Petrogenesis of LREE-rich pegmatitic granite dykes in the central Grenville Province by partial melting of Paleoproterozoic-Archean metasedimentary rocks: Evidence from zircon U-Pb-Hf-O isotope and trace element analyses

Hafnium (Hf) isotopes in zircon are important tracers of granite petrogenesis and continental crust evolution. However, zircon in granites generally shows large Hf isotope variations, and the reasons for this are debated. We applied U-Pb geochronology, trace-element, and Hf isotope analyses of zircon from the Miocene Himalayan granites to address this issue. Autocrystic zircon had εHf values (at 20 Ma) of –12.0 to –4.3 (median = –9). Inherited zircon yielded εHf values (at 20 Ma) of –34.8 to +0.3 (median = –13); the majority of εHf values were lower than those of autocrystic zircon. The εHf values of inherited zircon with high U concentrations resembled those of autocrystic zircon. Geochemical data indicates that the granites were generated during relatively low-temperature (<800 °C) partial melting of metasedimentary rocks, which, coupled with kinetic hindrance, may have led to the preferential dissolution of high-U zircon that could dissolve more efficiently into anatectic melt due to higher amounts of radiation damage. Consequently, Hf values of autocrystic zircon can be biased toward the values of U-rich zircon in the source. By contrast, literature data indicate that granites generated at high temperatures (<820–850 °C) generally contain autocrystic and inherited zircons with comparable Hf isotope values. During higher-temperature melting, indiscriminate dissolution of source zircon until saturation is reached will result in near-complete inheritance of Hf isotope ratios from the source. Our results impose an extra layer of complexity to interpretation of the zircon Hf isotope archive that is not currently considered.

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The ca. 2785–2805 Ma High Temperature Ilivertalik Intrusive Complex of Southern West Greenland

Geosciences ◽

10.3390/geosciences8090319 ◽

2018 ◽

Vol 8 (9) ◽

pp. 319 ◽

Cited By ~ 1

Author(s):

Tomas Næraa ◽

Thomas F. Kokfelt ◽

Anders Scherstén ◽

Andreas Petersson

Keyword(s):

High Temperature ◽

Trace Element ◽

Partial Melting ◽

Source Region ◽

Intrusive Complex ◽

Large Role ◽

Rock Record ◽

O Isotope ◽

Granitoid Intrusions

Ferroan granitoid intrusions are rare in the Archaean rock record, but have played a large role in the evolution of the Proterozoic crust, particular in relation to anorthosite-mangerite-charnockite-granite suites. Here we discuss the petrogenesis of the ca. 2785–2805 Ma ferroan Ilivertalik Intrusive Complex, which has many geochemical similarities to Proterozoic iron rich granitoids. We present major and trace element whole rock chemistry and combined in-situ zircon U-Pb, Hf and O isotope data. The intrusive complex divides into: (i) minor tabular units of mainly diorite-tonalite compositions, which are typically situated along contacts to the host basement and (ii) interior larger, bodies of mainly granite-granodiorite composition. Geochemically these two unites display continuous to semi-continuous trends in Haker-diagrams. Whole rock REE enrichment display increases from Yb to La, from 10–25 to 80–100 times chondrite, respectively. The diorite-tonalite samples are generally more enriched in REE compared to the granite-granodiorite samples. The complex has hafnium isotope compositions from around +1.5 to −2.5 epsilon units and δ18O compositions in the range of 6.3 to 6.6‰. The complex is interpreted to be derived from partial melting in a crustal source region during anomalously high crustal temperatures.

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Geochemistry of two metavolcanic arc suites from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e91-126 ◽

1991 ◽

Vol 28 (9) ◽

pp. 1429-1443 ◽

Cited By ~ 12

Author(s):

