The P-T-t history of blocks in serpentinite-matrix mélange, west-central Baja California

Research Article| January 01, 1992 The P-T-t history of blocks in serpentinite-matrix mélange, west-central Baja California SUZANNE L. BALDWIN; SUZANNE L. BALDWIN 1Department of Geological Sciences, State University of New York at Albany, Albany, New York 12222 Search for other works by this author on: GSW Google Scholar T. MARK HARRISON T. MARK HARRISON 1Department of Geological Sciences, State University of New York at Albany, Albany, New York 12222 Search for other works by this author on: GSW Google Scholar Author and Article Information SUZANNE L. BALDWIN 1Department of Geological Sciences, State University of New York at Albany, Albany, New York 12222 T. MARK HARRISON 1Department of Geological Sciences, State University of New York at Albany, Albany, New York 12222 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1992) 104 (1): 18–31. https://doi.org/10.1130/0016-7606(1992)104<0018:TPTTHO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation SUZANNE L. BALDWIN, T. MARK HARRISON; The P-T-t history of blocks in serpentinite-matrix mélange, west-central Baja California. GSA Bulletin 1992;; 104 (1): 18–31. doi: https://doi.org/10.1130/0016-7606(1992)104<0018:TPTTHO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Thermochronologic, petrologic, and geochemical analyses of epidote-amphibolite-, amphibolite-, eclogite-, and blueschist-facies blocks in serpentinite-matrix mélanges from East San Benito Island and Cedros Island, west-central Baja California, provide constraints on the P-T-t history of this disrupted terrane. Results of 40Ar/39Ar step heating experiments on minerals separated from these blocks vary according to metamorphic grade and indicate different P-T-t histories. Mid-Jurassic (160-170 Ma) epidote-amphibolite-and amphibolite-facies blocks were probably derived from oceanic crust and associated sediments that were metamorphosed during initiation of subduction. Coarse-grained blueschist blocks were likely metamorphosed during continued subduction in late Early Cretaceous time (that is, 115-100 Ma). Some epidote-amphibolite blocks are partially over-printed by blueschist-facies mineral assemblages and apparently record both metamorphic events. Fission-track analyses of apatites indicate that the blocks underwent significantly different post-metamorphic cooling histories. Epidote-amphibolite and amphibolite blocks cooled below ∼100 °C from mid-Jurassic to Paleocene time; blueschist blocks cooled below ∼100 °C in Oligocene-Miocene time. In general, mafic blocks have trace-element concentrations and REE patterns characteristic of ocean-floor basalts. This study demonstrates that samples with very different P-T-t histories can evidently occur over relatively small length scales (< <1 km) in serpentinite-matrix mélanges. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.