Plate tectonics through geological time

1981 ◽  
Vol 301 (1461) ◽  
pp. 207-215 ◽  
Keyword(s):  
Plate Tectonics ◽  
Space Distribution ◽  
Island Arcs ◽  
Geological Time ◽  
Polar Wander ◽  
Crustal Rocks ◽  
Geological Processes ◽  
Time Space ◽  
Progressive Growth ◽  
Metamorphic Terranes

Geological processes controlled by plate tectonics govern the time-space distribution of key rock assemblages. Stratal components of geosynclinal prisms, igneous provinces of orogenic belts, and regional facies of metamorphic terranes all display patterns controlled by inferred plate motions. Similarities between most Precambrian rock assemblages and Phanerozoic counterparts, coupled with analogies between Precambrian and Phanerozoic apparent polar wander paths, suggest that most surviving crustal rocks of all ages owe their origins to plate-tectonic processes. Archaean crustal blocks resemble collages of oceanic island arcs and volcanic archipelagoes whose tectonic juxtaposition to form cratonic nuclei was probably accomplished by subduction and crustal collision. Thereafter, similar Proterozoic oceanic elements were gradually accreted to growing continental margins and eventually crushed between colliding continental blocks of progressively larger size. Meanwhile, Archaean terranes within the interiors of cratons were generally shielded from further deformation, with their oceanic aspects largely preserved. In time, Phanerozoic oceanic terranes will systematically be destroyed by subduction or modified by incorporation into consolidated continental blocks. Differences between Precambrian and Phanerozoic plate tectonics and related assemblages reflect secular decline in global heat flux of radiogenic origin and progressive growth in the dimensions of cratonic blocks of continental crust.

6. The Earth’s heat

2018 ◽  
pp. 92-105
Author(s):  
William Lowrie
Keyword(s):  
Heat Transfer ◽  
Geomagnetic Field ◽  
Plate Tectonics ◽  
Internal Heat ◽  
Outer Core ◽  
Radioactive Isotopes ◽  
Convection Heat ◽  
Crustal Rocks ◽  
Geological Processes ◽  
The Earth

The Earth’s internal heat is its greatest source of energy. It powers global geological processes such as plate tectonics and the generation of the geomagnetic field. ‘The Earth’s heat’ explains that the internal heat arises from two sources: the decay of radioactive isotopes in crustal rocks and the mantle, and primordial heat left over from the planet’s fiery formation. The internal heat has to find its way out of the Earth. The three basic forms of heat transfer are radiation, conduction, and convection. Heat is also transferred in compositional and phase transitions. Heat transport by conduction is most important in solid regions of the Earth, while thermal convection occurs in the viscoelastic mantle and molten outer core.

scholarly journals Titanium isotopes as a tracer for the plume or island arc affinity of felsic rocks

2019 ◽  
Vol 116 (4) ◽  
pp. 1132-1135 ◽  
Author(s):  
Zhengbin Deng ◽  
Marc Chaussidon ◽  
Paul Savage ◽  
François Robert ◽  
Raphaël Pik ◽  
...  
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Indirect Evidence ◽  
Island Arc ◽  
Island Arcs ◽  
Calc Alkaline ◽  
Magma Differentiation ◽  
Isotopic Signatures ◽  
Crustal Rocks ◽  
Felsic Rocks

Indirect evidence for the presence of a felsic continental crust, such as the elevated 49Ti/47Ti ratios in Archean shales, has been used to argue for ongoing subduction at that time and therefore plate tectonics. However, rocks of intermediate to felsic compositions can be produced in both plume and island arc settings. The fact that Ti behaves differently during magma differentiation in these two geological settings might result in contrasting isotopic signatures. Here, we demonstrate that, at a given SiO2 content, evolved plume rocks (tholeiitic) are more isotopically fractionated in Ti than differentiated island arc rocks (mainly calc-alkaline). We also show that the erosion of crustal rocks from whether plumes (mafic in average) or island arcs (intermediate in average) can all produce sediments having quite constant 49Ti/47Ti ratios being 0.1–0.3 per mille heavier than that of the mantle. This suggests that Ti isotopes are not a direct tracer for the SiO2 contents of crustal rocks. Ti isotopes in crustal sediments are still a potential proxy to identify the geodynamical settings for the formation of the crust but only if combined with additional SiO2 information.

