scholarly journals Tectonothermal ordovician evolution of the western margin of the Famatinian magmatic arc: metamorphism of the mafic and ultramafic rocks of Sierra de la Huerta -Las Imanas (Pampean Ranges, Argentina)

2010 ◽  
Vol 33 (2) ◽  
pp. 277
Author(s):  
Juan A. Murra ◽  
Edgardo G. Baldo
Keyword(s):  
Ultramafic Rocks ◽  
Compositional Variation ◽  
Sierras Pampeanas ◽  
Middle Ordovician ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
Erosion Rates ◽  
Continental Magmatic Arc ◽  
Uplift And Erosion ◽  
East West

An important magmatic and tectonometamorphic activity of Early and Middle Ordovician age is registered in the pre-Andean basement of the Sierras Pampeanas of Argentina. These were linked to the development of a continental magmatic arc during the Famatinian Orogeny, resulting from the approach and attachment of an alleged exotic terrane (the Precordillera Terrane), to the south western Gondwana's margin (present coordinates). A suit of meta-mafic and ultramafic rocks are exposed in the Sierras de La Huerta and Las Imanas, at the western limit of the famatinian orogen. Metaperidotites (Ol-Opx-Cpx-Am-Spl), coronitic metapyroxenites (Opx-Cpx-Spl-Am-Pl), metaquartz-norites (Opx-Pl-Am-Qtz-Bt±Grt) and metadiorites (Pl-Am-Qtz-Bt-Ep) are associated with metasedimentary rocks (marbles, gneisses and migmatites with Sil+Kfs+Grt) that reached the peak and post-peak conditions of metamorphism at middle Ordovician time. The meta-mafic rocks record a first high-grade metamorphic event (M1-730ºC and 8.4±0.5 kbar) and a second lower pressure event (M2, 720ºC and 4.5 kbar) with Cum+Hbl+Mag in a coronitic assemblage. The meta-ultramafic rocks also record the two metamorphic events, but only for the second one it was possible to calculate the P-T conditions. At latitude 32º30'S, the Famatinian magmatic arc shows a systematic compositional variation normal to its trend, i.e. in an east-west direction, which could be related to present erosion levels. In this context, the mafic and ultramafic units of Sierras de La Huerta and Las Imanas, probably represent the deepest levels of the magmatic arc which is consistent with the position that they show marginal to the orogenic belt, i.e., where the uplift and erosion rates were larger.

scholarly journals Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

Geosphere ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1225-1248
Author(s):  
Hannah J. Blatchford ◽  
Keith A. Klepeis ◽  
Joshua J. Schwartz ◽  
Richard Jongens ◽  
Rose E. Turnbull ◽  
...  
Keyword(s):  
New Zealand ◽  
Thermal Structure ◽  
Shear Zones ◽  
Arc Magmatism ◽  
Magmatic Arc ◽  
Continental Arcs ◽  
Metasedimentary Rocks ◽  
Spatio Temporal ◽  
Continental Magmatic Arc ◽  
Lower Crustal

Abstract Recovering the time-evolving relationship between arc magmatism and deformation, and the influence of anisotropies (inherited foliations, crustal-scale features, and thermal gradients), is critical for interpreting the location, timing, and geometry of transpressional structures in continental arcs. We investigated these themes of magma-deformation interactions and preexisting anisotropies within a middle- and lower-crustal section of Cretaceous arc crust coinciding with a Paleozoic boundary in central Fiordland, New Zealand. We present new structural mapping and results of Zr-in-titanite thermometry and U-Pb zircon and titanite geochronology from an Early Cretaceous batholith and its host rock. The data reveal how the expression of transpression in the middle and lower crust of a continental magmatic arc evolved during emplacement and crystallization of the ∼2300 km2 lower-crustal Western Fiordland Orthogneiss (WFO) batholith. Two structures within Fiordland’s architecture of transpressional shear zones are identified. The gently dipping Misty shear zone records syn-magmatic oblique-sinistral thrust motion between ca. 123 and ca. 118 Ma, along the lower-crustal WFO Misty Pluton margin. The subhorizontal South Adams Burn thrust records mid-crustal arc-normal shortening between ca. 114 and ca. 111 Ma. Both structures are localized within and reactivate a recently described >10 km-wide Paleozoic crustal boundary, and show that deformation migrated upwards between ca. 118 and ca. 114 Ma. WFO emplacement and crystallization (mainly 118–115 Ma) coincided with elevated (>750 °C) middle- and lower-crustal Zr-in-titanite temperatures and the onset of mid-crustal cooling at 5.9 ± 2.0 °C Ma−1 between ca. 118 and ca. 95 Ma. We suggest that reduced strength contrasts across lower-crustal pluton margins during crystallization caused deformation to migrate upwards into thermally weakened rocks of the mid-crust. The migration was accompanied by partitioning of deformation into domains of arc-normal shortening in Paleozoic metasedimentary rocks and domains that combined shortening and strike-slip deformation in crustal-scale subvertical, transpressional shear zones previously documented in Fiordland. U-Pb titanite dates indicate Carboniferous–Cretaceous (re)crystallization, consistent with reactivation of the inherited boundary. Our results show that spatio-temporal patterns of transpression are influenced by magma emplacement and crystallization and by the thermal structure of a reactivated boundary.

