Petrogenesis of a high‐temperature metamorphic terrane: a new tectonic interpretation for the north Dabieshan, central China
Petrogenesis of a high‐temperature metamorphic terrane: a new tectonic interpretation for the north Dabieshan, central China
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DOI：
10.1111/j.1525-1314.1996.00319.x
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发表时间：
1996-05
影响因子：
3.4
通讯作者：
R. Zhang;J. Liou;Chin-Ho Tsai
中科院分区：
文献类型：
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作者：
R. Zhang;J. Liou;Chin-Ho Tsai
北方大别山由多种变质岩组成，有少量的镁铁质-超镁铁质岩块，并有丰富的侏罗-白垩纪花岗质岩体。变质岩包括正片麻岩、斜长角闪岩、混合片麻岩和少量麻粒岩及变质沉积岩，未发现榴辉岩及其它高压变质岩，各种成分的麻粒岩以透镜体、块状或层状形式出现在含单斜辉石的斜长角闪岩或片麻岩中。大多数混合岩片麻岩的古质体含有单斜辉石;黑质体和浅色体紧密混杂，紧密折叠，可能是原地形成的。麻粒岩形成于800-830 °C和10-14 kbar的压力下，表现出近等温减压P-T路径，可能是地壳碰撞增厚的结果。镁铁质和超镁铁质麻粒岩中石榴子石和基质PI + Hbl组合周围的斜长石-角闪石冠状岩形成于约750-800 °C。片麻岩中角闪石部分交代单斜辉石是角闪岩相退变质作用的标志。斜长角闪岩相正片麻岩和层间斜长角闪岩形成于680-750 °C，c. 6千巴。在T ≤ 490°C的混合片麻岩中，斜长石之后形成了斜长石+正长石反条纹长石，这是退变质重结晶的最后阶段。这些P-T估计表明，北方大别变质麻粒-角闪岩相沉积形成于中低压变质场梯度为20-35 °C km-1的环境中，可能代表了三叠纪俯冲过程中中的中朝上盘，形成了南部的高磷单元和富磷单元。碰撞后侵入的镁铁质-超镁铁质堆晶杂岩发生由于俯冲板片的断裂。
The northern Dabie terrane consists of a variety of metamorphic rocks with minor mafic-ultramafic blocks, and abundant Jurassic-Cretaceous granitic plutons. The metamorphic rocks include orthogneisses, amphibolite, migmatitic gneiss with minor granulite and metasediments; no eclogite or other high-pressure metamorphic rocks have been found. Granulites of various compositions occur either as lenses, blocks or layers within clinopyroxene-bearing amphibolite or gneiss. The palaeosomes of most migmatitic gneisses contain clinopyroxene; melanosomes and leucosomes are intimately intermingled, tightly folded and may have formed in situ. The granulites formed at about 800–830 °C and 10–14 kbar and display near-isothermal decompression P–T paths that may have resulted from crust thickened by collision. Plagioclase-amphibole coronae around garnets and matrix PI + Hbl assemblages from mafic and ultramafic granulites formed at about 750–800 °C. Partial replacement of clinopyroxene by amphibole in gneiss marks amphibolite facies retrograde metamorphism. Amphibolite facies orthogneisses and interlayered amphibolites formed at 680–750 °C and c. 6 kbar. Formation of oligoclase + orthoclase antiperthite after plagioclase took place in migmatitic gneisses at T ≤ 490°C in response to a final stage of retrograde recrystallization. These P–T estimates indicate that the northern Dabie metamorphic granulite-amphibolite facies terrane formed in a metamorphic field gradient of 20–35 °C km-1 at intermediate to low pressures, and may represent the Sino-Korean hangingwall during Triassic subduction for formation of the ultrahigh- and high-P units to the south. Post-collisional intrusion of a mafic-ultramafic cumulate complex occurred due to breakoff of the subducting slab.