Global factors of lead-zinc ore formation

2019 ◽  
pp. 3-10
Author(s):  
A. L. Dergachev
Keyword(s):  
Continental Crust ◽  
Island Arcs ◽  
Geological Time ◽  
Crust Formation ◽  
Ore Formation ◽  
Global Factor ◽  
Lead And Zinc ◽  
Lead Zinc ◽  
Cyclic Changes

Tectonic evolution of the Earth is a principle global factor responsible for uneven distribution of lead and zinc reserves in geological time. Cyclic changes in productivity of lead-zinc ore-formation processes resulted from periodical amalgamation of most blocks of continental crust, formation, stabilization and final break-up of supercontinents. Many features of age spectrums of lead and zinc reserves are caused by gradual increase of volume of continental crust resulting from accretion of island arcs to ancient cratons, widening of distribution of ensialic environments of ore-formation and increasing role of continental crust in magmatic processes.

scholarly journals Precambrian faulting episodes and insights into the tectonothermal history of North Australia: Microstructural evidence and K–Ar, <sup>40</sup>Ar–<sup>39</sup>Ar, and Rb–Sr dating of syntectonic illite from the intracratonic Millungera Basin

2020 ◽  
Author(s):  
I. Tonguç Uysal ◽  
Claudio Delle Piane ◽  
Andrew Todd ◽  
Horst Zwingmann
Keyword(s):  
Large Scale ◽  
Active Tectonics ◽  
Mineral Resources ◽  
Sedimentary Basins ◽  
Integrated Approach ◽  
Space Distribution ◽  
Seismic Survey ◽  
North Central ◽  
Time Space ◽  
Central Australia

Abstract. Australian terranes concealed beneath Mesozoic cover record complex Precambrian tectonic histories involving a successive development of several Proterozoic to Paleozoic orogenic systems. This study presents an integrated approach combining K–Ar, 40Ar–39Ar, and Rb–Sr geochronology of Precambrian authigenic illites from the recently discovered Millungera Basin in north-central Australia. Brittle deformation and repeated fault activity are evident from the sampled cores and their microstructures, probably associated with the large-scale faults inferred from interpretations of seismic survey. Rb–Sr isochron, 40Ar–39Ar total gas, and K–Ar ages are largely consistent indicating late Mesoproterozoic and early Proterozoic episodes (~ 1115 ± 26 Ma, ~ 1070 ± 25 Ma, ~ 1040 ± 24 Ma, ~ 1000 ± 23 Ma, and ~ 905 ± 21 Ma) of active tectonics in north-central Australia. K–Ar results show that illites from fault gouges and authigenic matrix illites in undeformed adjacent sandstones precipitated contemporaneously, indicating that advection of tectonically mobilised fluids extended into the undeformed wall rocks above or below the fracture and shear (fault gouge) zones. This study provides insight into the enigmatic time-space distribution of Precambrian tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant energy and mineral resources.

scholarly journals Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

2020 ◽  
Vol 90 (1) ◽  
pp. 48-66
Author(s):  
Jeremy C. Rushton ◽  
Doris Wagner ◽  
Jonathan M. Pearce ◽  
Christopher A. Rochelle ◽  
Gemma Purser
Keyword(s):  
Time Scales ◽  
Co2 Storage ◽  
Pyrite Oxidation ◽  
Carbon Capture And Storage ◽  
Spatial Relationship ◽  
Oxidation Reactions ◽  
Geological Time ◽  
Genetic Link ◽  
Geological Processes ◽  
Red Bed

ABSTRACT Improving our ability to predict the interactions between CO2 and reservoir rocks at geological time scales is of key importance if carbon capture and storage (CCS) is to have a role in climate-change mitigation, particularly in the light of likely regulatory requirements. Understanding and identifying the relevant geological processes over long time scales can be obtained only at natural-analogue sites. At one such site, in the Salt Wash Graben area of Utah, USA, widespread bleaching affects the Middle Jurassic red-bed “wet dune” Entrada Sandstone. Previous work has proposed a genetic link between the bleaching and spatially concomitant recent and modern CO2-rich fluids. The results presented here challenge some of the previous models and come from a detailed petrographic examination of mineralized fractures in the Entrada Sandstone that are centered in vertical extensions to the bleaching. These fractures typically contain complex mineralization assemblages. Pyrite was a paragenetically early phase, identifiable from common pseudomorphs of mixed iron oxides and oxyhydroxides that rarely contain relict pyrite. The pyrite contains up to 3 wt% arsenic. The volume of fracture-adjacent bleached sandstone is sufficient to have been the source of iron for the pyrite originally present in the fracture. The pyrite pseudomorphs occur at the center of fracture- and pore-filling cements that comprise intergrowths of hematite–goethite–jarosite–gypsum, an assemblage that suggests that their formation resulted from the oxidative alteration of pyrite, a genetic link supported by the arsenic present in the iron-bearing minerals. The presence of jarosite and proximal removal of earlier, sandstone-hosted carbonates are consistent with, and indicative of, the low-pH conditions associated with pyrite oxidation reactions. Calcite- and gypsum-cemented fractures crosscut, and contain fragments of, the pyrite-pseudomorphic and -oxidation assemblages, proving that they postdate pyrite formation and its subsequent oxidation, and that pyrite oxidation was not a result of modern weathering reactions. In outcrop, some calcite- and gypsum-cemented fractures link with travertine deposits associated with the modern and recent CO2-rich fluids. The mineral assemblages observed here, and the paragenetic sequence that we have inferred, suggest that the fracture-associated bleaching patterns result from the fracture-fed movement of sulfur-bearing reducing fluids, with hydrogen sulfide the most likely bleaching agent. We conclude that bleaching adjacent to fractures is not genetically related to modern CO2-bearing fluids despite the spatial relationship. The bleaching was already present when the modern fluids utilized the same fracture-based fluid pathways. We suggest that the more widespread regional bleaching formed contemporaneously with the fracture bleaching and followed similar mechanisms. This study highlights the complexity of interpreting analogue sites and the importance of using field and petrographic observations to unravel textures and events that are juxtaposed spatially but not temporally.

