Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)

Abstract

Suprasubduction zone (SSZ) ophiolites of the northern Appalachians (eastern North America) have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian orogen. The central and southern Appalachians, which extend from southern New York to Alabama (USA), also contain numerous ultra- mafic-mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins, alongside the range of possible magmatic affinities, have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian orogen and its relationship with the northern Appalachian orogen. We present the results of field observations, petrography, bulk-rock geochemistry, and spinel mineral chemistry for ultramafic portions of the Baltimore Mafic Complex, which refers to a series of ultramafic-mafic bodies that are discontinuously exposed in Maryland and southern Pennsylvania (USA). Our data indicate that the Baltimore Mafic Complex comprises SSZ ophiolite fragments. The Soldiers Delight Ultramafite displays geochemical characteristics—including highly depleted bulk-rock trace element patterns and high Cr# of spinel—characteristic of subduction-related mantle peridotites and serpentinites. The Hollofield Ultramafite likely represents the “layered ultramafics” that form the Moho. Interpretation of the Baltimore Mafic Complex as an Iapetus Ocean–derived SSZ ophiolite in the central Appalachian orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along thousands of kilometers of orogenic strike.

Phase equilibria and microstructural constraints on the high‐T building of the Kohistan island arc: The Jijal garnet granulites, northern Pakistan

“…However, preservation of primary magmatic spinel is relatively uncommon owing to the propensity for spinel to be compositionally altered during metamorphism (e.g. Guice et al, 2021), and the widespread prediction of accessory spinel does not negate the general applicability of the results. At 14 kbar and ≥4 wt% H 2 O, late fractionated solids contain titanite in equilibrium with garnet below ~860°C, and at 10-14 kbar and 2-4 wt% H 2 O corundum and oxides are in equilibrium with feldspar and minor garnet.…”

The nature of insoluble organic matter in Sutter's Mill and Murchison carbonaceous chondrites: Testing the effect of x‐ray computed tomography and exploring parent body organic molecular evolution

“…The experimental synthesis and reduction of a chemical simulant of chondritic IOM, called syn-IOM, was performed at the Earth and Planets Laboratory by George Cody. Reactions involving formaldehyde in liquid water (Cody et al, 2011;Foustoukos et al, 2021;Kebukawa et al, 2013;Kebukawa & Cody, 2015) yield organic solids that are nearly identical to actual IOM at the functional group level. For this study, synthetic IOM was derived from glucose (equivalent to six formaldehyde molecules) in water through hydrocarbonization as follows.…”

“…The bulk H, C, and N elemental and isotopic analyses were performed at the Earth and Planets Laboratory by Dionysis Foustoukos using previously established protocols (Alexander et al, 2012(Alexander et al, , 2013Foustoukos et al, 2021). For H, C, and N analyses, samples were weighed into Ag (for H; 2.1-3.6 mg) and Sn (for C and N; 7.8-9.1 mg) capsules.…”

Drainage area estimates for synorogenic clastic wedges in the Central Appalachian Basin (sink) with implications for terrane accretion in the hinterland (source)

“…Granites associated with the Taconic arc range in age from 441 to 489 Ma (Sinha et al, 2012). Associated with the Chopawamsic–Milton–Potomac arc terranes are melanges and ophiolitic meta‐mafic and ‐ultramafic slivers (Baltimore and Westminster terranes) (Figure 1) (Guice et al, 2021). The Smith River allochthon is of probable Laurentian affinity (Carter et al, 2006).…”