Tectonic setting and origin of the Proterozoic rapakivi granites of southeastern Fennoscandia

1992 ◽  
Vol 83 (1-2) ◽  
pp. 165-171 ◽  
Author(s):  
Ilmari Haapala ◽  
O. Tapani Rämö
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Transitional Zone ◽  
Isotopic Evolution ◽  
Domal Structure ◽  
Deep Seismic Soundings ◽  
Mafic Magmas ◽  
Thin Crust ◽  
High Level ◽  
Dyke Swarms

ABSTRACTThe 1·65–1·54 Ga rapakivi granites of southeastern Fennoscandia represent the silicic members of a bimodal magmatic association in which the mafic members are tholeiitic diabase dykes and minor gabbroic-anorthositic bodies. They are metaluminous to slightly peraluminous A-type granites and occur as high-level batholiths and stocks in an E-W-trending belt extending from Soviet Karelia to southwestern Finland. The Soviet Karelian granites were emplaced into the contact zone between Archaean craton and Svecofennian juvenile 1·9Ga-old crust, while the Finnish granites were intruded into the Svecofennian crust. Deep seismic soundings show that the rapakivi granites and the contemporaneous, mainly WNW or NW-trending diabase dyke swarms are situated in a zone of relatively thin crust. Below the Wiborg Batholith there exists a domal structure in the lithosphere in which a transitional zone (mafic underplate) occurs between the crust and the mantle.The Nd isotopic evolution of the rapakivi granites (εNd(T) −3·1—−0·2) corresponds to the evolution of the 1·9Ga-old Svecofennian crust, as do their Pb isotopic compositions. This implies that the Finnish granites represent anatectic melts of the Svecofennian crust. In contrast, the Soviet Karelian granites show isotopic composition indicative of substantial incorporation of Archaean lower crust material. Petrochemical modelling of one of the Finnish batholiths shows that its parental magma could have been generated by c. 20% melting of a granodioritic source and that fractional crystallisation was important during the subsequent evolution of this magma.The rapakivi granites are redefined as A-type granites that show the rapakivi texture at least in larger batholiths. The field, geochemical, and seismic data indicate that the classical Finnish rapakivi granites were generated in an anorogenic extensional regime by partial melting of the lower/middle crust. The melting, and possibly also the extensional tectonics, were related to upwellings of hot mantle material which led to intrusion of mafic magmas at the base and into the crust.

Neoproterozoic Amdo and Jiayuqiao microblocks in the Tibetan Plateau: Implications for Rodinia reconstruction

2020 ◽  
Author(s):  
Yiming Liu ◽  
Yuhua Wang ◽  
Sanzhong Li ◽  
M. Santosh ◽  
Runhua Guo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
South China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
South China Craton ◽  
Neoproterozoic Magmatism ◽  
T Values

The Tibetan Plateau is composed of several microblocks, the tectonic affinity and paleogeographic correlations of which remain enigmatic. We investigated the Amdo and Jiayuqiao microblocks in central Tibet Plateau with a view to understand their tectonic setting and paleogeographic position within the Neoproterozoic supercontinent Rodinia. We present zircon U-Pb and Lu-Hf isotope, and whole-rock geochemical data on Neoproterozoic granitic gneisses from these microblocks. Zircon grains from the Jiayuqiao granitic gneiss yielded an age of 857 ± 9 Ma with variable εHf(t) values (−8.9 to 4.0). The Amdo granitic gneisses yielded ages of 893 ± 5 Ma, 807 ± 5 Ma, and 767 ± 11 Ma, with εHf(t) values in the range of −4.9 to 3.5. Geochemically, the granitoids belong to high-K calc-alkaline series, with the protolith derived from partial melting of ancient crustal components. The ascending parental magma of the Amdo granitoids experienced significant mantle contamination as compared to the less contaminated magmas that generated the Jiayuqiao intrusions. In contrast to the Lhasa, Himalaya, South China, and Tarim blocks, we suggest that the Amdo and Jiayuqiao microblocks probably formed a unified block during the Neoproterozoic and were located adjacent to the southwestern part of South China craton. The Neoproterozoic magmatism was probably associated with the subduction of the peripheral ocean under the South China craton and the delamination of lithospheric mantle beneath the Jiangnan orogen.

