Previous   |    Close   |    Next

Figure F30. Sketch of a hypothetical outcrop in a future Site 1256 ophiolite of the dike–gabbro transition zone showing the contact relationships observed in the cores and junk basket rocks recovered during Expedition 335. A. Diorite dikelet, comprised predominantly of primary igneous amphibole and plagioclase, crosscutting granoblastic basalt (Sample 335-1256D-Run19-RCJB-Rock C). B. Fine-grained dike chilled against coarser grained dike (Sample 335-1256D-Run12-RCJB-Rock S). The entire sample is recrystallized to granoblastic assemblages of plagioclase, orthopyroxene, clinopyroxene, magnetite, and ilmenite. Later fine post-contact metamorphic hydrothermal amphibole veins (not shown) cut across the contact and both dikes. C. Chilled and brecciated dike margin recrystallized to granoblastic assemblages (Sample 335-1256D-Run14-EXJB-Foliated). Angular clasts consist of granoblastic plagioclase with minor orthopyroxene, clinopyroxene, ilmenite, and magnetite and are recrystallized from chilled dike margin breccia protolith. Clast matrix is orthopyroxene rich with minor clinopyroxene, plagioclase, and oxides and is recrystallized from hydrothermal minerals (amphibole and chlorite) that veined and cemented the breccia protolith. D. Subophitic texture in gabbro (Sample 335-1256D-Run11-EXJB [Thin Section 12]). E. Diorite vein crosscutting a conjugate set of metamorphic orthopyroxene veins (Sample 335-1256D-Run19-RCJB-Rock B). F. Post-contact-metamorphic hydrothermal hornblende vein cutting granoblastic basalt (Sample 335-1256D-238R-1, 2–4 cm [Piece 1]). G. Granoblastic basalt with a diorite patch (Sample 335-1256D-Run11-EXJB-Rock [Thin Section 13]). H. Granoblastic orthopyroxene vein, recrystallized from precursor hydrothermal vein, in granoblastic dike (Sample 335-1256D-238R-1, 2–4 cm [Piece 1]). Orthopyroxene vein is cut by small post-contact-metamorphic hydrothermal amphibole vein. I. Post-contact-metamorphic hydrothermal amphibole vein cutting granoblastic basalt, with 1 mm wide amphibole-rich alteration halo where pyroxenes are replaced by amphibole (Sample 335-1256D-Run12-RCJB-Rock B).

Previous   |    Close   |    Next   |    Top of page