and the tectonic definition of the Armorica microplate: a reviewThe Variscan belt of western Europe is part of a large Palaeozoic mountain system, 1000 km broad and 8000 km long, which extended from the Caucasus to the Appalachian and Ouachita mountains of northern America at the end of the Carboniferous. This system, built between 480 and 250 Ma, resulted from the diachronic collision of two continents: Laurentia–Baltica to the NW and Gondwana to the SE. Between these two continents, small, intermediate continental plates separated by oceanic sutures mainly have been defined (based on palaeomagnetism) as Avalonia and Armorica. They are generally assumed to have been detached from Gondwana during the early Ordovician and docked to Laurentia and Baltica before the Carboniferous collision between Gondwana and Laurentia–Baltica. Palaeomagnetic and palaeobiostratigraphic methods allow two main oceanic basins to be distinguished: the Iapetus ocean between Avalonia and Laurentia and between Laurentia and Baltica, with a lateral branch (Tornquist ocean) between Avalonia and Baltica, and the Rheic ocean between Avalonia and the so‐called Armorica microplate. Closure of the Iapetus ocean led to the Caledonian orogeny: a belt resulting from collision between Laurentia and Baltica, and from softer collisions between Avalonia and Laurentia and between Avalonia and Baltica. Closure of the Rheic ocean led to the Variscan orogeny by collision of Avalonia plus Armorica with Gondwana. A tectonic approach allows this scenario to be further refined. Another important oceanic suture is defined: the Galicia–Southern Brittany suture, running through France and Iberia and separating the Armorica microplate into North Armorica and South Armorica. Its closure by northward (or/and westward?) oceanic and then continental subduction led to early Variscan (430–370 Ma) tectonism and metamorphism in the internal parts of the Variscan belt. As no Palaeozoic suture can be detected south of South Armorica, this latter microplate should be considered as part of Gondwana since early Palaeozoic times and during its Palaeozoic north‐westward drift. Thus, the name Armorica should be restricted to the microplate included between the Rheic and the Galicia–Southern Brittany sutures.
Tập 13 Số 2 - Trang 122-128 - 2001
The remarkable Re–Os chronometer in molybdenite: how and why it worksThe Re–Os (rhenium–osmium) chronometer applied to molybdenite (MoS2 ) is now demonstrated to be remarkably robust, surviving intense deformation and high‐grade thermal metamorphism. Successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite, unique to each sample, such that recognized spatial decoupling of 187 Re parent and 187 Os daughter within individual molybdenite crystals is overcome. Highly precise, accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry (ID‐NTIMS). Spatial decoupling of parent–daughter precludes use of the laser ablation ICP‐MS microanalytical technique for Re–Os dating of molybdenite. The use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons. The Rb–Sr, K–Ar and 40 Ar/39 Ar chronometers are susceptible to chemical and thermal disturbance, particularly in terranes that have experienced subsequent episodes of hydrothermal/magmatic activity, and therefore should not be used as a basis for establishing accuracy in Re–Os dating of molybdenite, as has been done in the past. Re–Os ages for molybdenite are almost always in agreement with observed geological relationships and, when available, with zircon and titanite U–Pb ages. For terranes experiencing multiple episodes of metamorphism and deformation, molybdenite is not complicated by overgrowths as is common for some minerals used in U–Pb dating (e.g. zircon, monazite, xenotime), nor are Re and Os mobilized beyond the margins of individual crystals during solid‐state recrystallization. Moreover, inheritance of older molybdenite cores, incorporation of common Os, and radiogenic Os loss are exceedingly rare, whereas inheritance, common Pb and Pb loss are common complications in U–Pb dating techniques. Therefore, molybdenite ages may serve as point‐in‐time markers for age comparisons.