Evolution of regional metamorphism during back-arc stretching and subsequent crustal shortening in the 1.9 Ga Wopmay Orogen, Canada

1987 ◽  
Vol 321 (1557) ◽  
pp. 199-218 ◽  
Keyword(s):  
Regional Metamorphism ◽  
Thermal Relaxation ◽  
Time Interval ◽  
Magmatic Arc ◽  
Mineral Growth ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Continental Magmatic Arc ◽  
Uplift And Erosion ◽  
Structural Levels

The stratigraphic units, structural elements and metamorphic mineral assemblages of a regional metamorphic culmination in the 1.9 Ga Wopmay Orogen are exposed over greater than 30 km of composite structural depth, in a series of oblique sections produced by cross folding. Regional metamorphism developed continuously in three sequential, rapidly changing thermo-tectonic régimes within an evolving continental magmatic arc. At ca . 1900 Ma, stretching of intra-arc crust resulted in the accumulation of clastic sediment and bimodal volcanic rift-fill deposits. The onset (first stage) of regional metamorphism is marked by high- T low P mineral assemblages, condensed metamorphic zonal sequences and extensive areas of high-grade gneisses devoid of associated plutons. These features are interpreted in terms of a high thermal gradient related to stretching and thinning of the continental lithosphere. Five to ten million years after stretching, following deposition of a west-facing sedimentary prism, a suite of 1896—1878 Ma plutons was emplaced into the rift and margin deposits as they underwent subhorizontal shortening and deformation during the Calderian Orogeny. Thrusted and folded syn-orogenic foredeep deposits are also intruded by the syn-tectonic plutons. At high and intermediate structural levels, syn-tectonic metamorphic mineral growth and metamorphic zonal sequences which are spatially related to the plutons, document heat advection into the deforming marginal prism and mark a second stage of regional metamorphism related to the emplacement of the plutonic bodies. Inverted mineral isograds in autochthonous Proterozoic units beneath a basal décollement record downward thermal relaxation of isotherms following east-directed Calderian transport of the deformed, thickened, and still hot marginal prism over a relatively cold basement. Derivation of multi-point P - T trajectories from post-tectonic, poikiloblastic garnets charts metamorphic mineral growth during uplift and erosion of the internal zone, documenting the third (final) stage of regional metamorphism in Wopmay Orogen. The short erosional time interval (less than 11 Ma) between tectonic thickening and the end of uplift constrains the heat required for this last metamorphic stage to be inherited from the two preceding thermo-tectonic régimes: epicontinental stretching and the emplacement of the syn-tectonic plutonic suite.

scholarly journals U - Pb geochronology and composition of zircon mineral from granodiorite in the G18 Gold mine, Quang Nam and its significance in regional tectonics

2021 ◽  
Vol 62 (2) ◽  
pp. 1-11
Author(s):  
Thanh Xuan Ngo ◽  
Hau Vinh Bui ◽  
Hai Thanh Tran ◽  
Binh Van Phan ◽  
Bat Van Dang ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Trace Element Composition ◽  
Gold Mine ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Magmatic Arc ◽  
The North ◽  
Continental Magmatic Arc ◽  
Zircon Mineral ◽  
Ophiolitic Complex

The Tam Ky - Phuoc Son suture zone (TPSZ) is located in central Indochina and is referred to as a amalgamation site between the Truong Son and Kon Tum terranes during the early Paleozoic. The amphibolite and ultramafic rocks within the region were considered as a part of the Tam Ky - Phuoc Son ophiolitic complex. In this study, the authors present results of the U - Pb dating and trace element composition of the zircon grains derived from a granodioritic sample collected in the G18 gold mine in Quang Nam province in order to clarify the timing of magma emplacement and tectonic setting. The U - Pb dating data indicates that the granodioritic rocks formed at 447,4±2,9 Ma while the U/Yb ratio is ̴1 (average: 1.32) and the Sc/Yb ratio is ̴ 1.04, high Hf content (Average Hf: 10937 ppm) and low Yb content (Average Yb: 308 ppm). These geochemical values are comparable with the zircon, which is formed in the continental magmatic arc. Combination with the pre - existing data allowed us to confirm the existence of two contrast magma members in the North Kontum massif: The Middle Cambrian island arc complex and the Middle Ordovician continental complex.

