摘要
现有的测试数据反映，钾长石在K—Ar定年中存在很多问题，最常见的情况是年龄值偏年轻，有时也出现比共存矿物年龄偏老的情况。钾长石在实验过程中不完全释氩是造成年龄值偏年轻的原因之一，对此前人已经提出几个解决方案，但在实际应用中都不够完善。钾长石的封闭温度低（130～150℃）是放射成因氩丢失的最主要因素，个别情况下也出现捕获围岩中的放射成因氩，从而出现过剩氩。低温钾长石（如冰长石）的氩保存能力和结构有关系，通常情况下随着三斜度的升高所保存的放射成因氩会相应减少。不同地质环境中产出的钾长石在K—Ar定年中适用性有所不同，侵入岩中的钾长石（微斜长石和条纹长石等）不适合于K—Ar定年，而喷出岩中的钾长石（透长石和歪长石等）是非常好的定年矿物；低温钾长石可有条件应用。
K-feldspar, a ubiquitous mineral in igneous and metamorphic rocks, has long been used in K-Ar dating. However, a number of problems exist in K-Ar dating of K-feldspar. For example, K-feldspar usually yields younger ages than the co-existed minerals such as biotite. K-feldspar may also yield older ages in some cases. It is suggested that incomplete extraction of radiogenic argon from K-feldspar is one of the main reasons that leads to a younger age. Several solutions have been put forward to resolve the problem, but none of them has been successfully used in experiments. K-feldspar has low closure temperature （about 130 -150℃ ）, which can easily cause radiogenic argon lose; In addition, radiogenic argon from the wall rock as excess argon may also enter the K- feldspar. The low temperature K-feldspar （such as adularia ） shows capability to maintain various amounts of radiogenic argon which is related to their textures. The content of radiogenic argon in adularia is decreased with the increase of their triclinities. In summary, the applicabilities of K-feldspars from different geological environments are various in K-Ar dating. K-feldspars （such as micro cline and perthite） from intrusive rocks can not be used in K-Ar dating, while those （sanidine and anorthoclase） from extrusive rocks are very good ones, and the low temperature K-feldspars （adularia） can be used in dating conditionally.
出处
《高校地质学报》
CAS
CSCD
北大核心
2006年第3期375-377,共3页
Geological Journal of China Universities
基金
本文受到泰兆基金
国家自然科学基金(40372033)资助.
