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- MakaleYalnız künye2019Scopus SJRQ1Combined boron, radiogenic (Nd, Pb, Sr), stable (C, O) isotopic and geochemical investigations of carbonatites from the Blue River Region, British Columbia (Canada): Implications for mantle sources and recycling of crustal carbon
Çimen, Okay; Kuebler, Corinne; Simonetti, Stefanie S.; Corcoran, Loretta; Mitchell, Roger; Simonetti, Antonio
This study reports the combined major, minor and trace element compositions, and stable (C, O), radiogenic (Nd, Pb, and Sr) isotopic compositions, and first δ11B isotopic data for the Fir, Felix, Gum, and Howard Creek carbonatites from the Blue River Region, British Columbia (Canada). These sill-like occurrences were intruded into Late Proterozoic strata during rifting and extensional episodes during the Late Cambrian and Devonian -Mississippian, and subsequently deformed and metamorphosed to amphibolite grade in relation to a collisional-type tectonic environment. The carbonatites at Fir, Gum, and Felix contain both calcite and dolomite, whereas the carbonatite at Howard Creek contains only calcite. The dolomite compositions reported here are consistent with those experimentally determined by direct partial melting of metasomatized peridotitic mantle. The combined major and trace element compositions and δ13CPDB (−5.37 to −4.85‰) and δ18OSMOW (9.14 to 9.62‰) values for all the samples investigated are consistent with those for primary igneous carbonate and support their mantle origin. However, these signatures cannot be attributed to closed system melt differentiation from a single parental melt. The initial Nd, Pb, and Sr isotopic ratios are highly variable and suggest generation from multiple, small degree parental melts derived from a heterogeneous mantle source. The δ11B values for carbonates from Felix, Gum, and Howard Creek vary between −8.67 and −6.36‰, and overlap the range for asthenospheric mantle (−7.1 ± 0.9‰), whereas two samples from Fir yield heavier values of −3.98 and −2.47‰. The latter indicate the presence of recycled crustal carbon in their mantle source region, which is consistent with those for young (<300 Ma) carbonatites worldwide. The radiogenic and B isotope results for the Blue River carbonatites are compared to those from contrasting, anorogenic tectonic settings at Chipman Lake, Fen, and Jacupiranga, and indicate that similar upper mantle sources are being tapped for carbonatite melt generation. The pristine, mantle-like δ11B values reported here for the Blue River carbonatites clearly demonstrate that this isotope system is robust and was not perturbed by post-solidification tectono-metamorphic events. This observation indicates that B isotope signatures are a valuable tool for deciphering the nature of the upper mantle sources for carbonates of igneous origin.
AtıfScopus28OpenAlex25
İncele - MakaleYalnız künye2018Scopus SJRQ1Boron, carbon, oxygen and radiogenic isotope investigation of carbonatite from the Miaoya complex, central China: Evidences for late-stage REE hydrothermal event and mantle source heterogeneity
Çimen, O.; Kuebler, C.; Monaco, B.; Simonetti, S.S.; Corcoran, L.; Chen, W.; Simonetti, A.
The Miaoya carbonatite complex (MCC) is located within the southern edge of the Qinling orogenic belt in central China, and is associated with significant rare earth element (REE) and Nb mineralization. The MCC consists of syenite and carbonatite that were emplaced within Neo- to Mesoproterozoic-aged supracrustal units. The carbonatite intruded the associated syenite as stocks and dikes, and is mainly composed of medium- to fine-grained calcite and abundant REE-bearing minerals. Carbonatite melt generation and emplacement within the MCC occurred during the Silurian (at ~440 Ma), and was subsequently impacted by a late-stage hydrothermal event (~232 Ma) involving REE-rich fluids/melt. This study reports trace element and stable (B, C, and O) and radiogenic (Nd, Pb, and Sr) isotope data for the MCC carbonatite, and these have been subdivided into three groups that represent different REE contents, interpreted as varying degrees of hydrothermal interaction. Overall, the group of carbonatites with the lowest enrichment in LREEs (i.e., least affected by hydrothermal event) is characterized by δ11B values that vary between −7 (typical asthenospheric mantle) and + 4‰; δ11B values and B abundances (~0.2 to ~1 ppm) do not correlate with LREE contents. The Sm-Nd and Pb-Pb isotope systems have both been perturbed by the late-stage, REE-rich hydrothermal activity and corroborate open-system behavior. Contrarily, initial 87Sr/86Sr ratios (vary between ~0.70355 and 0.70385) do not correlate significantly with both LREEs and Sr abundances, nor with initial 143Nd/144Nd ratios. The late-stage hydrothermal event overprinted the Nd and Pb isotope compositions for most of the carbonatite samples examined here, whereas a majority of the samples preserve their variable B and Sr isotope values inherited from their mantle source. The B and Sr isotope data for carbonatites exhibiting the least LREE enrichment correlate positively and suggest carbonatite melt generation from a heterogenous upper mantle source that records the input of recycled crustal material. This finding is consistent with those previously reported for young (<300 Ma old) carbonatites worldwide.
AtıfScopus42WoS39İncele