Geochemistry of plutonic spinels from the North Kamchatka Arc: comparisons with spinels from other tectonic settings

1993 ◽  
Vol 57 (389) ◽  
pp. 575-589 ◽  
Author(s):  
Pavel K. Kepezhinskas ◽  
Rex N. Taylor ◽  
Hisao Tanaka
Keyword(s):  
Tectonic Setting ◽  
Transitional Zone ◽  
Late Eocene ◽  
Accessory Mineral ◽  
Volatile Content ◽  
Complex Chemical ◽  
Chemical Zoning ◽  
Magmatic Arc ◽  
The North ◽  
Tectonic Settings

AbstractUltramafic to marie plutons in the Olyutor Range, North Kamchatka, represent the magmatic roots of a late Eocene arc, related to the westward subduction of the Komandorsky Basin beneath the Asian continental margin. Olyutor Range plutons are concentrically zoned with cumulate dunite cores mantled by a wehrlite-pyroxenite transitional zone and, in turn, by a narrow gabbroic rim.Spinel is a common accessory mineral in these arc plutonics, and we present analyses of spinels from a range of lithologies. A continuous compositional trend is observed from Cr-spinel in the ultramafics to Cr-rich magnetite in marginal gabbros. Complex chemical zoning patterns within individual spinel grains suggest an interplay between fO2, fractionation, volatile content and subsequent sub-solidus reequilibration of spinel with co-existing silicates (mainly olivine).In general, the spinels from magmatic arc environments are characterised by high total Fe and high Fe3+ contents compared to MORB and boninitic spinels and higher Cr-values relative to oceanic basin spinels. These differences imply a high oxygen fugacity during arc petrogenesis. Differences are also observed between plutonic spinels from arcs and low-Ti supra-subduction zone ophiolites. Low-Ti ophiolitic spinels are generally poorer in iron and richer in Cr, and hence are similar in composition and perhaps tectonic setting to fore-arc boninitic spinels.

The 2405 Ma and 2310 Ma Mafic Dyke Swarms in the Karelian Craton: Age, Chemical and Sr-Nd Isotope Composition, and Tectonic Setting

2016 ◽  
Vol 90 (s1) ◽  
pp. 123-123
Author(s):  
A.V. Stepanova ◽  
E.B. Salnikova ◽  
A.V. Samsonov ◽  
Yu.O. Larionova ◽  
S.V. Egorova ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Tectonic Setting ◽  
Mafic Dyke ◽  
Karelian Craton ◽  
Nd Isotope ◽  
Dyke Swarms ◽  
Nd Isotope Composition

scholarly journals Petrology, Geochronology and Geochemistry of Late Triassic Alkaline Rocks of the Bailinchuan District in Liaodong Peninsula, Northeast China

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 528
Author(s):  
Xihui Cheng ◽  
Jiuhua Xu ◽  
Hao Wei ◽  
Fuquan Yang ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Late Triassic ◽  
Geochemical Data ◽  
Geodynamic Setting ◽  
Growth Zoning ◽  
Geochemical Studies ◽  
Alkaline Complexes

