Peperites Associated Pillow Lavas within Ophiolites and New Insight to Tectonic Setting: Comparative Study between Oman and West Junggar of China

Peperites are generated by magma intruding and mingling with wet unconsolidated or poorly consolidated sediments.Late Paleozoic peperites have been identified in the Darbut and Baijiantan ophiolitic belts at West Junggar,NW China.The peperites form successions up to 500 m thick interbedded with basaltic lava(sometimes pillow lava)and sedimentary rocks(i.e.limestones).The peperites are described and interpreted as resulting from basaltic lava bulldozed into wet,unconsolidated sediments at their basal contacts.The peperitebearing units are generally undeformed,occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the Darbut and Baijiantan ophiolitic belts,in contrast to the highly deformed slices of ophiolite.They demonstrate that the Darbut and Baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin.Jordan et al.(2008)reported an occurrence of peperite in the Oman—United Arab Emirates(UAE)border region.In this border area the field relations of the pillow lavas surrounded by limestone with deformed bedding and peperite boundaries between the pillows and the limestone are consistent with the pillow lavas forming directly within carbonate sediments.The pillow lavas in Oman-UAE border area likely have formed as intrusions into water-saturated carbonate sediments deposited along the edges of seamounts.Based on the comparative study on the peperites associated pillow lavas within ophiolites between West Junggar and Oman,this paper proposes that the ophiolites with peperites associated pillow lavas surrounded by limestone were not formed in a typical ocean basin,but a shallow remnant ocean basin.

Peperites in the Permian Tarim large igneous province in Northwest China and their constraints on the local eruption environments

Peperites are special kinds of volcaniclastic materials generated by mingling of magma and unconsolidated sediments. They directly demonstrate the contemporaneity of volcanism and sedimentation, and hence they can be used to constrain the local paleoenvironments during volcanic eruptions. We identified peperites in the lower sequence of the northwest outcrops（Inggan-Kalpin area） of Permian Tarim large igneous province（TLIP）, Northwest China. In Inggan, blocky peperites were observed at the base of lava flows generated in the second eruption phase. This kind of peperites is generated by quenching of magma in a brittle fragmentation mechanism. While in Kalpin, both the second and the fourth eruption phases preserved peperites in the base of lava flows. Not only blocky but also fluidal peperites can be observed in Kalpin. The fluidal peperites were generated in vapor films, which insulated the magmas from cold sediments and avoided direct thermal shock, and therefore kept the fluidal forms of magma. All of these peperites are hosted by submarine carbonates. In lava sequences generated in the same eruption phases but located in Kaipaizileike, ~15 km east to Inggan, terrestrial flood basalts developed while peperites are absent, implying a paleoenvironmental transition between Kaipaizileike and Inggan-Kalpin area. Gathering information from observed peperites, TLIP lava flows, and the Lower Permian sedimentary strata, we precisely constrained the spatial distribution and temporal evolution of sedimentary facies of the early stage of TLIP. As a result, two marine transgressions were identified. The first transgression occurred contemporaneous with the second eruption phase. The transition from submarine to subaerial is located between Kaipaizileike and Inggan. The second transgression occurred contemporaneous with the forth eruption phase, and the transition from submarine to subaerial occurred between Inggan and Kalpin.