Isotope evidence for the origin of Andean granites

1988 ◽  
Vol 79 (2-3) ◽  
pp. 123-133 ◽  
Author(s):  
R. J. Pankhurst ◽  
M. J. Hole ◽  
M. Brook
Keyword(s):  
Antarctic Peninsula ◽  
Nd Isotope ◽  
Depleted Mantle ◽  
Wide Range ◽  
Mantle Sources ◽  
Subducted Oceanic Crust ◽  
Isotope Evidence ◽  
The Antarctic ◽  
Isotope Systematics ◽  
Material Input

ABSTRACTThe genesis of subduction-related magmas in the Andean region of South America and the Antarctic Peninsula is considered in relation to the Palaeozoic to Cenozoic granitoids belts which are thought to parallel palaeo-coastlines. Their Sr-Nd isotope systematics show a wide range of initial compositions (87Sr/86Sr0 0·7038 to >0·710; εNd, +4 to –10) requiring material input from both depleted mantle and continental crust. In local transects there are consistent trends with time of emplacement, from enriched (crustal) to depleted (mantle) sources, regardless of the sense of migration of magmatism (towards or away from the continent). These trends represent mixing between mantle-derived material and anatectic melts of the lower crust: in each case the crustal end-member reflects the age and isotopic composition of the local deep crustal basement (Precambrian in the easternmost Andes, Palaeozoic in the W and in the Antarctic Peninsula). The depleted end-member could be derived by melting within the subducted oceanic crust, the overlying mantle or previously crystallised mafic underplating. One of the most important factors controlling the mixing process is the angle of subduction, resulting in magma generation under variable tectonic conditions.

scholarly journals Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 711
Author(s):  
Irina Nedosekova ◽  
Nikolay Vladykin ◽  
Oksana Udoratina ◽  
Boris Belyatsky
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Crustal Evolution ◽  
Trace Element Data ◽  
The Urals ◽  
Nd Isotope ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Geochemical Specialization

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky сomplex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

Early Tertiary basalts from the Labrador Sea floor and Davis Strait region

1989 ◽  
Vol 26 (5) ◽  
pp. 956-968 ◽  
Author(s):  
D. B. Clarke ◽  
B. I. Cameron ◽  
G. K. Muecke ◽  
J. L. Bates
Keyword(s):  
Volcanic Rocks ◽  
Labrador Sea ◽  
Baffin Island ◽  
Nd Isotope ◽  
Sea Floor ◽  
West Greenland ◽  
Depleted Mantle ◽  
Davis Strait ◽  
Isotope Systematics ◽  
Seawater Exchange

Fine- to medium-grained, phyric and aphyric basalt samples from ODP Leg 105, site 647A, in the Labrador Sea show little evidence of alteration. Chemically, these rocks are low-potassium (0.01–0.09 wt.% K2O), olivine- to quartz-normative tholeiites that compare closely with the very depleted terrestrial Paleocene volcanic rocks in the Davis Strait region of Baffin Island and West Greenland. However, differences exist in the Sr–Nd isotope systematics of the two suites; the Labrador Sea samples have ε Nd values (+9.3) indicative of a more depleted source, and are higher in 87Sr/86Sr (0.7040), relative to the Davis Strait basalts (ε Nd +2.54 to +8.97; mean 87Sr/86Sr 0.7034). The higher 87Sr/86Sr in the Labrador Sea samples may reflect seawater exchange despite no petrographic evidence for significant alteration. The Labrador Sea and early Davis Strait basalts may have been derived from a similar depleted mantle source composition; however, the later Davis Strait magmas were generated from a different mantle. None of the Baffin Island, West Greenland, or Labrador Sea samples show unequivocal geochemical evidence for contamination with continental crust.

scholarly journals Trace-Element and Pb Isotope Evidence on Extracting Sulfides from Potassic Melts beneath Longmenshan and Molabushan Volcanoes, Wudalianchi, Northeast China

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 319 ◽  
Author(s):  
Sergei Rasskazov ◽  
Yi-Min Sun ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Chen Yang ◽  
...  
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Volcanic Field ◽  
Lava Flows ◽  
Pb Isotope ◽  
Linear Pattern ◽  
Wide Range ◽  
Mantle Sources ◽  
Isotope Evidence ◽  
Isotope Study

