A 71-year-old Rockland woman was killed in a fire in her kitchen Tuesday morning, police said. Responders found Mary Gammon unresponsive in her Market Street home around 11:35 a.m., police said. Gammon, who had extensive burns to her body, was pronounced dead at the scene, the statement said. State Fire Marshal Stephen Coan said Gammon’s clothing caught on fire while she was cooking. Pending autopsy results, Coan said the fire has been preliminarily determined to be accidental. Coan said kitchen fires are the leading cause of fire deaths among the elderly in Massachusetts, and the state is undertaking an educational campaign to address the issue.