Identification of survived Archean continental fragments in the Paleoproterozoic Trans-North China Orogen

Abstract

The late Archean granulite was found as tectonic slices amalgamated with the late Paleoproterozoic metamorphic rocks in the Pingquan area within the Paleoproterozoic Trans-North China Orogen. The late Archean intermediate granulite rocks with distinctive ‘red-eye socket’ texture record anticlockwise P-T paths and were metamorphosed at ∼2.5 Ga, whereas the late Paleoproterozoic mafic granulite and amphibolite with “white-eye socket” texture record clockwise P-T paths and were metamorphosed at 1.86–1.80 Ga. The ⁴⁰Ar/³⁹Ar ages (1.81–1.79 Ga) of hornblende further constrain the synchronous exhumation of these disparate metamorphic units, providing critical constraints on the Paleoproterozoic uplifting and cooling process. The juxtaposition of late Archean continental fragments with Paleoproterozoic subduction-related lithologies within a confined orogenic zone highlights the capacity of orogenic systems to preserve both juvenile accreted terranes and reworked more ancient continental fragments, implying remarkable longevity of continental materials through accretionary cycles. This phenomenon suggests that without detailed metamorphic-petrochronological analyses, amalgamated tectonic slices formed at different ages may remain unresolved, potentially leading to erroneous interpretations.