Tập 13 Số 6 - Trang 479-486 - 2001
Subduction and eduction of continental crust: major mechanisms during continent‐continent collision and orogenic extensional collapse, a model based on the south Norwegian CaledonidesABSTRACT During continental collision in the middle Silurian, the thickness of the lithosphere under the Caledonides of S. Norway was doubled by subduction of the western margin of Baltica, including the Western Gneiss Region, under Laurentia. Crustal rocks of the Baltic plate reached sub‐Moho depths of near 100 km or more as inferred from the presence of coesite in eclogites. Isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage. The subducted lithosphere experienced vertical constrictional strains as a result of slab‐pull by its heavy and cold root. Eduction of the deeply buried crustal material was initiated by decoupling of the Thermal Boundary Layer in the subducted lithosphere. Isostatic rebound resulted in very rapid uplift (1–2 mm yr‐1 ), and the deep crust was exhumed, mainly by tectonic extensional stripping over a period of 30–40 Myr. The eduction was probably related to a rolling hinge, footwall uplift mechanism, and the early high‐pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels. The model explains the present‐day normal crustal thickness under the exhumed deep rocks without necessarily invoking large‐scale lateral flow of material in the lower crust or igneous underplating.
Tập 3 Số 3 - Trang 303-310 - 1991
Age refinement of the Messinian salinity crisis onset in the MediterraneanAbstract We propose a revised age calibration of the Messinian salinity crisis onset in the Mediterranean at 5.971 Ma based on the recognition of an extra gypsum cycle in the transitional interval of the Perales section (Sorbas basin, Spain) and the revision of the magnetostratigraphy of the Monticino section (Vena del Gesso basin, Italy). This age re‐calibration allows to state more accurately that: (i) the interval encompassing theMSC ‐onset is continuous, thus ruling out any erosional feature or stratigraphic hiatus related to a major sea‐level fall affecting the Mediterranean; (ii) the first gypsum was deposited during the summer insolation peak at 5.969 Ma associated with an eccentricity minimum and roughly coincident with glacial stageTG 32; (iii) theMSC ‐onset was preconditioned by the tectonically‐driven reduction of the hydrological exchanges with the Atlantic Ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa.
Tập 25 Số 4 - Trang 315-322 - 2013
Neoproterozoic cap carbonates: a critical appraisal of existing models and the plumeworld hypothesisAbstract Evidence for glaciation during the mid‐late Neoproterozoic is widespread on Earth, reflecting three or more ice ages between 730 Ma and 580 Ma. Of these, the late Neoproterozoic Marinoan glaciation of approximately 635 Ma stands out because of its ubiquitous association with a characteristic, microcrystalline cap dolostone that drapes glacially influenced rock units worldwide. The Marinoan glaciation is also peculiar in that evidence for low altitude glaciation at equatorial latitudes is compelling. Three models have been proposed linking abrupt deglaciation with this global carbonate precipitation event: (i) overturn of an anoxic deep ocean; (ii) catastrophically accelerated rates of chemical weathering because of supergreenhouse conditions following global glaciation (Snowball Earth Hypothesis); and (iii) massive release of carbonate alkalinity from destabilized methane clathrates. All three models invoke extreme alkalinity fluxes into seawater during deglaciation but none explains how such alkalinity excess from point sources could be distributed homogeneously around the globe. In addition, none explains the consistent sequence of precipitation events observed within cap carbonate successions, specifically: (i) the global blanketing of carbonate powder in shallow marine environments during deglaciation; (ii) widespread and disruptive precipitation of dolomite cement; followed by (iii) localized barite precipitation and seafloor cementation by aragonite. The conceptual model presented here proposes that low latitude deglaciation was so massive and abrupt that the resultant meltwater plume could extend worldwide, physically separating the surface and deep ocean reservoirs for ≥103 years. It is proposed that cap dolostones formed primarily by microbially mediated precipitation of carbonate whitings during algal blooms within this low salinity plumeworld rather than by abiotic precipitation from normal salinity seawater. Many of the disruption features that are characteristic of cap dolostones can be explained by microbially mediated, early diagenetic dolomitization and cementation. The re‐initiation of whole ocean circulation degassed CO2 into the atmosphere in areas of upwelling, triggering localized, abiotic CaCO3 precipitation in the form of aragonite fans that overlie cap dolostones in NW Canada and Namibia. The highly oxygenated shallow marine environments of the glacial and post‐glacial Neoproterozoic world provided consistently favourable conditions for the evolutionary development of animals and other oxygenophiles.
