Aqueous Fluid Activity and Its Effects in the Subduction Zones: A Systematic Numerical Modeling Study
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摘要: 为探讨水流体活动对板块俯冲隧道过程及大陆碰撞造山的制约作用，采用热力学和动力学耦合的数值模拟方法，建立了系统的数值模型.结果显示俯冲隧道内的混杂岩存在两种不同的折返路径：（1）平行于俯冲隧道斜向上折返，形成靠近缝合带的高压-超高压变质岩；（2）近垂直穿过上覆地幔楔侵入地壳深度.这两种差异性的模式主要受控于俯冲带热结构.俯冲带的温度结构控制俯冲隧道内水流体和熔体活动，从而影响上覆地幔楔的弱化程度，最终导致俯冲带内物质的不同运移过程和折返路径.同时，大陆俯冲碰撞带的岩石圈变形和拆沉作用均与俯冲带的流体-熔体活动所导致的岩石圈弱化息息相关.数值模拟结果极大促进了对于板块俯冲带流体-熔体活动及其动力学过程的理解.Abstract: In order to study the effects of aqueous fluid activity on the subduction channel processes and continental collision dynamics,systematic numerical models were constructed with integrated thermodynamic and thermomechanical methods. The model results indicate that the subducted crustal materials may either exhume along the subduction channel to the surface near the suture zone,or extrude sub-vertically upward through the mantle wedge to the crust of the overriding plate. The contrasting modes are strongly dependent on the thermal structure of subduction zones. The temperature field controls the aqueous fluid and melt activities,which further regulates the weakening of overriding mantle wedge and finally dominates the material transportation in the subduction channel. Meanwhile,the lithospheric deformation during continental subduction and collision is also strongly dependent on the fluid-melt activity and the induced lithospheric weakening. The numerical models contribute significantly to the better understanding of subduction-zone fluid-melt activity and the geodynamic processes.
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Key words:
- subduction zone /
- fluid activity /
- exhumation /
- delamination /
- numerical modeling /
- geodynamics
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图 1 俯冲带含水流体活动的物质场演化数值模型
颜色代表岩石类型.模型的演化时间如图左下角所示(修改自李忠海等，2015)
Fig. 1. Composition evolution of the numerical model with fluid-melt activity in the subduction zones
图 2 会聚板块年龄或厚度对俯冲带温度结构的制约
a.参考模型演化至10 Ma时，温度场分布(俯冲大洋岩石圈年龄为tAo=60 Ma，上覆大陆岩石圈厚度为Tc=140 km，俯冲速率为Vx=5 cm/a)；黑色垂线b~e代表温度剖面位置.b、c.保持Tc=140 km和Vx=5 cm/a不变，不同年龄大洋岩石圈模型俯冲至10 Ma时，黑线b、c(x=2 720 km，2 840 km)位置对应的温度结构.d、e保持tAo=60 Ma和Vx=5 cm/a不变，不同上覆大陆岩石圈厚度模型演化至10 Ma时，黑线d、e(x=2 700 km，2 900 km)位置对应的温度结构.图修改自Liu et al.(2017)
Fig. 2. The constraints of age or thickness of convergent plates on the temperature structure of subduction zones
图 3 俯冲带物质折返模式相
Fig. 3. Regime diagram of material exhumation in the subduction zones
图 4 岩石圈弱化程度对大陆俯冲碰撞模式的制约
修改自Li et al.(2016);模型A和B的上覆岩石圈地幔采用干橄榄岩的流变强度，而模型C和D的上覆岩石圈地幔采用湿橄榄岩的流变强度(Ranalli，1995)
Fig. 4. Constraints of lithospheric weakening on the continental subduction and collision
图 5 阿尔卑斯-喜马拉雅构造域内三个典型造山带区域地质简图及壳幔结构示意
区域主要构造线及构造单元(从西至东)：EAF.东安纳托利亚断裂；NAF.北安纳托利亚断裂；NEAF.北东安纳托里利亚断裂；BS.Bitlis缝合带；ZFTB.扎格罗斯褶皱冲断带；HZ.高扎格罗斯；SSZ.Sanandaj-Sirjan区域；UDMA.Urumieh-Dokhtar岩浆弧；CIP.中部伊朗高原；MBT.主边界断裂；MCT.主中央断裂；STDS.藏南拆离系；ITS.雅江缝合带；BNS.斑怒缝合带；JS.金沙江缝合带；KF.喀喇昆仑断裂；修改自Huangfu et al.(2019)
Fig. 5. Major tectonic units and simplified crustal-lithospheric structure of three collisional orogenies within the Alpine-Himalayan belt
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