Geochemical and Nd-Pb isotopic systematics of late Archean granitoids, southwestern Slave Province, Canada: constraints for granitoid origin and crustal isotopic structure

1999 ◽  
Vol 36 (7) ◽  
pp. 1131-1147 ◽  
Author(s):  
Katsuyuki Yamashita ◽  
Robert A Creaser ◽  
James U Stemler ◽  
Tony W Zimaro
Keyword(s):  
Partial Melting ◽  
Regional Scale ◽  
Crustal Thickening ◽  
Crustal Material ◽  
Isotopic Data ◽  
Metasedimentary Rocks ◽  
Slave Province ◽  
Juvenile Crust ◽  
Direct Input

New geochemical and Nd-Pb isotopic data for ~ 2.62-2.59 Ga granitoids from the southwest Slave Province are used to determine the source(s) of granitoid magmas, to evaluate the role of pre-2.8 Ga basement during this magmatism, and to refine the existing Nd-Pb isotopic structure of the western Slave Province. The Pb isotopic data require crust older than ~3.2 Ga as a granitoid protolith, whereas the Nd isotopic data require input from juvenile crustal material. This discrepancy is explained if the granitoid protoliths are mixtures of ancient basement and ~2.7 Ga juvenile crust in varying proportions. Specifically, granitoids from the southwestern Slave Province require 10-30% basement, whereas granitoids from other parts of the western Slave Province require >50%. Incorporation of basement as a protolith may be achieved indirectly, by assimilation of basement during juvenile ~2.7 Ga magmatism, or directly during ~2.62-2.59 Ga magmatism. The granitoid isotopic data suggest that indirect basement input was important on a regional scale, but direct input may have also taken place in some areas of the western Slave Province, particularly along the ~111°W "isotopic boundary" zone previously recognized. The geochemical characteristics of these granitoids are compatible with an origin by partial melting of dominantly amphibolite and metasedimentary rocks to produce the ~2.61 Ga and ~2.59 Ga magmatism, respectively; partial melting occurred in response to regional crustal thickening at this time.

scholarly journals Strongly Peraluminous Granites across the Archean–Proterozoic Transition

2019 ◽  
Vol 60 (7) ◽  
pp. 1299-1348 ◽  
Author(s):  
Claire E Bucholz ◽  
Christopher J Spencer
Keyword(s):  
Partial Melting ◽  
Sedimentary Rock ◽  
Source Rocks ◽  
Crustal Thickening ◽  
Metasedimentary Rocks ◽  
Isotope Data ◽  
Source Regions ◽  
Peraluminous Granites ◽  
Rock Record ◽  
Sedimentary Source

Abstract Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean–Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean–Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O2 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al2O3/TiO2 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both ‘high-’ and ‘low-’temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na2O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary 18O/16O ratios increased across the Archean–Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites.

The role of pre-existing weak zones in the formation of the Himalaya and Tibetan plateau: 3-D thermomechanical modelling

2020 ◽  
Vol 221 (3) ◽  
pp. 1971-1983
Author(s):  
Lin Chen ◽  
Lijun Liu ◽  
Fabio A Capitanio ◽  
Taras V Gerya ◽  
Yang Li
Keyword(s):  
Tibetan Plateau ◽  
Early Stage ◽  
Crustal Thickening ◽  
The Tibetan Plateau ◽  
Crustal Material ◽  
Weak Zone ◽  
Orogenic Wedge ◽  
Orogenic Plateau ◽  
Weak Zones

SUMMARY The Tibetan crust is sliced by several east–west trending suture zones. The role of these suture zones in the evolution of the Himalayan range and Tibetan plateau remains unclear. Here we use 3-D thermomechanical simulations to investigate the role of pre-existing weak zones within the Asian Plate in the formation of orogen and plateau growth during continental collision. Our results show that partitioning of deformation along the convergent margin leads to scraping off of crustal material into an orogenic wedge above the margin and crustal thickening in the retro-continent, eventually forming a large orogenic plateau in front of the indenter. Pre-existing weak zone(s) within the retro-continent is reactivated at the early stage of convergence, and facilitates the northward propagation of strain and widening of the orogenic plateau. The northernmost weak zone sets the northern limit of the Tibetan plateau. Our models also show rheological weakening of the congested buoyant crust within the collisional zone drives wedge-type exhumation of deeply buried crust at the southern flank of the plateau, which may explain the formation of the Greater Himalayan Sequence.