Tập 17 Số 4 - Trang 299-310 - 2005
The Cimmerian Orogeny in northern Iran: tectono‐stratigraphic evidence from the forelandAbstract From the Permian onwards, the Gondwana‐derived Iran Plate drifted northward to collide with Eurasia in the Late Triassic, thereby closing the Palaeotethys. This Eo‐Cimmerian Orogeny formed the Cimmeride fold‐and‐thrust belt. The Upper Triassic–Middle Jurassic Shemshak Group of northern Iran is commonly regarded as the Cimmerian foreland molasse. However, our tectono‐stratigraphic analysis of the Shemshak Group resulted in a revised and precisely dated model for the Triassic–Jurassic geodynamic evolution of the Iran Plate: initial Cimmerian collision started in the Carnian with subsequent Late Triassic synorogenic peripheral foreland deposition (flysch, lower Shemshak Group). Subduction shifted south in the Norian (onset of Neotethys subduction below Iran) and slab break‐off around the Triassic–Jurassic boundary caused rapid uplift of the Cimmerides followed by Liassic post‐orogenic molasse (middle Shemshak Group). During the Toarcian–Aalenian (upper Shemshak Group), Neotethys back‐arc rifting formed a deep‐marine basin, which developed into the oceanic South Caspian Basin during the Late Bajocian–Late Jurassic.
Tập 21 Số 3 - Trang 211-218 - 2009
Are the oroclines of the Variscan belt related to late Variscan strike‐slip tectonics?Terra Nova, 23, 241–247, 2011 Abstract Early Variscan structures and magnetic anomalies delineate four oroclines along the Variscan belt. The arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes, which include ophiolites of the Rheic suture and units of Gondwanan derivation subducted on both sides of the Rheic Ocean. A transcurrent model dominated by right‐lateral motion explains the genesis and evolution of the oroclines and a simple plate‐tectonics scenario links late Variscan dextral strike‐slip movements in the Variscides to a broad intracontinental shear zone, kinematically equivalent to a transform fault. Terra Nova, 00, 1–7, 2011
Tập 23 Số 4 - Trang 241-247 - 2011
The Valanginian carbon isotope event: a first episode of greenhouse climate conditions during the CretaceousABSTRACT Lower Cretaceous pelagic carbonates outcropping along the Southern Alps of northern Italy provide a record of Tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle. The carbonate C‐isotope stratigraphy established at five selected localities in the Southern Alps allows an accurate picture to be drawn of the duration and amplitude of the Valanginian C‐isotope event. δ13 C values near 1.25–1.50% determined in Berriasian and lower Valanginian sediments are replaced by more pdsitive δ13 C values near 3% in the late Valanginian. The carbonate C‐isotope excursion ends in the early Hauterivian with values fluctuating between 1.5% and 2%. The carbonate C‐isotope excursion is accompanied by a positive excursion in the total organic carbon C‐isotope curve. The Valanginian C‐isotope excursion identified in Tethyan sediments correlates with a C‐isotope excursion recorded in the western North Atlantic, in the Gulf of Mexico, and in the Central Pacific (DSDP Sites 534,391,535 and 167). By analogy with the Aptian stage, also marked by a significant positive C‐isotope excursion, the time of positive δ13 C values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments. A warm and humid climate, possiblycoupled with a high atmospheric CO2 content and a high global sea‐level, may have triggered the acceleration of the global carbon cycling. In this case the Valanginian C‐isotope event would reflect a first episode of Greenhouse Earth conditions during the Cretaceous.
Tập 4 Số 3 - Trang 374-384 - 1992
Was Cathaysia part of Proterozoic Laurentia? – new data from Hainan Island, south ChinaAbstract We report here new field and analytical data from Precambrian rocks on Hainan Island of the Cathaysia Block, south China, and examine its probable connection to Laurentia. Granitoids and newly discovered felsic volcanic rocks dated at 1433 ± 6 Ma and 1439 ± 9 Ma (SHRIMP U‐Pb zircon) on Hainan Island are coeval with, and isotopically similar to the 1500–1350 Ma trans‐continental granite‐rhyolite province in southern Laurentia. Quartzites unconformably overlying the ca. 1430 Ma volcaniclastic rocks on Hainan Island are interpreted as locally‐sourced Grenvillian foreland basin deposits that can be correlated with the Deer Trail Group of south‐western Laurentia. The detrital provenance of the quartzites contains age populations comparable to the 1610–1490 Ma, westerly‐sourced non‐Laurentian detrital grains reported in the Belt Basin of south‐western Laurentia. Our new data thus make Cathaysia the most likely continental block next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.
Tập 20 Số 2 - Trang 154-164 - 2008