Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric mantle.These rocks are important for deciphering the composition and
The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we car...The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ？ 4 Ma for the cores and 508 ？ 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ？ 3 Ma for a coarse-grained felsic orthogneiss and 507 ？ 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged （i.e., Late Mesoproterozoic/Early Neoproterozoic） metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.展开更多
Titanite(CaTi2SiO5) is an important accessory mineral not only in magmatic and metamorphic rocks,but also commonly in hydrothermal mineral deposits. It incorporates appreciable amounts(usually 10×10-6 s to 100&#...Titanite(CaTi2SiO5) is an important accessory mineral not only in magmatic and metamorphic rocks,but also commonly in hydrothermal mineral deposits. It incorporates appreciable amounts(usually 10×10-6 s to 100×10-6 s) of U and Th into its structure and has a closure temperature of Pb diffusion higher than 660～700 ℃(Scott and St-Onge,1995) ,making it an ideal U-Th-Pb geochronometer. The Daye metallogenic district is located in the west of the giant Middle-Lower Yangtze River(MLYR) Cu-Fe-Au province,eastern China and is well endowed with Fe,Cu,and polymetallic skarn deposits.展开更多
This paper carried out a study on U--Th--Pb behavior of zircons in a ＂dry＂ rock system during high-grade metamorphism in the Archean basement of eastern Sbandong. The studied sample has a mineral assemblage of plagi...This paper carried out a study on U--Th--Pb behavior of zircons in a ＂dry＂ rock system during high-grade metamorphism in the Archean basement of eastern Sbandong. The studied sample has a mineral assemblage of plagioclase ＋ K-feldspar ＋ clinopyroxene ＋ biotite ＋ quartz and its pro- tolith is considered to be diorite. The zircons are stubby, equant or irregular in shape and show fir-leaf, sectorial, banded or oscillatory zoning. They contain inclusions, including mineral assemblages of clinopyroxene ＋ orthopyroxene ＋ hornblende ＋ quartz and plagioclase ＋ K-feldspar ＋ biotite ＋ quartz. Fifty SHRIMP analyses were performed on 34 zircon grains, which commonly yielded high Th/U ratios （mostly 〉0.5）. Most analyses are distributed along concordia from 2.54 to 2.25 Ga, with the youngest age being - 1.95 Ga. Compositions and ages show large variations even in a same zircon grain. Combined with early studies, conclusions can be drawn as follows： 1） the diorite underwent two episodes of high-grade metamorphism, at the end of the Neoarchean and the Paleoproterozoic （-2.50 Ga and 1.95 Ga or slightly later）; 2） high-grade metamorphism in a ＂dry＂ rock system may partially reset the U--Th--Pb system of zircons and, in this case, the ages between the oldest and youngest are chronologically meaningless; and 3） high Th/U ratios may be common features of zircons formed during high-grade metamorphic conditions.展开更多
文摘Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric mantle.These rocks are important for deciphering the composition and
基金financial support from the National Natural Science Foundation of China (Grant no.41530209)the Central Public-Interest Scientific Institution Basal Research Fund (Grant no.JYYWF201819)
文摘The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ？ 4 Ma for the cores and 508 ？ 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ？ 3 Ma for a coarse-grained felsic orthogneiss and 507 ？ 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged （i.e., Late Mesoproterozoic/Early Neoproterozoic） metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.
基金supported by the NSFC(Grants Nos.90814004 and 40821061)
文摘Titanite(CaTi2SiO5) is an important accessory mineral not only in magmatic and metamorphic rocks,but also commonly in hydrothermal mineral deposits. It incorporates appreciable amounts(usually 10×10-6 s to 100×10-6 s) of U and Th into its structure and has a closure temperature of Pb diffusion higher than 660～700 ℃(Scott and St-Onge,1995) ,making it an ideal U-Th-Pb geochronometer. The Daye metallogenic district is located in the west of the giant Middle-Lower Yangtze River(MLYR) Cu-Fe-Au province,eastern China and is well endowed with Fe,Cu,and polymetallic skarn deposits.
基金supported by the Key Program of the Ministry of Land and Resources of China(Grant Nos.1212010811033, 1212010711815)
文摘This paper carried out a study on U--Th--Pb behavior of zircons in a ＂dry＂ rock system during high-grade metamorphism in the Archean basement of eastern Sbandong. The studied sample has a mineral assemblage of plagioclase ＋ K-feldspar ＋ clinopyroxene ＋ biotite ＋ quartz and its pro- tolith is considered to be diorite. The zircons are stubby, equant or irregular in shape and show fir-leaf, sectorial, banded or oscillatory zoning. They contain inclusions, including mineral assemblages of clinopyroxene ＋ orthopyroxene ＋ hornblende ＋ quartz and plagioclase ＋ K-feldspar ＋ biotite ＋ quartz. Fifty SHRIMP analyses were performed on 34 zircon grains, which commonly yielded high Th/U ratios （mostly 〉0.5）. Most analyses are distributed along concordia from 2.54 to 2.25 Ga, with the youngest age being - 1.95 Ga. Compositions and ages show large variations even in a same zircon grain. Combined with early studies, conclusions can be drawn as follows： 1） the diorite underwent two episodes of high-grade metamorphism, at the end of the Neoarchean and the Paleoproterozoic （-2.50 Ga and 1.95 Ga or slightly later）; 2） high-grade metamorphism in a ＂dry＂ rock system may partially reset the U--Th--Pb system of zircons and, in this case, the ages between the oldest and youngest are chronologically meaningless; and 3） high Th/U ratios may be common features of zircons formed during high-grade metamorphic conditions.