The Bailinchuan alkaline syenite (BAS) is located in the easternmost part of the Triassic alkaline magmatic belt along the northern North China Craton (NCC). Based on a detailed study of the zircon U–Pb age, petrological, and geochemical data of the complex, the characteristics of the magmas system, petrogenesis and the nature of mantle source provide new constraints on the origin and tectonic setting of the Triassic alkaline belt. The BAS is composed of alkaline syenite and/or aegirine-nepheline syenite, with zircon U–Pb age of 226–229 Ma. Aegirine, Na-rich augite, biotite, orthoclase, and nepheline are the major minerals. Most of the zircons selected for the analysis show fine-scale to weak oscillatory growth zoning in CL images, suggesting a magmatic origin. Mineralogy, petrology and geochemical studies show that the parental magma of the BAS is SiO2-undersaturated, potassic, and is characterized by high contents of CaO, Fe2O3, K2O, Na2O. The BAS originated from a phlogopite-rich, enriched lithospheric mantle source in a garnet-stable area. The occurrence of the BAS, together with many other alkaline complexes of similar ages (235–209 Ma) in the northern NCC during the Late Triassic implies that the lithospheric mantle beneath the northern NCC was previously metasomatized by melts/fluids. Bailinchuan Late Triassic syenites were formed in a post-collisional extensional setting, which provides time constraints on the major geodynamic setting at the northern NCC.

Evolution of a high-level, high-silica magma chamber: the Pattison pluton, Nisling Range alaskites, Yukon

1984 ◽  
Vol 21 (4) ◽  
pp. 407-413 ◽  
Author(s):  
G. V. Lynch ◽  
C. Pride
Keyword(s):  
Parental Magma ◽  
Confining Pressure ◽  
Fine Grained ◽  
Vertical Extension ◽  
Eutectic Crystallization ◽  
Stratigraphic Position ◽  
High Silica ◽  
Volatile Phase ◽  
High Level ◽  
Water Saturated

The Pattison pluton is a high-level, high-silica Tertiary alaskite intruding rocks of the Yukon Crystalline Terrane. The pluton is roughly circular in form with a diameter of about 18 km. The intrusion is cut by a series of shallowly dipping aplite dikes. Mineralogically, the alaskite body and the aplite dikes are very similar, but the pluton is divided into a series of phases based on texture and "stratigraphic" position: a fine-grained upper border phase, a medium-grained, graphic, strongly miarolitic, porphyritic phase, and a lower, coarser grained phase, contacts being gradational.No strong major element trends are found within the pluton (including the aplite dikes) because of eutectic crystallization. The trace elements, particularly Ba, Sr, Rb, Zr, and the REE, however, do show a liquid line of descent, with the upper border phase as the least differentiated and the aplite dikes as the most differentiated phases. Rayleigh fractional crystallization of quartz, K-feldspar, and plagioclase (and accessory allanite) in eutectic proportions readily accounts for the observed trends.The parental magma was water undersaturated (< 1.2% H2O). Crystallization of anhydrous phases led to water-saturated conditions late in the pluton's history. Volatiles migrated to and concentrated in the upper parts of the chamber where the melting temperature was depressed, causing the pluton to crystallize from the bottom up. The volatile pressure eventually exceeded the confining pressure, resulting in failure of the surrounding rocks, retrograde boiling, vertical extension, and lateral injection of residual magma caused by filter pressing to form the aplite dikes. The escaping volatile phase resulted in quartz veining and Mo mineralization.

Magnetic fabric constraint on tectonic setting of Paleoproterozoic dyke swarms in the North China Craton, China

2019 ◽  
Vol 329 ◽  
pp. 247-261 ◽  
Author(s):  
Yonggang Yan ◽  
Liwei Chen ◽  
Baochun Huang ◽  
Zhiyu Yi ◽  
Jie Zhao
Keyword(s):  
North China Craton ◽  
North China ◽  
Tectonic Setting ◽  
Magnetic Fabric ◽  
The North ◽  
Dyke Swarms

The tectonic significance of some basic dyke swarms in the Canadian Superior Province with special reference to the geochemistry and paleomagnetism of the Mistassini swarm, Quebec, Canada

