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位于南襄盆地东部的泌阳凹陷为南断北超型断陷盆地,其古近纪核桃园组发育有世界上已知的最老沉积碱矿之一,即安棚碱矿.该含碱岩系包括细碎屑岩、泥质白云岩和层状碱矿层,其中碱矿层以重碳钠盐为主,含少量天然碱、芒硝和石盐.核桃园组三段上部-核二段含碱岩系中,白云质泥岩、泥质白云岩和碱矿层在Al2O3,TiO2,Na2O,MgO+CaO和LOI含量上具有明显差别.Na2O/(MgO+CaO)可用以指示Na碳酸盐相对于Mg-Ca碳酸盐的富集程度,据此可将泥质白云岩可分为<0.6和>0.6的两组.前者Na2O/(MgO+CaO)与Al2O3+TiO2含量呈正相关,随碎屑物质的减少倾向于形成纯的Mg-Ca碳酸盐岩,反映湖水蒸发量≤补给量,指示较潮湿气候;而后者中Na2O/(MgO+CaO)与Al2O3+TiO2含量呈反相关,随碎屑物质的减少向成碱方向发展,反映湖水蒸发量>补给量,指示较干旱气候.以Al作为标准,从泥质白云岩到碱矿层,随Na2O/(MgO+CaO)比值增大,Zr,Ti,La,K,Rb和Ba在碱矿层中明显相对富集,且PAAS(后太古宙平均页岩)标准化的Eu正异常也显著增强.结合碱矿层的高B含量及硅硼钠石的报道和区域伸展性构造背景的认识,该地球化学特征指示有深源热液流体通过边界深大断裂进入盆地而参与成碱过程.
The Biyang sag located in the east of the Nanxiang basin is the Nan-shengbei ultra-type fault basin. In the Paleogene Hetaoyuan Formation, there is one of the oldest known alkali deposits in the world, namely Anpeng alkali mine, The rock series include fine clastic rocks, dolomitic dolomites and stratiform alkali ore deposits, of which the alkali ore is dominated by heavy carbon sodium salt and contains a small amount of trona, mirabilite and stone salt. Alkaline mudstone, dolomitic mudstone, argillaceous dolomite and alkali seam have obvious differences in the contents of Al2O3, TiO2, Na2O, MgO + CaO and LOI. Na2O / (MgO + CaO) can be used to indicate that the ratio of Na carbonate to Mg-Ca carbonate enrichment, which can be divided into shale dolomite <0.6 and> 0.6 two groups.The former Na2O / (MgO + CaO) and Al2O3 + TiO2 content was positively correlated with the debris Substance reduction tends to form pure Mg-Ca carbonate rocks, reflecting the evaporation of the lake ≤ supply, indicating a more humid climate; while the latter Na2O / (MgO + CaO) and Al2O3 + TiO2 content was inversely correlated with the broken The reduction of the debris material to alkaline direction, reflecting the amount of evaporation of the lake water> recharge, indicating arid climate. With Al as the standard, from argillaceous dolomite to alkali seam, with the ratio of Na2O / (MgO + CaO) Large, Zr, Ti, La, K, Rb and Ba were significantly enriched in the basement ore layer, and the normalized Eu anomalies in the PAAS (average shale average shale) were also significantly enhanced. The report of Boraxite and the understanding of the regional extensional tectonic setting indicate that deep-hydrothermal fluids flow into deep basins along the border into the basin and participate in the alkali-forming process.