In the Wudalianchi volcanic field, eruptions started with low-Mg potassic lava flows 2.5–2.0 Ma ago and later changed to both low- and moderate-Mg potassic compositions. Volcanic rocks from the Molabushan and Longmenshan volcanoes record an unusually wide range of Pb abundances (from 3.7 ppm to 21 ppm relative to predominant range of 10–15 ppm). To determine the cause of these, we performed a comparative trace-element and Pb isotope study of rocks from these volcanoes and older lava flows. On a uranogenic lead diagram, older low-Mg lavas from lithospheric mantle sources plot on a secondary isochron with a slope corresponding to an age of 1.88 Ga. This contrasts with moderate-Mg volcanic rocks from the Molabushan cone, interpreted to have been derived from a recent convective mantle source, which define a flat linear pattern. Low-Mg rocks from the Molabushan flow have lead isotopic compositions that indicate mixed Gelaqiu and Molabu sources. Relative to rocks from the Molabushan cone, moderate-Mg lavas and slags from the East Longmenshan volcano have modified compositions characterized by Pb, S, and Ni abundances, Ni/Co, Ni/MgO ratios as well as 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, Ce/Pb, Th/Pb, and U/Pb ratios. We infer that the older Wudalianchi magmas were likely derived from a Paleoproterozoic lithospheric fragment, related to the evolved primordial mantle, and that later magmas were generated in the convecting mantle. These were influenced by segregation of small amounts of sulfides.

Petrogenesis of a rare Ediacaran tonalite–trondhjemite–granodiorite suite, Egypt, and implications for Neoproterozoic Gondwana assembly

2020 ◽  
pp. 1-22
Author(s):  
Abdel-Fattah M Abdel-Rahman
Keyword(s):  
Island Arc ◽  
Ionization Mass ◽  
East African ◽  
Wide Range ◽  
Mantle Sources ◽  
Nubian Shield ◽  
East African Orogen ◽  
Subducted Oceanic Crust ◽  
Late Stages ◽  
Arabian Nubian Shield

Abstract Most tonalite–trondhjemite–granodiorite (TTG) suites are Archean–Palaeoproterozoic in age, but those of Neoproterozoic–Phanerozoic age are scarce. A rare Ediacaran high-Al TTG suite has been identified at the Fannani Igneous Complex (FIC) in the northern Arabian–Nubian Shield, which is essentially composed of amalgamated Neoproterozoic island-arc Pan-African composite terranes that contain several ophiolitic sutures. The FIC exhibits a wide range of SiO2, Al2O3, Sr and Zr, shows moderate rare earth element (REE) enrichment, and K, Ti, Nb, Y and heavy REE depletion. It is a subsolvus suite with clear orogenic affinities and strong arc-geochemical signatures. The precise U–Pb zircon thermal ionization mass spectrometry age obtained (607.4 ± 1.95 Ma) indicates oceanic subduction extended to late stages of the East African Orogeny. The FIC exhibits 87Sr/86Sr compositions of 0.70346–0.71091 (Sr(i) ratio, 0.70284), and 143Nd/144Nd of 0.51254–0.51270 (ϵNd(t) = +5.12 to +7.16), typical of modern oceanic-arc rocks (as Japan-arc basalts), and suggestive of mantle sources and island-arc settings. The FIC possesses low values of Yb (1.55 ppm), Nb (14 ppm) and Y (24 ppm), and high ratios of Sr/Y (27), Zr/Sm (46) and Nb/Ta (11.8), typical of magmas produced by anatexis of a basaltic slab. Partial melting models show that the FIC magma was generated by melting (F = 0.25–0.50) of a subducted oceanic crust transformed into eclogite, leaving 10–25% garnet in the residue. The FIC and similar complexes produced via slab melting during the closure of the Mozambique Ocean formed large juvenile belts along the East African Orogen that sutured East and West Gondwana together into a united supercontinent.

scholarly journals Gabbroides of Peterman island (West Antarctica). First information on geochemistry

2019 ◽  
Vol 65 (4) ◽  
pp. 449-461
Author(s):  
G. V. Artemenko ◽  
V. I. Ganotskiy
Keyword(s):  
Antarctic Peninsula ◽  
High Strength ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
Magma Source ◽  
Magma Chambers ◽  
Small Bodies ◽  
Wide Range ◽  
The Antarctic ◽  
Crustal Magma