Luc Harnois ◽

John M. Moore

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Trace Element ◽

Partial Melting ◽

Volcanic Rocks ◽

Parental Magma ◽

Major Elements ◽

Grenville Province ◽

Element Abundances ◽

Felsic Rocks

Samples of two subalkaline metavolcanic suites, the Tudor formation (ca. 1.28 Ga) and the overlying Kashwakamak formation, have been analysed for major elements and 27 trace elements (including rare-earth elements). The Tudor formation is tholeiitic and contains mainly basaltic flows, whereas the Kashwakamak formation is calc-alkaline and contains mainly andesitic rocks with minor felsic rocks. The succession has been regionally metamorphosed to upper greenschist – lower amphibolite facies. Trace-element abundances and ratios indicate that rocks of the Tudor and Kashwakamak formations are island-arc type. Geochemical modelling using rare-earth elements, Zr, Ti, and Y indicates that the Tudor volcanic rocks are not derived from a single parental magma through simple fractional crystallization. Equilibrium partial melting of a heterogeneous Proterozoic upper mantle can explain the trace-element abundances and ratios of Tudor formation volcanic rocks. The intermediate to felsic rocks of the Kashwakamak formation appear to have been derived from a separate partial melting event. The data are consistent with an origin of the arc either on oceanic crust or on thinned continental crust, and with accretion of the arc to a continental margin between the time of extrusion of Tudor volcanic rocks and that of Kashwakamak volcanic rocks.

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

Geological Society of America Bulletin ◽

10.1130/b35837.1 ◽

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.

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

Journal of Petrology ◽

10.1093/petrology/egab005 ◽

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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Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

Mineralium Deposita ◽

10.1007/s00126-020-01039-8 ◽

2021 ◽

Author(s):

Mikael Vasilopoulos ◽

Ferenc Molnár ◽

Hugh O’Brien ◽

Yann Lahaye ◽

Marie Lefèbvre ◽

...

Keyword(s):

Trace Element ◽

Sulfur Isotope ◽

Mineral Chemistry ◽

Chemical Compositions ◽

Metasedimentary Rocks ◽

Metavolcanic Rocks ◽

Icp Ms ◽

Stage 1 ◽

Host Rocks ◽

Relationship Of

AbstractThe Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

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Geology and age of the Precambrian basement in the Windsor, Chatham, and Sarnia area, southwestern Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e82-139 ◽

1982 ◽

Vol 19 (8) ◽

pp. 1627-1634 ◽

Cited By ~ 3

Author(s):

A. Turek ◽

R. N. Robinson

Keyword(s):

Oil And Gas ◽

Precambrian Basement ◽

Grenville Province ◽

Metasedimentary Rocks ◽

Gas Drilling ◽

Arch System ◽

Grenvillian Orogeny ◽

Anomaly Map ◽

Paleozoic Rocks ◽

Basement Surface

Precambrian basement in the Windsor–Chatham–Sarnia area is covered by Paleozoic rocks that are up to 1300 m thick. The basement surface is characterized by a northeast–southwest arch system with a relief of about 350 m. Extensive oil and gas drilling has penetrated and sampled this basement, and an examination of core and chip samples from 133 holes and an assessment of the magnetic anomaly map of the area have been used to produce a lithologic map of the Precambrian basement. The predominant rocks are granite gneisses and syenite gneisses but also significant are gabbros, granodiorite gneisses, and metasedimentary rocks. The average foliation dips 50° and is inferred to have a northeasterly trend. The Precambrian basement has been regarded as part of the Grenville Province. An apparent Rb–Sr whole rock isochron, for predominantly meta-igneous rocks, yields an age of 1560 ± 140 Ma. This we interpret as pre-Grenvillian, surviving the later imprint of the Grenvillian Orogeny. Points excluded from the isochron register ages of 1830, 915, and 670 Ma, and can be interpreted as geologically meaningful.

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Geochemistry and geochronology of OIB-type, Early Jurassic magmatism in the Zhangguangcai range, NE China, as a result of continental back-arc extension

Geological Magazine ◽

10.1017/s0016756818000705 ◽

2018 ◽

Vol 158 (1) ◽

pp. 143-157 ◽

Cited By ~ 4

Author(s):

Guangying Feng ◽

Yildirim Dilek ◽

Xiaolu Niu ◽

Fei Liu ◽

Jingsui Yang

Keyword(s):

East Asia ◽

Trace Element ◽

Partial Melting ◽

Early Jurassic ◽

Ne China ◽

Mafic Rocks ◽

Asthenospheric Mantle ◽

Trace Element Contents ◽

Pacific Slab ◽

Back Arc

AbstractThe Zhangguangcai Range in the Xing’an Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ɛNd(t) values of 2.3–3.2 and positive ɛHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet- to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia.

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