Paleomagnetism of Rumuruti chondrites suggests a partially differentiated parent body

摘要

Different types of magnetic fields were at work in the early solar system: nebular fields generated within the protoplanetary nebula, solar fields, and dynamo fields generated within the solar system solid bodies. Paleomagnetic studies of extraterrestrial materials can help unravel both the history of these magnetic fields, and the evolution of solar system solid bodies. In this study we studied the paleomagnetism of two Rumuruti chondrites (PCA 91002 and LAP 03639). These chondrites could potentially bear the record of the different fields (solar, nebular, dynamo fields) present during the early solar system. The magnetic mineralogy consists of pseudo-single domain pyrrhotite in LAP 03639 and pyrrhotite plus magnetite in PCA 91002. Paleomagnetic analyses using thermal and alternating field demagnetization reveal a stable origin trending component of magnetization. Fields of 12 mu T or higher are required to account for the magnetization in PCA 91002, but the timing and exact mechanism of the magnetization are unconstrained. In LAP 03639, considering various chronological constraints on the parent body evolution and on the evolution of the different sources of magnetic field in the early solar system, an internally-generated (dynamo) field of similar to 5 mu T recorded during retrograde metamorphism is the most likely explanation to account for the measured magnetization. This result indicates the existence of an advecting liquid core within the Rumuruti chondrite parent body, and implies that, as proposed for CV and H chondrites, this chondritic parent body is partially differentiated. (C) 2019 Elsevier B.V. All rights reserved.