Experimental fluid-mediated alteration of zircon under lower greenschist facies conditions

2020 ◽  
Vol 58 (2) ◽  
pp. 247-265
Author(s):  
Colter J. Kelly ◽  
Daniel E. Harlov ◽  
David A. Schneider ◽  
Simon E. Jackson ◽  
Renelle Dubosq
Keyword(s):  
Ion Exchange ◽  
Inductively Coupled Plasma ◽  
Earth Science ◽  
Science Research ◽  
Aqueous Fluid ◽  
Mapping Technique ◽  
Geological Time ◽  
Geological Time Scale ◽  
Chemically Modified ◽  
Geological Processes

ABSTRACT The use of zircon in the dating of geological processes and tectonic events has become a standard approach in many aspects of Earth science research. As a result, understanding how zircon interacts with aqueous fluids during metasomatism has become increasingly important. The alteration of natural zircon is driven primarily by coupled dissolution–reprecipitation or by ion-exchange with an aqueous fluid. In this study, whole and intact, euhedral light-brown zircon crystals (100–250 μm in length; 2 mg) from the Oligocene Fish Canyon Tuff (FCT) were experimentally reacted with an alkali-bearing reactive fluid and a REE + P source (0.5 mg CePO4 or 0.5 mg YPO4). Experiments were conducted in sealed Au metal capsules at 350 °C and 100 MPa for 182 days. During the experiment, the zircon became colorless, indicating annealing of the radiation damage in the crystal. Two-dimensional element maps of the outermost 3 μm of unpolished zircon crystal surfaces were produced using a grind of contiguous 7 μm analytical spots via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The chemical maps indicate that the surface of the zircon crystals from each experiment heterogeneously reacted with the fluid, such that the Ce and Y concentration of chemically modified areas increased (by an order of magnitude) in the CePO4-bearing and YPO4-bearing experiments, respectively, when compared with the chemical maps of unaltered zircon grain surfaces. Helium ion microscopy of polished crystals revealed discontinuous micron-scale altered domains at the crystal margin, consistent with the findings of the unpolished mapping technique. Interestingly, the Th and U concentration of the altered zircon grain surfaces were consistent with the unaltered zircon regardless of the experiment. Incorporation of REEs on the zircon grain surface likely occurred via the coupled substitution REE3+ + P5+ ↔ Zr4+ + Si4+. The results from these experiments imply that the surfaces of minimally metamict zircon can be chemically modified by alkali-bearing fluids via ion exchange under lower greenschist pressures and temperatures over relatively short time periods with respect to the geological time scale.

scholarly journals Differential Distribution Analysis and Region and Grade Regulation on Auto-Parts Weathering External Factors with Non-Uniform Thermal Environment

2020 ◽  
Vol 10 (15) ◽  
pp. 5116
Author(s):  
Zhiyong Deng ◽  
Fengchong Lan ◽  
Jiqing Chen
Keyword(s):  
Thermal Environment ◽  
External Factors ◽  
Space Distribution ◽  
Physical Parameters ◽  
Distribution Analysis ◽  
Differential Distribution ◽  
Time Space ◽  
Auto Parts ◽  
Numerical Calculation Method ◽  
Outdoor Weathering

It is difficult to comprehensively master and precisely regulate the external factors distribution of automobile weathering in non-uniform thermal environment as well as the consequent disequilibrium weathering problem, while exploring weather-resistant materials in uniform thermal environment. Thus, a numerical calculation method for the weathering external factors is proposed, on the basis of annual experimental study on the outdoor weathering inconsistencies of auto-parts. The time–space distribution characteristics and day–night variation rules of the external factors are studied, and the disequilibrium weathering mechanism among parts is revealed from the perspective of non-uniform distribution of external factors. The laws of automotive physical parameters, orientations and locations, as well as their influences on external factors distribution are analyzed in detail, and hereby the targeted schemes to effectively reduce the local external factor intensity and the thermal gradient between parts are investigated. The method can be used to rapidly predict weathering external factors distribution of vehicle exposed to outdoor in any direction during day and night, so as to provide auto-parts with differentiated test schemes in accelerated tests and IP/DP box tests, and it also contributes to present some pertinence guidance for the accurate regulation of automobile disequilibrium weathering on regions at different levels.

Sign in / Sign up

Export Citation Format

Share Document