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红土型风化壳和次生锰矿床形成于温暖和潮湿的古气候条件 ,其中含有丰富的表生钾锰矿物。因此 ,对表生钾锰矿物进行精确的40 Ar/ 3 9Ar年龄测定 ,不仅能查明大陆化学风化和矿床次生富集的时间和过程 ,而且可以为区域古气候的反演提供重要的年代学资料。透射电子显微镜、热重分析、离子交换实验和40 Ar/ 3 9Ar同位素分析表明 ,层状结构的黑锌锰矿、锂锰矿和钠水锰矿以及具有 1× 1隧道结构的软锰矿不适合于40 Ar/ 3 9Ar年龄测定 ;而隐钾锰矿、锰钡矿和锰铅矿因具有致密和稳定的 2× 2隧道结构及很强的保存K Ar体系的能力 ,是40 Ar/ 3 9Ar同位素定年的理想对象。硬锰矿和钙锰矿分别具有 2× 3和 3× 3隧道结构 ,由于隧道孔径过大 ,晶体结构的稳定性较差 ,其作为40Ar/ 3 9Ar测年的适用性有待于进一步证实。采用精细的激光阶段加热技术 ,可以有效克服表生钾锰矿物40 Ar/ 3 9Ar测年过程中3 9ArK 的反冲损失、多世代表生钾锰矿物的共生 ,以及表生钾锰矿物中原生矿物的污染和过量大气氩的存在等问题 ,并获得有意义的风化年龄。已有数据表明 ,表生钾锰矿物的形成主要集中在白垩纪末期、始新世末期—渐新世早期、中新世和上新世中期等 4个时期 ,可能记录了地史时期周期性的化学风化及气候的交替演变
Lateritic weathering crusts and secondary manganese deposits formed in warm and humid paleoclimatic conditions, which are rich in raw potash-manganese minerals. Therefore, the accurate 40 Ar / 3 9Ar dating of supergene potassium-manganese minerals can not only identify the time and process of chemical weathering and secondary enrichment in the continent, but also provide an important date for the retrieval of regional paleoclimate Learn information Transmission electron microscopy, thermogravimetric analysis, ion exchange experiments and isotope analysis of 40 Ar / 3 9Ar show that lanthanum ore, lanthanum ore and sodium manganite with a layered structure and pyrolusite with a 1 × 1 tunnel structure are not suitable for 40 Ar / 3 9Ar dating, whereas cryptocupromas, manganites and manganites are ideal for 40 Ar / 3 9Ar isotope dating due to their dense and stable 2 × 2 tunnel structure and their strong ability to store K Ar systems Object The hard-manganese ore and the calcium-manganese ore have 2 × 3 and 3 × 3 tunneling structures, respectively. Due to the large tunnel aperture, the stability of the crystal structure is poor. Its applicability as a 40Ar / 3 9Ar dating site needs to be further confirmed. The fine laser stage heating technology can effectively overcome the 3 9ArK recoil loss during the dating of 40 Ar / 3 9Ar and the symbiosis of many representative potash-manganese minerals, Mineral contamination and the presence of excessive atmospheric argon and other issues, and to obtain meaningful weathering age. The available data show that the formation of epithermal potassium mineral mainly in the late Cretaceous, late Eocene - Oligocene, Miocene and mid-Pliocene period of 4, may record the period of geostatistics The chemical weathering and the alternating climate change