U-Pb, Th-Pb and Ar-Ar geochronology from the southern Sierras Pampeanas, Argentina: implications for the Palaeozoic tectonic evolution of the western Gondwana margin
U-Pb, Th-Pb and Ar-Ar geochronology from the southern Sierras Pampeanas, Argentina: implications for the Palaeozoic tectonic evolution of the western Gondwana margin
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阿根廷潘皮纳斯山脉南部的 U-Pb、Th-Pb 和 Ar-Ar 地质年代学：对冈瓦纳西部边缘古生代构造演化的影响
DOI：
10.1144/gsl.sp.1998.142.01.13
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
R. Miró
中科院分区：
文献类型：
--
作者：
J. P. Sims;T. Ireland;A. Camacho;P. Lyons;P. Pieters;R. Skirrow;P. Stuart;R. Miró
本文利用新的SHRIMP锆石和独居石206 Pb/238 U和208 Pb/232 Th年龄和剪切组构40 Ar-39 Ar步进加热年龄，确定了南Sierras Pampeanas地区三次明显的区域构造事件。第一次是帕玛诺尔事件，涉及冈瓦纳大陆西缘新元古代晚期盆地的闭合。碎屑锆石上的新边缘和独居石的同时生长表明变质峰是由c。530 Ma。第二个事件，Famatinian造山带，标志着西冈瓦纳大陆边缘向东倾斜俯冲的开始，并可能代表了更早的Pamatinian事件的延续。来自圣路易斯山脉的变质沉积岩中的锆石主要为早寒武世碎屑岩，表明其来源于帕莫提斯。这些岩石中的变质峰与长英质、镁铁质和超镁铁质岩石的侵位是同时发生的。480 Ma的碰撞环境。独居石年龄和有限的新锆石生长的变质沉积岩表明，法马廷造山运动已经停止了约450马。这与拉里奥哈省南部山脉晚期剪切作用的450-460 Ma Ar-Ar年龄具有很好的相关性。第三个构造事件，Achalian造山运动，涉及W方向的压缩和多个，大量的花岗岩侵入体的侵位。在此事件中的变形之间的离散剪切区和区域的开放到紧密的折叠。剪切带在W向逆冲断层和NNW向左行剪切带之间交替。从低级剪切组构的Ar-Ar数据表明，压扭变形持续通过大部分的泥盆纪。
Abstract New SHRIMP zircon and monazite 206Pb/238U and 208Pb/232Th ages on structurally controlled units and 40Ar-39Ar step-heating ages from shear fabrics, define three distinct regional tectonic events in the southern Sierras Pampeanas. The first, the Pampean orogeny, involved closure of a late Neoproterozoic basin on the western margin of Gondwana. New rims on detrital zircons and concurrent monazite growth suggest that the metamorphic peak was attained by c. 530 Ma. The second event, the Famatinian orogeny, marks the initiation of eastward-dipping subduction on the western Gondwana margin, and may represent a continuation of the earlier Pampean event. Metasedimentary rocks from the Sierras de San Luis have zircons with a predominantly Early Cambrian detrital age, indicating a Pampean source. The metamorphic peak in these rocks was contemporaneous with the emplacement of felsic, mafic and ultramafic rocks at c. 480 Ma in a collisional setting. Monazite ages and limited new zircon growth in the metasedimentary rocks suggest that the Famatinian orogeny had ceased by about 450 Ma. This correlates well with a 450–460 Ma Ar-Ar age for late shearing in the southern sierras of La Rioja province. The third tectonic event, the Achalian orogeny, involved W-directed compression and emplacement of multiple, voluminous, granite intrusions. Deformation during this event was partitioned between discrete shear-zones and regions of open to tight folding. The shear zones alternate between W-directed thrusts and NNW-trending, sinistral shear-zones. Ar-Ar data from the low-grade shear fabrics indicate that transpressional deformation continued through most of the Devonian.