Mineral age patterns in ca. 3700 my old rocks from West Greenland
Mineral age patterns in ca. 3700 my old rocks from West Greenland
复制标题
大约的矿物年龄模式。
DOI：
10.1016/0012-821x(73)90154-4
复制
发表时间：
1973
影响因子：
5.3
通讯作者：
G. Turner
中科院分区：
文献类型：
--
作者：
R. Pankhurst;S. Moorbath;D. Rex;G. Turner
KSingle Bondar，40ArSingle Bond39Ar和RbSingle Bondsr测年报告了来自西格陵兰岛Godthaabsfjord地区约3700年的我的老Amätsoq和Isua片麻岩的矿物。黑云母和角闪岩上的KSingle Bondar日期范围约为1900至3500 My，而角闪石的范围比黑云母要窄得多(约2250-2750 My)。一种来自伊苏阿的黑云母给出了令人难以置信的高Kone邦达年龄4940 My。40 Arone Bond39Ar矿物年龄在整个表观年龄范围内与传统的Kone Bondar年龄非常一致。在角闪石中观察到少量过量Ar的存在，但黑云母中的放射性成因和过剩Ar是完全均一的，无法区分。黑云母的Rb-Sr测量结果非常一致，表明所有黑云母在1600-1700My附近完全开放了放射性成因87Sr的扩散。这是目前在西格陵兰太古宙发生区域性热事件的第一个证据，尽管在北部和南部的元古界也有类似的年龄。证据表明，这些Kone Bondar黑云母的年龄大于约2700-2800 My，这是在大约这个年龄的热事件期间，或者更有可能是在1600-1700 My锶同位素均一事件期间合并的过量放射性成因Ar的结果。散布在2700My以下的矿物年龄也可能至少部分是由于1600年至1700年My事件的叠加。与GodthaAsford地区最后一次重大成岩事件有关的伟晶岩，即QOˆRqut花岗岩的单邦达矿物年龄和Rb-Sr矿物等时线表明，侵位年龄为2580±30My。
Ksingle bondAr,40Arsingle bond39Ar and Rbsingle bondSr dates are reported for minerals from the ca. 3700 my-old Amîtsoq and Isua gneisses of the Godthaabsfjord area of West Greenland. Ksingle bondAr dates on biotites and hornblendes range from about 1900 to 3500 my, with hornblendes having a much narrower range (ca. 2250–2750 my) than biotites. One biotite from Isua gives an impossibly high Ksingle bondAr date of 4940 my.40Arsingle bond39Ar mineral dates are in close agreement with conventional Ksingle bondAr dates over the entire range of apparent age values. The presence of minor amounts of excess argon is observed in the hornblendes, but radiogenic and excess argon in the biotites are completely homogenised and cannot be differentiated.Rb-Sr measurements on biotites are closely concordant and show that all biotites were completely open to diffusion of radiogenic87Sr at about 1600–1700 my. This is the first proof of a regional thermal event at this time in the Archaean of West Greenland, although similar dates are well known from the Proterozoic belts to the north and south.The evidence suggests that those Ksingle bondAr biotite dates greater than about 2700–2800 my result from excess radiogenic argon incorporated during a thermal event of about this age or, more probably, during the 1600–1700 my Sr isotope homogenisation event. Scatter of mineral dates below about 2700 my could also be due, at least in part, to overprinting by the 1600–1700 my event.Ksingle bondAr mineral dates and an Rb-Sr mineral isochron from a pegmatite associated with the last major rock-forming event in the Godthaabsfjord area, namely the Qoˆrqut granite, indicate an age of emplacement of 2580 ± 30 my.