Four-dimensional thermal evolution of the East African Orogen: accessory phase petrochronology of crustal profiles through the Tanzanian Craton and Mozambique Belt, northeastern Tanzania
Four-dimensional thermal evolution of the East African Orogen: accessory phase petrochronology of crustal profiles through the Tanzanian Craton and Mozambique Belt, northeastern Tanzania
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DOI：
10.1007/s00410-020-01737-6
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发表时间：
2020-10
影响因子：
3.5
通讯作者：
F. Apen;R. Rudnick;J. Cottle;A. Kylander‐Clark;M. Blondes;P. Piccoli;G. Seward
中科院分区：
文献类型：
--
作者：
F. Apen;R. Rudnick;J. Cottle;A. Kylander‐Clark;M. Blondes;P. Piccoli;G. Seward
坦桑尼亚东北部的深地壳捕虏体和露头的U-Pb岩石年代学追踪了新元古代东非造山运动（EAO）和随后的新近纪裂谷作用后莫桑比克带和坦桑尼亚盆地的热演化。在克拉通边缘，中上地壳记录了太古代以来的热平静（花岗岩和角闪岩捕虏体中的2.8-2.5 Ga锆石、金红石和磷灰石）。克拉通的下地壳记录了与新太古代超高温变质作用有关的热脉冲（约200年）。2.64 Ga，> 900 °C锆石），EAO（600-500 Ma金红石），以及裂谷过程中的流体流入（< 5 Ma磷灰石）。石榴麻粒岩捕虏体中的金红石表现出部分Pb损失，这与EAO后下地壳的缓慢冷却有关，并表明在夹带之前居住在500-600 °C。与克拉通相反，莫桑比克带的整个地壳在EAO之后经历了差异冷却。上地壳和中地壳都记录了640 - 560 Ma的变质作用（锆石、独居石和钛铁矿）和510-440 Ma的快速折返作用（金红石和磷灰石）。下地壳捕虏体含有太古代锆石，但含有近零年龄的金红石和磷灰石，表明在喷发时温度高于650 °C（高于金红石和磷灰石的铅封闭层）。环带状钛铁矿记录了550 Ma下地壳冷却期间的生长，随后是缓慢冷却和折返期间的流体流入（450 Ma后为0.1-1 °C/Myr）。克拉通和造山带允许的地壳温度较低，表明通过地壳的地幔热流变化，反映地幔岩石圈厚度的差异，而不是对流加热裂谷。
U–Pb petrochronology of deep crustal xenoliths and outcrops across northeastern Tanzania track the thermal evolution of the Mozambique Belt and Tanzanian Craton following the Neoproterozoic East African Orogeny (EAO) and subsequent Neogene rifting. At the craton margin, the upper–middle crust record thermal quiescence since the Archean (2.8–2.5 Ga zircon, rutile, and apatite in granite and amphibolite xenoliths). The lower crust of the craton documents thermal pulses associated with Neoarchean ultra-high temperature metamorphism (ca. 2.64 Ga, > 900 °C zircon), the EAO (600–500 Ma rutile), and fluid influx during rifting (< 5 Ma apatite). Rutile in garnet granulite xenoliths exhibits partial Pb loss related to slow cooling of the lower crust after the EAO and suggests residence at 500–600 °C prior to entrainment. In contrast to the craton, the entire crust of the Mozambique Belt underwent differential cooling following the EAO. Both the upper and middle crust record metamorphism from 640 to 560 Ma (zircon, monazite, and titanite) and rapid exhumation at 510–440 Ma (rutile and apatite). Lower crustal xenoliths contain Archean zircon, but near-zero age rutile and apatite, indicating residence > 650 °C (above Pb closure of rutile and apatite) at the time of eruption. Zoned titanite records growth during cooling of the lower crust at 550 Ma, followed by fluid influx during slow cooling and exhumation (0.1–1 °C/Myr after 450 Ma). Permissible lower-crustal temperatures for the craton and orogen suggest variable mantle heat flow through the crust and reflect differences in mantle lithosphere thickness rather than advective heating from rifting.