Precambrian olistoliths masquerading as sills from Death Valley, California

Abstract

Olistolith production and magmatism are processes commonly associated with extensional tectonic settings, such as rift basins. We present a cautionary exemplar from one such Precambrian basin, in which we reinterpret metabasite bodies, previously documented as sills, to be olistoliths. We nevertheless demonstrate that, on the basis of field observation alone, the previous but erroneous sill interpretation is parsimonious. Indeed, it is only by using isotopic age and compositional analysis that the true identities of these metabasite olistoliths are revealed. We present new data from metabasites and metasedimentary strata of the Kingston Peak Formation (Cryogenian) and Crystal Spring Formation (Mesoproterozoic) of Death Valley, USA. These include field observations, U–Pb apatite ages, U–Pb zircon ages (detrital and igneous) and whole-rock geochemistry. These data also provide a new maximum age for the base of the Pahrump Group and suggest that the Crystal Spring Diabase was more tholeiitic than previously thought. Similar sill/olistolith misinterpretations may have occurred elsewhere, potentially producing erroneous age and tectonic-setting interpretations of surrounding strata. This is particularly relevant in Precambrian rocks, where fossil age constraints are rare. This is illustrated herein using a potential example from the Neoproterozoic literature of the Lufilian belt, Africa. We caution others against Precambrian olistoliths masquerading as sills. Supplementary material: Details of a meta-igneous boulder from P12 of the Silurian Hills, LA-ICP-MS and whole-rock geochemistry methods and standards, and U–Pb apatite and zircon isotopic data, including standards and selected cathodoluminescence images, are available at https://doi.org/10.6084/m9.figshare.c.3990639

A slippery slope for Cryogenian diamictites?

“…It is therefore more likely that rebound‐related deposits were diachronous, underscoring the argument that they have scant chronostratigraphic value. Absolute age constraint from within the Kingston Peak Formation cannot resolve this issue, as there are no syn‐depositional ages and the youngest maximum depositional ages are Mesoproterozoic (Mahon et al., ; Vandyk et al., ). In the Valjean Hills, Mrofka and Kennedy (, p. 453) also noted that ‘Noonday Dolomite clasts are included in diamictite of the KP4 member or are in diamictite interbedded with KP4 member sedimentary breccia’, suggesting that the model proposed herein can also be extended to those sections, although further work to establish this is required.…”

“…Quadrat analysis of the upper diamictite in the Kingston Range ( Figure 11) illustrates that the clast populations are more heterogeneous than their counterparts in the Saddle Peak or Alexander Hills. Particularly notable are large clasts of metabasite in the study area ( Figure 11a): very similar to metabasites forming megaclasts further down the succession (Le , derived from a 1.08 Ga diabase intrusion into the Crystal Spring Formation (Calzia et al, 2000;Heaman & Grotzinger, 1992;Vandyk et al, 2018). In terms of clast populations, whilst dolostone is the dominant lithology (62%) and sandstone accounts for almost a quarter (23%) of described clasts, metamorphic clasts (schist and gneiss) make up 8% of the 313 counted clasts (Figure 11b).…”

“…Given this, distinguishing between diamictites of glacial versus slope origin in the rock record is a vital, yet often problematic, component of correct palaeo‐environmental and climate interpretations (Kennedy, Eyles, & Broughton, ; Letsch & Kiefer, ). This is especially true for Cryogenian diamictites of Death Valley, which often record coeval glaciation and rifting (Eyles & Januszczak, ; Miller, ; Prave, ; Vandyk et al., ). In the Silurian Hills outcrop belt (Figure ), Le Heron, Tofaif, Vandyk, and Ali () proposed that diamictites ultimately of glacial origin were characteristically far travelled, typically comprising well rounded clasts from basement lithologies.…”

Syn‐rift mass flow generated ‘tectonofacies’ and ‘tectonosequences’ of the Kingston Peak Formation, Death Valley, California, and their bearing on supposed Neoproterozoic panglacial climates

“…Hoffman et al, 1998). Ongoing sedimentological study shows these deposits to be much more complex than envisaged by panglacial climate modelling, and to reflect a complex interplay of climate and intrabasinal tectonics during the breakup of Rodinia (Le Heron et al, 2014Vandyk et al, 2018;Tofaif et al, 2019). The Kingston Peak Formation exposed on the western slopes of the Panamint Range and at other localities lying between the southernmost tip of the Black Mountains and the Kingston Range areas of Death Valley in eastern California, USA ( Fig.…”

“…This underscores the importance of magmatic activity during basin extension of the basin. Recent work has considered the igneous bodies of the Silurian Hill and Kingston Range as displaced olistoliths derived from the Crystal Springs Formation (Table 1; Vandyk et al, 2018); if correct this indicates cannibalization of volcanics as faulting continued and the basin expanded.…”