1986 ◽  
Vol 23 (2) ◽  
pp. 238-253 ◽  
Author(s):  
W. F. Fahrig ◽  
K. W. Christie ◽  
E. H. Chown ◽  
D. Janes ◽  
N. Machado
Keyword(s):  
Genetic Relationship ◽  
Early Stage ◽  
Tectonic Setting ◽  
Superior Province ◽  
Plate Boundaries ◽  
Basic Dyke ◽  
Tectonic Significance ◽  
Fold Belts ◽  
Opening And Closing ◽  
Dyke Swarms

The Mistassini dykes extend northwest from the Mistassini embayment and comprise both tholeiitic and komatiitic suites. They are probably > 2000 Ma old and yield two major paleomagnetic components. One of these, with a pole at 131°W, 13°S, is thought to be an overprint related to the Elsonian Disturbance 1400–1500 Ma ago. A very steeply down (and reversed) component may be primary and has a pole at 080°W, 50°N.These spacial, chemical, and age relationships between the Mistassini, Molson, Marathon, and Payne River dyke swarms and the Aphebian supracrustal fold belts on the perimeter of the Superior Province suggest a genetic relationship between the dyke swarms and the fold belts. The supracrustal belts are evidence of the opening and closing of oceans, and the dyke swarms are evidence of early-stage failed arms related to these openings. More rarely (for example, the Payne River dykes), early-stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries. Presumably if a spreading episode stops, the dykes themselves may remain as the only evidence of that event. Probably all the world's great continental dyke swarms have the above-described tectonic setting, and the number and extent of dyke swarms during a geological epoch may be a measure of the number and vigour of spreading events.

Structural correlation within the Kapuskasing uplift

1994 ◽  
Vol 31 (7) ◽  
pp. 1081-1095 ◽  
Author(s):  
J. T. Bursnall ◽  
A. D. Leclair ◽  
D. E. Moser ◽  
J. A. Percival
Keyword(s):  
Fault Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Transitional Zone ◽  
Metamorphic History ◽  
Ductile Shear Zones ◽  
Supracrustal Belt ◽  
Ductile Shear ◽  
High Level ◽  
Multiple Stages

Comparison of progressive deformation and metamorphic history within and between the tectonic domains of the Kapuskasing uplift indicates significant variation in age and style of deformation across this large segment of the central Superior Province; multiple stages of tonalite and granitoid intrusion, melt generation, polyphase diachronous deformation, and likely rapid deep burial of supracrustal rocks collectively produced the complex character of this example of Archean mid to deep crust. At least four Archean deformation phases are recognized, although not all are of regional extent. Dated structural chronology suggests that the locus of the earliest recorded deformations migrated to deeper crustal levels with time. Pre-2680 Ma deformation (local D1–D2) within high-level tonalites is correlated with deformation in the Michipicoten supracrustal belt. The apparent earliest deformational fabrics at deeper crustal levels in the granulite terrane of the Kapuskasing structural zone occurred between 2660 and 2640 Ma. Archean third and fourth phase deformation phases (~ 2667 to ~ 2629 Ma) are present at mid-crustal and deeper levels and deform post-2667 Ma metaconglomerate; these resulted in large-scale folding and subhorizontal ductile shear zones, which seem to represent an important transitional zone that separated a passive upper crust from continued ductile strain at deeper levels.Subsequent uplift of the high-grade rocks was accomplished in multiple stages, initiated prior to 2.45 Ga and likely culminated around 1.9 Ga, although continued movement occurred as late as 1.14 Ga. The Ivanhoe Lake fault zone, along which much of the uplift must have occurred, exhibits some evidence of ductile deep-thrust-related fabrics, but most of the observed structures are brittle to brittle–ductile and steeply inclined. A broad zone of pervasive cataclasis and brittle–ductile shear zones is a characteristic feature of the fault zone throughout its length, and both dextral and sinistral offset are locally present. Clear ground evidence for major transcurrent or thrust displacements, however, has not been recognized.

Sign in / Sign up

Export Citation Format

Share Document