scholarly journals A preserved early Ediacaran magmatic arc at the northernmost portion of the Transversal Zone central subprovince of the Borborema Province, Northeastern South America

2016 ◽  
Vol 46 (4) ◽  
pp. 491-508 ◽  
Author(s):  
Benjamim Bley de Brito Neves ◽  
◽  
Edilton José dos Santos ◽  
Reinhardt Adolfo Fuck ◽  
Lauro César Montefalco Lira Santos ◽  
...  

ABSTRACT: Magmatic arcs are an essential part of crust-forming events in planet Earth evolution. The aim of this work was to describe an early Ediacaran magmatic arc (ca. 635-580 Ma) exposed in the northernmost portion of the Transversal Zone, central subprovince of Borborema Province, northeast Brazil. Our research took advantage of several syntheses by different authors, including theses and dissertations, carried out on magmatic rocks of the study area for the last 30 years. The ca. 750 km long and up to 140 km wide arc, trending ENE-WSW, is preserved to the south of the Patos Lineament, between 35º15' and 42º30'W and 7º15' and 8ºS. About 90 different stocks and batholiths of I-type granitic rocks were mapped along this orogenic zone, preferentially intruding low-grade schists of the Cryogenian-Ediacaran Piancó-Alto Brígida (SPAB) belt. Three igneous supersuites are recognized: a) epidote-bearing granodiorites and tonalites ("Conceição" type); b) high-K calc-alkaline granites ("Itaporanga" type); c) biotite granodiorites of trondhjemite affinity ("Serrita" type). A fourth group of peralkalic and shoshonitic rocks occurs to the south of the previous ones, reflecting special tectonic conditions. NNE-SSW trending Paleoproterozoic fold belts, surrounding Archean nuclei, characterize the continental part of the northern lower plate. The oceanic fraction of this lower plate was recycled by subduction and scarce remnants of which may be seen either within the enclosing low-grade schists or as xenoliths within the arc intrusions. The upper continental plate presents WSW-ENE structural trends and is composed of Neoproterozoic fold belts and Paleoproterozoic reworked basement inliers. Available data bear clear evidence of an Ediacaran magmatic arc built at the northern portion of the Transversal Zone in the Borborema Province, northeast Brazil.

2016 ◽  
Vol 6 (4) ◽  
pp. 5-35 ◽  
Author(s):  
Alejandro Silva Arias ◽  
Liliana Andrea Paez Acuña ◽  
Daniel Rincón Martínez ◽  
Javier Alfonso Tamara Guevara ◽  
Pedro David Gomez Gutierrez ◽  
...  

1991 ◽  
Vol 28 (12) ◽  
pp. 1982-1991 ◽  
Author(s):  
E. D. Ghent ◽  
J. Nicholls ◽  
P. S. Simony ◽  
J. H. Sevigny ◽  
M. Z. Stout

Hornblende geobarometry has been applied to granitic rocks of the Middle Jurassic Nelson Batholith, British Columbia, locally containing magmatic epidote. Geobarometry suggests equilibration pressures of less than 4.5 kbar (1 kbar = 0.1 GPa) in the northern part of the batholith, which lacks magmatic epidote. This part of the pluton shows clear magmatic intrusive relations, and the contact metamorphic rocks contain andalusite, which suggests that the equilibration and emplacement pressures are compatible.In the southern part of the batholith, granitic rocks containing magmatic epidote have equilibration pressures of 4.8–6.4 kbar. South and west of Nelson, there is a distinct contrast in pressure between the pluton and the country rock. Both the contact metamorphic rocks and the low-grade regional metamorphic rocks suggest pressures in the 2–3 kbar range.The pressure difference of about 2 kbar across the southwestern contact and the variation in pressure within the batholith can be explained by a model combining a late postequilibration upsurge (diapiric) of a deeper part of the pluton in the south, with a much later rotation and tilting of the batholith, associated with Eocene motion on the upper listric portion of the Slocan Lake Fault. The late diapiric (?) upsurge may account for the pressure contrast across the southwestern contact.


