A 40Ar / 39Ar and U / Pb isotopic study of the Ilímaussaq complex, South Greenland: Implications for the 40K decay constant and for the duration of magmatic activity in a peralkaline complex
A 40Ar / 39Ar and U / Pb isotopic study of the Ilímaussaq complex, South Greenland: Implications for the 40K decay constant and for the duration of magmatic activity in a peralkaline complex
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对格陵兰岛南部 Ilímaussaq 杂岩体进行 40Ar / 39Ar 和 U / Pb 同位素研究：对 40K 衰变常数和过碱性杂岩岩浆活动持续时间的影响
DOI：
10.1016/j.chemgeo.2005.10.004
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发表时间：
2006
期刊：
影响因子：
3.9
通讯作者：
G. Markl
中科院分区：
文献类型：
--
作者：
Thomas V. Krumrei;I. Villa;M. Marks;G. Markl
南格陵兰加尔达省的岩浆活动与1280 Ma和1180 ~ 1140 Ma的两次主要裂谷事件有关。很少有人知道在一个特定的复杂的岩浆活动的持续时间。伊利毛萨克岩体属于第二期裂谷作用，由非常多样的花岗岩和正长岩类组成，在三次连续的岩浆事件中侵入和分离。由于侵入体包含地球上一些最进化的、不相容的元素丰富的岩石，因此选择它进行详细的地质年代学研究，以量化熔体产生、侵入、分馏和冷却的持续时间。角闪石在伟晶岩和晚岩浆脉岩等各种岩石类型中都很丰富，用40 Ar/39 Ar法测年。由于大部分演化熔体的固相线温度低于角闪石的闭合温度，且没有后期加热事件发生，因此40 Ar/39 Ar年龄反映了岩浆结晶作用，可用于确定岩浆分异作用的持续时间。40 Ar/39 Ar坪年龄为1142.6±2.2 Ma ~ 1152.3±3.7 Ma [Steiger，R.H.和Jäger，E.，（1977年）。地质年代学小组委员会：关于在地质和宇宙年代学中使用衰变常数的公约。地球行星。Sci. Lett. 36、359-362。] 40 K衰变常数。这些年龄都小于第一批岩浆中斜锆石的U-Pb年龄（1160±5 Ma）。我们的结果表明，Steiger和Jäger的40 K衰变常数可能太高;类似于Kwon等人提出的λ [Kwon，J.，Min，K.，Bickel，P.和Renne，P.R.，（2002年）的报告。联合估计40 K衰变常数和定年标准年龄的统计方法。Math.Geol.34，457-474.] 40 Ar/39 Ar与U-Pb年龄相匹配。
Magmatism in the Gardar Province, South Greenland, is related to two main rifting events at 1280 Ma and 1180 to 1140 Ma. Little is known about the duration of the magmatic activity in a specific complex. The Ilímaussaq intrusion belongs to the second period of rifting and comprises an extraordinary diversity of granitic and syenitic rock types, which intruded and fractionated in three successive magmatic events. As the intrusion contains some of the most evolved, incompatible element-rich rocks on Earth, it was chosen for a detailed geochronological study to quantify the duration of melt production, intrusion, fractionation and cooling. Amphiboles, which are abundant in all rock types, including pegmatites and late magmatic veins, were dated using the40Ar/39Ar technique. Since the solidus temperature of the most evolved melts is below the closure temperature of amphibole, and no later heating event occurred, the40Ar/39Ar ages reflect the magmatic crystallisation and can be used to determine the duration of igneous differentiation. The40Ar/39Ar plateau ages range between 1142.6±2.2 Ma and 1152.3±3.7 Ma using the Steiger and Jäger [Steiger, R.H. and Jäger, E., (1977). Subcommision on Geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth Planet. Sci. Lett. 36, 359–362.]40K decay constant. These ages are younger than an U–Pb age of 1160±5 Ma on baddeleyite from the first magma batch. Our results indicate that the40K decay constant of Steiger and Jäger may be too high; a lambda similar to that proposed by Kwon et al. [Kwon, J., Min, K., Bickel, P. and Renne, P.R., (2002). Statistical methods for jointly estimating decay constant of40K and age of a dating standard. Math. Geol. 34, 457–474.] is required to make the40Ar/39Ar match the U–Pb age.