Do microplates in subduction zones leave a geological record?

Active microplate boundaries in ocean-continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc. We discuss two modern cases. The first is the South Gorda-Juan de Fuca plate boundary in the Cascadia subduction zone, where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation. The second case is the Cocos-Rivera plate boundary in the Middle America trench, where the overlying Colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub-duction-related volcanism is spatially and geochemically complex. We apply these observations to boundaries of the Arguello, Monterey, Guadalupe, and Magdalena microplates, which existed in the subduction zone west of Baja California at various times from 20 to 12.5 Ma. The past positions of these boundaries relative to Baja California are constrained by global plate reconstructions, closure of the Gulf of California, and an estimate of extension in the Mexican Basin and Range province. Existing regional mapping and our additional reconnaissance mapping show that Paleocene to Eocene fluvial and marine sedimentary rocks south of Ensenada along the western Baja California peninsula and eastward to the mid-Miocene volcanic arc are undeformed. Limited available data reveal no major spatial or geochemical variations in the mid-Miocene volcanic arc that might correlate with the past positions of the microplate boundaries. Thus these microplate boundaries had little to no effect on the overriding continental plate. The nature of Guadalupe and Magdalena interactions with North America may have been closer to the South Gorda-Juan de Fuca example, with possible internal deformation of the microplates. The Monterey and Arguello microplates may have behaved like the modern Explorer plate, with largely strike-slip motion relative to North America during their last stages of existence. Tectonic patterns similar to these examples may be expected from other plate boundaries where a plate is fragmenting as it enters a subduction zone (e.g., the Aluk plate in the trench beneath West Antarctica in early Tertiary time). Whether these microplates subsequently become attached to the overriding continental plate or to a larger oceanic plate and whether this causes deformation in the region of the former subduction zone may depend on the velocities of the nearby major plates and the relative orientations of the microplate boundaries

In situ Raman analyses of deep-sea hydrothermal and cold seep systems (Gorda Ridge and Hydrate Ridge)

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q05023, doi:10.1029/2005GC001204.The Deep Ocean Raman In Situ Spectrometer (DORISS) instrument was deployed at the Sea Cliff Hydrothermal Field and Hydrate Ridge in July 2004. The first in situ Raman spectra of hydrothermal minerals, fluids, and bacterial mats were obtained. These spectra were analyzed and compared to laboratory Raman measurements of standards and samples collected from the site. Spectra of vent fluid (∼294°C at the orifice) at ∼2700 m depth were collected with noncontact and immersion sampling optics. Compared to spectra of ambient (∼2°C) seawater, the vent fluid spectra show changes in the intensity and positions of the water O-H stretch bands due to the elevated temperature. The sulfate band observed in seawater spectra is reduced in vent fluid spectra as sulfate is removed from vent fluid in the subseafloor. Additional components of hydrothermal fluid are present in concentrations too low to be detected with the current Raman system. A precision underwater positioner (PUP) was used to focus the laser spot on opaque samples such as minerals and bacterial mats. Spectra were obtained of anhydrite from actively venting chimneys, and of barite deposits in hydrothermal crusts. Laboratory analysis of rock samples collected in the vent field also detected the presence of gypsum. Spectra of bacterial mats revealed the presence of elemental sulfur (S8) and the carotenoid beta-carotene. Challenges encountered include strong fluorescence from minerals and organics and insufficient sensitivity of the instrument. The next generation DORISS instrument addresses some of these challenges and holds great potential for use in deep-sea vent environments.Funding was provided by the David & Lucile Packard Foundation

Ecdysteroids affect Drosophila ovarian stem cell niche formation and early germline differentiation

Ecdysteroids affect Drosophila ovarian stem cell niche formation and early germline differentiation. The steroid hormone ecdysone regulates germline development and stem cell niche establishment in the Drosophila ovary by modulating TGF-β signalling and cell adhesion

Caste development and reproduction: a genome-wide analysis of hallmarks of insect eusociality

