四川里伍黑牛洞矿床中石榴石的Sm-Nd同位素年龄及其意义
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摘要
黑牛洞矿床中的石榴石有三个期次:早期的石榴石呈顺片理拉长的条带,中期的石榴石呈颗粒碎块发育,硫化物常沿早期和中期的石榴石的裂隙和颗粒边缘填充,晚期石榴石呈完整细粒变晶产出。本文测得晚期石榴石的Sm-Nd年龄为101±26M a(初始143Nd/144Nd=0.511765±0.000025),其可能代表黑牛洞矿床最后一期中高级变质作用的时代,与形成富矿体的脆韧性变形作用同期。
The Heiniudong copper deposit in the Liwu copper mining district is a newly found Cu-rich deposit in western Sichuan,and characteristic of polyphyletic,polyphase and polygenetic origins.Three phases of garnet are found in this deposit.Both the earliest garnet as bands along schistosity and subsequent one as grains are found to be filled by sulfides along fractures or around the grains.The latest garnet occurs as fine-grained crystalloblasts,and gives a Sm-Nd age of 101±26 Ma and an initial 143Nd/144Nd value of 0.511765±0.000025,which may be the age of the latest medium-to high-grade metamorphism.On the basis of the 39Ar/40Ar ages of biotite from the Heiniudong copper deposit(136.4±0.8 Ma) and Zhongzui copper deposit(143.4±1.9 Ma),and emplacement age of granites(K-Ar age of 131±5 Ma),the mineralization in individual deposits of the Liwu copper mining district has gone through a long period(15~20 Ma) of hydrothermal processes.
The Heiniudong copper deposit in the Liwu copper mining district is a newly found Cu-rich deposit in western Sichuan,and characteristic of polyphyletic,polyphase and polygenetic origins.Three phases of garnet are found in this deposit.Both the earliest garnet as bands along schistosity and subsequent one as grains are found to be filled by sulfides along fractures or around the grains.The latest garnet occurs as fine-grained crystalloblasts,and gives a Sm-Nd age of 101±26 Ma and an initial 143Nd/144Nd value of 0.511765±0.000025,which may be the age of the latest medium-to high-grade metamorphism.On the basis of the 39Ar/40Ar ages of biotite from the Heiniudong copper deposit(136.4±0.8 Ma) and Zhongzui copper deposit(143.4±1.9 Ma),and emplacement age of granites(K-Ar age of 131±5 Ma),the mineralization in individual deposits of the Liwu copper mining district has gone through a long period(15~20 Ma) of hydrothermal processes.
引文
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[6]马国桃,汪名杰,姚鹏,等.2009.四川省九龙县黑牛洞富铜矿矿床黑云母40Ar-39Ar测年及其地质意义[J].地质学报,2009,83,671-679.
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[9]GANGALY J,TIRONE M,HERVIG R L.Diffusion kinetics ofsamarium and neodymium in garnet,and a method for determiningcooling rates of rocks[J].Science,1998,281(5378):805-807.
[10]LI S,JAGOUTZ E,CHEN Y et al.Sm-Nd and Rb-Sr isotopicchronology and cooling history of ultrahigh pressure metamorphicrocks and their country rocks at Shuanghe in the Dabie Mountain,central China[J].Geochimica et Cosmochimica Acta,2000,64(6):1077-1093.
[2]李曙光,侯振辉,李秋立.超高压变质岩的放射性同位素体系及年代学方法[J].岩石学报,2005,21:1929-1942.
[3]四川省地质局第一区域地质测量大队.1974.1∶20万金矿幅区域地质调查报告[R].
[4]宋鸿林,田竞亚,颜丹平,等.1995.扬子地台西缘江浪变质核杂岩体变形变质作用及李伍式铜矿成矿模式,“八五”地质矿产部重点科技攻关项目研究成果报告[R].
[5]姚鹏,汪名杰,李建忠,等.里伍式富铜矿床同位素示踪及其成矿地质意义[J].地球学报,2008,29(6):691-696.
[6]马国桃,汪名杰,姚鹏,等.2009.四川省九龙县黑牛洞富铜矿矿床黑云母40Ar-39Ar测年及其地质意义[J].地质学报,2009,83,671-679.
[7]DOSON M H.Closure temperature in a cooling geochronlogicaland petrological system[J].Contributions to Mineralogy andPetrology,1973,40(3):259-274.
[8]BURTON K W,KOHN M J,COHEN A S et al.The relativediffusion of Pb,Nd,Sr and O in garnet[J].Earth and PlanetaryScience Letters,1995,133(1):199-211.
[9]GANGALY J,TIRONE M,HERVIG R L.Diffusion kinetics ofsamarium and neodymium in garnet,and a method for determiningcooling rates of rocks[J].Science,1998,281(5378):805-807.
[10]LI S,JAGOUTZ E,CHEN Y et al.Sm-Nd and Rb-Sr isotopicchronology and cooling history of ultrahigh pressure metamorphicrocks and their country rocks at Shuanghe in the Dabie Mountain,central China[J].Geochimica et Cosmochimica Acta,2000,64(6):1077-1093.
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