2019 ◽  
Vol 21 (2) ◽  
pp. 81-93
Author(s):  
Abner Monteiro Nunes Cordeiro ◽  
Islane Pinto de Carvalho ◽  
Frederico De Holanda Bastos ◽  
Danielle Lopes de Sousa Lima

A estrutura litológica de um determinado relevo tem papel fundamental na sua dinâmica e evolução, tendo em vista as propriedades geomorfológicas das rochas. A Serra de Uruburetama é um dos muitos maciços residuais que pontuam o semiárido cearense, cuja constituição litológica tem relação direta com a gênese e evolução de macroformas e microformas graníticas encontradas nesse relevo serrano. Inserido no Domínio Ceará Central da Província Borborema, na porção norte do estado do Ceará, esse maciço é composto, predominantemente por rochas granitoides, sendo imprescindível o conhecimento da composição litológica para compreensão da sua evolução geomorfológica. O presente artigo tem como objetivo expor as principais litologias encontradas na área de estudo, suas propriedades geomorfológicas e as formas de relevo associadas. Para tanto, foi realizado levantamento de literatura referente às propriedades geomorfológicas das rochas graníticas, assim como do quadro geológico e geomorfológico do Maciço de Uruburetama a fim de compreender sua composição e evolução, além de levantamentos cartográficos e utilização de técnicas de geoprocessamento. O Maciço de Uruburetama apresenta diferentes feições graníticas com formas e dimensões variadas, cuja formação, desenvolvimento e exposição dessas feições se devem ao controle estrutural imposto por litologias graníticas e suas descontinuidades estruturais, bem como pela influência de condições paleoclimáticas e pelos processos de erosão diferencial, a que foram submetidas.Palavras-chave: Evolução geomorfológica; Propriedades geomorfológicas das rochas; Formas graníticas. ABSTRACTThe lithological structure of a given landform plays a fundamental role in its dynamics and evolution, considering the geomorphological properties of the rocks. The Mountain of Uruburetama is one of the many residual masses that punctuate the semi - arid region of Ceará, whose lithological constitution is directly related to the genesis and evolution of macroforms and granitic microforms found in this mountain relief.  Located in the Central Ceará Domain of the Borborema Province, in the northern portion of the state of Ceará, this massif is composed predominantly of granitoid rocks, being essential the knowledge of the lithological composition to understand its geomorphological evolution. The present article has as objective to expose the main lithologies found in the study area, its geomorphological properties and the associated relief forms. For that, a literature survey was carried out regarding the geomorphological properties of the granitic rocks, as well as the geological and geomorphological framework of the Uruburetama Massif in order to understand its composition and evolution, as well as cartographic surveys and the use of geoprocessing techniques. The Uruburetama Massif presents different granitic features with different shapes and dimensions, whose formation, development and exposition of these features are due to the structural control imposed by granite lithologies and their structural discontinuities, as well as by the influence of paleoclimatic conditions and the processes of differential erosion, to which they were submitted.Keywords: Geomorphological evolution; Geomorphological properties of rocks; Granite shapes. RESUMENLa estructura litológica de un determinado relieve tiene papel fundamental en su dinámica y evolución, teniendo en vista las propiedades geomorfológicas de las rocas. La Sierra de Uruburetama es uno de los muchos macizos residuales que puntúan el semiárido cearense, cuya constitución litológica tiene relación directa con la génesis y evolución de macroformas y microformas graníticas encontradas en ese relieve Serrano. Insertado en el Dominio Ceará Central de la Provincia Borborema, en la parte norte del estado de Ceará, este macizo está compuesto, predominantemente por rocas granitoides, es imprescindible el conocimiento de la composición litológica para comprender su evolución geomorfológica. El presente artículo tiene como objetivo exponer las principales litologías encontradas en el área de estudio, sus propiedades geomorfológicas y las formas de relieve asociadas. Para ello, se realizó estudio de literatura referente a las propiedades geomorfológicas de las rocas graníticas, así como del cuadro geológico y geomorfológico del macizo de Uruburetama a fin de comprender su composición y evolución, además de encuestas cartográficas y el uso de técnicas de geoprocesamiento. El macizo de Uruburetama presenta diferentes facciones graníticas con formas y dimensiones variadas, cuya formación, desarrollo y exposición de estos rasgos se deben al control estructural impuesto por litologias graníticas y sus discontinuidades estructurales, así como la influencia de las condiciones paleoclimáticas y de los procesos de erosión diferencial a los que han sido sometidas.Palabras clave: Evolución geomorfológica; Propiedades geomorfológicas de las rocas; Formas graníticas.