The honey bee queen and worker castes are a model system for developmental plasticity. We used established expressed sequence tag information for a Gene Ontology based annotation of genes that are differentially expressed during caste development. Metabolic regulation emerged as a major theme, with a caste-specific difference in the expression of oxidoreductases vs. hydrolases. Motif searches in upstream regions revealed group-specific motifs, providing an entry point to cis-regulatory network studies on caste genes. For genes putatively involved in reproduction, meiosis-associated factors came out as highly conserved, whereas some determinants of embryonic axes either do not have clear orthologs (bag of marbles, gurken, torso), or appear to be lacking (trunk) in the bee genome. Our results are the outcome of a first genome-based initiative to provide an annotated framework for trends in gene regulation during female caste differentiation (representing developmental plasticity) and reproduction

Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge

Forty-nine hydrothermal sulfide-sulfate rock samples from the Endeavour Segment of the Juan de Fuca Ridge, northeastern Pacific Ocean, were dated by measuring the decay of 226Ra (half-life of 1600 years) in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years. This dating method is effective for samples ranging in age from ∼200 to 20,000 years old and effectively bridges an age gap between shorter- and longer-lived U-series dating techniques for hydrothermal deposits. Results show that hydrothermal venting at the active High Rise, Sasquatch, and Main Endeavour fields began at least 850, 1450, and 2300 years ago, respectively. Barite ages of other inactive deposits on the axial valley floor are between ∼1200 and ∼2200 years old, indicating past widespread hydrothermal venting outside of the currently active vent fields. Samples from the half-graben on the eastern slope of the axial valley range in age from ∼1700 to ∼2925 years, and a single sample from outside the axial valley, near the westernmost valley fault scarp is ∼5850 ± 205 years old. The spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship, with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift. These relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years

Transcriptional Control in the Segmentation Gene Network of Drosophila

The segmentation gene network of Drosophila consists of maternal and zygotic factors that generate, by transcriptional (cross-) regulation, expression patterns of increasing complexity along the anterior-posterior axis of the embryo. Using known binding site information for maternal and zygotic gap transcription factors, the computer algorithm Ahab recovers known segmentation control elements (modules) with excellent success and predicts many novel modules within the network and genome-wide. We show that novel module predictions are highly enriched in the network and typically clustered proximal to the promoter, not only upstream, but also in intronic space and downstream. When placed upstream of a reporter gene, they consistently drive patterned blastoderm expression, in most cases faithfully producing one or more pattern elements of the endogenous gene. Moreover, we demonstrate for the entire set of known and newly validated modules that Ahab's prediction of binding sites correlates well with the expression patterns produced by the modules, revealing basic rules governing their composition. Specifically, we show that maternal factors consistently act as activators and that gap factors act as repressors, except for the bimodal factor Hunchback. Our data suggest a simple context-dependent rule for its switch from repressive to activating function. Overall, the composition of modules appears well fitted to the spatiotemporal distribution of their positive and negative input factors. Finally, by comparing Ahab predictions with different categories of transcription factor input, we confirm the global regulatory structure of the segmentation gene network, but find odd skipped behaving like a primary pair-rule gene. The study expands our knowledge of the segmentation gene network by increasing the number of experimentally tested modules by 50%. For the first time, the entire set of validated modules is analyzed for binding site composition under a uniform set of criteria, permitting the definition of basic composition rules. The study demonstrates that computational methods are a powerful complement to experimental approaches in the analysis of transcription networks

Functional Conservation of Cis-Regulatory Elements of Heat-Shock Genes over Long Evolutionary Distances

Transcriptional control of gene regulation is an intricate process that requires precise orchestration of a number of molecular components. Studying its evolution can serve as a useful model for understanding how complex molecular machines evolve. One way to investigate evolution of transcriptional regulation is to test the functions of cis-elements from one species in a distant relative. Previous results suggested that few, if any, tissue-specific promoters from Drosophila are faithfully expressed in C. elegans. Here we show that, in contrast, promoters of fly and human heat-shock genes are upregulated in C. elegans upon exposure to heat. Inducibility under conditions of heat shock may represent a relatively simple “on-off” response, whereas complex expression patterns require integration of multiple signals. Our results suggest that simpler aspects of regulatory logic may be retained over longer periods of evolutionary time, while more complex ones may be diverging more rapidly