Peterman Island is located in the archipelago of the Wilhelm Islands on the west coast of the Antarctic Peninsula (Graham Land). It is composed of gabbroids and granitoids of the Andean complex, which formed almost 100 million years later than the volcanic group of the Antarctic Peninsula. To clarify their genesis and geodynamic conditions of formation, gabbroids of the Andean complex are of particular interest, since the petrological models of their formation are well developed. Gabbroid intrusions comprise small bodies that are widespread along the Antarctic Peninsula. Among them stand out olivine gabbros, normal gabbros, norites and hornblende gabbros. Also are found small bodies of melanogabbro-pegmatites and intramagmatic dykes, that are associated with the manifestations of ore mineralization of magnetite, ilmenite and sulfides. For this reason, they are of interest for both the minerals search and for solving the question of their genesis. To this end, we performed geochemical studies of Peterman Island gabbroids. Gabbroids of Peterman Island are represented by amphibolized medium-grained gabbro with hypidiomorphic texture. Among them, xenoliths of thinly stratified gabbroids 3 × 8 m in size were found, which are characteristic of stratified intrusions, for example, Stillwater, Bushveld, etc. Gabbroids of Peterman Island have low content of silica and potassium and according to the petrochemical characteristics correspond to peridotite gabbro. They have low contents of Cr, Ni, V and high strength lithophilic Y and Nb elements. Gabbroids have been crystallized from basic magma, differentiated in the intermediate crustal magma chambers. Positive anomalies of Sr, Eu, and Ti in the multielement diagrams and positive anomalies of europium Eu/Eu* suggest the accumulation of plagioclase and apparently, ilmenite in the magmatic chamber. The primary magma source for gabbroids was probably the primitive mantle (PM). Gabbroids are contaminated with crustal matter. This contamination is probably due to their regressive metamorphism, caused by the introduction of later intrusions of Andean complex granitoid. Finely layered xenolithic gabbroids do not differ from other homogeneous gabbros of Peterman Island in terms of chemical composition.This xenolith most likely represents a part (fragment) of the wall of the magma chamber in which the differentiation of the initial main magma took place. According to the obtained geochemical data, a wide range of compositions of the Andean complex gabbroids formed as a result of crystallization differentiation of magma melted from rocks of the composition of the primitive mantle (PM) in crustal magma chambers, which also resulted in the accumulation of ore elements — V, Co, and Cu in the residual magmatic melts.

The role of crustal and mantle sources in the genesis of granitoids of the Antarctic Peninsula and adjacent crustal blocks

2001 ◽  
Vol 158 (5) ◽  
pp. 855-867 ◽  
Author(s):  
I. L. MILLAR ◽  
R. C. R. WILLAN ◽  
C. D. WAREHAM ◽  
A. J. BOYCE
Keyword(s):  
Antarctic Peninsula ◽  
Mantle Sources ◽  
The Antarctic

Glaciological research in the Antarctic Peninsula

1977 ◽  
Vol 279 (963) ◽  
pp. 161-183 ◽  
Keyword(s):  
Sea Level ◽  
Antarctic Peninsula ◽  
Ice Core ◽  
Weddell Sea ◽  
Surface Velocity ◽  
Oxygen Isotope Fractionation ◽  
Core Drilling ◽  
Position Errors ◽  
Wide Range ◽  
The Antarctic

The Antarctic Peninsula is a good place for studies that take advantage of its wide range of latitude. Other worthwhile investigations are those that set in context the glacier/climate relationships and provide a framework of basic glaciological data. In order to speed reconnaissance mapping a series of seven 1:250 000 map sheets was published which used satellite imagery as the only source for planimetric detail. In preparation for intermediate depth ice core drilling for glaciological and palaeoclimatic investigations a wide-ranging programme of radio echo sounding has been pursued since 1963; flight tracks now total 80000 km. Experimental results are presented for an area at the base of the peninsula between latitudes 73° S and 80° S. Track plotting was controlled by relating observed subglacial topographic features with the surface expression of the same features revealed in a Landsat image mosaic. Thus navigation was not subject to the cumulative position errors generally encountered on long flights far from fixed points (nunataks). Redefinition of the earlier speculative boundary of the inland ice sheet added 38000 km2 to the land area of Antarctica while reducing the area of Ronne Ice Shelf by 11%. An unmapped nunatak was found 187 km from the nearest known outcrop. Three major inlets contained the thickest floating ice ever measured. Floating ice 1860 m thick was identified at a point only 17 km from the Ellsworth Mountains; thus within 60 km of the highest mountain in Antarctica (5140 m) there is a trench reaching 1600 m below sea level. Subglacially, there is potentially a channel well below sea level that connects the Bellingshausen Sea with the Weddell Sea. A radio echo sounder was adapted to measure the surface velocity of glaciers by reference to the spatial fading pattern of the bottom echo. Checks on Fleming Glacier with optical survey instruments showed that the true rate of movement was 44% faster than indicated by the fading pattern. It was concluded that the sounder had measured surface velocity with reference to a reflecting horizon which itself was deforming or sliding over the glacier bed. Experiments on ice shelves have been used to extend the flow law of ice to stresses lower than can be studied in the laboratory. At least down to the lowest stress considered (0.04 MN m-2) the results supported a power law with a stress exponent of 3 as found in the laboratory for higher stresses. Ultra-clean sampling techniques were developed for detecting extremely low levels of impurities in snow (3 x 10 -14 g g -1 ). Thus DDT concentrations were found to be 40-100 times smaller than earlier reported for snow from central Antarctica. An extensive reconnaissance programme of 10 m ice core drilling has been pursued with the object of studying relationships between oxygen isotope fractionation and ice and air temperatures. The ice, water, and energy balances of two representative local glaciers have been studied as a contribution to the International Hydrological Decade.

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