Applications and limitations of thermobarometry in migmatites and granulites using as an example rocks of the Araçuaí Orogen in southern Bahia, including a discussion on the tectonic meaning of the current results

In southern Bahia, there are outcrops of migmatites and granulites in the Jequitinhonha Complex, which is part of the northern portion of the Araçuaí Orogen. Migmatites (garnet-cordierite diatexite) dominate the metamorphic rocks and host lenses and layers of felsic garnet granulite. The conditions of temperature and pressure of metamorphism were calculated using conventional thermobarometry and the software THERMOCALC. Values around 850 °C and 7 kbar were obtained with THERMOCALC. The calculations for the garnet-cordierite diatexite were made considering aH2O equal to 1, but the best results of calculations for the granulites are obtained with aH2O values of 0.3. Pressure values obtained with GAPES resulted in consistent values with THERMOCALC, but the pair garnet-orthopyroxene always produces low values for temperature and high ones for pressure. The results are consistent with the presence of the pair garnet and cordierite in diatexite and orthopyroxene in felsic granulite. From the tectonic point of view, the setting in which metamorphism of these rocks occurred requires high heat flow with a thermal anomaly in mid continental crust, as indicated by values of 7 kbar. Recent studies have favored the closure of a back-arc basin for this tectonic setting, but it does not solve the problem that the time span between metamorphic peak and the end of granite intrusions, involving large bodies of charnockite, is more than 80 million years. The model of tectonic switching is suggested here as it can explain the maintenance of high temperatures for a more extended interval of time.

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Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/ggub.v181.5114 ◽

1999 ◽

pp. 65-78

Author(s):

Henrik Rasmussen ◽

Lars Frimodt Pedersen

Keyword(s):

Tectonic Setting ◽

Trace Element Geochemistry ◽

Element Geochemistry ◽

West Greenland ◽

North West ◽

North East ◽

Metavolcanic Rocks ◽

Arc Setting ◽

Area North ◽

Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

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Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

Atlantic Geology ◽

10.4138/atlgeol.2021.012 ◽

2021 ◽

Vol 57 ◽

pp. 239-273

Author(s):

Allan Ludman ◽

Christopher McFarlane ◽

Amber T.H. Whittaker

Keyword(s):

New Brunswick ◽

Subduction Zone ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Calc Alkaline ◽

East Central ◽

Arc Volcanism ◽

Middle Ordovician ◽

Volcanic Suite ◽

Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

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Growth of wedge-shaped plutons at the base of active half-grabens

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300001097 ◽

2004 ◽

Vol 95 (1-2) ◽

pp. 309-317 ◽

Cited By ~ 7

Author(s):

S. W. Richards ◽

W. J. Collins

Keyword(s):

High Temperature ◽

Structural Model ◽

Tectonic Setting ◽

Shear Bands ◽

Shaped Body ◽

The Core ◽

Lachlan Orogen ◽

Eastern Australia ◽

Back Arc ◽

East West

ABSTRACTCombined field and geophysical data show that plutons from the Bega Batholith are elongate, meridional, wedge-shaped bodies which intruded during a period of regional east–west extension in the Palaeozoic eastern Lachlan orogen, eastern Australia. Plutons within the core of the batholith have intruded coeval, syn-rift sediments and co-magmatic volcanics. The batholith is bound by high-temperature, dip-slip faults, and contains several major NE-trending transtensional faults which were active during batholith construction. In the central part of the batholith, the Kameruka pluton is an asymmetric, eastward-thickening, wedge-shaped body with the base exposed as the western contact, which is characterised by abundant, shallow-dipping schlieren migmatites which contain recumbent folds and extensional shear bands. A shallow (<30°), east-dipping, primary magmatic layering in the Kameruka pluton steepens progressively westward, where it becomes conformable to the east-dipping basal migmatites. The systematic steepening of the layering is comparable to sedimentary units formed during floor depression in syn-rift settings. The present authors suggest that the wedge-shaped plutons of the Bega Batholith are the deeper, plutonic expression of a hot, active rift. The batholith was fed and sustained by injection of magma through sub-vertical dykes. Displacement along syn-magmatic, NE-trending faults suggests up to 25 km of arc-perpendicular extension during batholith construction. The inferred tectonic setting for batholith emplacement is a continental back-arc, where modern half-extension rates of 20–40 mm yr−1 are not unusual, and are sufficient to emplace the entire batholith in ∼1 Ma. This structural model provides a mechanism for the emplacement of some wedge-shaped plutons and is one solution to the ‘room problem’ of batholith emplace

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New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2019-0140 ◽

2020 ◽

Vol 57 (7) ◽

pp. 840-854

Author(s):

Richard A. Volkert

Keyword(s):

Tectonic Setting ◽

Hanging Wall ◽

Sediment Source ◽

Slow Cooling ◽

Grenville Province ◽

Magmatic Arc ◽

Metamorphic History ◽

Arc Setting ◽

Appalachian Piedmont ◽

Back Arc

New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.

