In general, Archean rocks exhibit rather ordinary moderate-P-high-T facies series metamorphism; neither blueschists nor any record of deep continental subduction and return are documented. However, the abundance scale ultrahigh-temperature (UHT) metamorphic belts from Neoarchean to Cambrian imply a significant change in geodynamics during Era, after which transient sites high heat flow were available at intervals throughout this period Earth evolution. Many Neoproterozoic-Cambrian UHT appear...

At low temperatures (<750 °C at moderate to high crustal pressures), the production of sufficient melt reach connectivity transition (∼7 vol%), enabling drainage, requires an influx aqueous fluid along structurally controlled pathways or recycling via migration and exsolution during crystallization. higher temperatures, melting occurs by fluid-absent reactions, particularly hydrate-breakdown reactions involving micas and/or amphibole in presence quartz feldspar. These produce 20–70 vol%,...

Research Article| November 01, 2006 Duality of thermal regimes is the distinctive characteristic plate tectonics since Neoarchean Michael Brown 1Laboratory for Crustal Petrology, Department Geology, University Maryland, College Park, Maryland 20742, USA Search other works by this author on: GSW Google Scholar Author and Article Information Publisher: Geological Society America Received: 28 Mar Revision 07 Jun Accepted: 10 First Online: 09 2017 Online ISSN: 1943-2682 Print 0091-7613 The...

On the contemporary Earth, distinct plate tectonic settings are characterized by differences in heat flow that recorded metamorphic rocks as apparent thermal gradients. In this study we compile gradients [defined temperature/pressure (T/P) at peak] and ages of metamorphism (defined timing peak) for 456 localities from Eoarchean to Cenozoic Eras test null hypothesis through time did not vary outside range expected each these settings. Based on gradients, classified into three natural groups:...

Significant volume of wet melting requires an influx H 2 O-rich volatile phase. In hydrate-breakdown melting, initial melt accumulation is diffusion-controlled and accumulates around peritectic phases in low-pressure sites. As the melt-bearing rock weakens, it becomes porous at a few per cent melt, initiating advective flow regime; as reaches connectivity transition, may be lost from system first several melt-build-up–melt-loss events. Using mineral equilibria modelling, major accessory...

If we accept that a critical condition for plate tectonics is the creation and maintenance of global network narrow boundaries separating multiple plates, then to argue during Archean requires more than local record subduction. A case made back early Paleoproterozoic, when cycle breakup collision led formation supercontinent Columbia, bimodal metamorphism registered globally. Before this, less preserved crust survivorship bias become greater concerns, geological may yield only lower limit on...

Ages retrieved from accessory minerals in high-grade metamorphic rocks place important constraints on the timing of events and rates tectonometamorphic processes operating deep crust. In suprasolidus rocks, dissolution growth zircon monazite are strongly dependent P–T conditions metamorphism chemistry quantity anatectic melt present. Along a clockwise path, prograde heating above solidus leads to episodic loss changes that have implications for monazite. this study, phase equilibria...

In the early 1980s, evidence that crustal rocks had reached temperatures >1000 °C at normal lower pressures while others followed low thermal gradients to record characteristic of mantle conditions began appear in literature, and importance melting tectonic evolution orogens metamorphic–metasomatic reworking lithospheric was realized. parallel, new developments instrumentation, expansion situ analysis geological materials increases computing power opened up fields investigation. The robust...

Crustal thickening during transpressive orogenesis may produce anatectic granites which then localize deformation leading to transcurrent movement. Granites be transported from sites of generation through the mid-crust in dyke-like channelways within relatively narrow strike-slip shear zones link major fault upper crust. Extensional jogs systems provide developing for assembly plutons magma arriving below. The model is based upon observations Cadomian belt NW France exposes sections middle...

Anatectic stromatic migmatites have a symmetrical layered structure with low ratio of thickness to length and periodicity, features that not been explained satisfactorily but which are related physical processes melt segregation. We evaluate the compaction model for segregation as it applies develop models based upon convection driven by volume change advection down pressure gradients result from applied differential stress acting on an anisotropic multilayer protolith. Compaction...

Barrow (1893) introduced three important ideas that furthered understanding of metamorphic processes: (i) the use critical index minerals in argillaceous rocks to define zones and elucidate spatial features regional metamorphism; (ii) concept progressive (iii) magmatic advection heat as a possible cause metamorphism. This article expands upon these themes by reviewing our dynamic evolution orogenic belts interpreted from P–T–t paths rocks, considering likely causes different kinds...

Sapphirine granulites from a new locality in the Palni Hill Ranges, southern India, occur small enclave of migmatitic, highly magnesian metapelites ( mg =85–72) within massive enderbitic orthogneiss. They show variety multiphase reaction textures that partially overprint coarse‐grained high‐pressure assemblage Bt+Opx+Ky+Grt+Pl+Qtz. The sequence reactions as deduced corona and symplectite assemblages, together with petrogenetic grid considerations, records clockwise P–T evolution four...

Abstract Many migmatites and granulites preserve evidence of a clockwise P–T evolution involving decompression (decrease in P ) while close to the thermal peak. The extent post‐thermal peak reaction is influenced by several factors, including: (1) path relation invariants system Clapeyron slopes equilibria; (2) rate cooling; (3) availability fluid (H 2 O‐rich volatile phase or melt) for fluid‐consuming reactions. Reaction may occur between products prograde (increasing T fluid‐generating as...