U–Pb and Hf isotopic study of detrital zircons from the Lüliang khondalite, North China Craton, and their tectonic implications

2009 ◽  
Vol 146 (5) ◽  
pp. 701-716 ◽  
Author(s):  
XIAOPING XIA ◽  
MIN SUN ◽  
GUOCHUN ZHAO ◽  
FUYUAN WU ◽  
LIEWEN XIE
Keyword(s):  
North China Craton ◽  
North China ◽  
Detrital Zircons ◽  
Crustal Material ◽  
Isotopic Data ◽  
Isotopic Study ◽  
Metasedimentary Rocks ◽  
The North ◽  
Wide Range ◽  
Western Block

AbstractTwo types of metasedimentary rocks occur in the Trans-North China Orogen of the North China Craton. One type consists of highly metamorphosed supracrustal rocks with protoliths of mature cratonic shale, called khondalites, as found in the Lüliang Complex; rocks of the other type are also highly metamorphosed but less mature, as represented by the Wanzi supracrustal assemblage in the Fuping Complex. U–Pb isotopic data for detrital zircons from khondalites show a provenance dominated by 1.9–2.1 Ga Palaeoproterozoic rocks. These detrital zircons display a wide range of εHfvalues from −16.0 to +9.2 and give Hf isotopic model ages mostly around 2.3 Ga. The high positive εHfvalues approach those for the depleted mantle at 2.1 Ga, highlighting a juvenile crustal growth event in Palaeoproterozoic times. Hf isotopic data also imply thatc.2.6 Ga old crustal material was involved in the Palaeoproterozoic magmatic event. These data are similar to those for the khondalitic rocks from the interior of the Western Block of the North China Craton, suggesting a common provenance. In contrast, other metasedimentary rocks in the Trans-North China Orogen, such as the Wanzi supracrustal assemblage in the Fuping Complex, have a source region with both Palaeoproterozoic and Archaean rocks. Their detrital zircon Hf isotopic data indicate reworking of old crustal material and a lack of significant juvenile Palaeoproterozoic magmatic input. These rocks are similar to the coevally deposited meta-sedimentary rocks in the interior of the Eastern Block. We propose that the Lüliang khondalites were deposited on the eastern margin of the Western Block in a passive continental margin environment and were thrust eastward later during collision with the Eastern Block. Other metasedimentary rocks in the Trans-North China Orogen were deposited on the western margin of the Eastern Block in a continental arc environment. Our data support the eastward subduction model for the Palaeoproterozoic tectonic evolution of the North China Craton.

scholarly journals The role of phyllosilicate partial melting in segregating tungsten and tin deposits in W-Sn metallogenic provinces

Geology ◽  
2021 ◽  
Author(s):  
Panlao Zhao ◽  
Xu Chu ◽  
Anthony E. Williams-Jones ◽  
Jingwen Mao ◽  
Shunda Yuan
Keyword(s):  
Partial Melting ◽  
Geochemical Data ◽  
Dehydration Melting ◽  
Metasedimentary Rocks ◽  
Partial Melt ◽  
Tin Deposits ◽  
Higher Temperature ◽  
Biotite Dehydration Melting ◽  
Highly Evolved

Most tungsten (W) and tin (Sn) deposits are associated with highly evolved granites derived from the anatexis of metasedimentary rocks. They are commonly separated in both space and time, and in the rare cases where the W and Sn mineralization are part of a single deposit, the two metals are temporally separate. The factors controlling this behavior, however, are not well understood. Our compilation of whole-rock geochemical data for W- and Sn-related granites in major W-Sn metallogenic belts shows that the Sn-related granites are generally the products of higher-temperature partial melting (~800 °C) than the W-related granites (~750 °C). Thermodynamic modeling of partial melting and metal partitioning shows that W is incorporated into the magma formed during low-temperature muscovite-dehydration melting, whereas most of the Sn is released into the magma at a higher temperature during biotite-dehydration melting; the Sn of the magma may be increased significantly if melt is extracted prior to biotite melting. At the same degree of partial melting, the concentrations of the two metals in the partial melt are controlled by their concentration in the protolith. Thus, the nature of the protolith and the melting temperature and subsequent evolution of the magma all influence the metallogenic potential of a magma and, in combination, helped control the spatial and temporal segregation of W and Sn deposits in all major W-Sn metallogenic belts.

Structure of the Lac Nominingue – Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province

2001 ◽  
Vol 38 (5) ◽  
pp. 787-802
Author(s):  
L B Harris ◽  
B Rivard ◽  
L Corriveau
Keyword(s):  
Regional Scale ◽  
Shear Zones ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Gneiss Dome ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
East West

The Lac Nominingue – Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation – transposed compositional layering (S1; host to peak-pressure parageneses) has been folded by isoclinal folds (F2 and F3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F3 folds, indicating that 1.20–1.18 Ga granulite-facies metamorphism post-dated D3. D3 structures are cut by ductile shear zones and boudinaged in D4 and are folded by regional-scale, open, upright north–south folds (F5). Folds with shallowly dipping axial surfaces (F6) are subsequently developed in the Sourd group. F5 (and probably F6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue–Chénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F2 to F5 folds may have formed during either subhorizontal, east–west contraction or east–west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE–WNW contraction and NNE–SSW (orogen-parallel) extension in D7 syn- to post-intrusion of the Chevreuil suite. F8 folds imply a late, Grenvillian SSE–NNW contraction.

