PORPHYROBLAST INCLUSION TRAILS - THE KEY TO OROGENESIS
PORPHYROBLAST INCLUSION TRAILS - THE KEY TO OROGENESIS
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DOI：
10.1111/j.1525-1314.1989.tb00598.x
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发表时间：
1989-05-01
影响因子：
3.4
通讯作者：
JOHNSON, SE
中科院分区：
文献类型：
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作者：
BELL, TH;JOHNSON, SE
对成百上千个岩石中常见的螺旋状包裹体轨迹的包裹体轨迹进行了详细的显微结构分析，结果表明，螺旋形包裹体轨迹不是通过生长的成斑斑岩相对于地理坐标旋转而形成的。相反，它们是通过在几组彼此相继叠印的近乎正交的叶理上发生斑裂而逐渐生长形成的。在所研究的所有成斑岩中，这些近正交叶理的方向交替地近垂直和近水平。这些爆斑岩记录的变形路径表明，造山过程经历了多次重复的两阶段旋回：(1)地壳缩短和增厚，发育近垂直的面理和陡峭的拉伸线理；(2)重力不稳定和坍塌，发育近水平的面理、重力扩张、近同轴垂直缩短和随后在造山带边缘的逆冲。在野外观察到的斑岩中的包裹体拖尾叠印关系和不对称性与叶理叠印关系的关联可以确定所研究的岩石在造山带内的位置和移动。这些信息结合有关斑岩中化学分带的信息，提供了岩石所遵循的构造/变质(P-T-t)路径的详细信息。造山过程中斑岩可以相对于地理坐标旋转的韧性变形环境在空间上仅限于大陆地壳中垂直的韧性撕裂/横流断层，在这些断层上不存在整体缩短或扭压的成分。
Detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral‐shaped inclusion trails are common indicates that spiral‐shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates. They formed instead by progressive growth by porphyroblasts over several sets of near‐orthogonal foliations that successively overprint one another. The orientations of these near‐orthogonal foliations are alternately near‐vertical and near‐horizontal in all porphyroblasts examined. This provides very strong evidence for lack of porphyroblast rotation.The deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two‐stage cycle of: (1) crustal shortening and thickening, with the development of a near‐vertical foliation with a steep stretching lineation; followed by (2) gravitational instability and collapse of this uplifted pile with the development of a near‐horizontal foliation, gravitational spreading, near‐coaxial vertical shortening and consequent thrusting on the orogen margins. Correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen. This information, combined with information about chemical zoning in porphyroblasts, provides details about the structural/metamorphic (P‐T‐t) paths the rocks have followed.The ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical, ductile tear/transcurrent faults across which there is no component of bulk shortening or transpression.