The Peninsular Ranges Batholith: an insight into the evolution of the Cordilleran batholiths of southwestern North America

1988 ◽  
Vol 79 (2-3) ◽  
pp. 105-121 ◽  
Author(s):  
L. T. Silver ◽  
B. W. Chappell
Keyword(s):  
Baja California ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Radiometric Dating ◽  
Island Arcs ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
Basaltic Composition ◽  
Peninsular Ranges ◽  
General Aspects

ABSTRACTThe Peninsular Ranges Batholith of southern and Baja California is the largest segment of a Cretaceous magmatic arc that was once continuous from northern California to southern Baja California. In this batholith, the emplacement of igneous rocks took place during a single sequence of magmatic activity, unlike many of the other components of the Cordilleran batholiths which formed during successive separate magmatic episodes. Detailed radiometric dating has shown that it is a composite of two batholiths. A western batholith, which was more heterogeneous in composition, formed as a static magmatic arc between 140 and 105 Ma and was intrusive in part into related volcanic rocks. The eastern batholith formed as a laterally transgressing arc which moved away from those older rocks between 105 and 80 Ma, intruding metasedimentary rocks. Rocks of the batholith range from undersaturated gabbros through to felsic granites, but tonalite is the most abundant rock throughout. Perhaps better than elsewhere in the Cordillera, the batholith shows beautifully developed asymmetries in chemical and isotopic properties. The main gradients in chemical composition from W to E are found among the trace elements, with Ba, Sr, Nb and the light rare earth elements increasing by more than a factor of two, and P, Rb, Pb, Th, Zn and Ga showing smaller increases. Mg and the transition metals decrease strongly towards the E, with Sc, V and Cu falling to less than half of their value in the most westerly rocks. Oxygen becomes very systematically more enriched in18O from W to E and the Sr, Nd and Pb isotopic systems change progressively from mantle values in the W to a more evolved character on the eastern side of the batholith. In detail the petrogenesis of the Peninsular Ranges Batholith is not completely understood, but many general aspects of the origin are clear. The exposed rocks, particularly in the western batholith, closely resemble those of present day island arcs, although the most typical and average tonalitic composition is distinctly more felsic than the mean quartz diorite or mafic andesite composition of arcs. Chemical and isotopic properties of the western part of the batholith indicate that it formed as the root of a primitive island arc on oceanic lithosphere at a convergent plate margin. Further E, the plutonic rocks appear to have been derived by partial melting from deeper sources of broadly basaltic composition at subcrustal levels. The compositional systematics of the batholith do not reflect a simple mixing of various end-members but are a reflection of the differing character of the source regions laterally and vertically away from the pre-Cretaceous continental margin.

Emplacement ages and exhumation rates for intrusion-hosted Cu–Mo–Sb–Au mineral systems at Freegold Mountain (Yukon, Canada): assessment from U–Pb, Ar–Ar, and (U–Th)/He geochronometers

2012 ◽  
Vol 49 (5) ◽  
pp. 653-670 ◽  
Author(s):  
Thierry Bineli Betsi ◽  
David Lentz ◽  
Brent McInnes ◽  
Noreen J. Evans
Keyword(s):  
Hydrothermal Systems ◽  
Mountain Area ◽  
Erosion Rates ◽  
Late Tertiary ◽  
History Of ◽  
Fast Cooling ◽  
Exhumation Rates ◽  
Uplift And Erosion ◽  
Combined Data ◽  
Hydrothermal Event

