Sedimentation and Tectonics of the Khomas Hochland Accretionary Prism, along a Late Proterozoic Continental Margin, Damara Sequence, Central Namibia

Author(s):  
P. A. Kukla ◽  
I. G. Stanistreet
2015 ◽  
Vol 7 (2) ◽  
pp. 1827-1876 ◽  
Author(s):  
J. Escuder-Viruete ◽  
A. Suárez-Rodríguez ◽  
J. Gabites ◽  
A. Pérez-Estaún

Abstract. In northern Hispaniola, the Imbert Formation (Fm) has been interpreted as an orogenic "mélange" originally deposited as trench-fill sediments, an accretionary (subduction) complex formed above a SW-dipping subduction zone, or the sedimentary result of the early oblique collision of the Caribbean plate with the Bahama Platform in the middle Eocene. However, new stratigraphical, structural, geochemical and geochronological data from northern Hispaniola indicate that the Imbert Fm constitutes a coarsening-upward stratigraphic sequence that records the transition of the sedimentation from a pre-collisional forearc to a syn-collisional piggy-back basin. This piggy-back basin was transported on top of the Puerto Plata ophiolitic complex slab and structurally underlying accreted units of the Rio San Juan complex, as it was emplaced onto the North America continental margin units. The Imbert Fm unconformably overlies different structural levels of the Caribbean subduction-accretionary prism, including a supra-subduction zone ophiolite, and consists of three laterally discontinuous units that record the exhumation of the underlying basement. The distal turbiditic lower unit includes the latest volcanic activity of the Caribbean island arc; the more proximal turbiditic intermediate unit is moderately affected by syn-sedimentary faulting; and the upper unit is a (caotic) olistostromic unit, composed of serpentinite-rich polymictic breccias, conglomerates and sandstones, strongly deformed by syn-sedimentary faulting, slumping and sliding processes. The Imbert Fm is followed by subsidence and turbiditic deposition of the overlying El Mamey Group. The 40Ar / 39Ar plagioclase plateau ages obtained in gabbroic rocks from the Puerto Plata ophiolitic complex indicate its exhumation at ∼ 45–40 Ma (lower-to-middle Eocene), contemporaneously to the sedimentation of the overlying Imbert Fm. These cooling ages imply the uplift to the surface and submarine erosion of the complex to be the source of the ophiolitic fragments in the Imbert Fm, during of shortly after the emplacement of the intra-oceanic Caribbean island-arc onto the continental margin.


1984 ◽  
Vol 121 (6) ◽  
pp. 599-614 ◽  
Author(s):  
Wang Hongzhen ◽  
Qiao Xiufu

AbstractThe time span of the Proterozoic is taken as from 2600 to 600 Ma with subdivision boundaries at 1850 and 1050 Ma respectively, as 2600 Ma seems more appropriate for the initial Proterozoic in China, Siberia and parts of Gondwanaland, and 600 Ma is an inferred age of the Precambrian–Cambrian boundary based on recent study of the Yangtze Gorge section. The Proterozoic of China includes the Lower Proterozoic Wutaian and Hutuo-an, the Middle Proterozoic Changchengian and Jixianian and the Upper Proterozoic Qingbaikou-an and Sinian.Based mainly on tectono-sedimentary types and associations, seven stratigraphic super-regions are recognized in the Proterozoic of China and stratigraphic successions of various representative regions are shown in two tables, one for the Sinian and another for the Pre-Sinian Proterozoic. Palaeogeographic outline of the main super-regions and chronometric limit of the principal stratigraphic units are briefly discussed. Three types of stable Sinian successions are distinguished, the Yangtze type, the Quruktagh type and the Jiaoliao type, which are correlated mainly on the basis of tillite horizons and of sabelliditids and the Ediacara type of fossils. Semi-stable and mobile types of Sinian deposits in Southeast China are also briefly mentioned.The Proterozoic tectonic units of China and the nature of their boundaries are shown on a sketch map showing basement structures. Crustal sectors of continental nature are designated as continental tectonic domains, while broad and complicated crustal sectors of mainly transitional and partly oceanic nature may be called continental margin tectonic domains. The boundaries between these domains are usually the principal crustal consumption zones. On this basis, three continental domains, the North China, the South China and the Southern (Gondwana), and two continental margin domains, the Northern (Siberian–Mongolian) and the East China, are distinguished. Platforms, continental nuclei, massifs and uplifts are used to denote subdivisions within the tectonic domains. The development of aulacogens is an outstanding feature in the continental domains, especially in the Middle Proterozoic. Aulacogens may be classified into an intra-platform type and a platform margin type. Early Proterozoic aulacogens are usually brachy-axial and intermittent, and show conspicuous deformation at closure, much like a geosyncline. Thirteen aulacogens of different types are shown on the sketch map.The boundary nature of continental domains is analysed in terms of island arcs and marginal seas, and also of emplacement of granite rocks in border parts. The North China Domain was basically consolidated at around 1850 Ma and has a passive northern margin stretching from Nei Mongol to Central Tianshan, but the southern margin was active and was twice subducted by the Qinling marine realm at 1700 and 1000 Ma approximately. The Yangtze Platform was not completely consolidated until 1050 Ma BP but has a core older than 1850 Ma. A broad continental margin terrain had developed in the Jiangnan region and farther to the southeast in the Middle and Late Proterozoic. At least two island arc belts with interarc basins, an inner Fanjingshan and an outer Sibao, may be discerned in the Middle Proterozoic, and a Late Proterozoic island arc zone over 1000 km in length was developed along the southern margin of the Jiangnan Uplift, represented by the Banxi Group and equivalent strata. This kind of broad complicated continental margin tract which has a long development history may be called the open type or the West Pacific type.