Mesozoic crustal melting and metamorphism in the U.S. Cordilleran hinterland: Insights from the Sawtooth metamorphic complex, central Idaho

2021 ◽  
Author(s):  
Chong Ma ◽  
David A. Foster ◽  
Paul A. Mueller ◽  
Barbara L. Dutrow ◽  
Jeffery Marsh
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Regional Metamorphism ◽  
Crustal Thickening ◽  
Surface Erosion ◽  
Metamorphic Complex ◽  
Upper Crust ◽  
Metasedimentary Rocks ◽  
The U.S ◽  
Central Idaho

In this study, we present whole-rock geochemistry and Sm-Nd data; zircon trace element, U-Pb, and Lu-Hf data; titanite U-Pb dating; and structural analysis of igneous and metasedimentary rocks of the Sawtooth metamorphic complex that provide insight into regional metamorphism, partial melting, and crustal thickening in the Idaho batholith segment of the Cordilleran orogen. Four magmatic events are revealed: (1) pre-tectonic felsic magmatism at ca. 156 Ma, (2) syn-tectonic mafic and felsic magmatism between ca. 100 Ma and ca. 92 Ma, (3) felsic magmatism concurrent with late-stage deformation at ca. 89−84 Ma, and (4) post-tectonic felsic magmatism at ca. 77 Ma. The multiple generations of felsic magmatism include a variety of sedimentary- and igneous-derived granitoids distinguished by zircon trace element compositions (e.g., U/Ce versus Th and Ce/Sm versus Yb/Gd) and were sourced from progressively more evolved crustal components as shown by Lu-Hf and Sm-Nd isotopic data. U-Pb data of metamorphic zircons and titanites from high-grade metasedimentary rocks suggest that regional metamorphism occurred from ca. 100−93 Ma, which was characterized by granulite-facies partial melting and concurrent growth of metamorphic zircons and garnets. The episodic magmatism in the Sawtooth metamorphic complex records pervasive melt migration in a hot, mid-crustal setting at ca. 100‒92 Ma and additional magma ascent in a cool, upper-crustal setting at ca. 77 Ma. The uplift of the Sawtooth metamorphic complex from mid- to upper-crust was likely caused by underthrusting at lower crustal levels coupled with erosion and thinning of the upper crust. This work suggests that the crust of the Cordilleran hinterland in the Idaho batholith region underwent significant thickening from ca. 100‒84 Ma, and a crust of Andean-like thickness was probably achieved by ca. 84 Ma. By ca. 77 Ma, the central Idaho crust started to thin likely due to mid-crustal flow and surface erosion. The new data from the Sawtooth metamorphic complex are consistent with the two major magmatic flare-ups in the Late Jurassic and Late Cretaceous in the U.S. Cordilleran orogen.

Geochemical and isotopic studies of the sedimentary and granitic rocks of the Altai orogen of northwest China and their tectonic implications

2002 ◽  
Vol 139 (1) ◽  
pp. 1-13 ◽  
Author(s):  
BIN CHEN ◽  
BOR-MING JAHN
Keyword(s):  
Oceanic Crust ◽  
Significant Proportion ◽  
Northwest China ◽  
Passive Margin ◽  
Granitic Rocks ◽  
Crustal Material ◽  
Isotopic Data ◽  
Margin Setting ◽  
Metasedimentary Rocks ◽  
Back Arc

The Altai orogen (northwest China) represents the southwestern margin of the Central Asian Orogenic Belt. Geochemical and Nd–Sr isotope analyses were carried out on the Palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen. Nd isotopic data for both the granites and sediments suggest a significant proportion of middle Proterozoic crust beneath the Altai orogen. However, addition of juvenile material (arc/back-arc oceanic crust) during Palaeozoic times is also significant. Trace elements and isotopic data of sediments suggest their sources were immature. They represent mixtures between a Palaeozoic juvenile component and an evolved continental crust. The early Palaeozoic sediments show εNd(T) = −3.4 to −5.0, TDM = 1.5–1.8 Ga, and ISr = 0.710–0.712. They represent a passive margin setting, with a predominance of evolved crustal material in the source. The Devonian sequences, however, might have been deposited in a back-arc basin setting, produced by subduction of the Junggar oceanic crust along the Irtysh fault. A significant addition of arc material into the sedimentary basin is responsible for the highly variable εNd values (−6 to 0) and ISr (0.711–0.706). The Carboniferous rocks were also deposited in a back-arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in εNd(T) (+6 to +3) and decrease in ISr (0.7045–0.7051). Voluminous syn-orogenic granitoids have εNd(T) = +2.1 to −4.3, ISr = 0.705–0.714 and TDM = 0.7–1.6 Ga. They were not derived by melting of local metasedimentary rocks as suggested by previous workers, but by melting of a more juvenile source at depth. Post-orogenic granites have higher εNd(T) (∼ +4.4) than the syn-orogenic granitoids, indicating their derivation from a deeper crustal level where juvenile crust may predominate.

scholarly journals Transcriptomic and isotopic data reveal central role of ammonium in facilitating the growth of the mixotrophic dinoflagellate, Dinophysis acuminata

Harmful Algae ◽  
2021 ◽  
Vol 104 ◽  
pp. 102031
Author(s):  
Theresa K. Hattenrath-Lehmann ◽  
Deepak Nanjappa ◽  
Huan Zhang ◽  
Liying Yu ◽  
Jennifer A. Goleski ◽  
...  
Keyword(s):  
Isotopic Data ◽  
Dinophysis Acuminata

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

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