2021 ◽  
pp. 1-24
Author(s):  
Petros Koutsovitis ◽  
Konstantinos Soukis ◽  
Panagiotis Voudouris ◽  
Stylianos Lozios ◽  
Theodoros Ntaflos ◽  
...  

2001 ◽  
Vol 173 (1-3) ◽  
pp. 107-123 ◽  
Author(s):  
Hartmut Beurlen ◽  
Marcelo R.R. da Silva ◽  
Claudio de Castro

2021 ◽  

Mesozoic plate convergence in SE Sundaland has been a source of debate for decades. A determination of plate convergence boundaries and timing have been explained in many publications, but not all boundaries were associated with magmatism. Through integration of both plate configurations and magmatic deposits, the basement can be accurately characterized over time and areal extents. This paper will discuss Cretaceous subductions and magmatic arc trends in SE Sundaland area with additional evidence found in JS-1 Ridge. At least three subduction trends are captured during the Mesozoic in the study area: 1) Early Jurassic – Early Cretaceous trend of Meratus, 2) Early Cretaceous trend of Bantimala and 3) Late Cretaceous trend in the southernmost study area. The Early Jurassic – Early Cretaceous subduction occurred along the South and East boundary of Sundaland (SW Borneo terrane) and passes through the Meratus area. The Early Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo and Paternoster terranes) and pass through the Bantimala area. The Late Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo, Paternoster and SE Java – South Sulawesi terranes), but is slightly shifted to the South approaching the Oligocene – Recent subduction zone. Magmatic arc trends can also be generally grouped into three periods, with each period corresponds to the subduction processes at the time. The first magmatic arc (Early Jurassic – Early Cretaceous) is present in core of SW Borneo terrane and partly produces the Schwaner Magmatism. The second Cretaceous magmatic arc (Early Cretaceous) trend is present in the SW Borneo terrane but is slightly shifted southeastward It is responsible for magmatism in North Java offshore, northern JS-1 Ridge and Meratus areas. The third magmatic arc trend is formed by Late Cretaceous volcanic rocks in Luk Ulo, the southern JS-1 Ridge and the eastern Makassar Strait areas. These all occur during the same time within the Cretaceous magmatic arc. Though a mélange rock sample has not been found in JS-1 Ridge area, there is evidence of an accretionary prism in the area as evidenced by the geometry observed on a new 3D seismic dataset. Based on the structural trend of Meratus (NNE-SSW) coupled with the regional plate boundary understanding, this suggests that both Meratus & JS-1 Ridge are part of the same suture zone between SW Borneo and Paternoster terranes. The gradual age transition observed in the JS-1 Ridge area suggests a southward shift of the magmatic arc during Early Cretaceous to Late Cretaceous times.


