All of My Faults Are Stress Related

I made a promise to myself that every month, I would at least look through the abstracts on my RSS feeds and note interesting articles that I wanted to find time to read. So now it’s May 30, and I’d better do it before the June issues come out.

So… articles in the May issue of Geology that look interesting:

Extensional tectonics: Extension rates, crustal melting, and core complex dynamics. Metamorphic core complexes are made up of metamorphic and igneous rocks that have been brought nearer to the surface by continental extension. They’re characterized by mylonites that separate the hotter, deeper rocks from the colder, shallower (usually brittlely faulted sedimentary) rocks. In some of them, the deep rocks reflect older metamorphism, but in other ones, the rocks partially melted in the process of being exhumed. P. Rey, Christian Teyssier, and Donna Whitney modeled the deformation and crystallization of the core complex rocks, and concluded that the difference reflects differences in strain rates. [Part of me wants to take this work and look at an area near my dissertation field area, and part wonders how the recent paper arguing that heat flow is slower in hot rocks would affect these conclusions.]

More extensional tectonics: Synconvergent surface-breaking normal faults of Late Cretaceous age within the Sevier hinterland, east-central Nevada. During the late Cretaceous, Wyoming and Utah were shortening, but Nevada was extending. At least, that’s what the metamorphic rocks say. There wasn’t evidence of extension in the sedimentary rocks above them, however… until now.

Strike-slip structures: Downdip segmentation of strike-slip fault zones in the brittle crust. Where the San Jacinto fault (southern California) jumps from one steep strand to another, slip follows the bedding of weak shale layers. It’s a geometry that isn’t described in textbooks. Worth knowing about. I wonder how common that geometry is?

Subduction zones: Two studies using chlorine in melt trapped within minerals to understand magmatism associated with subduction: Chlorine enrichment in central Rio Grande Rift basaltic melt inclusions: Evidence for subduction modification of the lithospheric mantle and {delta}37Cl systematics of a backarc spreading system: The Lau Basin. Evidence of subduction-modified lithosphere in New Mexico is consistent with a gently dipping subducting plate during the Laramide Orogeny – a model that’s been around since the 1970′s, but which takes a beating from alternate models every now and then.

…and weird critters: Giant trilobites and trilobite clusters from the Ordovician of Portugal. Kevin Zelnio has pictures of these at Deep Sea News. What on earth were those trilobites doing when they died, anyway? (Trilobites are my favorite invertebrate. Yes, I know they’re extinct. They’re still cool.)