MKED1: A new titanite standard for in situ microanalysis of trace elements, Sm-Nd isotopes, and U-Pb geochronology

Abstract:

Titanite has great potential as a petrogenetic indicator and mineral geochronometer as it can host high trace element concentrations and it occurs in a wide range of rock types. Here, we describe a potential new titanite standard for calibration of the chemical and isotopic composition of titanite of varying age and origin. Through comprehensive bulk analysis of mm-size crystal fragments and in-situ microanalysis, we show that the titanite, labeled MKED1, is largely free of inclusions and is homogenous at the level of analytical precision for major element, U-Pb isotope and Sm-Nd isotope composition. Some minor zoning in trace element composition is recognized using backscatter electron imaging, although the trace element concentrations of each of these zones are also very homogenous. MKED1 has high contents of REE, Th, U, and radiogenic Pb, but very low levels of common Pb. U-Pb isotope data (ID-TIMS and LA-ICP-MS) show MKED1 to be concordant with an age of ca. 1518 Ma. Cross calibration with other titanite standards demonstrates that MKED1 can be used as a primary standard for determining U-Pb ages of titanite ranging in age from Precambrian to Neogene. We also show that MKED1 is suitable as a Sm-Nd isotope standard due to its high REE concentrations and homogenous ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd content.

We suggest MKED1 can be employed as a trace element, U-Pb isotope and Sm-Nd isotope standard for in situ or bulk analytical methods, including techniques that allow simultaneous collection of multiple elemental and/or isotopic data sets in situ. We present two case studies to demonstrate the potential of titanite analysis for resolving geological problems: The first examines the genesis of Cu-REE skarn mineralization from the Mt Isa Inlier, Australia, and the second study investigates the timing and origin of volcanism and sedimentation in the Western Branch of the East African Rift.