ABSTRACT

Whole rock O-isotopes of the Panjal Traps are presented in order to assess the influence of crustal contamination and hydrothermal alteration in their genesis. The basalts from the eastern Kashmir Valley and Lidder Valley have enriched δ¹⁸O_VSMOW values (9.0‰ to 12.0‰). The basalt with the lowest δ¹⁸O_VSMOW values (9.0‰ and 9.2‰) were likely affected by deuteric alteration but their values could be close to the original melt composition as the rocks do not show trace element (Th/Nb_PM ≈0.8; Nb/U ≈ 50; Th/La ≈0.1) or isotopic evidence of crustal contamination (⁸⁷Sr/⁸⁶Sr_i = 0.7043 to 0.7045; ε_Nd(t) = +1.1 to +1.3). The δ¹⁸O_VSMOW (> 12‰) values and Nd isotopes (ε_Nd(t) < −8.6) of the silicic Panjal Traps are consistent with derivation from continental crust. The remaining mafic rocks have enriched Sr-Nd-O isotopic values that indicate crustal (10–30%) contamination (ε_Nd(t) = −1.9 to −6.1; ⁸⁷Sr/⁸⁶Sr_i = 0.7051 to 0.7087; δ¹⁸O = 10.1‰ to 12.0‰) with the upper flows exhibiting further enrichment by hydrothermal alteration. The basalts from the Pir Panjal Range, western Kashmir Valley, have variable Nd isotopic values (ε_Nd(t) = −6.8 to +4.3) and the lowest δ¹⁸O_VSMOW values (6.8‰ to 7.9‰) of the study. The results demonstrate that the rocks from the Pir Panjal Range preserved not only differences in radiogenic isotopes but also the O-isotopes as well. The change in the Nd and O isotopes of the basalt from Guryal Ravine and Lidder Valley to the more depleted values of the Pir Panjal Range is likely due to a transition from a chondritic mantle source to a depleted mantle source as the continental rift evolved to a sea-floor spreading environment.

摘要

为了评估地壳污染和热液改变对其成因的影响，我们展示了 Panjal 陷阱的全岩 O 同位素。东部克什米尔河谷和利德河谷的玄武岩富集了δ ¹⁸ O _VSMOW值（9.0‰~12.0‰）。^{δ 18} O _VSMOW值最低（9.0‰ 和 9.2‰）的玄武岩可能受到氘化蚀变的影响，但由于岩石不显示微量元素（Th/Nb _PM ≈0.8； Nb/U ≈ 50; Th/La ≈0.1) 或地壳污染的同位素证据 ( ⁸⁷ Sr/ ⁸⁶ Sr _i  = 0.7043 至 0.7045; ε _Nd ( t) = +1.1 至 +1.3)。硅质 Panjal 圈闭的 δ ¹⁸ O _VSMOW (> 12‰) 值和 Nd 同位素 (ε _Nd ( t ) < -8.6) 与来自大陆地壳的推导一致。剩余的基性岩富含 Sr-Nd-O 同位素值，表明地壳 (10-30%) 污染（ε _Nd ( t ) = -1.9 至 -6.1；⁸⁷ Sr/ ⁸⁶ Sr _i  = 0.7051 至 0.7087；δ ¹⁸ O = 10.1‰ 到 12.0‰），上部水流通过热液蚀变进一步富集。来自克什米尔山谷西部 Pir Panjal 山脉的玄武岩具有可变的 Nd 同位素值 (ε _Nd ( t) = -6.8 至 +4.3) 和研究中的最低 δ ¹⁸ O _VSMOW值（6.8‰ 至 7.9‰）。结果表明，Pir Panjal Range 的岩石不仅保留了放射性同位素的差异，而且还保留了 O 同位素。从 Guryal Ravine 和 Lidder Valley 到 Pir Panjal Range 玄武岩的 Nd 和 O 同位素变化可能是由于随着大陆裂谷演化为从球粒状地幔源转变为贫化地幔源。海底传播环境。