New geochronological constraints on the thermal and exhumation history of the Lesser and Higher Himalayan Crystalline Units in the Kullu-Kinnaur area of Himachal Pradesh (India).
New geochronological constraints on the thermal and exhumation history of the Lesser and Higher Himalayan Crystalline Units in the Kullu-Kinnaur area of Himachal Pradesh (India).
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DOI：
10.1016/j.jseaes.2012.02.015
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发表时间：
2012-06-30
影响因子：
3
通讯作者：
Horschinegg M
中科院分区：
文献类型：
--
作者：
Thöni M;Miller C;Hager C;Grasemann B;Horschinegg M
► 我们报告了来自喜马拉雅山西北部变质楔的新 Sm-Nd 和 Rb-Sr 数据。 ► 始喜马拉雅事件期间的融化受到 40 Ma 左右的 Sm-Nd 年龄的限制。 ► 变质峰值和地核的初始折返发生在 29 Ma 左右。 ► 19 Ma 左右，楔体上方的岩体侵入明显晚于主构造。 ► 7 Ma 古老的伟晶岩脉在持续的碰撞过程中限制了地壳的融化。来自喜马偕尔邦（印度）Beas-Sutlej 地区的新地质年代学、岩石学和结构数据被用来重建喜马拉雅造山带这一部分的构造热和折返历史。在 Malana-Parbati 地区逆变质高喜马拉雅晶体 (HHC) 的伟晶石上获得的 Sm-Nd 石榴石年龄为 40.5 ± 1.3 Ma，可能标志着初始减压期间的局部熔化。延性变形隐色片麻岩中正在进行的折返受到 29 ± 1 Ma 的 Sm-Nd 石榴石年龄和 24-20 Ma 左右的白云母 Rb-Sr 年龄的限制，而 Bt Rb-Sr 年龄表明在 15 至 12 Ma 之间区域变质温度下降到 300 °C 以下。萨特莱杰峡谷深处暴露出小喜马拉雅结晶体 (LHC) 的中品位片麻岩和元古界正片麻岩，这些岩体被沿主中央逆冲断层 (MCT) 的 HHC 推覆。 HHC 中的云母冷却年龄在 14–11 Ma 范围内。在 HHC 的挤压楔上方，Leo Pargil 淡色花岗岩和相关岩脉侵入特提斯喜马拉雅山 (TH) 弱变质古中生代沉积物下方的海曼塔单元 (HU)。 Leo Pargil 淡色花岗岩产生的 Sm-Nd 石榴石平均年龄为 19 ± 1 Ma，Rb-Sr 白云母和黑云母冷却年龄为 16.4 至 11.6 Ma。大型强子对撞机单位显着的年轻挤压导致造山带更多正面部分的差异化折返/冷却。王图附近大型强子对撞机片麻岩非常年轻的韧性变形受到横切主要糜棱岩叶理的晚期运动伟晶岩侵入的限制。这些伟晶岩的 Sm-Nd 石榴石和 Rb-Sr 白云母年龄范围在 7.9 ± 0.9 至 5.5 ± 0.1 Ma 之间。已发表的磷灰石 FT 年龄低至 0.6 Ma 还记录了造山带不同部分的加速历时次新折返。结合文献中的地质年代学数据，新的结果表明，HHC和HU在始喜马拉雅期（始新世晚期-渐新世）期间因缩短和地壳增厚而变形，随后在新喜马拉雅期（早中新世）期间出现强烈的热压印和花岗岩侵入。在 HHC 和极低品位的小喜马拉雅沉积物之间挤压之前，LHC 在晚中新世经历了角闪岩相变质条件。与气候变化相结合，喜马拉雅造山带中部的年轻构造活动可能对河流切割和侵蚀产生了强烈影响，因此加速了隆升，这一点可以从西部地区萨特莱杰河跨喜马拉雅源头赞达盆地中晚中新世到早更新世河湖沉积物的广泛堆积所表明。 西藏。
► We report new Sm–Nd and Rb–Sr data from metamorphic wedges in the NW-Himalayas. ► Melting during the Eohimalayan event is constrained by Sm–Nd ages around 40 Ma. ► Peak metamorphism and initial exhumation of the core is dated around 29 Ma. ► Intrusion of plutons above the wedges around 19 Ma clearly postdate the main fabric. ► 7 Ma old pegmatite dykes constrain melting of the crust during ongoing collision. New geochronological, petrological and structural data from the Beas–Sutlej area of Himachal Pradesh (India) are used to reconstruct the tectonothermal and exhumation history of this part of the Himalayan orogen. Sm–Nd garnet ages at 40.5 ± 1.3 Ma obtained on a pegmatoid from the inverse metamorphic High Himalayan Crystalline (HHC) in the Malana–Parbati area probably mark local melting during initial decompression. Ongoing exhumation in ductilely deformed leuco-gneiss is constrained by Sm–Nd garnet ages at 29 ± 1 Ma and white mica Rb–Sr ages around 24–20 Ma, while Bt Rb–Sr ages indicate a drop of regional metamorphic temperatures below 300 °C between 15 and 12 Ma. The deep Sutlej gorge exposes medium-grade paragneisses and Proterozoic orthogneisses of the Lesser Himalayan Crystalline (LHC), overthrust by the HHC along the Main Central Thrust (MCT). Mica cooling ages in the HHC are in the range of 14–11 Ma. Above the extruded wedge of the HHC, the Leo Pargil leucogranite and associated dykes intrude the Haimanta Unit (HU) below the weakly metamorphic Palaeo-Mesozoic sediments of the Tethyan Himalayas (TH). The Leo Pargil leucogranite yielded a mean Sm–Nd garnet age of 19 ± 1 Ma and Rb–Sr muscovite and biotite cooling ages between 16.4 and 11.6 Ma. Marked young extrusion of LHC units resulted in differentiated exhumation/cooling of more frontal parts of the orogen. Very young ductile deformation of LHC gneisses near Wangtu is constrained by late-kinematic pegmatite intrusions crosscutting the main mylonitic foliation. Sm–Nd garnet and Rb–Sr muscovite ages of these pegmatites range between 7.9 ± 0.9 and 5.5 ± 0.1 Ma. Published apatite FT ages down to 0.6 Ma also document accelerated diachronous sub-recent exhumation of different parts of the orogen. Together with geochronological data from the literature, the new results demonstrate that the HHC and the HU were deformed by shortening and crustal thickening during the Eohimalayan phase (Late Eocene–Oligocene), followed by a strong thermal overprint and intrusions of granitoids during the Neohimalayan Phase (Early to Middle Miocene). The LHC experienced amphibolite facies metamorphic conditions in the Late Miocene prior to extrusion between the HHC and the very low-grade Lesser Himalayan sediments. In conjunction with climate changes, young tectonic activity in this central part of the Himalayan orogen may have strongly influenced fluvial incision and erosion, and therefore, contributed to the accelerated uplift, as indicated by extensive accumulation of Late Miocene to Early Pleistocene fluviatile–lacustrine sediments in the Zanda basin, the Transhimalayan headwaters of the Sutlej, in Western Tibet.