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Neoproterozoic hybrid forearc – MOR ophiolite belts in the northern Arabian-Nubian Shield: no evidence for back-arc tectonic setting

International Geology Review ◽

10.1080/00206814.2020.1836523 ◽

2020 ◽

pp. 1-13 ◽

Cited By ~ 1

Author(s):

Haytham Sehsah ◽

Ahmed M. Eldosouky

Keyword(s):

Tectonic Setting ◽

Nubian Shield ◽

Back Arc ◽

Arabian Nubian Shield

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Geochronology, geochemistry, and origin of plagiogranitic rocks and related granitic dikes in the Dar Gaz district, Kahnouj ophiolite complex, SE Iran: Analysis of their petrogenesis in a back-arc tectonic setting

Lithos ◽

10.1016/j.lithos.2020.105832 ◽

2020 ◽

pp. 105832

Author(s):

Majid Ghasemi Siani ◽

Behzad Mehrabi ◽

Franz Neubauer ◽

Shuyun Cao ◽

David R. Lentz

Keyword(s):

Tectonic Setting ◽

Ophiolite Complex ◽

Back Arc

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Applicability of Diamond-Coated Tools for Ball End Milling of Sintered Tungsten Carbide

International Journal of Automation Technology ◽

10.20965/ijat.2020.p0018 ◽

2020 ◽

Vol 14 (1) ◽

pp. 18-25

Author(s):

Haruhiko Suwa ◽

Soushi Sakamoto ◽

Masafumi Nagata ◽

Kazuhiro Tezuka ◽

Tetsuo Samukawa ◽

...

Keyword(s):

Surface Roughness ◽

Tungsten Carbide ◽

End Milling ◽

High Hardness ◽

High Heat ◽

Point Of View ◽

Cutting Conditions ◽

Cutting Condition ◽

Ball End Milling ◽

Sintered Tungsten

Sintered tungsten carbide which has high hardness and high heat resistance, has been widely used in molds and dies. Research on the development of a cutting technology for sintered tungsten carbide (sintered WC-Co alloy) has been pursued mainly with the use of a turning process. We focused on building an efficient milling method for sintered tungsten carbide by using diamond-coated ball end tools, and have investigated their basic properties under specific cutting conditions. This study extends our previous work by enhancing cutting distance in the milling of sintered tungsten carbide, especially that with a “fine” WC grain. The surface roughness of cut workpieces is evaluated from the point of view of the quality of surface roughness. A series of cutting experiments under different cutting conditions were carried out, and the possibility of deriving a suitable cutting condition for the ball end milling of sintered tungsten carbide is discussed.

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Geodynamic setting, crustal architecture, and VMS metallogeny of ca. 2720 Ma greenstone belt assemblages of the northern Wawa subprovince, Superior Province

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2014-0163 ◽

2015 ◽

Vol 52 (3) ◽

pp. 196-214 ◽

Cited By ~ 7

Author(s):

Robert W.D. Lodge ◽

Harold L. Gibson ◽

Greg M. Stott ◽

James M. Franklin ◽

George J. Hudak

Keyword(s):

Trace Element ◽

Greenstone Belt ◽

Tectonic Setting ◽

Geodynamic Setting ◽

Trace Element Geochemistry ◽

Superior Province ◽

Suprasubduction Zone ◽

Greenstone Belts ◽

Arc Setting ◽

Back Arc

The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, “hot” subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic Ni–Cu sulphide and relative gold endowment of this belt.

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COMPETITIVENESS AND EFFICIENCY FOR THE RUBBER TREE PRODUCTION SYSTEM IN SOUTHERN BAHIA (BRAZIL) THROUGH BY THE POLICY ANALYSIS MATRIX (PAM)

Revista Árvore ◽

10.1590/1806-90882018000600006 ◽

2018 ◽

Vol 42 (6) ◽

Author(s):

Adrielli Santos de Santana ◽

Naisy Silva Soares ◽

Cristian Arnecke Schröder

Keyword(s):

Policy Analysis ◽

Production System ◽

Rubber Tree ◽

Point Of View ◽

Strong Impact ◽

Product Price ◽

Profitability Analysis ◽

Southern Bahia ◽

Policy Analysis Matrix ◽

Tree Production

ABSTRACT The objective of this survey was to analyze the competitiveness and economic efficiency of the rubber tree (Hevea brasiliensis) production system in the southern of Bahia, through by the Policy Analysis Matrix (PAM). The analysis was divided into four categories: profitability analysis; efficiency analysis; protection analysis; and net transfer of policies. The results it possible to affirm that rubber tree production system is a profitable and competitive activity, in the long term, from a private and social point of view. However, the results point out that producers are penalized for the presence of political measures, which focus on product price and productive inputs. In the sensitivity analysis, it was observed that the indicators are sensitive to the fluctuations in the exchange rate and the social income, thus the changes in the price of natural rubber have a strong impact on determining the competitiveness of this productive system.

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