It is suggested in this paper that the famous Taylor’s model for the compdrition and evolution of the continental crust consists of three closely related key links. These links include an assumption that the surficia...It is suggested in this paper that the famous Taylor’s model for the compdrition and evolution of the continental crust consists of three closely related key links. These links include an assumption that the surficial environment has no effect on the sedimentary REE patterns and the REE patterns in shales can reflect the composition of their provenancel a discovery about the discrepancy of sedimentary REE patterns between Archean and Proterozoic, and a deduc-tion that there was a global scale K-granitoid event at the end of the Archean. Based on a de-tailed discussion, this paper substantially negates the rationality of the Taylor’s model and ar-gues that its three critical links be three great errors indeed. Moreover, some other deficiencies or problems it confronts are described in this paper. The authors suggest that what led to the errors involved in the Taylor’s model is its wrongly neglecting the effect of the sedimentary en-vironment on the chemical composition of sediments, and that the environment should be an important factor affecting the distribution patterns of trace elements in the sediments.展开更多
The Ukwortung area of the Obudu Plateau exposes high-grade metamorphic rocks of upper amphibolite to granulite facies. Zircon grains from three locations of Southwest Obudu Plateau were dated by the Pb-Pb dating metho...The Ukwortung area of the Obudu Plateau exposes high-grade metamorphic rocks of upper amphibolite to granulite facies. Zircon grains from three locations of Southwest Obudu Plateau were dated by the Pb-Pb dating method. This single zircon radiometric dating method confirms the occurrence of Mesoproterozoic crust in the southeastern Nigeria basement complex. The pyroxene gneiss (granulite facies) sample from Biereberi near Ukpe yielded a mean age of 2061.4±0.4 Ma, suggesting the presence of Paleoproterozoic crust. The combined 207Pb/206Pb ratios from the garnet-biotite gneiss in the area gave a mean age of 1794.4±0.4 Ma. This further confirms the pres-ence of Paleoproterozoic crustal components within the Obudu Plateau. The Mesoproterozoic (1548.8±0.5 Ma) and Neoproterozoic (619.8±0.9 Ma) ages were obtained from two populations of zircon grains from the leucogranite in Okordem, Southwest Obudu. These "signatures" collaborate the occurrence of Mesoproterozoic ages in the Afar region and Cameroon basements along with the southeastern Nigerian basement complex, constituting the major portion of the West Central African mobile belt. The zircon age of 1794.4±0.4 Ma may probably be the maximum depositional age of the meta-sediment (garnet-biotite gneiss) and the age of 1548.8±0.5 Ma may be interpreted as the time of emplacement of the granitoid. The Neoproterozoic age (619.8±0.9 Ma) probably records the metamorphic event that was prevalent during the Pan-African period and thus affected the area.展开更多
文摘It is suggested in this paper that the famous Taylor’s model for the compdrition and evolution of the continental crust consists of three closely related key links. These links include an assumption that the surficial environment has no effect on the sedimentary REE patterns and the REE patterns in shales can reflect the composition of their provenancel a discovery about the discrepancy of sedimentary REE patterns between Archean and Proterozoic, and a deduc-tion that there was a global scale K-granitoid event at the end of the Archean. Based on a de-tailed discussion, this paper substantially negates the rationality of the Taylor’s model and ar-gues that its three critical links be three great errors indeed. Moreover, some other deficiencies or problems it confronts are described in this paper. The authors suggest that what led to the errors involved in the Taylor’s model is its wrongly neglecting the effect of the sedimentary en-vironment on the chemical composition of sediments, and that the environment should be an important factor affecting the distribution patterns of trace elements in the sediments.
文摘The Ukwortung area of the Obudu Plateau exposes high-grade metamorphic rocks of upper amphibolite to granulite facies. Zircon grains from three locations of Southwest Obudu Plateau were dated by the Pb-Pb dating method. This single zircon radiometric dating method confirms the occurrence of Mesoproterozoic crust in the southeastern Nigeria basement complex. The pyroxene gneiss (granulite facies) sample from Biereberi near Ukpe yielded a mean age of 2061.4±0.4 Ma, suggesting the presence of Paleoproterozoic crust. The combined 207Pb/206Pb ratios from the garnet-biotite gneiss in the area gave a mean age of 1794.4±0.4 Ma. This further confirms the pres-ence of Paleoproterozoic crustal components within the Obudu Plateau. The Mesoproterozoic (1548.8±0.5 Ma) and Neoproterozoic (619.8±0.9 Ma) ages were obtained from two populations of zircon grains from the leucogranite in Okordem, Southwest Obudu. These "signatures" collaborate the occurrence of Mesoproterozoic ages in the Afar region and Cameroon basements along with the southeastern Nigerian basement complex, constituting the major portion of the West Central African mobile belt. The zircon age of 1794.4±0.4 Ma may probably be the maximum depositional age of the meta-sediment (garnet-biotite gneiss) and the age of 1548.8±0.5 Ma may be interpreted as the time of emplacement of the granitoid. The Neoproterozoic age (619.8±0.9 Ma) probably records the metamorphic event that was prevalent during the Pan-African period and thus affected the area.