2020 ◽  
Vol 39 (8) ◽  
pp. 543-550
Author(s):  
Roberto Fainstein ◽  
Juvêncio De Deus Correia do Rosário ◽  
Helio Casimiro Guterres ◽  
Rui Pena dos Reis ◽  
Luis Teófilo da Costa

Regional geophysics research provides for prospect assessment of Timor-Leste, part of the Southeast Asia Archipelago in a region embracing the Banda Arc, Timor Island, and the northwest Australia Gondwana continental margin edge. Timor Island is a microcontinent with several distinct tectonic provinces that developed initially by rifting and drifting away from the Australian Plate. A compressive convergence began in the Miocene whereby the continental edge of the large craton collided with the microcontinent, forming a subduction zone under the island. The bulk of Timor Island consists of a complex mélange of Tertiary, Cretaceous, Jurassic, Triassic, Permian, and volcanic features over a basal Gondwana craton. Toward the north, the offshore consists of a Tertiary minibasin facing the Banda Arc Archipelago, with volcanics interspersed onshore with the basal Gondwana pre-Permian. A prominent central overthrust nappe of Jurassic and younger layers makes up the mountains of Timor-Leste, terminating south against an accretionary wedge formed by this ongoing collision of Timor and Australia. The northern coast of the island is part of the Indonesian back arc, whereas the southern littoral onshore plus shallow waters are part of the accretionary prism. Deepwater provinces embrace the Timor Trough and the slope of the Australian continental margin being the most prospective region of Timor-Leste. Overall crust and mantle tectonic structuring of Timor-Leste is interpreted from seismic and potential field data, focusing mostly on its southern offshore geology where hydrocarbon prospectivity has been established with interpretation of regional seismic data and analyses of gravity, magnetic, and earthquake data. Well data tied to seismic provides focal points for stratigraphic correlation. Although all the known producing hydrocarbon reservoirs of the offshore are Jurassic sands, interpretation of Permian and Triassic stratigraphy provides knowledge for future prospect drilling risk assessment, both onshore and offshore.


2020 ◽  
Author(s):  
Joaquina Alvarez-Marrón ◽  
Dennis Brown ◽  
Juan Alcalde ◽  
Ignacio Marzán ◽  
Hao Kuo-Chen

<p>The region of Taiwan is undergoing active, oblique arc-continent colision between the Luzon Arc on the Philippine Sea Plate and the continental margin of Eurasia. The Fold-and-Thrust Belt (FTB) in Taiwan passes southwards into a submarine accretionary wedge at the Manila subduction zone. The aim of this contribution is to examine how an on land FTB changes into a marine accretionary prism in the context of an oblique arc-continent collision. The Miocene pre-orogenic sediments of the continental margin are widespread in the FTB ca. 23° latitude while the offshore wedge is built up dominantly by Pliocene to recent syn-orogenic sediments. In the transition area from the marine accretionary wedge ca. 21° latitude to the on land FTB, the thrust wedge is climbing up the slope of the Eurasian continental margin. The deformation front is at sea floor depth of ca. 4 km in the south to less than 1 km as it reaches the coast line. Here we use the island surface geology, marine reflection seismic profiles, and seismic tomography models to construct contour maps of the basal thrust and the depth to the Moho across a transition area from near 23° to near 21° latitude. In this zone, the deformation front draws a convex curvature as the wedge widens from ca. 50 in the north and south, to more than 130 km near 22° latitude. The basal thrust surface shows a scoop shape as its dip changes from southeast near the coast line to east southward. The basal thrust reaches over 7 km deep beneath the rear of the FTB before ramping into de basement and merging into the Chaochou fault at 10 km depth. Offshore, it shows a gentler dip from 7 km to c. 10 km depth before getting steeper towards the east below the Hengchung Ridge. The basal cuts laterally along-strike through the margin’s sedimentary cover to incorporate thicker Miocene pre-orogenic sediments onto its hanging wall as it passes from the offshore wedge to the on land FTB.</p><p>In the offshore area, the Moho (we use a Vp proxy of 7.5 km/s extracted from the seismic tomography) shallows southeastward, from near 25 km depth below the shelf slope break to less than 17 km depth below the offshore wedge near 21.5° latitude before it starts to deep east towards beneath the Taiwan coast. The Moho dips northeast from near 25 km depth below the coast near Kaohsiung, to near 40 depth below the rear of the FTB at 23.5°, latitude. This complex morphology of the Moho may be related to the changes in crustal thickness and the obliquity of the collision. Because of this, crustal thickening is less pronounced beneath southern Taiwan where the thinner part of the margin is colliding with the arc.</p><p>This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency from the Ministry of Science Innovation and Universities of Spain.</p>


