Unconformity-like Reflection Pattern under the Moho in the Sulu Area

1.IntroductionSincethediscoveryofcoesiteandndcrodiamond,theDabie-Suluultra-highPressure(UHP)meta-morphicbelthasbeenattractingworldwideattentionsofgeoscientists.Studyingthisoutstandinggeologicalregionmaygreatlyenhanceourunderstandingofmetamorphism,deepeffectsofcontinentalcollisionandgeodynandcsinconvergentplateboundaries.Thestudymayalsobeveryhelpfultoprovideevidencetorevealinteractionbetweenthecrustandthemantle,andtheformationofnewtypesofdiamonddeposits.EncouragedbytheinternationalContinenta…

Unconformity-like Reflection Pattern under the Moho in the Sulu Area

When seismic exploration is carried out for finding oil/gas traps in a sedimentary basin, angular unconformity-like reflectors often appear in a seismic profile, indicating some promising structures such as pinchout. People usually think that the angular unconformity-like reflection pattern could occur only in a sedimentary basin within the upper crust because the pattern corresponds to a combination of a flat layer and some dipping layers, and they belong to different sedimentary sequences. In order to find optimal site for continental scientific drilling in the Dabie-Sulu ultra-high pressure metamorphic belt containing minerals such as coesite and micro-diamond, I have been in charge of geophysical investigations in these Proterozoic metamorphic ter- ranes of crystalline rocks. The investigation includes deep seismic reflection, magnetotelluric survey, gravity and magnetic studies, together with large-scale geological mapping on the surface. In the Shimen site located in southeast Shandong Province, East China, I have found a very clear angular reflection pattern, similar to those obtained by petroleum seismic exploration in sedimentary basins, appearing from 10.3 s to 13 s, right under the Moho discontinuity. This unusual and strange event from the uppermost mantle seems significant and might provide some clues for understanding the interaction between the crust and the mantle. Therefore I present the result here for further studies and worldwide comparison. I shall start with the basic geological settings of this area, then deal with the data acquisition and processing parameters as well as the deep seismic reflection sections to identify the deep angular unconformity-like pattern (see Fig. 4), finally, a brief discussion on interpretation of this type of reflection events.