熊耳地体南侧中晚元古代地层碳氧同位素组成:CMF模式的证据

Qi JP,Zhang J and Tang GJ.2005.Carbon and oxygen isotope composition of the Meso-Neoproterozoic strata south of the Xiong'er terrane:evidence of the CMF model.

前人运用 CMF 模式(碰撞造山成岩成矿与流体作用模式)推断熊耳地体金银矿床的成矿流体主要来自其南侧中晚元古代地层(官道口群和栾川群)的陆内俯冲变质脱水作用,并推测该套地层富放射成因铅和锶,δ^(13)C 和δ^(18)O 值较高。为检验该推论和 CMF 模式正确与否,作者对该套地层开展了研究,本文报道了碳氧同位素研究结果。13件岩石样品δ^(18)O 值变化于9.1‰～16.7‰,平均13.3‰;4件δ^(13)C_(CaCO_3)值为-2.8‰～0.8‰,平均-0.9‰,计算表明,该套地层在320～373℃(熊耳地体多数矿床早阶段成矿温度范围)变质脱水所形成流体的δ^(18)O值为2.6‰～14.6‰,与推测结果一致,覆盖了熊耳地体已有早阶段成矿流体的δ^(18)O值(5.1‰～12.6‰),计算的中晚元古代地层变质流体的δ^(13)C_(CO_2)随介于-0.7‰～4‰,也与熊耳地体成矿流体的δ^(13)C_(CO_2)值(-2.1‰～4‰,成矿早阶段一般δ^(13)C_(CO_2)>0)一致。如此以来,我们的研究结果证明了前人的推论和 CMF 模式的科学性与实用性,CMF 模式可以用于指导熊耳地体或类似构造环境的矿床勘查和地质研究。

In terms of the CMF model （ Tectonic Model for Collisional Orogeny, Metallogeny and Fluid Flow）, former researchers inferred that the ore - forming fluids and metals of gold/silver deposits in the Xiong＇er Terrane had been mainly sourced from intracontinental subduction - related metamorphic devolatilization of the Meso - Neoproterozoic strata （ Guandaokou and Luanchuan Groups） south of the Xiong＇er Terrane, and that the strata should be enriched in radiogenic Pb and St, and have high δ^13C and δ^18O values. To examine this inference and the CMF model, we have studied the Meso - Neoproterozoic strata and report the C and O isotope results in this paper. Thirteen δ^18O analyses of bulk - rock samples range 9.1‰- 16.7‰ and average 13.3‰; four δ^13CCaCO3 values range -2.8‰～0.8‰ and average - 0.9‰. Calculations show that the δ^18Ow values of the fluids, supposed to be sourced from metamorphic devolatilization of the strata at temperature span of 320 - 373℃（ early - stage metallogenic temperature of most deposits in the Xiong’er Terrane） , must be in the range of 2.6‰- 14.6‰. The calculated δ^18Ow, range, as inferred by former researchers, fully covers the available δ^18Ow values of the early - stage ore - fluids in the Xiong＇er Terrane （δ^18Ow= 5.1‰ - 12.6‰）. The calculated δ^13CCO2 values for fluids originated from metamorphic devolatilization of the strata are between -0.7‰- 4.0‰, consistent with the δ^13CCO2 values （ -2.1‰- 4.0‰, mostly 〉 0 in early stage） of ore - forming fluid - systems in the Xiong＇er Terrane. Therefore, our study strongly supports previous inference mentioned above and the science and utility of the CMF model. The CMF model can be employed to guide future exploration and geological study in the Xiong＇er Terrane and comparable tectonic settinzs.