1996 ◽  
Vol 133 (06) ◽  
pp. 739 ◽  
Author(s):  
R. E. Bevins ◽  
S. C. White ◽  
D. Robinson

2021 ◽  
Author(s):  
Mark Emmanuel Bishop ◽  
Wilson Lalla ◽  
Xavier Ravi Moonan

Abstract Lease Operatorship block WD-8, lies within the Forest Reserve oilfield. Forest Reserve is known for having the ENE-WSW trending, south easterly verging Forest Reserve anticline which plunges into NW-SE trending Los Bajos Fault. Regionally to the south of the Forest Reserve anticline lies the south westerly plunging Siparia syncline and to the north of the Forest Reserve anticline is the Morne L′ Enfer syncline. WD-8 is situated on the northern flank of the Forest Reserve anticline with the axis of the anticline occurring within the southern part of the block. Prior to 2018, TETL last drilled within the WD-8 block in the year 2014. Drilling within the WD-8 block pre-2018 was mainly in the southern portion of the block. The year 2018 saw TETL drill five wells in the northern part of the WD-8 block. The results from these wells prompted an evaluation within the Northern portion of the WD-8 block to determine the structure and extent of the Lower Cruse and Navet reservoirs. Field wide mapping post 2018 drills within the block highlighted the sand trend at the Cruse level is in a WSW-ENE direction and that these sands in northern WD-8 are very narrow with maximum widths ranging between 100 ft – 150 ft. Additionally, it showed that by using a smaller well spacing, wells would encounter different producing sand bodies not seen in adjacent wells. Differences in the sand character between wells in the Southern part of the block to wells in the northern part of the block at the Lower Cruse level were also seen. The Lower Cruse section in the southern part of the WD-8 block tends to have thick stacked slope channel sand deposits, while the northern part of WD-8 has relatively thin stacked slope/base of slope channel deposits. Structurally, the presence of an ENE-WSW fault which separates the southern wells from the northern wells was also revealed. Abnormal stratigraphy was also found in Northern WD-8 where the Eocene Navet formation was encountered below the Late Miocene Lower Cruse formation. Two (2) wells in the northern portion of the block found the Navet formation resistive with only one well testing this reservoir. This then presents a new under exploited target reservoir with the block. Mapping of the Navet Formation indicates that this reservoir trends in a WSW-ENE direction. This updated geological model for the WD-8 block resulted in six infill developmental wells being identified to further exploit the remaining reserves within the Lower Cruse and Navet Formations in the WD-8 block.


2021 ◽  
Author(s):  
Wanli Gao ◽  
Zongxiu Wang

<p><strong><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.67d6c7216eff55356050161/sdaolpUECMynit/12UGE&app=m&a=0&c=5572aca4b392eef83f52919e1be673e9&ct=x&pn=gepj.elif&d=1" alt="">Abstract</strong>:The Zongwulong tectonic belt (ZTB) is located between the northern Qaidam tectonic belt and the south Qilian orogenic belt and contains Late Paleozoic and Early- Middle Triassic strata. Structural features and geochronology of Zongwulong ductile shear zone have key implications for the tectonic property of the ZTB. This study integrated field structure, microscopic structure and <sup>40</sup>Ar/<sup>39</sup>Ar laser probe analysis. The shear zone strikes ~NEE-SWW and dips at a high angle, with a NWW-SEE trending and WE stretching lineation, indicating the shear zone as a thrust- slip shear ductile shear. The asymmetric folds, rotating porphyroclast,structural lens and crenulation cleavage can be seen in the field. Mica fish, S − C fabrics, σ type quartz porphyroclastic and quartz wire drawing structure can also be observed under microscope, indicating that the strike- slip- related ductile deformation and mylonitization occurred under low- grade greenschist facies conditions at temperatures of <em>300° C − 400° C</em>.  The highly deformed<br>mylonite schist yielded <sup>40</sup>Ar/<sup>39</sup>Ar ages <em>(245.8±1.7)Ma </em>and <em>(238.5±2.6)</em>Ma for muscovite and biotite, respectively, indicating that the shear deformation occurred during the Early- Mid Triassic. Combined with comprehensive analysis of regional geology and petrology, the authors hold that the age of ductile shear deformation represents the time of Triassic orogeny in the ZTB. The oroginic activity was probably related to the oblique collision between the South Qilian block and the Oulongbuluke block after the closure of the northermost Paleo-Tethys ocean.</p>


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