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南秦岭晚三叠世胭脂坝岩体的岩石磁学及磁组构可靠性约束

Magnetic mineralogy and fabric reliability constraint of Late Triassic Yanzhiba pluton in South Qinling

中文摘要英文摘要

胭脂坝岩体是秦岭造山带内具典型代表性意义的晚三叠世花岗岩,磁组构研究很好的揭示了该岩体的内部组构特征。本文开展了岩体的岩石磁学分析,结合其岩相学特征,探讨了用磁组构约束岩体内部组构这一方法的可靠性。研究表明,胭脂坝岩体样品的平均磁化率Km值和校正磁化率各向异性度PJ值总体较低,与顺磁性花岗岩类一致。磁滞回线分析表明,绝大部分样品的磁化率来自顺磁性矿物的贡献,少部分高磁化率样品含有铁磁性矿物的贡献,但其浓度极低。高磁化率值样品的IRM获得和反向退磁曲线及χ-T曲线分析表明,铁磁性矿物为磁铁矿,且为多畴颗粒。结合岩相学特征,可以认为胭脂坝岩体低场磁组构反映了顺磁性的云母类矿物的组构特征,磁组构特征真实记录了样品的内部组构。

Yanzhiba pluton is one of the typical Late Triassic granite plutons in Qinling, previous magnetic fabrics works constrained its internal fabrics well. However, the reliability of magnetic fabric method is not specifically studied. In this paper, we presented an elaborate magnetic mineralogy analysis, combining with previous petrographical data, to shed light on this problem. Mean susceptibility Km and corrected anisotropy degree PJ of Yanzhiba pluton are low, which are consistent with paramagnetic granite. Hysteresis loops show susceptibility of most samples originates from paramagnetic minerals, a small portion include ferrimagnetic contribution, but its concentration is very low. Isothermal remanent magnetization acquisition (IRM) and DC-Field demagnetization curves show the ferrimagnetic component in pluton is mainly soft magnetic mineral, χ-T curves confirmed it is magnetite. The hysteresis parameter ratios on Day plot further indicate multi-domain magnetite. Our results testified the magnetic fabric results from Yanzhiba pluton is reliable, recorded actually the mica fabrics and thus internal fabrics of the pluton.

张国伟、梁文天、陶威

地质学地球物理学

MS,IRM,磁滞回线,热磁曲线,铁磁性矿物,顺磁性花岗岩

MSIRMHysteresis loopshermomagnetic analysesFerrimagnetic mineralsParamagnetic grantie

张国伟,梁文天,陶威.南秦岭晚三叠世胭脂坝岩体的岩石磁学及磁组构可靠性约束[EB/OL].(2014-02-24)[2025-08-25].http://www.paper.edu.cn/releasepaper/content/201402-467.点此复制

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