Petrotectonics of ultrahigh-pressure crustal and upper-mantle rocks—Implications for Phanerozoic collisional orogens
Petrotectonics of ultrahigh-pressure crustal and upper-mantle rocks—Implications for Phanerozoic collisional orogens
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DOI：
10.1130/2007.2433(02
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
W. Ernst;B. Hacker;J. Liou
中科院分区：
文献类型：
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作者：
W. Ernst;B. Hacker;J. Liou
收缩造山带中的超高压（UHP）变质地体反映了大陆地壳在90 - 140公里深处与密集的海洋板块结合的下降。所有已知的记录良好的超高压复合物形成于显生宙。岩石强烈回退到低压组合，在坚硬、难熔的寄主矿物中保留了罕见的残余超高压相。复活的超高压板主要由石英岩和蛇纹岩组成；致密镁铁+超镁铁岩性占出土岩体的10%以下。伴生的含石榴石超镁铁透镜体一般有四种成因：A型橄榄岩+榴辉岩荚果反映了幔楔中的前变质作用；B型岩浆为俯冲前升入地壳的幔源超镁铁质岩浆；C型构造透镜体存在于海底流动之前的海洋岩石圈；和D型石榴石橄榄岩的深层地幔矿物学形成于A、B和c型石榴石橄榄岩的uhp相组合的俯冲事件之前，并且独立于此。地质年代学限制了片麻岩、超镁铁岩和榴辉岩的原岩、峰值和逆行再结晶的时间。往返压力-温度（P-T）路径在<5 - 10米/小时内完成，上升速度接近俯冲速度。从深部挖掘涉及近绝热减压，通过P-T油田的低压变质相。许多复合体由薄的异域薄片组成，但中国东部和挪威西部的复合体厚度约为10公里。在俯冲带中产生的延展性变形推覆体，随着片状超高压复合体的上升，热量被带走，在上下表面冷却。较厚的超高压块状也必须淬火。沿俯冲通道的上升主要受相对于周围地幔的低密度地壳物质的浮力驱动。快速挖掘阻止了在俯冲带建立一个更正常的地热制度。h2o的缺乏阻碍了反反应，而它的存在则加速了转化
Ultrahigh-pressure (UHP) metamorphic terranes in contractional orogens refl ect descent of continental crust bonded to a dense, dominantly oceanic plate to depths of 90‐140 km. All recognized well-documented UHP complexes formed during Phanerozoic time. Rocks are intensely retrogressed to low-pressure assemblages, with rare relict UHP phases retained in tough, refractory host minerals. Resurrected UHP slabs consist chiefl y of quartzofeldspathic rocks and serpentinites; dense mafi c + ultramafi c lithologies comprise <10% of exhumed masses. Associated garnet-bearing ultramafi c lenses are of four general origins: type A peridotite + eclogite pods refl ect premetamorphic residence in the mantle wedge; type B masses were mantle-derived ultramafi c-mafi c magmas that rose into the crust prior to subduction; type C tectonic lenses were present in the oceanic lithosphere prior to underfl ow; and type D garnet peridotites achieved their deep-seated mantle mineralogy long before—and independent of—the subduction event that produced the UHP-phase assemblages in garnet peridotite types A, B, and C. Geochronology constrains the timing of protolith, peak, and retrograde recrystallization of gneissic, ultramafi c, and eclogitic rocks. Roundtrip pressure-temperature (P-T ) paths were completed in <5‐10 m.y., where ascent rates approximated subduction velocities. Exhumation from profound depth involves near-adiabatic decompression through P-T fi elds of much lower-pressure metamorphic facies. Many complexes consist of thin, allochthonous sheets, but those in eastern China and western Norway are about 10 km thick. Ductilely deformed nappes generated in subduction zones allow heat to be conducted away as sheet-like UHP complexes rise, cooling across both upper and lower surfaces. Thicker UHP massifs also must be quenched. Ascent along the subduction channel is driven mainly by buoyancy of low-density crustal material relative to the surrounding mantle. Rapid exhumation prevents establishment of a more normal geothermal regime in the subduction zone. Lack of H 2 O impedes back reaction, whereas its presence accelerates transformation