1997 ◽  
Vol 34 (8) ◽  
pp. 1059-1071 ◽  
Author(s):  
Yan Ducharme ◽  
Ross K. Stevenson ◽  
Nuno Machado

The Lacorne Block in the Southern Volcanic Zone of the Abitibi Subprovince is composed of interleaved metavolcanic and metasedimentary rocks that are intruded by syn- to posttectonic diorites, granodiorites, and granites. These rocks form the Lacorne, Lamotte, and Preissac plutons, which can be divided into an early suite of dioritic–granodioritic rocks and a later suite of S-type, leucocratic granites with an estimated age of 2640 Ma. This study presents Sm–Nd data and U–Pb monazite and titanite ages for the late leucocratic granites of the Preissac and Lamotte plutons. A biotite–muscovite monzogranitic phase of the Lamotte pluton is dated at 2647 ± 2 Ma, but similar phases of the Preissac pluton are dated at 2681–2660 Ma. These ages extend the period of leucogranitic plutonism for this area to 40 Ma and suggest that the age of collision of the Abitibi and the Pontiac subprovinces occurred before 2685 Ma. The εNd values for the leucogranites range from −1 to +3 and suggest an origin largely through melting of sediments having a juvenile isotopic signature (i.e., a short crustal residence time). Possible sources of the leucogranites include metasedimentary rocks of the Pontiac Subprovince, the Lacorne Block, and the Southern Abitibi Volcanic Zone, but the εNd values of the granites are most consistent with melting of metasediments of the Southern Volcanic Zone. We suggest that sediments of the Southern Volcanic Zone formed an accretionary prism along the southern continental margin of the Abitibi before collision with the Pontiac Subprovince. This prism was subsequently trapped between the two colliding margins, subducted, and partially melted to produce the Lamotte, Preissac, and Lacorne leucogranites.


2012 ◽  
Vol 52 (2) ◽  
pp. 704
Author(s):  
Anand Tripathi ◽  
Will Jones ◽  
Adrian Williams

The interpretation of recently acquired regional-deep, 2D seismic data across the Timor/Tanimbar Trough has provided a new insight into the structure of this continent/arc collision zone. This data is mostly recorded to 10–12 seconds with an 8 km dual sensor streamer, providing increased resolution and improved penetration compared with vintage data, particularly in the deeper part of the section. A major improvement in the new data is the imaging of the Australian continental margin succession continuously from the Australian side of the Timor-Tanimbar Trough for a distance of a few tens of km underneath the accretionary prism on the northwest side of the trough. Structures observed in the accretionary prism itself include fold and thrust belts, imbricate thrusts and extensional half grabens. The detachment surface at its base may provide a regional seal for traps involving Jurassic and Triassic reservoirs in underlying thrusts for which there is some evidence on the seismic data. The improved visibility of the Mesozoic succession below the accretionary prism allows possible Jurassic source rocks to be followed to the northwest below a growing overburden to a depth at which maturity may be expected. There is also a graben, probably including a greater Jurassic thickness, under the Timor Trough.


2003 ◽  
Vol 40 (2) ◽  
pp. 269-284 ◽  
Author(s):  
Peter J Thompson ◽  
Thelma B Thompson

This paper presents evidence for an early Taconian, west-directed fault in northern Vermont, the Prospect Rock thrust, which represents the trace of the contact between the Taconian oceanic accretionary prism (Dunnage Zone) and less allochthonous, continental margin rocks (Humber Zone). Mapping at 1 : 24 000 over the last decade has led to reassessment of units within the Camels Hump Group, resulting in newly defined lithotectonic packages: the Green Mountain slice and the Prospect Rock slice. Rocks in these slices may be of similar age, but those in the Green Mountain slice were originally deposited as more proximal sediments and remained on the Humber side of the sub duction zone, whereas those in the Prospect Rock slice were transferred by underplating to the accretionary prism. Both slices contain ultramafics. Motion on the Prospect Rock thrust (D1) preceded Taconian garnet-grade metamorphism and subsequent east-directed back-folding. However, D1 structures were diachronous across the orogen. Late Taconian (D2) structures record a change from east-verging back-folds in northern Vermont and southern Quebec to west-verging folds farther south. The Prospect Rock thrust does not correspond exactly to Cameron's line nor to the Baie Verte – Brompton line as originally defined. However, our understanding of the geometry of the Prospect Rock thrust demonstrates that the Dunnage Zone extends farther west than previously recognized and may also explain features farther to the east.


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