To decipher the thermal history of mineralized systems across the Freegold Mountain area (Yukon, Canada), a combined geochronology (zircon U–Pb and hornblende, biotite, and whole rock Ar–Ar) and thermochronology (apatite and zircon (U–Th)/He) study was carried out. Previous U–Pb data combined with new U–Pb and Ar–Ar data show that intrusive bodies across the Freegold Mountain were emplaced during two protracted episodes, the first spanning from 109.6 to 98 Ma and the second between 79 and 68 Ma. Overprinting of the first intrusive event by a second magmatic hydrothermal event is suggested by a zircon U–Pb age of 108.7 ± 0.4 Ma for a chlorite-altered dyke and a whole rock Ar–Ar plateau age of 76.25 ± 0.53 Ma. Zircon (U–Th)/He data are between 66 and 89 Ma, whereas apatite (U–Th)/He data are scattered (38.7–109.9 Ma) and bracket the two magmatic emplacement events. Our combined data reveal a complex history of reheating that led to resetting of numerous chronometers. In most of the investigated magmatic hydrothermal systems, early fast cooling from igneous emplacement through hydrothermal alteration (between 900 and 200 °C) was followed by later and slower cooling accompanying post mineralization uplift and erosion (between 200 and 70 °C). Preliminary models indicate intrusive bodies associated with the Stoddart Cu–Mo ± W prospect cooled slowly (23 °C/Ma) compared with the ones spatially associated with the Revenue Au–Cu prospect (43 °C/Ma), and the similarity of the zircon U–Pb and (U–Th)/He ages from Revenue dyke further supports a rapid cooling from 700 to 180 °C. Erosion rates of 0.035–0.045 mm/year are consistent with tectonic quiescence during the Late Tertiary combined with the lack of Pleistocene glaciation in central Yukon. Such low rates of exhumation favour the formation and preservation of supergene mineralization, such as that found north of Freegold Mountain.

Origin of the Tulameen ultramafic-gabbro complex, southern British Columbia

1969 ◽  
Vol 6 (3) ◽  
pp. 399-425 ◽  
Author(s):  
D. C. Findlay
Keyword(s):  
British Columbia ◽  
Internal Structure ◽  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Upper Triassic ◽  
Ultramafic Rocks ◽  
Metasedimentary Rocks ◽  
Gabbroic Intrusion

The Tulameen Complex is a composite ultramafic-gabbroic intrusion that outcrops over 22 sq. mi. (57 km2) in the Southern Cordillera of British Columbia. The complex intruded Upper Triassic metavolcanic and metasedimentary rocks of the Nicola Group, and on the basis of geologic relations and a K–Ar age determination (186 m.y.) is tentatively dated as Late Triassic.The principal ultramafic units — dunite, olivine clinopyroxenite, and hornblende clinopyroxenite — form an elongate, non-stratiform body whose irregular internal structure is best explained by deformation contemporaneous with crystallization of the rocks. The derivation of the ultramafic rocks is attributed to fractional crystallization of an ultrabasic magma. The gabbroic mass, which consists of syenogabbro and syenodiorite, partly borders and partly overlies the ultramafic body and was apparently intruded by it.The ultramafic and gabbroic parts of the complex probably formed from separate intrusions of different magmas, but the two suites have sufficient mineralogical and chemical features in common to indicate an ultimate petrogenic affinity of the magmas. Comparison of the Tulameen rocks with nearby intrusions of the same general age, in particular the Copper Mountain stock, suggests that they are members of a regional suite of alkalic intrusions. The possibility is also raised that these intrusions may be comagmatic with the Nicola volcanic rocks.

Jurassic Arc: Reconstructing the Lost World of eastern Gondwana

Geology ◽  
2021 ◽  
Author(s):  
Elliot K. Foley ◽  
R.A. Henderson ◽  
E.M. Roberts ◽  
A.I.S. Kemp ◽  
C.N. Todd ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Tectonic Setting ◽  
Magmatic Arc ◽  
Continental Arc ◽  
Key Factor ◽  
Igneous Activity ◽  
Competing Models ◽  
Juvenile Crust ◽  
Sedimentary Fill ◽  
Continental Magmatic Arc

The tectonic setting of the Australian sector of the eastern Gondwanan margin during the Jurassic and Cretaceous is enigmatic. Whether this involved convergent tectonism and a long-lived continental magmatic arc or rift-related extension unrelated to subduction is debated. The paucity of Australian Jurassic–Cretaceous igneous outcrops makes resolving these competing models difficult. We used the detrital zircon record of the Jurassic–Cretaceous Great Australian Superbasin (GAS) as a proxy for igneous activity. We attribute the persistent magmatism recorded in GAS sedimentary fill throughout the Mesozoic to ca. 95 Ma to continuation of the established Paleozoic continental arc system. The detrital zircon record signals short (~10 m.y.) pulses of elevated Jurassic and Cretaceous magmatic activity and strongly positive εHf values, indicating juvenile crust or mantle-derived magmatism. Margin reconstruction indicates sustained continental growth at rates of at least ~55 km3 km–1 m.y.–1, mainly to the tract now represented by submerged northern Zealandia, due to the retreat of this arc system. We posit that arc retreat was a key factor in rapid crust generation and preservation, and that continental sedimentary systems globally may host cryptic records of juvenile crustal addition that must be considered in estimating crustal growth rates along convergent plate margins.

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