P–T evolution and timing of a late Palaeozoic fore-arc system and its heterogeneous Mesozoic overprint in north-central Chile (latitudes 31–32°S)
P–T evolution and timing of a late Palaeozoic fore-arc system and its heterogeneous Mesozoic overprint in north-central Chile (latitudes 31–32°S)
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DOI：
10.1017/s0016756811000641
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发表时间：
2011-08
影响因子：
2.3
通讯作者：
A. Willner;H. Massonne;U. Ring;M. Sudo;S. Thomson
中科院分区：
文献类型：
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作者：
A. Willner;H. Massonne;U. Ring;M. Sudo;S. Thomson
在智利中北部晚古生代弧前体系中，在纬度31-32°S(自西向东)，中生代走滑事件(在支架中获得峰值P-T条件)在短距离内套叠了三个岩石构造单元：(1)基性增生的Choapa变质杂岩(CMC；350-430°C，6-9kbar)；(2)前缘增生的Arraán组(AF；280-320°C，4-6kbar)；(3)Huentelauquén组的楔形后盆地(HF；280；320°C，3-4kbar)。在CMC中，Ar-Ar斑点年龄为P-T峰期和279-242 Ma早期折返过程中白云母形成的局部年龄。在局部的石榴石云母片岩夹层(570-585℃，11-13kbar)中，Ar-Ar斑点年龄指的是307-274 Ma从俯冲通道上升。部分CMC在6.6-8.5kbar的条件下等压加热至510-580°C。房颤峰值P-T条件的年龄只能模糊地由≥310 Ma的残余裂变径迹年龄来近似，这与前锋吸积发生在基底吸积之前的观测结果一致。锆石裂变径迹年龄显示，CMC和AF在~248 Ma的温度低于~280°C，同时也形成了区域不整合。中生代伸缩事件的Ar-Ar白云母斑点年龄分别为~245~240 Ma、~210~200 Ma、~174~159 Ma和~142~127 Ma。锆石裂变径迹年龄局部重置为109-96 Ma。Ar-Ar白云母年龄的全部重置被认为是在局部渗透的水合流体存在的情况下，通过低温下的原位溶解/沉淀而发生的。因此，尽管弧前系统中的同生事件和后增积事件具有复杂的非均质后叠加，但仍然可以区分它们并确定其年代。
Abstract In the late Palaeozoic fore-arc system of north-central Chile at latitudes 31–32°S (from the west to the east) three lithotectonic units are telescoped within a short distance by a Mesozoic strike-slip event (derived peak P–T conditions in brackets): (1) the basally accreted Choapa Metamorphic Complex (CMC; 350–430°C, 6–9 kbar), (2) the frontally accreted Arrayán Formation (AF; 280–320°C, 4–6 kbar) and (3) the retrowedge basin of the Huentelauquén Formation (HF; 280–320°C, 3–4 kbar). In the CMC, Ar–Ar spot ages locally date white-mica formation at peak P–T conditions and during early exhumation at 279–242 Ma. In a local garnet mica-schist intercalation (570–585°C, 11–13 kbar) Ar–Ar spot ages refer to the ascent from the subduction channel at 307–274 Ma. Portions of the CMC were isobarically heated to 510–580°C at 6.6–8.5 kbar. The age of peak P–T conditions in the AF can only vaguely be approximated at ≥ 310 Ma by relict fission-track ages consistent with the observation that frontal accretion occurred prior to basal accretion. Zircon fission-track dating indicates cooling below ~ 280°C at ~ 248 Ma in the CMC and the AF, when a regional unconformity also formed. Ar–Ar white-mica spot ages in parts of the CMC and within the entire AF and HF point to heterogeneous resetting during Mesozoic extensional and shortening events at ~ 245–240 Ma, ~ 210–200 Ma, ~ 174–159 Ma and ~ 142–127 Ma. The zircon fission-track ages are locally reset at 109–96 Ma. All resetting of Ar–Ar white-mica ages is proposed to have occurred by in situ dissolution/precipitation at low temperature in the presence of locally penetrating hydrous fluids. Hence syn- and postaccretionary events in the fore-arc system can still be distinguished and dated in spite of its complex heterogeneous postaccretional overprint.