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Tectonic setting and exhumation history of the Pingtan–Dongshan Metamorphic Belt along the coastal area, Fujian Province, Southeast China

2002; Elsevier BV; Volume: 20; Issue: 7 Linguagem: Inglês

10.1016/s1367-9120(01)00066-9

1878-5786

Wen‐Shan Chen, Hsiao‐Chin Yang, Xin Wang, Hui Huang,

earthquake and tectonic studies

In the coastal region of the Fujian Province, the semi-ductile Changle–Nanao shear zone is spatially associated with the Pingtan–Dongshan Metamorphic Belt and a Late Cretaceous Magmatic Belt. The Metamorphic Belt was thrust onto the rocks of the Magmatic Belt along the Changle–Nanao shear zone. Uplifting of the Metamorphic Belt may have resulted in oblique underplating of an ancient Pacific plate, forming a left-lateral reverse strike-slip or transcurrent fault at the rear of a forearc basin. Based on 40Ar/39Ar ages, it is shown that this Metamorphic Belt was active from 132 to 82 Ma. The timing of exhumation varied spatially from north to south and appears to become younger in a southward direction. In the northern part of the Metamorphic Belt, the metamorphic rocks cooled rapidly at a rate of about 47°C/m.y. from 132 to 126 Ma, but the cooling rate decreased to 13–20°C/m.y. during the period 126–110 Ma. As constrained by the plateau dates of the overlying volcanic rocks (∼110 Ma), the rocks now at the surface had reached at the surface by ∼110 Ma. No conspicuous exhumation had occurred since then. In contrast, the exposed rocks from the middle and southern part of the Metamorphic Belt started cooling much later, dropping to 550°C by ∼110 Ma. They appear to have cooled at an average rate of 40–50°C/m.y. from 550–300°C, followed by slower cooling at circa 15–30°C/m.y. to 300–150°C.